Page 34 - ILLS Annual Report 2018

SOFT MATTER
Christine M. Papadakis. German
Technical University of Munich, Germany
‘My group uses scattering methods to investigate, among other things, self-assembling and (multi-)responsive polymer systems. A recent emphasis is on time-resolved neutron scattering experiments after a temperature or pressure jump.’
Fast and furious: pressure jumps combined with time-resolved small-angle neutron scattering reveal aggregate growth in a stimuli-responsive polymer
Small-angle scattering diffractometer D11
Aggregation processes are ubiquitous in soft matter, e.g. in polymers, colloids and proteins, and frequently evolve through transient states. While small-angle neutron scattering (SANS) provides structural information on length scales of ~1−100 nm and
a time-resolution of milliseconds, pressure jumps allow a rapid change of state. In the present study, we apply a pressure jump to a semidilute solution of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) in D2O [1], inducing phase separation, and employ kinetic SANS to study the aggregation process with a focus on the early stages of mesostructure formation.
Figure 1
a) Coexistence line in the temperature-pressure frame (black line). The red arrow indicates the pressure jump carried out. Inset) Chemical structure of PNIPAM.
b) SANS data before (black) and after (coloured) the pressure jump. The growth regimes I (blue), II (red) and III (orange) are indicated.
AUTHORS
B.-J. Niebuur, X. Zhang, F. Jung, Ch.M. Papadakis (Technical University of Munich, Germany)
L. Chiappisi (ILL and Technical University of Berlin, Germany)
A. Schulte (University of Central Florida, Orlando, USA)
ARTICLE FROM
ACS Macro Lett. 7 (2018) 1155—doi: 10.1021/acsmacrolett.8b00605
REFERENCES
[1] V. Aseyev, S. Hietala, A. Laukkanen, M. Nuopponen, O. Confortini, F.E. Du Prez and H. Tenhu, Polymer 46 (2005) 7118
[2] R. Stepanyan, J.G.J.L. Lebouille, J.J.M. Slot, R. Tuinier and M.A. Cohen-Stuart, Phys. Rev. Lett. 109 (2012) 138301
[3] K. Kyriakos, M. Philipp, J. Adelsberger, S. Jaksch, A.V. Berezkin, D.M. Lugo, W. Richtering, I. Grillo, A. Miasnikova, A. Laschewsky, P. Müller-Buschbaum and C.M. Papadakis, Macromolecules 47 (2014) 6867
[4] T. Tanaka, J. Phys. Condens. Matter 12 (2000) R207
Pressure jumps present a well-controlled way to trigger the phase transition of PNIPAM, because they allow a fast change of state even for large sample volumes—as they
are necessary for SANS—without thermal effects. In our experiment, a temperature-controlled copper beryllium pressure cell was used, in which the sample is separated from the pressurising medium by a movable piston. The pressure jump was accomplished within less than 0.1 s by a pneumatically driven valve. Starting in the one-phase regime at 31 MPa and 35.1 °C, a sudden pressure reduction by Δp = -15 MPa triggered the phase transition (figure 1a). Kinetic SANS measurements were carried out on instrument D11 with a time resolution of 0.05 s.
ANNUAL REPORT 2018