INTERFACIAL BEHAVIOR OF BLOCK POLYELECTROLYTES .1. EVIDENCE FOR NOVEL SURFACE MICELLE FORMATION

Monolayers of a polystyrene/poly-4-vinylpyridine AB diblock ionomer, (PS)260 (4-PVP)240, fully quaternized with decyl iodide have been studied at the air/water interface with the Langmuir film balance technique. Surface pressure/area isotherms exhibit an abrupt onset and an apparent first-order phase transition at high pressures. Transmission electron micrographs of LB films deposited on carbon-coated copper grids provide direct evidence of self-assembly of the diblock copolymers into circular surface micelles. These surface micelles appear to be quite regular and have an aggregation number of approximately 120. The distance between micelles (at low surface pressures) is consistent with fully extended dec-4-PVP+ chains extending radially from a central core of PS coils. These aggregates pack with a surface density approximately 10(10) particles per cm2 at the lowest detectable surface pressures. The apparent first-order phase transition correlates with transmission electron micrograph observations and may originate from a process where the decylated polyelectrolyte block proceeds from a surface-adsorbed state to a submerged, aqueous state as the film is compressed. The entropy of this transition is +7.6 eu and is consistent with the polymeric micelles passing from an ordered 2D state to a less ordered quasi-2D state.