Amphiphilic diblock copolymer gels: the relationship between structure andtheology

Block copolymers dissolved in a selective solvent form micelles that can be regarded as model colloidal dispersions because by tailoring the copolymer composition, the relative size of core and, corona can be controlled. This enables the interaction potential to be varied, such that; either hard or soft sphere ordering can be observed above the liquid-solid (sol-gel) trans ition. Here we review recent work on the structure and theology of micellar phases formed by block copolymers in solution. First, the structure of sol id and liquid micellar phases is considered, and its relationship to flow p roperties of gels and sols is discussed. Then the ordering of hard versus s oft spheres is considered in the context of experimental phase diagrams for poly(styrene)-poly(isoprene) in decane and poly(oxyethylene)-poly(oxybutyl ene) diblock copolymers in water. The use of experiments in the linear visc oelastic regime to locate the gelation (liquid-solid) transition is then re viewed, and the application of measurements in the linear viscoelastic regi me to study relaxation phenomena is also outlined. The nonlinear flow behav iour of micellar block copolymer solutions is then considered. In particula r the focus is on the development of a yield stress in the solid phase, cre ep and stress relaxation measurements which throw light on flow mechanisms, and Fourier transform theology which provides a quantitative measure of no nlinear viscoelasticity under oscillatory shear. Finally, an overview is pr ovided of recent small-angle scattering experiments that have probed the me chanisms of macroscopic alignment of body-centred and face-centred cubic mi cellar phases subjected to large-amplitude oscillatory shear or steady shea r in a Couette eel.