Influence of Temperature, Molecular Weight, and Molecular Wegith Dispersity on the Surface Tension of PS, PP, and PE. I. Experimental

摘要

In this work, the influence of temperature, molecular weight (M_n), and molecular weight dispersity (MWD) on the surface tension of polystyrene (PS) was evaluated using the pendant drop method. The inlfuence of temperature on the surface tension of isotatic polypropylene (i-PP) and of linear low-density polyethylene (LLDPE) was also studied here. It was shown that surface tension decreases linearly with increasing temperature for all the polymers studied. The temperature coefficient -d_(#gamma#)/dT (where #gamma# is the surface tension, and T, the tempeature) was shown to decrease with increasing molecular weight and to increase with increasing MWD. The surface tension of PS icnreased when the molecular weight was varied from 3400 to 41,200 g/mol. When the molecular weight of PS was further increased, the surface tension was shown to level off. The surface tension was shown to decrease with increasing molecular weight distribution. Contact angles formed by drops of diiomethane and water on films of PS with different molecular weights were measured at 20 deg C. The surface energies of those polymers were then evaluated using the values of the different pairs of contact angles obtained here using two different models: the harmonic mean equation and the geometric mean equation. It was shown that the values of the surface energy obtained are slightly less than are the ones extrapolated from surface-tesnion measurements in the rubbery states.