1998 E.W.R. Steacie Award Lecture Asymmetric amphiphilic block copolymers in solution: a morphological wonderland

Abstract

Asymmetric amphiphilic diblock copolymers self-assemble in selective solvents. Since 1995, when we first reported the systematic preparation of a sequence of various "crew-cut" aggregate morphologies from this class of copolymer in solution (1), we have identified a vast array of structures and have begun a detailed investigation of the thermodynamic and kinetic parameters that induce morphogenesis. Not only spheres, rods, bilayer and bicontinuous architectures, as well as inverted structures are observed, but also a selection of mixed, combined and much more complex aggregates is documented. All of these aggregates have a phase-separated insoluble core and a crew-cut soluble corona. Thus, all parameters that permit selective modification of the component of either phase or of the interface provide a window for morphological control. By carefully adjusting the polymer chain environment, it has been possible to develop a systematic understanding of morphogenic parameters, which include, among others, polymer composition, common solvent, initial concentration, temperature, type and concentration of added ions, method of preparation, and added homopolymer. To date, more than 30 publications have appeared in the literature from our group alone on this subject. One of the problems inherent with such a complicated system is the taxonomy or classification: which morphologies correspond to equilibrium positions and which are intermediate or trapped? An attempt at a logical presentation of the observed aggregates is given, preceded by a qualitative discussion of the thermodynamic framework for this system. Where possible, the transitions between morphologies are explained in the context of the thermodynamic parameters. Finally, parallels are drawn between the copolymer aggregates and biological architectures.Key words: crew-cut, morphology, block copolymer, self-assembly, amphiphile.