Abstract
We investigate relaxation dynamics of entangled 1,4-polybutadiene (PBD) melts and concentrated polystyrene/diethyl phthalate (PS/DEP) solutions near an attractive glass substrate. Narrow molecular weight distribution PBD melts and PS/DEP solutions covering a broad range of molecular weights (6.7 × 103 ≤ Mw,PBD ≤ 5.15 × 105; 1.3 × 105 < φMw,PD < 1.1 × 106 g/(mol)) were used in the study. A new experimental method, evanescent wave laser polarimetry (EWLP), was developed to investigate near-surface relaxation dynamics in these materials. The method relies on total internal reflection of phase-modulated laser light at an interface between a high refractive index transparent hemisphere and the polymer liquid to probe shear-induced changes in molecular orientation in a fluid layer within approximately 80 nm of the polymer/substrate interface. A characteristic near-surface relaxation time τsurface determined from step shear EWLP relaxation experiments using PBD melts was found to be a much stronger function of...
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