Study on the surface tensions of polymer melts using axisymmetric drop shape analysis

Abstract

It is shown that Axisymmetric Drop Shape Analysis (ADSA) is well‐suited for the study of polymer melt surface tensions. The technique is not restricted to equilibrium surface (interfacial) tensions; it is also suitable for measuring the time dependence (or kinetics) of surface tension of polymer melts. Results for three polymers, polypropylene, polyethylene, and polystyrene, at temperatures above 170°C are reported. Contrary to the well‐known decrease of surface tension in low molecular weight surfactant solutions as a result of equilibration, an increase in the melt surface tension is observed under isothermal conditions.

Effect of Temperature and Pressure on Surface Tension of Polystyrene in Supercritical Carbon Dioxide

“…Expressions for these partition functions are given below in equations (10), (11), and (12). The variation of (1) with…”

“…This method relies on the determination of a drop profile of dense liquid in another fluid, and the surface tension of the liquid is obtained from the best fit of the Laplace equation ofcapillarity to the experimentally determined drop profile [8,9]. Although the pendant drop method is theoretically simple, the research to date for determining surface tension of polymers has been limited because of experimental difficulties in handling high viscosity polymer melts under high temperature and high pressure [10,11,12]. In fact, there have been only limited surface tension data available for a few select polymers, and the range of experimental conditions, to which polymers are subjected during their measurements, has been rather narrow.…”

Activation of organoclays and preparation of polyethylene nanocomposites

“…As a first approximation, the critical surface tension of the organoclay can be taken to be 22 mJ·m -2 , which is the value given by Zisman [16] for a -CH 3 crystal surface. The surface tension of the polyethylene melt is reported to be 22.7 mJ· m -2 at 180°C [17]. The surface energies are probably too close to warrant any significant conclusions from the contact angle calculation.…”

“…However, as the temperature of the polymer melt is reduced, the surface tension of the polymer quickly rises and a non-wetting state can be anticipated. For example, at 140°C the interfacial tension of the polymer melt increases to 24.5-26.5 mJ·m -2 [17]. This rise in surface tension will produce contact angles at the basal plane that are as high as 110 degrees, which are sufficient to cause the organoclay to flocculate and phase separate from the polymer melt.…”

“…In the case of polypropylene, which has a surface tension of 21 mJ·m -2 at 180°C [17], the polymer would spontaneously wet the organoclay surface. However, at room temperature, the surface tension of polypropylene increases to values ranging from 30 to 33 mJ·m -2 .…”