Polyethylene crystallization from dilute solutions: adsorption isotherm on the growth face
Abstract
The growth kinetics of single crystals of polyethylene form dilute solution have been studied. Special emphasis was placed on the role of adsorption of polyethylene chains on the growth face prior to the process of surface nucleation. It has been argued that an adsorption isotherm determines the concentration dependence of the growth rate and introduces a change in the dependence. The change in the concentration (C) dependence of the growth rate (G) is basically from G∝C1/2 to G∝C with decreasing concentrations. The Langmuir adsorption isotherm explains the change as a transition from a dilute to a plateau regime corresponding to the saturation of the growth face with adsorbed polymer. Experiments have been carried out with several molecular-weight fractions to examine the molecular-weight dependence of the crossover concentration of the solution. There is found to be an exponential decrease in crossover concentration with increasing molecular weight. This result agrees with the prediction derived from the models of Langmuir-type polymer adsorption and provides strong support for the above argument.