Macromolecules, Vol.42, No.1, 299-307, 2009
Self-Assembly of Coil/Liquid-Crystalline Diblock Copolymers in a Liquid Crystal Solvent
Diblock copolymers having a random-coil polymer block (polystyrene, PS) connected to a side-group liquid crystal polymer (SGLCP) self-assemble in a nematic liquid crystal (LC), 4-pentyl-4'-cyanobiphenyl, into micelles with PS-rich cores and SGLCP-rich coronas. The morphologies of block copolymers with varying PS content are characterized as a function of temperature and concentration using small-angle neutron scattering, rheometry. and transmission electron microscopy. Unlike conventional solvents, the nematic LC can undergo a first-order transition between distinct fluid phases, accessing the regimes of both strong and slight selectivity in a single polymer/solvent pair. Micelles dissolve away above a microphase separation temperature (MST) that is often equal to the solution's isotropization point. T-NI. However. increasing or decreasing the polymer's PS content can shift the MST to be above or below T-NI. respectively. and in the former case, micelles abruptly swell with solvent at T-NI. Comparable effects can be achieved by modulating the overall polymer concentration.