Slip in entangled polymers /
Slip in entangled polymer solutions and melts was studied using a plane-Couette shear flow cell capable of measuring shear stress and slip velocity simultaneously. On bare silica surface a log-log plot of slip velocity vs. shear stress displayed several powerlaw regimes. Pattern of microscopic sli...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1998.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=737708761&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Slip in entangled polymer solutions and melts was studied using a plane-Couette shear flow cell capable of measuring shear stress and slip velocity simultaneously. On bare silica surface a log-log plot of slip velocity vs. shear stress displayed several powerlaw regimes. Pattern of microscopic slip, stick-slip, and macroscopic slip was observed with increasing shear stress. Stick-slip flow was observed only for polymer melts with Mw > 86500 and was characterized by the oscillation frequency of shear stress characterized by the oscillation frequency of shear stress function of the physical and the chemical nature of the surface. A scaling model was developed to estimate the frictional drag on a probe polymer chain (N-mer) pulled by one of its ends through an entangled polymer (Pmer,v). This model takes into account changes in the probe chain conformation and relaxation processes of the probe and the surrounding chains. The model is extended to study slip of an entangled polymer over a weakly grafted solid surface and its predictions are found to be in good agreement with the experimental results. Relationship between the molecular level kinematics of interfacial polymer chains and the dynamics of sharkskin phenomena is established. A new evidence of secondary flow during plane Couette shearing of entangled polystyrene solutions and a polyisobutylene melt was reported. The secondary flow was shown to be driven by normal stress imbalances at the free edges of the samples, and was accompanied by spatial variation in birefringence. Effect of accompanied by spatial variation in birefringence. Effect of could be minimized by (a) using larger plates with narrow gaps; (b) performing measurements at low Weissenberg numbers; and (c) employing a measuring technique such as laser birefringence that permits stress measurements close to the center of the sample. |
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| Item Description: | Vita. "Major Subject: Chemical Engineering". |
| Physical Description: | xviii, 147 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 143-146 . |