Structural forces in soft matter systems: unique flocculation pathways between deformable droplets

Tabor R.F., Lockie H., Chan D., Grieser F., Grillo I., Mutch K.J., Dagastine R.R.
Soft Matter, 2011, 7, 11334-11344

Oscillatory structural forces caused by colloidal additives including micelles, microemulsion droplets and particles were explored between rigid and deformable interfaces using direct force measurements with the atomic force microscope. The observed oscillations from rigid surfaces become distorted when confinement occurs between deformable interfaces, giving rise to a force hysteresis between approaching and separating interfaces. Small-angle neutron scattering was used to determine the bulk structure of the colloidal additives, as a basis for comparison with their behaviour when confined in thin films. It is seen that confinement itself does not appear to significantly alter the structure of the colloidal additive when compared to the bulk; however, at small separations, interactions with the confining interfaces may become important. The combined approach uncovered an unique flocculation pathway that is available to deformable emulsion droplets, and that the strength of this flocculation can be tuned by changes in the size and concentration of the structuring colloid, the emulsion droplet size, and the ionic strength of the solution.

Prévost S., Riemer S., Fisher W., Haag R., Böttcher C., Gummel J., Grillo I., Appavou M.-S., Gradzielski M.
Biomacromolecules, 2011, 12, 4272-4282

Polyplexes of short DNA-fragments (300 b.p., 100nm) with tailor-made amine-based polycations of different architectures (linear and hyperbranched) were investigated in buffer solution as a function of the mixing ratio with DNA. The resulting dispersed polyplexes were characterized using smallangle neutron and X-ray scattering (SANS, SAXS) as well as
cryo-TEM with respect to their mesoscopic structure and their colloidal stability. The linear polyimines form rather compact structures that have a high tendency for precipitation. In contrast, the hyperbranched polycation with enzymatic-labile pentaethylenehexamine arms (PEHA) yields polyplexes colloidally stable for months. Here the polycation coating of DNA results in a homogeneous dispersion based on a fractal network with low structural organization at low polycation amount. With increasing polycation, bundles of tens of aligned DNA rods appear that are interconnected in a fractal network with a typical correlation distance on the order of 100 nm, the average length of the DNA used.

With higher organization comes a decrease in stability. The 3D network built by these beams can still exhibit some stability as long as the material concentration is large enough, but the structure collapses upon dilution. SAXS shows that the complexation does not affect the local DNA structure. Interestingly, the structural findings on the DNA polyplexes apparently correlate with the transfection efficiency of corresponding siRNA complexes. In general, these finding not only show systematic trends for the colloid stability, but may allow for rationaln approaches to design effective transfection carriers.

S. Manet, A. Lecchi, M. Impéror-Clerc, V. Zholobenko, D. Durand,C. L.P. Oliveira, J. S. Pedersen, I. Grillo, F. Meneau, C. Rochas
J. Phys. Chem. B, 2011, 115, 11318–11329

The micellar state of Pluronic P123, which is a poly-(ethylene oxide)-b-poly(propylene oxide)-b- poly(ethylene oxide) block polymer (EO20PO70EO20), has been investigated using SANS, SAXS,and differential scanning calorimetry under the conditions utilized in the synthesis of ordered mesoporous materials, such as SBA-15. The absolute intensity measurements, both with SANS and SAXS, have provided a detailed quantitative description of the P123 micelles in the framework of a simple coreshell spherical model.

The model developed has been used to establish the structure of the copolymer micelles, including their size, shape, aggregation number and detailed composition, as well as the structural changes induced by varying reaction conditions. The effects of temperature, pH, acidic source and the addition of swelling agents (toluene and TMB) are reported and discussed.

Manet S., Schmitt J., Impéror-Clerc M., Zholobenko V., Durand D., Oliveira C.L.P., Pedersen J.S., Gervais C., Baccile N., Babonneau F., Grillo I., Meneau F., Rochas C.
J. Phys. Chem. B, 2011, 115, 11330–11344

The different steps of the self-assembly in solution of several 2D-hexagonal silica nanostructured SBA-15 materials have been investigated by SAXS and SANS in situ experiments. Unique quantitative information about the shape and size evolution upon time of the micellar aggregates throughout the self-assembly process is obtained using a complete model that describes well the scattering data for the various synthesis conditions.

In all cases, before the precipitation of the material, the micelles shape changes from spherical to rod-like, where the structure of the rod-like micelles is linked to the structure of the 2D-hexagonal precipitated material. In addition, the kinetics of hydrolysis of the inorganic precursor (TEOS) has been determined by in situ Raman spectroscopy. More specifically, by comparing synthesis made with different acids (HNO3, HBr,HCl,H2SO4, andH3PO4), it is found that materials prepared using the “salting-out” anions (SO4 2- and H2PO4-) are much better ordered than with the “salting-in” anions (NO3- and Br-).

S. Junaid S. Qazi, A. R. Rennie, I. Tucker, J. Penfold, I. Grillo
J. Phys Chem., 2011, 115, 3271-3280

Small-angle neutron scattering, SANS, has been used to study the alignment of a sterically stabilized colloidal dispersion of nickel hydroxide induced by elongational flow. Two different concentrations, 20 and 23 wt %, of well-defined hexagonal platelets have been studied. Significant anisotropy in the scattering patterns has been observed for the higher concentration dispersion that increases with increasing elongational strain rate. The effect of pipe flow (shear flow) on the orientational ordering at the inlets is also described. Near the outlets there is also a shear stress and this tends to increase the alignment.

The orientational distribution of the particles under flow is described in terms of an order parameter calculated with respect to an individual director for each scattering pattern. The experimental measurements are supported by comparison with computer simulations which help to explain the effects of local velocity on the alignment induced by elongational flow. A slight decrease in the observed alignment was found after continuous flow for approximately 30 min and possible reasons are discussed.

Qazi S. J. S., Rennie A., Tucker I., Penfold J., Grillo I.
J. Phys. Chem. B, 2011, 35, 10413-10424

This article describes the behavior under elongational flow of mixtures of lamellar fragments and platelike colloidal particles. Mixtures of a dialkyl chain cationic surfactant, DHTAC (15 wt %), and the nonionic surfactant Brij 97 (0.5 wt %) form dispersions of lamellar phase fragments, and these were studied in the presence of smaller platelike colloidal particles of Ni(OH)2 stabilized with sodium polyacrylate. Small-angle neutron scattering was used to follow the changes in the lamellar phase fragments in the mixture under elongational flow.

The addition of a small fraction of the Ni(OH)2 dispersion resulted in significantly increased viscosity and reduced the structure and size of the lamellar fragments, and this effect was further enhanced because of the flow induced alignment. The behavior of the mixture under elongational flow is described, and the induced orientation is discussed in terms of order parameters at the different positions using spatially resolved small-angle scattering. The effect of flow rate on the orientational alignment in the mixture is also described.

I. Grillo, P. Levitz, Th. Zemb, The European Journal B (1999), 10, 29-34

We study adsorption of two nonionic surfactants (C12E5 and C12E8) on a dispersed suspension of negatively charged laponite particles. First, we quantify adsorption, i.e the amount of adsorbed molecules per gram of dried solid. Then, we show that contrast variation experiments under controlled conditions along the adsorption isotherm of surfactant on dispersed laponite particles allow to determine the average thickness of a nonionic surfactant layer adsorbed on a solid anisotropic particle.

I. Grillo, P. Levitz, Th. Zemb, Langmuir (2000) 16, 4830-4839

We have studied the structure of ternary systems made of anionic anisotropic laponite particles in coexistence with negatively charged lamellar phases of AOT. Firstly, we measured the adsorption of surfactant monomers on the mineral area. Then, after determination of the stable monophasic domain in the ternary system, we studied the occurrence of possible microstructures. SAXS measurements combined with osmotic pressure measurements show that small inorganic negatively charged particles can be forced to be included in the hydrophobic part of the surfactant bilayers when the interlayer water thickness becomes smaller than the particle thickness. 

F. Né, I. Grillo, O. Taché, Th. Zemb, Journal de Physique IV (2000) 10, 403-413

Nous présentons la calibration d’une caméra de type Guinier-Méring couplée à une anode au molybdène (l= 0,711 Å) et à un monochromateur de quartz. Trois jeux de fentes réduisent le faisceau à 2 mm de largeur sur 15 mm de hauteur dans le plan de l’échantillon. Une chambre à vide primaire est placée entre l’échantillon et le détecteur pour réduire l’absorption des photons diffusés par l’air. La détection se fait par des plaques photosensibles et nous utilisons le numériseur “PhosphorImager” (Molecular Dynamics™). Pour obtenir un diagramme de diffusion où l’intensité absolue en cm-1 est tracée en fonction du vecteur d’onde q en Å-1, trois problèmes doivent être résolus : la calibration de l’axe des vecteurs d’onde ; la soustraction de la cellule vide et la calibration de l’intensité en cm-1 ; la déconvolution pour se ramener au diagramme idéal qui serait obtenu avec un faisceau ponctuel dans le plan du détecteur. La procédure peut être utilisée pour toute caméra de diffusion aux petits angles associée à des plaques photostimulables.

We present here the calibration of a Guinier-Méring small angle X-ray camera. A molybdenum anode source, followed by a quartz monochromator, allows a monochromatic beam with high energy (E=17 keV, l=0.71 Å) to be obtained. Three set of slits limit the beam size to 2 mm width and 15 mm high at the sample position. Air scattering is reduced with a primary vacuum chamber set between the sample and the detector. An image plate is used as 2D detector. The final spectrum (absolute intensity in cm-1 plotted versus the q-vector in Å-1) requires three steps in data treatment : the calibration of the q axis, the subtraction of the empty cell and calibration of the intensity and the desmearing to make the scattering pattern what it is supposed to be with a punctual source. The method described here may be applied for any small angle X-ray camera using sensitive flat image plates.

S. Nave and J. Eastoe, R. K. Heenan, D. Steytler, I. Grillo, Langmuir (2000), 16, 8741-8748

The aim was to identify why Aerosol-OT is such an efficient surfactant for forming microemulsions and in pursuit of this, 11 Aerosol-OT-related compounds have been investigated. These surfactants were from two separate homologous series, with either linear or branched hydrocarbon tails. Hence, it was possible to examine the effect of chain structure on packing in curved interfacial film at oil-water interfaces. With the linear dichain compounds, water-in-oil microemulsion phases could be formed only in the presence of a short-chain alcohol. On the other hand, all the branched surfactants formed microemulsions without cosurfactant. Within the range of structures studied, it was possible to identify a minimum branching necessary to stabilize a ternary microemulsion. With branched sulfosuccinates the single-phase microemulsion region only differed by its location on the temperature scale, and this was correlated with subtle variation in hydrophobicity, caused by different chain structures. Small-angle neutron scattering was used to characterize the microemulsion aggregates and absorbed films. Packing at the oil-water interface, and the water droplet radius, was shown to be related to chain architecture, and the same pattern of behavior was found as at the air-water interface. Therefore, with regard to microemulsion formation Aerosol-OT is no special case, but it possesses a chain structure that gives optimum aqueous-phase solubility around room temperature.

P. M. Claesson, M. Bergstrom, A. Dedinaite, M. Kjellin, J.-F. Legrand, I. Grillo, J. Phys. Chem. B (2000), 104, 11689-11694

Small-angle neutron scattering (SANS) data for solutions containing a highly charged cationic polyelectrolyte and an anionic surfactant are presented. The scattering data in pure D2O, emphasizing the scattering from the polyelectrolyte, and in a H2O/D2O mixture that contrast matches the polyelectrolyte. In the absence of surfactant, a broad scattering peak due to the mesh size of the polyelectrolyte solution is the most characteristic feature. This peak moves to larger q-values (smaller distances) as the polyelectrolyte concentration is increased, as expected for semidilute polyelectrolyte solution. Addition of small amount of surfactant reduces and finally removes this peak.

Instead, a sharp diffraction peak appears at high q-values. This Bragg peak corresponds to a characteristic distance of 37-39 angstroms, and it is observed when either the polyelectrolyte or the surfactant is contrast match solvent. Once this peak is appeared, its position does not change when the surfactant concentration is increased. The intensity of the peak grows, however, until a stochiometric polyelectroyte-surfactant complex has been formed. The Bragg peak remains in excess surfactant solution. These results are discussed  in relation to the structure of the polyelectrolyte-surfactant aggregates and in connection with recent results from surface force and turbidity measurements using the same polyelectrolyte-surfactant pair. 

M. Gradzielski, M. Bergmeier, H. Hoffman, M. Muller, I. Grillo, J. Phys. Chem. B (2000), 104, 11594 - 11597

For the first time the formation of a gel phase of densely packed unilamellar vesicles that is prepared by simple mixing of a surfactant solution and a cosurfactant (octanol) has been observed. This striking process of self-organization of a low viscous micellar phase into a vesicle phase with solidlike properties was monitored with respect to the structural and the macroscopic properties. The originally present micelles first grow in size and then form small unilamellar vesicles, which are finally monodisperse enough to form highly ordered state. This opens a very easy way to form well-defined colloidal structures by a simple mixing process which could be of much interest for potential applications where one intends to incorporate active agents into such a vesicle phase. 

I. Grillo, P. Levitz, Th. Zemb, The European Journal E (2001) 5, 377-386

We have established experimentally the region of existence of smectic and sponge lyotropic microstructures in the presence of synthetic hydrophilic clay particles. Taking into account the adsorption isotherm, we determined the extension of the single-phase regions by visual inspection and by low-q behaviour of the small angle neutron scattering. Conditions of stability such as geometric constraints associated with fluctuation quenching are discussed.

I. Grillo,  ILL report ILL01GR08T (2001)

The aim of Small Angle Neutron Scattering experiments is to extract the shape, distribution in size and structure of scatterers from data measured in reciprocal space. Ideal form factors models have been known for many years and have been further developed by many authors. The knowledge of the instrumental resolution is as important as the choice of the model. The finite divergence and size of direct beam, the wavelength resolution and the pixel size contribute to the smearing of the real intensity scattered by the sample. In this paper, the effects of the instrumental resolution and polydispersity of the scatterers are investigated and compared. Is the instrumental resolution a limitation for the structural characterization? The geometry of the spectrometer D22 (Institut Laue Langevin, Grenoble) will be taken as reference for the numerical and experimental applications but the equations are general and can be applied to others small angle neutron spectrometers. The calculations show that the effects of polydispersity or wavelength resolution are very similar, mainly smoothing of the form factor oscillations and broadening of Bragg peaks. 

P. Griffiths, I. Fallis, P. Teerapornchaisit, I. Grillo, Langmuir (2001), 17,  2594-2601

The interaction between a series of hydrophobically modified gelatins and the anionic surfactant sodium dodecyl sulfate in a pH=6.6/34 mM buffer has been investigated by surface tension, pulsed-gradient spin-echo NMR, viscosity and small-angle neutron scattering. In the absence of the surfactant, the bulk viscosity of all the gelatins examined here is dependent only on the gelatin concentration and is independent of the number and size of any grafted hydrophobe.  Similarly, the small-angle scattering for all samples could be well-described by a two length-scale model. In this model, the smaller dimension represents the local structure of the gelatin molecule and is unaffected by the presence of the hydrophobe(s), while a larger dimension characterizing the network structure increases significantly with the presence of the hydrophobe but not their size.

On addition of the anionic surfactant sodium dodecyl sulfate (SDS), the interaction between surfactant and the hydrophobic gelatin with low grafting densities starts at a slightly lower surfactant concentration (CMC(1)) compared with a "blank" material that has no grafted hydrophobe. At higher grafting densities, (CMC(1)) is greater than the CMC(1) values for the lower grafting density series.  For both grafting densities, neither the length nor the number of hydrophobes present has an appreciable  effect on CMC(1). There is no change in the amount of SDS bound to the gelatin at saturation. The viscosities of the hydrophobically modified gelatin/SDS solutions do depend on the length of the hydrophobe, albeit rather weakly, but only at the higher density. In summary, the interaction between these gelatin samples and SDS is dominated by the electrostatics of the system; The effects of the hydrophobe are proposed to be largely manifestations of the change in the electrostatic character of the gelatin induced by grafting process, rather than the hydrophobe per se. 

V. O. Aseyev, S. I. Klenin, H. Tenhu, I. Grillo, E. Geissler, Macromolecules (2001) 34, 3706-3709

The polycationic polyelectrolyte poly(methacryloylethyl trimethylammonium methyl sulfate) (PMETMMS) of high molecular weight (ca 26x106 g mol-1) in dilute solutions with acetone-water mixtures displays a coil-globule transition above a certain threshold of acetone. SANS observations of this system indicate that the collapsed state of this molecule consists of a sequence of dense spheres with smooth surfaces connected by regions of loose polymer. The radius of the spheres, 28 nm, is smaller than either the hydrodynamic radius (RH=39 nm) or the radius of gyration (RG=42 nm). The number of such collapsed regions is small (3-4), the volume fraction of polymer inside them being about 8%. 

H. Endo, M. Mihailescu, M. Monkenbusch, J. Allgaier, G. Gomper, D. Richter, B. Jakobs. T. Sottmann, R. Strey, I. Grillo, J. Chem. Phys. (2001) 115, 580-600

The effect of amphiphilic diblock copolymers of several molecular weights on the structure and phase behavior of ternary amphiphilic systems (water, oil, and nonionic surfactant) is investigated. Small amounts of amphiphilic block copolymer polyethylenoxide-polyethylpropylene lead to a dramatic decrease of the amount of total surfactant needed to solubilize given equal volumes of water and oil in a bicontinuous microemulsion. Neutron scattering experiments employing a high-precision two-dimensional contrast variation technique demonstrate that the polymer is distributed uniformly on the surfactant membrane. Based on these observations, we propose a mechanism for the enhancement of the swelling behavior, which is due to the variation of the membrane curvature elasticity by polymer mushrooms anchored to the interface. 

M. Summers, J. Eastoe, S. Davis, Z. Du, R. Richardson, R.K. Heenan, D. Steytler, I. Grillo, Langmuir (2001) 17, 5388-5397

Mixtures of polimerizable surfactants have been employed to select control over interfacial curvature and phase structure, in aqueous micelles, lyotropic mesophases, and water-in-oil microemulsions. These surfactants were 11-(methacryloyxy)undecyltrimethylammonium bromide (A), dodecyl(11-(methacryloyxy)undecyl)dimethylammonium bromide (B) and cetyltrimethylammonium 4-vinylbenzoate (C). The single chain A and double chain B have reactive hydrophobic chain tips, whereas the single chain C possesses a polimerizable vinyl benzoate hydrophilic counterion. Aqueous micelles ,composed of mixtures of these surfactants, can be polymerized to yield single-phase, stable solutions. Polymerization was confirmed by disappearance of characteristic vinyl signals in the 1H NMR spectra, and line broadening, as would be expected in polymerized micelles. Furthermore, small angle neutron scattering (SANS) indicates that micelle structures were broadly retained after polymerization. SANS has shown that these polymerized structures persist below the critical micelle concentration of the nonpolymerized system. With lyotropic mesophases, polarizing light microscopy coupled with SAXS indicates retention of the lamellar phase (La) after polymerization and for hexagonal phases (H1), evidence of long-range order in the polymerized sample. Finally, films in water-in-oi microemulsions composed of A and B surfactant mixtures were also studied. After polymerization, NMR indicated around 35% conversion to the surface active polymer. SANS showed that the droplet size may be turned by film composition and that the parent droplet structure was retained after polymerization. 

D. Gräbner, M. Gradzielski, I. Grillo ILL Annual report 2001

The formation of unilamellar vesicles was studied by means of the stopped-flow technique. The high neutron flux, on the small-angle scattering instrument D22 allows to study the formation process with a temporal resolution of 200 ms, thereby reaching the current limits of such structural investigations. Vesicles were formed by  mixing a Na oleate surfactant solution with the cosurfactant octanol. After mixing emulsion droplets of octanol are present from which it diffuses into the micellar aggregates. By this simple diffusion mechanism first a growth of rod-like aggregates is induced which is followed by a two-dimensional growth at larger times. After about 2 mins formation of vesicles is observed. During the next 20-30 mins these unilamellar vesicles grow in size and become more monodisperse until a final state is reached. This shows that in this system by simple diffusion well-defined, monodisperse  vesicles are formed by a process of self-organisation. The stopped-flow technique has allowed the observation of the various stages  in this complex, multi-step reorganisation  process with a good time-resolution.

C. Janot, M. de Boissieu, S Agliozzo, S. Loreto, L. Farinato, R. Sato, T. J. Tsai, I. Grillo Physica B (2001) 300, 52-60

Icosahedral Al-Pd-Mn and decagonal Al-Ni-Co quasicristal were investigated using small angle neutron scattering. Both isotropic scattering were observed. It is consistent with the existence of free volume due to dodecahedral and quasi-spherical voids in the icosahedral quasicristal. In the docagonal specimens prismatic holes and chemical inhomogeneities seem to be responsible for the scattering observed at small angles. 
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What is so special about aerosol-OT? Part III-glutaconate versus sulfosuccinate headgroups and oil-water interfacial tensions

S. Nave, J. Eastoe, R. K. Heenan, D. Steytler, I. Grillo Langmuir (2002) 18, 1505-1510

Syntheses, adsorption, and aggregation properties of two novel double-chain anionic sulfoglutaconate surfactants are described. These compounds are similar to the more common sulfosuccinates, such as Aerosol-OT, but with a modified hydrophilic moiety bearing one extra -CH2- spacer. For comparison purposes, two related linear n-hexyl- and branched 2-ethylhexyl- hydrophobic groups were used to form the surfactants, which are denoted di-C6GLU and AOTGLU. The planar air-aqueous solution surface was characterized by drop volume tensiometry, whereas small-angle neutron scattering and spinning-drop tensiometry were used to study microemulsions and oil-water interfaces. Dilute binary surfactant water end ternary water-in-oil microemulsion phase behavior is also described. In terms of molecular packing both glutaconate and sulfosuccinate systems are found to be very similar, showing the minor role of the headgroup compared to larger effects of the tail structure, as noted before in part I and II. Interestingly, the AOTGLU proved to be even more efficient than normal AOT in terms of its capacity to microemulsify water in heptane. The results point to subtle effects of hydrophilic group structure on physicochemical properties of these AOT-type surfactants, especially in microemulsions. 

E. Grell, E. Lewitzki, R. Schneider, G. Ilgenfritz, I. Grillo J. Therm. Anal. Cal. (2002) 68, 469-478

Differential scanning calorimetry (DSC) studies of micellar, 60mM solutions of the octaethyleneglycol alkylethers C14E8 and C16E8 provide evidence for a narrow endothermic transition at 41 and 32 oC respectively, characterized by an enthalpy change of 2 kJ mol-1 for both detergent. The observed thermal transition is indicative of a concerted transition of the surfactant molecules, as illustrated on the basis of a simple molecular model. The effect of co-solvents such as different alcohols on the thermal transition is investigated. Glycerol markedly lowers the transition temperature whereas the transition is absent in the presence of at least 10% ethanol. The calorimetric transition correlates with the temperature dependent increase of viscosity and static light scattering as well as with changes observed by small angle neutron scattering (SANS). The SANS results provide clear evidence for a distinct structural change  occurring at the transition temperature, which is interpreted as a sphere-rod transition of the detergent micelles. Moreover, the rod length increases with increasing temperature. We suggest that the process causing the thermal transition acts as the prerequisite of the growth process. 

A. Fernández-Barbero, A. Fernández-Nieves, I. Grillo, E. López-Cabarcos Physical Review E (2002), 66, 051803

Small angle neutron scattering and dynamic light scattering have been used to study the thermodynamics of swelling and the associated structure modifications of highly cross-linked temperature-sensitive Poly(NIPAM) microgels in D2O. A particle core-shell model is proposed, with the core containing most of the cross-linker molecules. The Flory-Rehner theory, with the inclusion of a concentration dependent Flory solvency parameter, successfully describes the experimental swelling, despite the inhomogeneous character of the particles. Interestingly, the shell evolution with temperature controls the whole particle swelling, exerting an external pressure over the core, which in turns influences its size during the swelling process. Scaling laws for the correlation lengths were found with respect to temperature and polymer concentration. Finally, it has been encountered that for the collapsed microgel states, the particle surface seems to have a fractal character. 

Novel core-shell structure for colloids made from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactants

P. Hervé, M. Destarac, F.-F. Berret. J. Lal, J. Oberdisse, I. Grillo Europhysics Letters,  (2002), 58, 912-918

Using neutron and light scattering experiments, we show that neutral/polyelectroyte diblock copolymers and oppositely charged surfactant in dilute aqueous solutions associate into colloidal aggregates which have an original core-shell microstructure. We have found that the core is constituted from densely packed surfactant micelles, most likely connected between them by the polyelectrolyte blocks. the outer part of the colloid is a corona and is made from the neutral chains. We suggest that the mechanism of formation of these colloids is identical to that of the associative transition reported in homopolyeoelctrolyte/surfactant solutions. However, here, the macroscopic phase separation is hindered by the presence of the neutral chains.

F. Horkay, A.-M. Hecht, I. Grillo, P. Basser, E. Geissler, J. Chem. Phys. (2002) 117, 9103-9106

The small angle neutron scattering (SANS) behavior of fully neutralized sodium polyacrylate gels is investigated in the presence of calcium ions. Analysis of the SANS response reveals the existence of three characteristic length scales, two of which are of thermodynamic origin, while the third length is associated with the frozen-in structural inhomogeneities. This latter contribution exhibits power law behavior with a slope of about -3.6, reflecting the presence of interfaces. The osmotically active component of the scattering signal is defined by two characteristic length scales, a correlation length xi and a persistence length L.

E. Alami, S. Abrahmsen-Alami, J. Eastoe, I. Grillo, R.K. Heenan J. Colloid and interface Sc. (2002), 255(2), 403-409

The microstructure of complexes between hydroxypropylcyclodextrins (HPCDs) (alpha, beta, and gamma) and a novel gemini surfactant has been investigated by small-angle neutron scattering (SANS). This nonionic hetero-gemini surfactant (denoted NIHG750) contains two hydrophobic groups and two hydrophilic groups. One is a methyl-capped polyoxyethylene chain with 16 oxyethylene units and the other is a secondary hydroxyl group. Various form factor models have been considered for fitting the SANS data. Spherical aggregates (25 to 40 Angstrom) with a size slightly larger than that of NIHG750 micelles (about 23 Angstrom) appear in mixed systems. These could be micellar aggregates partly covered with a few cyclodextrin molecules. In addition, the results indicate rod formation (r similar to 8 Angstrom, L similar to 70 Angstrom) for the NIHG-HPCD complexes. This result is consistent with the threading of HPCDs onto NIHG750 to such an extent that the surfactant molecule takes an extended conformation at high levels of HPCD. Also, the results indicate that HPCDs may interact with the oxyethylene groups of the spherical micellar aggregates leading to an increase in micelle size and a gradual transformation to rod-shaped aggregates. The tendency to form rods increases in the order gamma-CD < alpha-CD < beta-CD. An increase in HPCD concentration results in an increased amount of rods in the system. All spherical aggregates disappear at relative amounts of HPbetaCD above 4 to 5 (molar ratio). However, for HPalphaCD and HPgammaCD spherical aggregates coexist with rod shaped aggregates in the whole range of concentrations investigated here. 

I. Grillo, E.I. Kats, A.R. Muratov, Langmuir (2003), 19(11) 4573-4581

We present the first kinetic Small Angle Neutron Scattering experiments carried out on the instrument D22 (Institut Laue Langevin, Grenoble) with a stopped-flow apparatus (Bio-LogicTM company). D22 offers unique features for real-time experiments. The high flux and the large q-range covered in only one instrumental configuration combined with the rapid electronics open possibilities of few hundred millisecond resolution measurements. We have used these technical developments to study the formation and growth of spontaneous vesicles after addition of salts (NaCl, NaBr, KCl, KBr) in a micellar solution of AOT in D2O from 500 ms to 5 hours after mixing. The vesicle radii and the growth rate depend on the salt concentration and decrease with increasing ionic strength. The driving force of the transition is the screening of the electrostatic repulsion between adjacent surfactant head groups that favour formation of a locally plane bilayer. Assuming that the aggregation is controlled by micelle diffusion, a simple kinetic approach predicts that the average radius increases with the power law R=A t1/6,  in close agreement with the experimental data. 

Bumajdad A, Eastoe J, Nave S, Steytler DC, Heenan RK, Grillo I  Langmuir (2003), 19 (7) 2560-2567

Surfactant mixing in model water-in-heptane microemulsion interfaces has been investigated for blends of a cationic didodecyldimethylammonium bromide (DDAB) with poly(ethylene glycol) monododecyl ethers (C12EJ, J = 3, 4, 5, 6, 7, 8, and 23). Phase behavior studies, electrical conductivity, and contrast variation small-angle neutron scattering (SANS) have been employed to delineate the effects of systematic variation of ethylene oxide headgroup size. These mixtures are characterized by an overall surfactant concentration (0.10 mol dm-3) and mole fraction of nonionic, which was varied up 0.20. The larger ethylene oxide (EO) numbers of 5-7 and 23 lead to significant enhancements in the maximum microemulsion solubilization capacity compared to DDAB only, whereas the shortest surfactant employed, C12E3, caused a decrease in the phase stability. Microemulsion nanostructure and interfacial compositions were studied for the EO3, EO4, EO6, and EO7 systems in partial structure factor type SANS experiments, as described before for the EO5 analogue (Langmuir 1999, 15, 5271). Analysis of contrast variation SANS data showed that C12E7, C12E6, and C12E5 partition strongly into the DDAB layer. Under equivalent conditions the shorter EO chain surfactants C12E4 and C12E3 appear to adsorb much more weakly. Interfacial compositions determined by SANS have been used to rationalize trends in phase behavior and nanostructure, highlighting the importance of partitioning effects with nonionics in multicomponent mixtures of this type. 

Dupont A, Eastoe J, Barthelemy P, Pucci B, Heenan R, Penfold J, Steytler DC, Grillo I  J Colloid interf. sci. (2003) 261(1), 184-190

Dilute aqueous phase behavior of a novel tris(hydroxymethyl)acrylamidomethane (THAM)-derived telomer bearing a perfluorohexyl hydrophobic chain, F6THAM6, has been investigated. Fluorinated polyhydroxy surfactants of this kind find use in emerging biomedical applications. Neutron reflection (NR) and drop volume surface tension (DVT) methods have been used to determine the critical micelle concentration (cmc = 4.7 x 10-4 mol dm-3) and surface adsorption parameters (at the cmc NR gives a molecular area a(cmc) = 67.4 and 62 Angstrom2 and surface excess Gamma(cmc) = 2.46 x 10-6 mol m-2. The aggregation structures were determined by small-angle neutron scattering (SANS). indicating globular (polydisperse spheres) micelles of radius similar to30 Angstrom are present. These findings are compared with literature on surfactants with related structures. to identify how the unusual molecular structure of F6THAM6 affects surfactant properties.

E. De Luca, R.W. Richards, I. Grillo, S.M. King
J. Polym Sci Pol. Phys. (2003) 41(12): 1352-1361 

A series of fractions of a hyperbranched polyester in deutero tetrahydrofuran solution were investigated by small-angle neutron scattering. Concentrations of polymer from 2 to 5% w/v were used, and the molecular parameters were obtained from Zimm plots of the data. Second virial coefficients were positive, and these values were confirmed by dilute-solution light scattering on a small number of fractions with deutero tetrahydrofuran as a solvent. The small-angle neutron scattering data exhibited the general features predicted for the particle scattering functions of nonrandomly branched polymers, but an exact fit of the theoretical equation to the data could not be obtained for all fractions of the hyperbranched polymer, particularly those of high molecular weight. Excluded volume effects were cited as a possible cause for this disagreement. A fractal dimension of similar to2.5 was obtained from the scattering vector dependence of the differential scattering cross section of the polymer in deutero tetrahydrofuran solution, which agreed with the scaling exponent for the dependence of the radius of gyration on weight-average molecular weight. Hydrogenous tetrahydrofuran solutions of the hyperbranched polymer exhibited negative second virial coefficients that were attributed to isotopic influences on the thermodynamic properties of the polymer-solvent combination.  

I. Grillo Colloids and Surfaces A: Physicochemical and Engineering Aspects, in Press (June 2003)

"Pastis" is a famous aniseed based beverage, symbolic of hot summer days in the south of France. But who really knows the origin of the milky color when adding water? Each time you drink a glass of "Pastis", you observe a complex phenomenon in physical chemistry!
Pastis is mainly composed of anethol, an aromatic molecule, water, ethanol and additive compounds that improve the taste. Anethol has a very low solubility in water and further addition of water to the "dry" preparation induces the formation of an emulsion made of large anethol droplets in a water-plus-ethanol solvent that scatter light. The origin of the spontaneous formation of the emulsion is a well-known phenomenon, which appears in liquid systems with three or more compounds, when the sample composition is trapped between the binodal and spinodal curves on the phase diagram.
The radius of the droplets has been determined using the small-angle neutron scattering technique (D22, Institut Laue-Langevin, Grenoble). Of the order of a micron, the droplet size depends on the anethol/ethanol volume ratio and grows with time and temperature. 

F. Né, F. Testard, Th. Zemb, I. Grillo Langmuir (2003), 19(20), 8503-8510

In situ-time resolved small angle X-ray and neutron scattering have been used to investigate the mechanism of a bulk precipitation of a hexagonally ordered ZrO 2 /surfactant mesophase. Using CTAB as a structure-directing agent, the precipitation results from the addition of sulfate to an oxychloride zirconium/CTAB water solution. The precipitate obtained after a few seconds is organized in a 2D hexagonal network. There is no pre-existing cylindrical micelle in the precursor solution and the micelles act as a reservoir for monomer to feed the building grain. The precipitation occurs through a two step mechanism: a random nucleation/growing process and a first order reorganization from locally ordered cylinders to a hexagonal lattice in the grain at its final size. 

J. Bent, L.R. Hutchings, R.W. Richards, T. Cough, R. Spares, P.D. Coates, I. Grillo, O.G. Harlen, D.J. Read, R.S. Graham, 
A.E. Likhtman, D.J. Groves, T.M. Nicholson, T.C.B. McLeish     Science, 19 September 2003, 301, 1691-1695

Flows of complex fluids need to be understood as both macroscopic and molecular scales, because it is the macroscopic response that controls the fluid behavior, but the molecular scale that ultimately gives rise to rheological and solid-state properties. Here the flow field of an entangled polymer melt through an extended contraction, typical of many polymer processes, is imaged optically and by small-angle neutron scattering. The dual-probe technique samples both the macroscopic stress field in the flow and the microscopic configuration of the polymer molecules at selected points. The results are compared with a recent "tube model" molecular theory of entangled melt flow that is able to calculate both the stress and the single-chain structure factor from first principles. The combined action of the three fundamental entangled processes of reptation, contour length fluctuation, and convective constraint release is essential to account quantitatively for the rich rheological behavior. The multiscale approach unearths a new feature: orientation at the length scale of the entire chain decays considerably more slowly than at the smaller entanglement length.

A. Stenstam, G. Montalvo, I. Grillo, M. Gradzielski   J. Phys. Chem. B (2003) 107(44), 12331-12338

The lysozyme-sodium dodecyl sulfate-water system features several interesting aggregation phenomena and is also of interest as it constitutes a model system for mixtures of a charged colloid with an oppositely charged surfactant, as both colloid and surfactant are pure and monodisperse compounds. The structure of such mixed protein - surfactant systems has been investigated by means of SANS contrast variation experiments. Two interesting issues of protein-surfactant aggregation are discussed. First, a new set of data on the structure of the protein-surfactant complex in solution is added to the discussion of whether the model of "beads on a necklace", "protein decorated micelles", or "flexible helix" is most appropriate. It is our conclusion that the compact globule of lysozyme does not fit well into any of the mentioned models. Instead, transient clusters of lysozyme-SDS aggregates are proposed for the L-1 phase and more strongly bound locally linear clusters for the gel phase. Second, the structure and formation of a homogeneous, transparent gel at room temperature is analyzed and compared to the well-studied heat-set globular gels. The gel structure in different ionic strengths, lower than the one caused by naturally occurring buffer salts has also been analyzed and it seems that small amounts of salt render the system a more repulsive character than salt-free conditions. In addition to the equilibrated samples studied with the contrast variation technique, the complexation has been studied over time. 

Small-Angle Neutron Scattering Study of Mixtures of Cationic Polyelectrolyte and Anionic Surfactant: Effect of Polyelectrolyte Charge Density

M.L. Bergstroem,  M.U.R. Kjellin, P.M. Claesson, I. Grillo   J. Phys. Chem. B, (2004), 108, 1874-1881

We have studied mixtures of an anionic surfactant (deuterated sodium dodecyl sulfate, SDS-d) and cationic polyelectrolytes with different charge densities (10%, 30%, 60%, and 100%) using small-angle neutron scattering (SANS). Near compositions corresponding to charge neutralization, the solutions phase separate into a complex phase (precipitate) consisting of, in the cases of 30%, 60%, and 100% charge density, a two-dimensional (2D) hexagonal lattice of close-packed cylindrical micelles and a clear liquid. When either polyelectrolyte with charge density less than 100% or SDS-d is present in sufficient excess, the solution becomes clear and isotropic, and from the scattering data we may conclude that prolate or rod-shaped micelles are present. The micelles are seen to grow in length with increasing SDS-d concentration and polyelectrolyte charge density from about 80 Å to 550 Å, whereas the cross-sectional radius is 15 Å and approximately constant. The number of micelles per polyelectrolyte chain is found to be slightly larger than unity (1-6). In some of the (turbid) samples rod-shaped micelles are found to coexist with larger polyelectrolyte-surfactant complexes. Solutions consisting of 10% charged polyelectrolyte and SDS-d are very viscous and gellike, and the complex phase is much less defined with a much larger distance between adjacent aggregates in the complex phase.

Understanding the mechanism of action of poly(amidoamine)s as endosomolytic polymers: Correlation of physicochemical and biological properties

P.C.  Griffiths, A. Paul, Z. Khayat, K.W. Wan , S.M. King, I. Grillo, R. Schweins, P.  Ferruti, J. Franchini, R. Duncan
Biomacromolecules (2004) 5 (4), 1422-1427 

Bioresponsive poly(amidoamine)s (PAA)s are currently under development as endosomolytic polymers for intracellular delivery of proteins and genes. Here for the first time, small-angle neutron scattering (SANS) is used to systematically investigate the pH-dependent conformational change of an endosomolytic polymer, the PAA ISA 23. The radius of gyration of the ISA23 was determined as a function of pH and counterion, the aim being to correlate changes in polymer conformation with membrane activity assessed using a rat red blood cell haemolysis assay. With decreasing pH, the ISA23 radius of gyration increased to a maximum (R-g similar to 80 Angstrom) around pH = 3, before subsequently decreasing once more. At high pH and therefore high ionic strengths, the polymer is negatively charged and adopts a rather compact structure (R-g similar to 20 Angstrom), presumably with the dissociated carboxylic groups on the exterior of the polymer coil. At low pH, the coil again collapses (R-g < 20 Angstrom), presumably due to the effects of the high ionic strength. It is concluded that the nature of the salt form has no direct hearing on the size of the polymer coil, but it does indirectly determine the prevailing pH and, hence, polymer conformation. Pulsed-gradient spin-echo NMR measurements were in good agreement with the SANS estimates of the radius of gyration, although ISA23 polydispersity does complicate the data interpretation/comparison. These results support the proposed mode of action of PAAs, namely a coil expansion on passing from a neutral pH (extracellular) to an acidic pH (endosomal and lysosomal) environments. The results do, however, suggest that the charge on the polymer shows a closer correlation with the haemolysis activity rather than the polymer conformation.

J.F. Berret, B.  Vigolo, R.  Eng, P. Herve, I. Grillo, L. Yang
Macromolecules (2004) 37 (13), 4922-4930 

We report on the formation of colloidal complexes resulting from the electrostatic self-assembly of polyelectrolyte-neutral diblock copolymers and oppositely charged surfactant. The copolymers investigated are asymmetric and characterized by a large neutral block. Using light, neutron, and X-ray scattering experiments, we have shown that the colloidal complexes exhibit a core-shell microstructure. The core is described as a dense microphase of micelles connected by the polyelectrolyte blocks, whereas the shell is a diffuse brush made from the neutral chains. For all copolymer/surfactant systems, we show the existence of a critical charge ratio Z(C) (similar to1) above which the formation of hierarchical structures takes place. Copolymers of different molecular weight and polyelectrolyte blocks have been studied in order to assess the analogy with another type of core-shell aggregates, the polymeric micelles made from amphiphilic copolymers. The present results indicate that the radius of the core depends essentially on the degree of polymerization of the polyelectrolyte block and not on that of the neutral chain. On the other hand, the size of the overall colloid increases with increasing molecular weights of the copolymers. Taking advantage of the resolution of X-ray scattering, we have also shown that the micelles in the core of the aggregates are structurally disordered.

B. van den Brandt, H. Glattli, I. Grillo, P. Hautle, H. Jouve, J. Kohlbrecher, J.A. Konter, E. Leymarie, S. Mango, R. May, A. Michels, H.B. Stuhrmann, O. Zimmer 
Nuclear Instruments & Methods in Physics Research Section A- Accelerators Spectrometers Detectors and Associated Equipment (2004) 526 (1-2), 81-90 

In the past 3 years a series of experiments have shed new light on the mechanism of dynamic nuclear polarisation (DNP). Time-resolved polarised small-angle neutron scattering and nuclear magnetic resonance have been used simultaneously to study the nuclear polarisation build-up around paramagnetic centres during DNP. This approach, which aims at visualising the nuclear polarisation process on a microscopic scale, shall be exemplified and the experimental techniques used described in some detail.

F. Nettesheim, I. Grillo, P. Lindner, W. Richtering 
Langmuir (2004) 20 (10): 3947-3953

We report on the influence of shear on a nonionic lamellar phase of tetraethyleneglycol monododecyl ether (C12E4) in D2O containing clay particles (Laponite RD). The system was studied by means of small-angle light scattering (SALS) and small-angle neutron scattering (SANS) under shear. The SANS experiments were conducted using a H2O/D2O Mixture of the respective scattering length density to selectively match the clay scattering. The rheological properties show the familiar shear thickening regime associated with the formation of multilamellar vesicles (MLVs) and a shear thinning regime at higher stresses. The variation of viscosity is less pronounced as commonly observed. In the shear thinning regime, depolarized SALS reveals an unexpectedly strong variation of the MLV size. SANS experiments using the samples with lamellar contrast reveal a change in interlamellar spacing of up to 30% at stresses that lead to MLV formation. This change is much more pronounced than the change observed, when shear suppresses thermal bilayer undulations. Microphase separation occurs, and as a consequence, the lamellar spacing decreases drastically. The coincidence of the change in lamellar spacing and the onset of MLV formation is a strong indication for a morphology-driven microphase separation.

C.L. Barrie, P.C. Griffiths, R. J. Abbott, I. Grillo, E.  Kudryashov, C. Smyth
J. of Colloid and Interface Sc. (2004) 272 (1) 210-217 

The interaction of carbon black with an acrylic resin has been investigated by rheology. Two carbon blacks, with similar particle size and surface characteristics but quite different particle morphologies, have been examined. These are somewhat arbitrarily denoted as "spherical" and "fractal" as shown by small-angle neutron scattering (SANS) and ultrasonic spectroscopy studies. In the absence of polymer, stable aqueous dispersions could not be obtained. Stable dispersions could be obtained, however, upon addition of polymer to a level corresponding to a ratio of 50 mg of polymer per 13 m(2) ( +/-1 m(2)) of surface area (i.e., 15 wt% particles). These stable dispersions exhibit flow typical of concentrated dispersions-Newtonian behavior up to some apparent "yield" or critical value, above which pronounced shear thinning is observed. The critical stress increases with increasing polymer concentration. When a significant amount of nonadsorbed polymer is also present, a second Newtonian plateau is superimposed on the shear-thinning behavior. This feature is observed for both particle types but is more pronounced for the fractal particle. When there is little or no nonadsorbed polymer, the viscosity of the fractal particle dispersions is greater than the viscosity of the spherical particle dispersions. At low polymer concentrations, the dispersions are predominantly viscous at low shear stresses. The phase angle decreases significantly over a narrow shear stress range and the rheology tends to more elastic behavior. At higher shear stresses, the dependence on particle morphology is weak.

P.C. Griffiths, A.Y.F. Cheung, C. Farley, I.A  Fallis, A.M. Howe, A.R. Pitt, R.K Heenan, S.M. King, I. Grillo
Langmuir (2004) 20 (17), 7313-7322 

Electron paramagnetic resonance, viscosity, and small-angle neutron scattering (SANS) measurements have been used to study the interaction of mixed anionic/nonionic surfactant micelles with the polyampholytic protein gelatin. Sodium dodecyl sulfate (SDS) and the nonionic surfactant dodecylmalono-bis-N-methylglucamide (C(12)BNMG) were chosen as "interacting" and "noninteracting" surfactants, respectively; SDS micelles bind strongly to gelatin but C(12)BNMG micelles do not. Further, the two surfactants interact synergistically in the absence of the gelatin. The effects of total surfactant concentration and surfactant mole fraction have been investigated. Previous work (Griffiths et al. Langmuir 2000, 16 (26), 9983-9990) has shown that above a critical solution mole fraction, mixed micelles bind to gelatin. This critical mole fraction corresponds to a micelle surface that has no displaceable water (Griffiths et al. J. Phys. Chem. B 2001, 105 (31), 7465). On binding of the mixed micelle, the bulk solution viscosity increases, with the viscosity-surfactant concentration behavior being strongly dependent on the solution surfactant mole fraction.

The viscosity at a stoichiometry of approximately one micelle per gelatin molecule observed in SDS-rich mixtures scales with the surface area of the micelle occupied by the interacting surfactant, SDS. Below the critical solution mole fraction, there is no significant increase in viscosity with increasing surfactant concentration. Further, the SANS behavior of the gelatin/mixed surfactant systems below the critical micelle mole fraction can be described as a simple summation of those arising from the separate gelatin and binary mixed surfactant micelles. By contrast, for systems above the critical micelle mole fraction, the SANS data cannot be described by such a simple approach. No signature from any unperturbed gelatin could be detected in the gelatin/mixed surfactant system. The gelatin scattering is very similar in form to the surfactant scattering, confirming the widely accepted picture that the polymer "wraps" around the micelle surface. The gelatin scattering in the presence of deuterated surfactants is insensitive to the micelle composition provided the composition is above the critical value, suggesting that the viscosity enhancement observed arises from the number and strength of the micelle-polymer contact points rather than the gelatin conformation per se.

M. Gradzielski , I. Grillo and T. Narayanan
Prog Colloid Polym Sci, 2004, 129, 32-39

Structural changes in amphiphilic systems can be triggered by mixing them with other surfactants or additives. In the described experiments such mixing was done rapidly by means of a stopped-flow device and followed by small-angle neutron scattering (SANS) or small-angle X-ray scattering (SAXS) as a structural detection method. In such experiments we followed the formation of unilamellar vesicles in a catanionic surfactant mixture and for an ionic surfactant solution upon the addition of a cosurfactant. For both cases slow formation of monodisperse unilamellar vesicles is observed that takes place in a way purely governed by diffusion, i.e. without the effect of external forces. The formation proceeds via disk-like intermediates in the first case and via rod-like intermediates in the second case. In another investigation the solubilisation of methyl heptanoate into a zwitterionic surfactant was studied, where the initially present emulsion droplets are slowly transformed into well-defined microemulsion droplets. However, this process does not follow the static phase diagram, in which a lamellar phase is present at intermediate concentrations, which is not observed as an intermediate in the solubilisation process that goes directly to the formation of microemulsion droplets. Finally the disintegration of micelles was followed as it occurs when mixing the micellar solution with a bad solvent for the micelles. Here it is observed that the disintegration process does not occur in a simple dissolution step but in a more complex way in which after passing through a minimum aggregation stage smaller micellar structures are reformed. In summary it can be stated that the stopped-flow method coupled to SANS/SAXS detection allows to obtain detailed information about the dynamics of structural transitions in amphiphilic systems with a time-resolution of down to 5–50 ms.

Sandra Ristori, Julian Oberdisse, Isabelle Grillo, Alessandro Donati, and Olivier Spalla
Biophys. J. , 2005, 88, 535-547

In this paper we report the physicochemical characterisation of cationic liposomes loaded with orthocarborane and with two of its sugar-containing derivatives. Carboranes are efficient boron delivery agents in Boron Neutron Capture Therapy (BNCT), an anti-cancer treatment based on neutron absorption by 10B nuclei. Cationic liposomes were prepared using the positively charged DOTAP and the zwitterionic DOPE, as a helper lipid. These liposomes are currently used in gene therapy for their ability of targeting the cell nucleus, therefore they can be considered appropriate vectors for BNCT, in the quest of reducing the high boron amount that is necessary for successful cancer treatment. Boron uptake was determined by an original in situ method, based on neutron absorption. The structural properties of the loaded liposomes were studied in detail by the combined use of small angle X-ray scattering and small angle neutron scattering. These techniques established the global shape and size of liposomes, and to describe their bilayer composition. The results were discussed in term of molecular properties of the hosted drugs. Differences found in the insertion modality were correlated with the preparation procedure or with the specific shape and lipophilic hydrophilic balance of each carborane.

J. Plestil, J. Kriz, C. Konak, H. Pospisil, P. Kadlec, Z. Sedlakova, I. Grillo, R. Cubitt Macromol. Chem. Phys. (2005), 206, 1206-1215

Multishell particles were prepared by gamma-radiation-induced polymerization of methyl methacrylate (MMA) in polystyrene-block-poly(methacrylic acid) (PS-b-PMA) aqueous micellar solution and their structure was studied by small-angle neutron scattering (SANS). Before polymerization, almost all MMA molecules are distributed in aqueous phase and only 1% of MMA is accumulated inside the micelles. The newly formed polymer (PMMA) is deposited on the surface of PS cores of the original micelles. The effect of the MMA concentration, micelle concentration, absorbed radiation dose, and absorbed dose rate on the characteristics of the resulting particles was examined. The thickness of the PMMA shell (20-218 angstrom for the presented series of samples) can be easily controlled by variation of monomer and/or micelle concentration. Universal plots of the core volume (PS+PMMA) and SANS curve were presented. These plots facilitate choosing proper monomer and micelle concentrations and detecting possible irregularities in the parameters of the resulting particles.

G. Brotons, M. Dubois, L. Belloni, I. Grillo, T. Narayanan, Th. Zemb Journal of Chemical Physics, (2005) 123, 024704

The structure and fluctuations of the swollen L-alpha lamellar phase of highly charged surfactant didodecyldimethylammonium halide fluid bilayers (DDA(+)X(-)) are studied using high-resolution small-angle x-ray scattering and medium-resolution, high-contrast small-angle neutron-scattering. The Caille parameter eta, as a function of the swelling (L-alpha periodicity d), was determined from the full q-range fits of the measured scattering profiles for three different counterions (X- = Cl-, Br-, and NO3-). This parameter quantifies the amplitude of the membrane fluctuations within the Landau-de Gennes smectic-A linear elasticity theory. The different anions used gave strong specific effects at the maximum swelling of the L-alpha phase, while at lower swellings a two-phase coexistence of swollen and collapsed lamellae (d similar to 30 and similar to 80 angstrom) was observed for bromide and nitrate ions. Over the intermediate dilution range for all three counterions, a single L-alpha phase can be continuously swollen with pure water which is governed by an equation of state (i.e., osmotic pressure versus period) and thermally excited fluctuation amplitudes that can be well described by the same Poisson-Boltzmann calculation. The membranes were found to be slightly stiffer than predicted by purely electrostatic repulsions, and this is tentatively attributed to an extra bending rigidity contribution from the surfactant chains.

P.C. Griffiths, A. Paul, Z. Khayat, R.K. Heenan, R. Ranganathan, I. Grillo Soft Matter (2005) 1 (2): 152-159

Small-angle neutron scattering (SANS) has been employed to characterize mixed micelles comprising the surfactants 1,2-diheptanoyl-sn-phosphatidylcholine (DHPC)/sodium dodecyl sulfate (SDS) and 1,2-diheptanoyl-sn-phosphatidylcholine (DHPC)/dodecyltrimethylammonium bromide (DTAB) using the classical model of a micelle consisting of a hydrocarbon core surrounded by a polar shell. Various constraints are applied to the data fitting, specifically the volume of the hydrocarbon core using the aggregation number determined from time-resolved fluorescence quenching (TRFQ) and the degree of micelle hydration as determined from an electron paramagnetic resonance (EPR) experiment. The morphologies of the DHPC/SDS and DHPC/DTAB mixed micelles are largely invariant with composition-as might be expected given the similarity in the tail volumes of the respective surfactants, and the observed behaviour of the aggregation number-with a radius comparable to the fully extended length of a dodecyl chain, i.e. the longer of the two hydrophobic moieties. The shell thickness is also largely invariant with composition, indicating that the phosphatidylcholine headgroup lies flat at the interface. For both cases, the degree of counter-ion dissociation extracted from the fitting of the SANS data increases significantly on addition of DHPC, in a manner very similar to that observed for related binary surfactant mixtures, provided there is only a small change in micelle aggregation number (micelle curvature). The coincidence of the degrees of counter-ion dissociation for these quite different systems suggests a common underlying behaviour in which the nonionic species merely dilutes the surface charge associated with the ionic headgroups.

I. Grillo, Actualité chimique (2005)41-44 Suppl. 289, AUG-SEP

Pastis is a famous aniseed based beverage, symbolic of hot summer days in the south of France. But who really knows the origin of the milky color when adding water? Each time you drink a glass of pastis, you observe a complex phenomenon in physical chemistry! Pastis is mainly composed of anethol, an aromatic molecule with anise taste, water, ethanol and additive compounds that improve the taste. Anethol is soluble in all proportion in ethanol but has a very low solubility in water and further addition of water to the << dry >> preparation induces the spontaneous formation of an emulsion made of large anethol droplets in a waterplus-ethanol solvent that scatter light. The diameter of the droplets has been determined using the small-angle neutron scattering technique on the instrument D22 at the Institut Laue-Langevin in Grenoble. Of the order of a micron, the droplet size grows with time and temperature. If one forgets to drink its glass, the emulsion breaks down and the beverage becomes transparent again.

Khayat Z., Griffiths P.C., Grillo I., Heenan R.K., King S.M., Duncan R. International Journal of Pharmaceutics (2006) 317, 175-186 

Abstract: Bioresponsive polymers are being developed as synthetic viral mimetics to enhance the intracellular delivery of macromolecular therapeutic agents such as genes, proteins and peptides. In this context we have designed pH-responsive, amphoteric polyamidoamines (PAAs) which change conformation on passing from a neutral pH (extracellular) to an acidic pH (endosomal and lysosomal) environments. PAAs have already demonstrated cytosolic delivery of genes and non-permeant toxins (e.g. gelonin and ricin A chain), The aim of this study was to use small-angle neutron scattering (SANS) to investigate the most likely shape of the hydrochloride salt form of one particular PAA (ISA23) in solution, under pH conditions that mimic those the polyrner would be expected to encounter during endocytic internalisation (pH 7.4-3). It was shown that models based on a Gaussian coil representation of the polymer conformation described the SANS data better over this pH range than models based on a rod-like conformation. The conformation of ISA23 at 37 degrees C was expanded (radius of gyration similar to 80 angstrom) at pH similar to 3 but collapsed with an increase in pH (radius of gyration similar to 20 angstrom at pH 7.4), a conclusion also reached in a model-firee analysis of the neutron data. Outside this pH range - at the extremes of high and low pH - the polymer coil collapsed and interpretation of the scattering was slightly complicated by the presence of a very weak structure factor indicating that the polymer coils are highly charged. The PAA concentration did not significantly affect the polymer size over the concentration range 10-50 mg/ml. Characterisation of the dynamics of these polymer solutions - diffusion coefficients and viscosity ostensibly suggest a very different conclusion with the polymer expanding as the pH is increased, but this arises due to weak aggregation of the amphoteric polymer coils.

Seguin C., Eastoe J., Clapperton R., Heenan R.K., Grillo I. Colloids and surfaces A Physucochemicla and engineering aspects (2006) 282, 134-142 

Adsorption and aggregation properties of model non-ionic CiE8 surfactants (octaethyleneoxide mono-n-alkyl ethers C12E8, C14E8 and C16E8) were studied in different solvents: water, water/ethylene glycol and water/propylene glycol mixtures, as well as pure ethylene and propylene glycol. Significant changes in critical micellar concentrations, surface tensions and surface excess were observed using surface tension, as a function of solvent type and surfactant tail length. Aggregation structures in these solvents were studied using small-angle neutron scattering (SANS). The SANS results were consistent with ellipsoidal, or cylindrical micelles, depending on solvent. Importantly, pure ethylene glycol is identified as a solvent in which CiE8 surfactants exhibit classic behavior, similar to that which has been well documented in water. On the other hand, C12E8 exhibits only very weak surfactant properties in pure propylene glycol: surface tension depressions were very small, and SANS signals were weak, suggesting only minimal adsorption and aggregation. Hence, surfactant behavior of a model non-ionic like C12E8 is strongly dependent on the type of glycol.

Graham R.S., Bent J., Hutchings L.R., Richards R.W., Groves D.J., Embery J., Nicholson T.M., McLeish T.C.B., Likhtman A.E., Harlen O.G., Read D.J., Gough T., Spares R., Coates P.D., Grillo I. Macromolecules (2006) 39, 2700-2709

Small-angle neutron scattering measurements on a series of monodisperse linear entangled polystyrene melts in nonlinear flow through an abrupt 4:1 contraction have been made. Clear signatures of melt deformation and subsequent relaxation can be observed in the scattering patterns, which were taken along the centerline. These data are compared with the predictions of a recently derived molecular theory. Two levels of molecular theory are used: a detailed equation describing the evolution of molecular structure over all length scales relevant to the scattering data and a simplified version of the model, which is suitable for finite element computations. The velocity field for the complex melt flow is computed using the simplified model and scattering predictions are made by feeding these flow histories into the detailed model. The modeling quantitatively captures the full scattering intensity patterns over a broad range of data with independent variation of position within the contraction geometry, bulk flow rate and melt molecular weight. The study provides a strong, quantitative validation of current theoretical ideas concerning the microscopic dynamics of entangled polymers which builds upon existing comparisons with nonlinear mechanical stress data. Furthermore, we are able to confirm the appreciable length scale dependence of relaxation in polymer melts and highlight some wider implications of this phenomenon.

Mendil H., Noirez L., Baroni P., Grillo I.  PRL (2006) 96 Art. No. 077801

Quenched isotropic melts of side-chain liquid-crystal polymers reveal surprisingly an anisotropic polymer conformation. This small-angle neutron-scattering (SANS) result is consistent with the identification of a macroscopic, solidlike response in the isotropic phase. Both experiments (rheology and SANS) indicate that the polymer system appears frozen on millimeter length scales and at the time scales of the observation. This result implies that the flow behavior is not the terminal behavior and that cross-links or entanglements are not a necessary condition to provide elasticity in melts.

Vesperinas A., Eastoe J., Wyatt P., Grillo I., Heenan R.K., Richards J.M., Bell G.A . J. of the American chemical society (2006) 128, 1468-1469

Eastoe J., Vesperinas A., Donnewirth A.C., Wyatt P., Grillo I., Heenan R.K., Davis S. Langmuir (2006) 22, 851-853

Stable vesicles are formed in a 1.4 wt% solution comprising a 1:3 mixture of the anionic photodestructible surfactant sodium 4-hexylphenylazosulfonate (C(6)PAS) and inert cationic cetyltrimethylamonium bromide (CTAB). UV irradiation drives an irreversible breakdown of the mixed C(6)PAS/CATB vesicles, owing to the selective degradation Of C(6)PAS. A light-induced transition from small spherical-like polydisperse vesicles to long needle-like aggregation is observed.

Vesperinas A, Eastoe J, Wyatt P, Grillo I, Heenan RK  Chem. Comm.  (2006) 42, 4407-4409

Employing photodestructible surfactants in gelatin-based aqueous gels presents novel possibilities for controlling colloidal and aggregation properties of surfactant gelatin complexes. Light-triggered breakdown of the gelatin-bound photosurfactant aggregates causes dramatic changes in viscosity and aggregation.

Clarke N, De Luca E , Bent J , Buxton G , Gough T, Grillo I, Hutchings LR  Macromolecules (2006) 39, 7607-7616

We have probed the coupling between flow and concentration fluctuations in polymer blends using small-angle neutron scattering. We utilized a recirculating cell with a slot die, enabling us to measure the behavior at the entrance, within and at the exit of a contraction-expansion flow. While, as expected, anisotropy was observed in all nonquiescent experiments, the correlation lengths associated with the concentration fluctuations are found to be "stretched" more in the direction perpendicular to the flow at all positions along the centerline of the flow, except at the slot die exit. To gain insight into the observations, we present calculations of the scattering based on a multiscale approach, which bridges the gap between macroscopic Newtonian fluid dynamics and the convection of nanoscale concentration fluctuations. However, we find that this model contains insufficient physics to correctly describe our observations. Consequently, we argue that the deformation of the correlation length is primarily due to the coupling between weakly non-Newtonian stresses and thermodynamics.

Morfin I , Ehrburger-Dolle F, Grillo I, Livet F, Bley F J.Synchrotron Radiation (2006), Part 6, 445-452

Small-angle X-ray scattering (SAXS) performed down to small q values ( q <= 10(-3) angstrom(-1)) is a powerful method for investigating the arrangement of filler aggregates in filled elastomers under uniaxial strain. Meanwhile, for vulcanized samples, zinc oxide is used as an additive. Owing to their high contrast, the ZnO particles remaining in the manufactured composite are strong X-ray scatterers. In the low-q domain, their scattering hides that of filler aggregates ( carbon black, pyrogenic silica) and must be quantified in order to be suppressed. To this end, anomalous SAXS (ASAXS) and small-angle neutron scattering ( SANS) have been performed. It is shown that ASAXS measurements can be performed down to small q values (q <= 10(-3) angstrom(-1)). Therefore ASAXS is well adapted to separate the contributions of ZnO and filler scattering. For neutron scattering the contrast of the ZnO particles is similar to that of carbon. Because the amount of ZnO is much smaller than that of filler, ZnO scattering can be neglected. Owing to multiple scattering effects, however, SANS can only be used for very thin samples ( less than about 0.25 mm). It is shown that, providing multiple scattering is avoided, ASAXS and SANS yield similar scattering curves for the filler aggregates.

Abecassis B , Testard F, Arleth L, Hansen S, Grillo I , Zemb T Langmuir (2006) 22  8017-8028

The ternary catanionic system octylammoniumoctanoate/octane/water is studied by combined SANS, light scattering, conductivity, and phase diagram approach in the water-poor microemulsion region. The sphere-to-cylinder growth and branching depends on the concentration, the water-to-surfactant ratio, and the temperature. The unidimensional growth leads to a network of interconnected wormlike micelles. Like most studied linear nonionic surfactants, in this true catanionic system at equimolarity of anionic and cationic surfactant, the curvature toward water increases with temperature, making connections between cylinders less frequent.

M. Impéror-Clerc, I. Grillo, A.Y. Khodakov, D. Durand and V.L Zholobenko, Chem. Comm. (2007) 23, 4199-4202

Time-resolved in situ SANS investigations have provided direct experimental evidence for the three initial steps in the formation of the SBA-15 mesoporous material: an induction period is followed by a shape transformation of the micelles from spherical to cylindrical ones followed by the precipitation of a two-dimensional hexagonal phase.

J. Penfold, R.K. Thomas, C.C. Dong, I. Tucker, K. Metcalfe, S. Golding, I. Grillo Langmuir (2007) 23, 10140-10149

Neutron reflectivity (NR) and small angle neutron scattering (SANS) have been used to investigate the equilibrium surface adsorption behavior and the solution microstructure of mixtures of the anionic surfactant sodium 6-dodecyl benzene-4 sulfonate (SDBS) with the nonionic surfactants monododecyl octaethylene glycol (C12EO8) and monododecyl triiscosaethylene glycol (C12EO23). In the SDBS/C12EO8 and SDBS/C12EO23 solutions, small globular mixed micelles are formed. However, the addition of Call ions to SDBS/C12EO8 results in a transition to a vesicle phase or a mixed vesicle/micellar phase for SDBS rich compositions. In contrast, this transition hardly exists for the SDBS/C12EO23 mixture, and occurs only in a narrow composition region which is rich in SDBS. The adsorption of the SDBS/C12EO8, mixture at the air-solution interface is in the form of a mixed monolayer, with a composition variation that is not consistent with ideal mixing. In water and in the presence of NaCl, the nonideality can be broadly accounted for by regular solution theory (RST). At solution compositions rich in SDBS, the addition of Call ions results in the formation of multilayer structures at the interface. The composition range over which multilayer formation exists depends upon the Ca2+ concentration added. In comparison, the addition of a simple monovalent electrolyte, NaCl, at the same ionic strength does not have the same impact upon the adsorption, and the surface structure remains as a monolayer. Correspondingly, in solution, the mixed surfactant aggregates remain as relatively small globular micelles. In the presence of Ca2+ counterions, the variation in surface composition with solution composition is not well described by RST over the entire composition range. Furthermore, the mixing behavior is not strongly correlated with variations in the solution microstructure, as observed in other related systems.

C. Seguin, J. Eastoe, R.K. Heenan, I.Grillo
Langmuir (2007), 23, 4199-4202

The extent of aggregation of nonionic surfactants can be controlled by the composition of mixed solvents with two miscible glycols, ethylene glycol (EG)/propylene glycol (PG). Three nonionic surfactants bearing a common E-8 ethoxylated headgroup, but with variations in the hydrocarbon chain, have been investigated: octaethylene monododecyl ether (C12E8), octaethylene monotetradecyl ether (C14E8), and octaethylene monohexadecyl ether (C16E8). The hydrogen-bonding solvents were EG/PG mixtures at different PG levels, defined in terms of the concentration (mol %) of PG. Aggregation was investigated using small-angle neutron scattering (SANS) with h-CiE8 surfactants, at 10 and 5 wt %, in deuterated glycol solvents to improve contrast. Increasing PG concentration (mol %) in the background EG/PG solvent leads to a consistent decrease in the SANS intensity, until in pure d-PG only very weak scattering is observed. These SANS data were analyzed using cylinder or ellipsoidal form factors for the EG-rich and PG-rich systems, respectively, hence demonstrating an aggregate shape change as a function of solvent composition. The results show that aggregation of nonionic surfactants occurs in glycol solvents and that the EG:PG ratio may be used as an effective means to switch aggregation "on" or "off", as required.

B. Abécassis, F. Testard, L. Arleth, S. Hansen, I. Grillo, Th. Zemb
Langmuir (2007) 23, 9983-9989

By means of small-angle neutron scattering and conductivity measurements, we study the microstructure of octylammoniumoctanoate/octane/water catanionic reverse microemulsions with an excess of anionic or cationic surfactant. Increasing the surface charge makes the microemulsion able to incorporate much more water than in the neutral case, up to 10 water molecules per surfactant. Even with charges in the surfactant film, wormlike micelles are present in the microemulsion domain. Along water dilution lines, the classical rod-to-sphere transition due to the minimization of the curvature energy of the rigid surfactant film is observed. When temperature is decreased, a re-entrant phase transition associated with the liquid-gas equilibrium of attractive cylinders is observed. Using the framework of the Tlusty-Safran theory, attraction could originate from junctions between wormlike reverse micelles. In any case, the spontaneous curvature of the catanionic surfactant film depends on both the temperature and the net charge, whatever the sign of the latter.


C. Seguin, J. Eastoe, R.K. Heenan, I. Grillo
J. Colloid and Interface Sc. (2007) 315, 714-720

Aggregation in mixed water-glycol and pure glycol solvents has been investigated with four related surfactants, bearing common C-12 tails: anionic, sodium dodecylsulfate (SDS); cationic, dodecyltrimethyl ammonium bromide (C(12)TAB); zwitterionic C-12-amidopropyidimethylamine betaine (betaine) and nonionic, octaethyleneglycol monododecyl ether (C12E8). The solvent media were water, water/ethylene glycol, and water/propylene glycol mixtures, as well as pure ethylene glycol (EG) and propylene glycol (PG), spanning relative dielectrics epsilon(r) from 79 to 30. Results from small-angle neutron scattering (SANS) experiments, employing deuterated solvents, were consistent with the presence of ellipsoidal, or cylindrical micelles, depending on solvent and surfactant type. In pure EG and PG solvents the ionic and zwitterionic surfactants exhibit only weak aggregation, with much smaller micelles than normally found in water. However, interestingly, pure EG is identified as a solvent in which nonionic C12E8 aggregates strongly, mirroring the behavior in water. In contrast when the solvent is changed to PG (,epsilon(r) = 30) aggregation of C12E8 is only minimal. Hence, aggregation is shown to be strongly dependent on surfactant type and identity of the glycol solvent.

E. Terriac, J. Emile J, M.A. Axelos, I. Grillo, F. Meneau, F. Boué
Colloids and Surface A- Physicochemical and engineering aspects (2007) 309, 112-116

We report on small angle neutron and X-ray scattering experiments on single common black films in ordered bamboo foams stabilized by sodium dodecyl sulfate and dodecanol. We observed anisotropic scattering perpendicular to the film. The integrated signal exhibits clear Kiessig fringes over a wide range of diffusion vector q. We were able to fit our data by a single layer (neutron with contrast matching water/SDS) or a "three slabs" (X-ray) reflectivity. We also discuss about the wide range of reflected angle, despite the narrow distribution of incident angles. Though thermal surface fluctuations may induce off-specular reflectivity, we show here a simple geometrical explanation of the phenomenon. This angle distribution is indeed compatible with the curvature of the film.