Kinetics of Wetting of Surfaces by Polymer Melts

Abstract

The kinetics of wetting of both high‐energy (aluminum, mica) and low‐energy (FEP Teflon) surfaces by thermostated polyethylene and ethylene‐vinyl acetate copolymer melts in air were followed by the rate of approach of the apparent contact angle θ to its final value θ∞ and the change of the radius of the base of the polymer melt drop, r, with time. The volume of the drops studied varied from 0.006 cm3 to 0.028 cm3 and θ could be studied in the interval from about 100°>θ≥θ∞. The melted polymer drops maintain the shape of a spherical segment. The reduced dimension r/r 0, where r 0 is the value of r when the contact angle is 90°, is a universal function of the reduced time aTt, a dimensionless quantity. The reduced contact angle cosθ/cosθ∞, where cosθ∞ is the value of cosθ at infinite time, can be represented by a function of the same variable aTt. The shift factor aT is given by γ/Lwη, where γ is the surface tension of the liquid, η is the viscosity, and Lw is a length characteristic of the polymer‐substrate system.