Complex phase behavior in solvent-free nonionic surfactants

Unsolvated block copolymers and surfactant solutions are 'soft materials' that share a common set of ordered microstructures. A set of polyethyleneoxide-polyethylethylene PEO-PEE) block copolymers that are chemically similar to the well-known alkane-oxyethylene (CnEOm) nonionic surfactants was synthesized here. The general phase behavior in these materials resembles that of both higher molecular weight block copolymers and lower molecular weight nonionic surfactant solutions. Two of the block copolymers exhibited thermally induced order-order transitions and were studied in detail by smallangle scaftering. The fundamental microstructural spacing was determined to be a crucial parameter in these transitions. Transitions from one ordered state to another occur only when the lattice spacing is nearly matched. These materials highlight the importance of epitaxy and molecular conformation in the phase tranqformations of soft material.
Amphiphilic molecules such as surfactants, phospholipids, and ionic soaps self-assemble into micelles in dilute aqueous solution because of the hydrophobic effect. As the concentration of the amphiphile increases, thermodynamically stable [...]