Influence of Viscosity on Forced and Spontaneous Spreading: Wilhelmy Fiber Studies Including Practical Methods for Rapid Viscosity Measurement
✍ Scribed by Bryan B. Sauer; William G. Kampert
- Publisher
- Elsevier Science
- Year
- 1998
- Tongue
- English
- Weight
- 198 KB
- Volume
- 199
- Category
- Article
- ISSN
- 0021-9797
No coin nor oath required. For personal study only.
✦ Synopsis
Sometimes they are referred to as forced and spontaneous
The Wilhelmy vertical probe wetting force method was used to wetting, respectively. For forced wetting, either the solid or determine dynamic contact angles on fibers. Forced wetting under liquid can be moved to drive the liquid front at the threesteady state fiber immersion or withdrawal rates was studied over phase contact line between solid/liquid/vapor at a given a wide range of contact line velocities (V ) and polymer viscosities contact line velocity, V. The experimental and theoretical (h). Both advancing and receding dynamic contact angles showed literature for forced wetting of many liquids on a variety of similar trends independent of fiber diameter and were scaled by solids including fibers is quite well established (3-5). The cos u Ç (hV/g) 0.7 , consistent with the literature. Because of the surface tension (g), liquid viscosity, and V govern the dyscaling with h, the method allows one to determine viscosity namic contact angle through the capillary number (Ca Å quickly and over a wide range of h, simultaneous with surface tension measurement. Spontaneous spreading was investigated on hV/g), but the spreading parameter (S) and the static constatic vertical fibers or plates by monitoring meniscus relaxation tact angle (u s ) do not contribute (2-5). The spreading pato equilibrium. The power law behavior of the spreading front was rameter is defined as (2, 3) characterized by u Ç t 00.5{0.1 for advancing menisci of moderate viscosity polymers on dry small diameter fiber surfaces, this devi-
ates from the well-known Tanner's law exponent of u Ç t 00.3 for flat surfaces. The t 00.3 dependence was verified with our Wilhelmy or introducing Young's equation, 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 ( h) for higher viscosities S Å g(cos u s 0 1), [2] up to ca. 300,000 Poise. It is shown that, with this method, one can rapidly measure viscosity simultaneous with surface tension where g S/V is the solid/vapor interfacial tension, g S/L is the of high viscosity melts and solutions as a function of temperature. solid/liquid interfacial tension, and g is the liquid/vapor