Determination of the Texture Viscosity and Elasticity of a Nematic PBLG/d-DMF Solution through Magnetic Field Alignment

Norman J. Wagner, Lynn M. Walker

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21 Scopus citations

Abstract

A moderate magnetic field is used to align a polydomain, nematic sample of 16 wt % poly- (γ-benzyl L-glutamate) (PBLG) in deuterated N,N-dimethylformamide (d-DMF) orthogonal to a small-angle neutron scattering beam. The temporal evolution of the resultant domain alignment is analyzed through a molecular model for the scattering and a mean-field mechanical model. The latter includes both the viscous and elastic responses of the defect texture, which is responsible for the polydomain mesophase. The effective structure factor for the nematic phase is extracted from the SANS measurements, showing a reduction in scattering intensity that is presumed to arise from excluded volume interactions. We also extract a texture elasticity of 5 × 10−7 dynes for a texture size of ≈3 μm from the steady-state alignment, and a shear viscosity of 28 Pa s at a characteristic shear rate of ≈2 × 10−4 s−1 from the long-time temporal response. The latter is over 20 times the measured nematic viscosity and suggests a possible influence of the texture on the very low shear viscosity. The short-time temporal response is found to be in good agreement with predictions from nematodynamics.

Original languageEnglish (US)
Pages (from-to)5979-5986
Number of pages8
JournalMacromolecules
Volume27
Issue number21
DOIs
StatePublished - Oct 1 1994
Externally publishedYes

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