Interfacial behaviour of ionic block copolymers

The surface properties of quaternized poly(styrene-block-4-vinylpyridinium) AB block copolymers in monolayers spread at the air/water interface were thoroughly studied using the Langmuir film balance technique and microscopy techniques (i.e. transmission electron microscopy and atomic force microscopy). The effects of both molecular structure (i.e. chain lengths of the two blocks, alkyl chain length, and the counterion of the quaternizing agent) and the experimental parameters (i.e. measurement temperatures, salt species and salt concentrations in the aqueous subphase, compression rates, and hysteresis) on interfacial behaviour of the ionic block copolymers were explored. Optimum conditions for the deposition of polymer monolayers from a water surface to a solid substrate for the microscopy studies were also investigated. Evidence for novel surface micelle formation is presented. Three morphologies of surface micelles (i.e. plane, rod, and starfish) are identified for the block copolymers. The appearance of each morphology is found to be related only to the relative chain lengths of the two blocks. Methods of calculating aggregation numbers in starfish micelles are developed. A phase transition phenomenon is observed in surface pressure-area isotherms of the polymer monolayers. This phase transition is found to be related to the pressure-induced solubilization process of the quaternized poly(4-vinylpyridinium) hydrophilic block chains. A model of a starfish-to-jellyfish transition is introduced to describe this phase transition phenomenon.