Abstract
Time-dependent changes in shear stress were observed in a number of polymer solutions sheared at constant velocity gradient in a cone-and-plate viscometer. More detailed studies were made of dilute solutions (0.05–0.1%) of high molecular weight ( M ∼ 10 7) polymethyl methacrylate and polystyrene, in a viscous solvent Aroclor ( η > 1 poise). Below 30°C. both rheopectic and thixotropic changes in shear stress were observed above a certain velocity gradient. Light scattering measurements showed that large aggregates were present. These aggregates disappeared on heating the solution to 50°C. and slowly re-formed, in a matter of hours, on cooling to room temperature. Comparisons were made of rapidly quenched and aged solutions to find how the level of aggregation affects flow properties. Little difference could be detected between the viscosities of these solutions or their time-dependent behavior. As aggregates, in themselves, were found to have little influence on flow properties, it is suggested that time-dependent behavior is due to the formation of polymer networks which are held together by reversible crosslinks which may be either broken (thixotropy) or formed (rheopexy) during shear.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
