Dynamic and slip phenomena of surface polymer using evanescent wave laser optical polarimetry and plane-Couette shear rheometry.

摘要

The dynamic of surface polymer as well as the slip, stick-slip phenomena at the polymer-solid interface were investigated using the Evanescent Wave Laser Optical Polarimetry (EWLP) and plane-Couette shear flow apparatus. Time-dependent step strain EWLP relaxation experiments using 1,4-polybutadiene melts indicate that a single exponential function completely describes orientation relaxation dynamics of fluid near the substrate. The characteristic decay time $tsurface$ determined from these experiments was found to be a much stronger function of bulk polymer molecular weight $tsurface\sim M4.2\pm 0.03W$ than the corresponding terminal properties of 1,4-polybutadiene melts in bulk, and . Comparison of the M_W-dependence of $tsurface$ with theoretical expectations for several alternative molecular mechanisms indicate that a constraint release tube renewal mechanism best explains the experimental observations. The sliding plate plane-Couette shear flow apparatus can be used to investigate the stick-slip phenomena of the polymer at the surface or the instabilities at the fluid and solid surface for complex fluid such as polymer. The stick-slip flow regime phenomena in the polybutadienes-aluminum interface is originated from the flow induced disentanglement of the physisorbed chains and the bulk polymer network. The onset to the stick-slip regime of the polymer has some dependence to the bulk state of the polymer. The critical stress is in the order of the plateau modulus and can be predicted from the Mhetar and Archer scaling theory which is G_e/(N_e) 1/2. A small change in the bidisperse polymer can greatly reduce the stick-slip phenomena and the existing of smaller chain polymer promote the slippage at the solid surface. The stick-slip flow regime phenomena of the polymer blend of PBD 335K and PBD 176K is originated from the flow induced disentanglement of the physisorbed chains and the bulk polymer network. The result from the lower grafting density substrate also reassured us about the results from previous studies that the stick-slip behavior was originated from the flow-induced disentanglement between bulk polymer and anchored chains at the surface.