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Weiche Materie Poster: Do., 13:00–15:30 D-P336
Dynamics of bicontinuous microemulsions on intermediate and short lengthscales
Olaf Holderer 1 , Henrich Frielinghaus 1 , Michael Monkenbusch 1 , Jürgen
Allgaier 1 , Dieter Richter 1 , Bela Farago 2
1 Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich – 2 Institut
Laue Langevin, Grenoble, BP 156, F38042 Grenoble Cedex 9, France
Bicontinuous microemulsions, consisting of water, oil and a surfactant (C10E4), have
been studied with neutron spin echo spectroscopy (NSE) and small angle neutron
scattering (SANS). Addition of diblock copolymers (PEPX-PEOX) or homopolymers
(PEPX and PEOX, X=5 k or 10 kg/mol molecular weight) allows a tuning of the
membrane properties such as the bending rigidity κ in such systems.
The dynamics of bicontinuous microemulsions has been studied with NSE. On lenght
scales of the order of the characteristic structural distance d (i.e. scattering angles
≈ qo = 2π/d) of the microemulsion, two contrasts for neutrons have been used: bulk
contrast, where the dynamics of the oil/water difference is visible, and film contrast
which reveals the surfactant layer fluctuations. Comparison with theoretical predicitons
of the relaxation shed light on hydrodynamic interactions in bicontinuous microemulsions.
On shorter length scales (i.e. larger scattering angles, q > 4q0), the bending modulus κ
is obtained from a numerical integration of the intermediate scattering function S(q, t)
of the Zilman-Granek model [1]. It is shown that the analysis of the dynamics gives
a direct access to the ”bare” membrane bending moduls κ, which is compared to the
renormalized one as obtained from SANS[2]. The difference between the two ways of determining
κ is the renormalization factor, as predicted by theory. A decrease (increase)
of the bending rigidity has been observed when homopolymers (diblock copolymers)
have been added, in agreement with theoretical predictions.
[1] A. Zilman, and R. Granek, Phys. Rev. Lett. 77 (1996) 4788.
[2] O. Holderer et al., J. Chem. Phys. 122 (2005) 094908.