Rheological Properties and Conformation of a Side-Chain Liquid Crystal Polysiloxane Dissolved In a Nematic Solvent
Polymers and High Performance Materials
We report measurements of the change in electrorheological response of the low molar mass nematic pentylcyanobiphenyl (5CB) on dissolution of small amounts of a side-chain liquid crystal polymer (SCLCP). From the ratio of the intrinsic viscosities with the field on and off, [eta(on)] and [eta(off)] respectively, we deduce a value for the ratio of the rms end-to-end distances of the SCLCP parallel and perpendicular to the nematic director, R-vertical bar vertical bar/R-perpendicular to = 1.17 +/- 0.02 via application of the Brochard hydrodynamic model, which indicates that the polymer has a slightly prolate shape. Small-angle neutron scattering measurements reveal a numerically similar value for the corresponding ratio of apparent rms radii of gyration, R-g vertical bar vertical bar/R-g perpendicular to = 1.12 +/- 0.06, for the SCLCP dissolved in deuterated 5CB. Observations of the shear stress transient response of a homeotropic monodomain indicate that, at a concentration between 0.01 and 0.02 g/mL, the solution exhibits a transition from director-aligning to director-tumbling behavior. This result is inconsistent with the Brochard model, which predicts such a transition only for a polymer with an oblate shape but agrees with a modified version, which assumes an additional contribution to viscous stress arises due to elastic coupling between the solvent and polymer directors.
Jamieson, A. M.,
Rowan, S. J.
(2005). Rheological Properties and Conformation of a Side-Chain Liquid Crystal Polysiloxane Dissolved In a Nematic Solvent. Macromolecules, 38(12), 5205-5213.
Available at: http://aquila.usm.edu/fac_pubs/2737