Structural rearrangements in hairy-rod polymer solutions undergoing shear |
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Authors: | Loic Hilliou Dimitris Vlassopoulos Matthias Rehahn |
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Institution: | Foundation for Research and Technology – Hellas (FO.R.T.H.) Institute of Electronic Structure and Laser P.O. Box 1527, 71110 Heraklion Crete, Greece e-mail: dvlasso@iesi.forth.gr, GR Polymer Institut, Universit?t Karlsruhe Kaiserstrasse 12, 76128 Karlsruhe Germany, DE
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Abstract: | We report on a rheooptical investigation of hairy-rod poly(p-phenylene) solutions at different concentrations and temperatures. These polymers have a reasonably high persistence length
(about 28 nm) and behave as worm-like chains in dilute solutions, whereas they form nearly spherical fractal aggregates with
internal anisotropy at higher concentrations. By exposing these systems to time-dependent simple shear and following the evolution
of birefringence in start-up and its subsequent relaxation upon the cessation of shear, we find a substantial broadening of
the cluster size distribution, resulting from flow-induced cluster deformation and break-up. In contrast to the very dilute
solutions, where polymers align in the flow direction, the deformed clusters main axes are aligned in the vorticity direction,
presumably due to their strong steric local pretransitional type of ordering, with the constituent polymers following the
velocity vector. At the highest concentration, which corresponds to a weak gel, shear is shown to break-up the gel and the
steady-state response of a broad-size aggregate suspension is eventually recovered.
Received: 18 February 1999/Accepted: 6 July 1999 |
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Keywords: | Rheooptics Birefringence Hairy-rod polymers Worm-like chains Aggregation |
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