Polymer vesicles in various media

Vesicles can be made from various polymers, from modified biological to who lly synthetic, in media ranging from complex to neat organics and water. Al though the canonical form of polymers that have the ability to assemble int o encapsulating vesicles is an amphiphilic H-P (hydrophobic-polar) diblock, additional block copolymers from triblocks to pentablocks have also been s hown to assemble into vesicles. Polydispersity seems to have a minimal effe ct, but solvent requirements may well depend on the proportion of H to P as well as the molecular weight. What is clear from all of the ultrastructura l characterization done on polymer vesicles is that the 'universal' thickne ss of 3-4 nm, which is well-known for natural lipid vesicles, reflects no p hysical limitation on the amphiphilic assembly at the nano-scale. Emerging material characterizations emphasize the dominance of the two-dimensional H -P interface and the unnatural robustness possible in the responses of poly mer membranes. (C) 2000 Elsevier Science Ltd. All rights reserved.