Influence of viscosity on forced and spontaneous spreading: Wilhelmy fiber studies including practical methods for rapid viscosity measurement

摘要

The Wilhelmy vertical probe wetting force method was used to determine dynamic contact angles on fibers. Forced wetting under steady state fiber immersion or withdrawal rates was studied over a wide range of contact line velocities (V) and polymer viscosities (eta). Both advancing and receding dynamic contact angles showed similar trends independent of fiber diameter and were scaled by cos theta similar to (eta V/gamma)(0.7), consistent with the literature. Because of the scaling with eta, the method allows one to determine viscosity quickly and over a wide range of eta, simultaneous with surface tension measurement. Spontaneous spreading was investigated on static vertical fibers or plates by monitoring meniscus relaxation to equilibrium. The power law behavior of the spreading front was characterized by theta similar to t(-0.5+/-0.1) for advancing menisci of moderate viscosity polymers on dry small diameter fiber surfaces, this deviates from the well-known Tanner's law exponent of theta similar to t(-0.3) for flat surfaces. The t(-0.3) dependence was verified with our Wilhelmy technique using a vertical plate. The experimental relaxation time of the meniscus on a static fiber was found to vary with d(1.0) and a near-linear dependence with viscosity (eta) for higher viscosities up to ca. 300,000 Poise. It is shown that, with this method, one can rapidly measure viscosity simultaneous with surface tension of high viscosity melts and solutions as a function of temperature. (C) 1998 Academic Press. [References: 24]