DYNAMIC LIGHT-SCATTERING FROM A NEMATIC MONODOMAIN CONTAINING A SIDE-CHAIN LIQUID-CRYSTAL POLYMER IN A NEMATIC SOLVENT

By combining dynamic light scattering data on nematic monodomains in three different scattering configurations with independent measurements on the bend elastic constant via the Freedericksz transition method, we have measured all of the elastic and viscosity coefficients associated with the splay, bend, and twist distortions of the nematic matrix. We performed VH scattering experiments on monodomains in the homogeneous orientation, with the nematic director aligned, respectively, inside and orthogonal to the plane formed by the incident and scattered wave vectors. Similar studies were carried out on homeotropic monodomains with the nematic director parallel to the incident wave vector. Numerical values of elastic and viscosity constants derived from such analyses on pure pentacyanobiphenyl (5CB) are consistent with literature results. The addition of a side-chain liquid crystal polymer, poly[6-(4-methoxy-alpha-methylstilben-4'-yl)oxy]hexyl methacrylate] (MSHMA), results in significant increases in the relaxation times for dynamic light scattering from all three scattering geometries. These changes are due to small decreases of the three elastic constants and larger increases of the three viscosities. Increase of polymer molecular weight results in a relatively small change in the elastic constants and a substantial increase in all three viscosities. The percent change is largest for the bend mode and smallest for the splay mode, which is consistent with the idea that the former involves translational motions of the backbone, whereas the latter requires relatively unhindered rotations around the backbone.