Self-Assembly of dPS-Liquid Crystalline Diblock Copolymer in a Nematic Liquid Crystal Solvent

• Published in: Macromolecules Vol. 45; no. 15; pp. 6168 - 6175
• Main Authors: Park, Soo-Young, Kavitha, Thangavelu, Kamal, Tahseen, Khan, Waliullah, Shin, Taegyu, Seong, Baekseok
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14-08-2012
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties; Thermotropic state; Temperature effect; Experimental study; Magnetic field effect; Organic solution; Side chain; Micellar critical concentration; Biphenyl derivatives; Liquid crystal polymers; Concentration effect; Diblock copolymer; Nematic solvent; Acrylate copolymer; Micellar solution; Styrene copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma300476j

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 Å 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.