Isotropic to nematic transition in solutions of cylindrical PB-PEO block copolymer micelles close to a wall

The influence of a flat interface on the isotropic to nematic (I/N) phase transition was investigated for aqueous solutions of cylindrical micelles of polybutadiene-poly(ethylene oxide) block copolymers using specular neutron reflectivity. While the I/N-transition in the bulk occurs at the solute volume fraction φN/I, we observed the formation of a condensed layer close to a silicon single crystal interface at volume fractions of about φi≈0.85×φI/N. The thickness of this layer does not vary if the solute fraction is changed, while it’s density increases drastically within a very narrow range of volume fractions. This observation is interpreted as the formation of a nematicaly ordered layer which is induced by the interface.