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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 44: Complex Fluids, Colloids, Micelles and Vesicles (joint session CPP/DY)

CPP 44.7: Talk

Thursday, March 21, 2024, 17:15–17:30, H 0110

Phase Behaviour and Structures Induced by Adding Cosurfactant to Nonionic Micelles - Rodlike Assembly of Small Micelles — Robert F. Schmidt¹, Sylvain Prévost², Miriam Simon³, Yeshayahu Talmon³, and •Michael Gradzielski¹ — ¹Stranski-Laboratorium für Physikalische Chemie, Inst f. Chemie, TU Berlin, Str. des 17. Juni 124, D-10623 Berlin, Germany — ²ILL, 71 Rue de Martyrs, Grenoble, France — ³Dep. of Chemical Engineering, Technion, Haifa 3200003, Israel

Addition of cosurfactant is a way to control systematically structure and properties of surfactant formulations. Normally this leads to continuously changing the packing parameter and transforming spherical to wormlike micelles and at higher concentration to bilayers via a first order phase transition. Here we show a completely different self-assembly behaviour seen for a classical nonionic surfactant (Tween 20) and 2-ethylhexylglycerol (EHG) as cosurfactant. Structural characterisation by light and neutron scattering (SANS) and cryo-TEM, shows that elongated assemblies are formed, which are composed of individual micelles that are locally ordered in a cylindrical fashion. A first-order phase transition takes place but only a smaller fraction of amphiphile is initially forming a bilayer structure and complete transformation to bilayers occurs within the single-phase region for EHG concentrations higher than the ones of the phase transition. This very uncommon structural evolution can be rationalised by the particular structure of the amphiphilic molecules involved and this finding extends our common assumptions about surfactant assembly.

Keywords: Self-Assembly; Micelles; SANS; cryo-TEM