Dynamic Surface Tension Measurement in Liquid Curtain Coating Systems
Dynamic surface tension at millisecond surface ages dictates liquid curtain stability and dynamic wetting limits in paperboard coating operations.
Ward-Tordai Equation
Diffusion Model
Analytical expressions that describe the diffusion of surfactant molecules from a bulk solution to a clean interface are used to study fast processes. The ward-tordai equation provides a mathematical link between the concentration of a substance and the resulting change in surface tension over time. This calculation is a requirement for understanding how wetting agents behave in high-speed coating and printing.
Adsorption Rate
Molecules do not reach the surface of a liquid instantly because they must travel through the fluid by random motion. The equation accounts for this travel time and identifies the rate at which the surface energy of a fresh droplet or film will drop. In industrial applications, the time available for a coating to wet a substrate is often less than one hundred milliseconds.
Chemists use this model to select surfactants that can reach the interface quickly enough to be effective.
Dynamic Tension
Predictions made using this model are compared against experimental data from bubble pressure tensiometers. If the measured tension does not match the predicted values, it may indicate the presence of an energy barrier at the surface. This information is used to refine the formulation of water-based inks and barriers.
The equation remains a fundamental tool for researchers in interfacial science.