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FIGARO (Fluid Interfaces Grazing Angles ReflectOmeter) is a high flux, flexible resolution, time-of-flight neutron reflectometer for the study of horizontal surfaces such as free liquids. It was launched as a user instrument at the ILL in April 2009 and has already generated over 100 peer-reviewed publications.

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Instruments & Support : Instruments & groups > FIGARO > More > Sample Environment

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Sample Environment

FIGARO has a range of versatile sample environment options including adsorption troughs, a Langmuir trough and an overflowing cylinder for air/liquid experiments, and a rack of sample cells for solid/liquid experiments.

Adsorption troughs

Adsorption troughs are used as a platform to study interfacial layers of molecules self-assembled from solution. The troughs assembly involves six sample positions each of which contains a PTFE trough of dimensions 220 mm x 50 mm. The volume required are 45 ml for liquids of high surface tension (such as water) and 25 ml for liquids of low surface tension (such as a concentrated surfactant solution). There are 20 trough inserts available so that some can be cleaned while others are in use. The alignment of samples is done through the instrument control software using a high-precision height sensor. The neutron windows (sapphire) and height sensor window (quartz) are all heated gently to avoid condensation. The option exists to heat the liquid in each trough with a dedicated strip heater, and there is also an option for three troughs to be connected to a thermostated water bath which is useful for cold measurements. The former heating option has not been fully commissioned yet, so for measurements away from ambient temperature please make this requirement clear to the instrument team well in advance of your experiment.

Langmuir trough

A Langmuir trough is available for measurements concerning insoluble monolayers at the air/water interface.  Typically the monolayer is made from a spreading solution of the material in a carrier solvent, and then barriers are used to compress the film.  Measurement of the surface pressure is carried out in situ.  The standard trough is 500 x 250 mm in area and takes about 600 ml of liquid.  There is an insert available which reduced the area and volume by about three quarters.  There are also borated (poorly reflecting to neutrons) glass plates which can sit in the large trough to reduce the volume by about one third without any detrimental effect to the maximum compression ratio that can be obtained.  There are two boxes for the trough to sit in.  The first is a essentially a dust cover where the pressure sensor sits on an aluminium bridge above the free liquid surface.  There are sapphire windows for the neutrons and optical sensor which are heated to prevent condensation.  The second box is an air-tight reaction chamber provided by Dr Christian Pfrang (Reading University, UK) suitable for gas phase reactions.  It has a heated lid making it suitable for measurements at elevated temperature.  In each case the trough has a conduction plate underneath it so that temperature can be controlled using a thermostated circulating water bath.  Measurements at 37 ºC have been carried out routinely on the beamline in the absence of particular problems concerning the uniformity of heating or condensation effects.  In such a case the sealed reaction chamber would be used as the box of choice both to limit evaporation and also to prevent rain falling on the sample!  The Langmuir trough is fully linked to the instrument control software NOMAD so that commands to reach a given surface area or surface pressure can be automated among neutron data acquisitions.

Solid/liquid interface cells

Solid/liquid interface cells are used to investigate the structure and composition of thin molecular films immersed in bulk liquids. Neutrons are transmitted through the solid substrate (i.e. a single crystal of silicon, quartz, or sapphire) and reflect from the bulk liquid at the solid/liquid interface. There are a range of cells that have been developed on FIGARO which are available for all users: 100 x 50 mm, 80 x 50 mm (most common; see picture left) or 50 x 50 mm. Fabricated from polyether ether ketone (PEEK), the base plate consists of a 0.5-mm deep solution reservoir, an o-ring for sealing to the substrate face, and inlet and outlet ports for solution exchange. These components are sandwiched between aluminium plates containing with circulating water channels for temperature control. Up to 7 solid-liquid cells can be mounted simultaneously on the sample table and translated into the neutron beam. For maximum flexibility, it is possible to mount the crystals with the solid above the liquid (reflection up at the sample) or the liquid above the solid (reflection down at the sample).  Solution changes can be automated through the instrument control software NOMAD using an HPLC pump and valve system (Knauer, Smartline; see picture centre) employing four independent input and six output lines. This system provides greater automation of measurements and precision control of solution mixing for contrast matching.  First time users are welcome to contact the instrument responsibles for arranging to use FIGARO's substrates: there are some 100 x 50 mm, 80 x 50 mm and 50 x 50 mm silicon as well as 100 x 50 mm and 80 x 50 mm sapphire crystals available. A recent development is the production of two sets of reflection up/down cells compatible with 80 x 50 mm (see picture right) or 50 x 50 mm crystals. Each cell has two solid/liquid interfaces: one with the solid oriented above the liquid (facing down) and the other with the solid oriented below the liquid (facing up). The cells have been used to good effect to determine the effects of bulk phase separation and gravity on the interfacial properties of several synthetic and biophysical polyelectrolyte/surfactant systems.

Overflowing cylinder

An overflowing cylinder has been developed on the FIGARO beamline for measurements at a dynamic air/liquid interface.  There is a flow of liquid up a vertical cylinder which then at the top flows radially out from the centre and down the sides for recirculation.  The neutron beam reflects off the continually expanding steady state liquid surface.  Information can be gained about the adsorption kinetics of amphiphilic materials at short timescales (typically < 1 s).  Also, as the surface is constantly regenerated the device can be used to gain information about adsorption mechanisms by separating the effects of surface and bulk interactions in strongly associating mixed systems.

Liquid/liquid interface

Regretably we do not yet have cells for studies of thin molecular layers at the liquid/liquid interface.  Hopefully there will progress in the provision of appropriate sample cells in the future.  But for the time being, it is necessary for users to provide sample cells for measurements at the oil/water interface .  This could perhaps be based on the approach of Prof. Ali Zarbakhsh and co-workers, which is to spin coat a contrast matched oil film on a silicon substrate then in the frozen state mount it in a custom-built round solid/liquid interface cell.  The neutron beam then transmits through the solid and the oil film to reflect at the oil/water interface.  Careful determination of the attenuation of the neutron beam through the oil is required.  You are also welcome also to get in touch with the instrument responsibles at any time to check if there is any recent progress in this area.

Other sample environments

FIGARO has also experienced measurements involving a range of other sample environments.  Some examples are listed here. (1) There is a rheometer which has been mounted on the beamline for measurements at the solid/liquid interface while the bulk liquid is under shear.  This option exploits the reflection down configuration of the instrument.  (2) A user-supplied dedicated sample box has been used to investigate solvent drying effects at the solid/liquid interface.  (3) A user-supplied pressure cell has been used to probe the structure of films at the solid/liquid interface at high pressures.  (4) Two sets of solid/liquid cells now exist for reflection up/down comparison experiments.  These cells are used for distinguishing surface induced self assembly versus bulk self assembly and transport of aggregates under gravity to explain the formation of thick mesostructured films in strongly interacting mixed systems.  For further information about any of these possibilities or to discuss the compatibility (e.g. geometric constraints) of any equipment you wish to mount on the FIGARO sample table please contact the instrument responsibles.