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Hole growth as a microrheological probe to measure the viscosity of polymers confined to thin films

Authors

  • Connie B. Roth,

    1. Department of Physics and the Guelph-Waterloo Physics Institute, University of Guelph, Guelph, Ontario N1G 2W1, Canada
    Current affiliation:
    1. Department of Chemical and Biological Engineering, Northwestern University, Evanston, Illinois 60208-3120
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  • John R. Dutcher

    Corresponding author
    1. Department of Physics and the Guelph-Waterloo Physics Institute, University of Guelph, Guelph, Ontario N1G 2W1, Canada
    • Department of Physics and the Guelph-Waterloo Physics Institute, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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Abstract

We review recent hole growth measurements performed at elevated temperatures in freely-standing polystyrene (PS) films, using optical microscopy and a differential pressure experiment (DPE). In the hole growth experiments, which were performed at temperatures close to the bulk glass-transition temperature of PS, Tmath image = 97 °C, we find evidence for nonlinear viscoelastic effects, which markedly affect the growth of holes in freely-standing PS films. The hole radius R initially grew linearly with time t before undergoing a transition to exponential growth characterized by a growth time τ. The time scale τ1 for the decay of the initial transient behavior prior to reaching steady state was consistent with the convective constraint release mechanism of the tube theory of entangled polymer dynamics, while the characteristic hole growth times τ of the holes were consistent with significant reductions in viscosity of over eight orders of magnitude with increasing shear strain rate due to shear thinning. DPE measurements of hole growth on very thin freely-standing films revealed that hole formation and growth occurs only at temperatures that are comparable to or greater than Tmath image, even for films for which the Tg value was reduced by many tens of degrees Celsius below the bulk value. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B:Polym Phys 44: 3011–3021, 2006

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