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Weiche Materie Poster: Do., 13:00–15:30 D-P329
SANS experiments on confined polymers in microemulsions
Henrich Frielinghaus 1 , Simona Maccarrone 1 , Jürgen Allgaier 1 , Dieter
Richter 1
1 Forschungszentrum Jülich GmbH, Institut für Festkörperforschung, D-52425 Jülich,
Germany
It has been established that amphiphilic diblock copolymers increase the efficiency of
surfactants in microemulsions (polymer boosting effect). These studies always considered
large oil and water domains of size d compared to the typical polymer size
Rg. Thus the confinement parameter Rg/d was small in these first studies. The ongoing
studies of this paper consider medium and higher confinement, where small angle
neutron scattering measurements reveal a new behaviour, which can be compared to
computer simulations by T. Auth [1].
Microemulsions consist of immiscible oil and water, and a third component, the surfactant.
The surfactant mediates between oil and water; thus a macroscopically homogenous
phase is formed. Microscopically, domains of oil and water are formed with a
surfactant film in between. The efficiency of a surfactant is measured by the minimum
amount of surfactant needed to form a one-phase microemulsion. In previous studies
[2] amphiphilic diblock copolymers proved to enhance the efficiency of surfactants dramatically
(polymer boosting effect). By SANS experiments using contrast variation it
was shown that the polymer decorated the film and the membrane bending rigidity is
increased. Thus larger domain structures are formed with a better surface to volume
ratio.
The current studies focus on microemulsions with smaller domain sized d compared
to the typical polymer size Rg. The variation of the ratio could be achieved by different
polymers and the use of different oils, since the efficiency of the surfactant is
oil dependent. At low confinement the result of the initial studies [2] is confirmed; at
intermediate confinement a slightly higher sensitivity of the polymer effect is obtained,
while at high confinement a reversed behaviour is observed. The theory of Auth [1]
predicts a much more enhanced sensitivity at medium confinement and a reversed behaviour
at larger confinement. These results are interesting for applications (enhanced
polymer boosting) and interpretations of biological membranes (reversed behaviour).
[1] T. Auth, PhD thesis, University Cologne, Cologne, Germany
[2] B. Jakobs, T. Sottmann, R. Strey, J. Allgaier, L. Willner, D. Richter, Langmuir 15,
6707 (1999); H. Endo, M. Mihailescu, M. Monkenbusch, J. Allgaier, G. Gompper, D.
Richter, B. Jakobs, T. Sottmann, R. Strey, I. Grillo, J. Chem. Phys. 115, 580 (2001)