COMPLEX PHASE-BEHAVIOR IN SOLVENT-FREE NONIONIC SURFACTANTS

Unsolvated block copolymers and surfactant solutions are ''soft materi als'' that share a common set of ordered microstructures, A set of pol yethyleneoxide-polyethylethylene (PEG-PEE) block copolymers that are c hemically similar to the well-known alkane-oxyethylene (C(n)EO(m)) non ionic surfactants was synthesized here. The general phase behavior in these materials resembles that of both higher molecular weight block c opolymers and lower molecular weight nonionic surfactant solutions. Tw o of the block copolymers exhibited thermally induced order-order tran sitions and were studied in detail by small-angle scattering, The fund amental microstructural spacing was determined to be a crucial paramet er in these transitions. Transitions from one ordered state to another occur only when the lattice spacing is nearly matched, These material s highlight the importance of epitaxy and molecular conformation in th e phase transformations of soft material.