The rheology of highly concentrated PBLG solutions

Lynn M. Walker, Norman J. Wagner

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73 Scopus citations

Abstract

We have characterized the rheology of two concentrated, liquid crystalline solutions of poly(ϒ benzyl—L-glutamate) of molecular weight 238 000 in m—cresol. Comparing these results to previous work on less concentrated, liquid crystalline solutions separates the effects of concentration from the direct influence of defect texture on liquid crystal polymer rheology. This work also defines the limitations of current polydomain models and suggests improvements. The solution at C = 37wt% PBLG behaves similarly to moderately concentrated nematic solutions (12wt% < C < 30wt%) and much of the rheology can be described by a polydomain texture model. The relaxation behavior upon cessation of flow, including stress relaxation, moduli evolution and strain recoil, demonstrates that two different mechanisms with different dependence on concentration drive the relaxation. The higher concentration 40wt% PBLG solution exhibits Region I behavior and a smaller characteristic texture size. The material exhibits two steady state viscosity branches; the lower branch is probably the equilibrium branch while the upper is a metastable “glass—like” structure induced by shearing beyond a critical rate. The observed anomalous transient behavior for this sample concurs with Region I behavior observed for other lyotropic systems, suggesting universal behavior.

Original languageEnglish (US)
Pages (from-to)925-952
Number of pages28
JournalJournal of Rheology
Volume39
Issue number5
DOIs
StatePublished - Sep 1995
Externally publishedYes

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