Self-assembly of dPS-liquid crystalline diblock copolymer in a nematic liquid crystal solvent

摘要

A diblock copolymer dPS(9.1K)-b-LCP(7.2K), the number in parentheses represents the number-averaged molecular weight) with a deuterated polystyrene (dPS) block connected to a side group liquid crystal polymer [poly(6-(4′-cyanobiphenyloxy)hexyl acrylate, LCP] was self-assembled into ～78 ? spherical micelles with a dPS core and LCP corona in a small-molecule nematic liquid crystal solvent, 4-pentyl-4′-cyanobiphenyl (5CB). The micellar structures were examined by small angle neutron scattering (SANS) at various block copolymer concentrations and temperatures. The SANS data was analyzed further using a curve fitting method. The critical micelle concentration (CMC) was as low as ～0.0027 wt % and the self-assembled micelles were dissociated reversibly into a unimer state at 33 °C, which is lower than the nematic to isotropic transition temperature (T _(ni)) of 5CB (36 °C). The entropic penalty imposed on the dPS by the ordered nematic state of the LC solvent caused phase separation of the flexible dPS block to form micelles and vanished above the T _(ni) of the LC solvent. A low CMC of ～0.0027 wt % suggests that 5CB was a strong selective solvent for dPS-b-LCP in the nematic state. The global orientation of 5CB, produced by a magnetic field (MF, 1.2 T) revealed the structure of the dPS core of the micelle to be prolate (elongated sphere) oriented with the long axis along the applied MF direction.