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No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner. JMD wishes to acknowledge the support and encouragement of McGill University for providing a working environment conducive to a major writing project. He also wishes to recognize the colleagues and research students who have played a vital role in the development of his understanding of polymer rheology and its applications. In addition, JMD wishes to express his appreciation to the University of Wisconsin, especially to R. B. Bird and A. S. Lodge, for their professional hospitality during the time when he got his part of the writing well launched.KFW wishes to acknowledge the management of Hoechst Celanese for their permission to participate in this book. He also PREFACE vii wishes to thank his many colleagues at Hoechst Celanese, in particular H. M. Yoon, and his colleagues at the University of Delaware, most especially A. B. Metzner, for their contributions to his experience and knowledge of the fields discussed in this book. Others to whom appreciation is due include W.

The free energy of polymer solutions must depend upon the conformation of the macromolecules, and hence upon the deformation state imposed on the system, as well as upon the more familiar thermodynamic state variables of temperature and composition. As one consequence of the importance of this additional thermodynamic state variable, the precipitation temperature (cloud point) of polymer solutions may be increased by several tens of degrees Centigrade by imposition of steady shearing at low deformation rates. As a second consequence, the precipitated phase is sometimes found to be a solid of new morphology, and one which is quite refractory to re-solution. In this work a quantitative theoretical analysis of solubility phenomena in deforming solutions is given. The free energy of macromolecules in stagnant solutions is obtained from the Flory-Huggins theory, and changes with deformation state are computed from Marrucci's analysis for dilute solutions of elastic dumbbells. The parameters in the theoretical analysis were evaluated, using solutions of polystyrene in dioctyl phthalate, by measurements of the thermodynamic interaction parameter and of the rheological properties. The theory, which contains no adjustable parameters, was used to make a priori predictions of the change in cloud point with deformation state. The experimentally observed changes, of 3-28 °C, were predicted with a mean deviation of about 3 °C.

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The rheological properties of a thermotropic polyester were determined in the nematic and isotropic states. In the isotropic state, the viscosity is almost constant and the polymer is only slightly elastic. The nematic phase has a lower viscosity than the isotropic, except at low frequencies or shear rates, where the viscosity increases as though the polymer had a yield stress. There is a marked dependence of the rheology on shear history. The effects of shearing can be erased by returning the material first to the isotropic state and then back to the nematic state. The results are discussed with reference to analogous observations in small‐molecule liquid crystals and in thermotropic aromatic co‐polyesters.