Issue-05 (03/2004)
Considerations Before Making Non-equilibrium Surface Tension Measurements
There are many applications that can benefit from the measurement of non-equilibrium surface tensions. These instances range from the basic study of surfactant diffusion and adsorption coefficients to the application of line-speed dependent coatings on moving substrates to the behavior of spray droplets in flight and upon adsorption to an appropriate substrate. The measurement of non-equilibrium/dynamic surface tensions by the maximum bubble pressure method has been known for many years. However, the measurement of non-equilibrium tensions by the Laplace solution to pendant drops has only recently become of interest due to the advent of higher speed computer processors. Three common methods for the measurement of surface tension (Wilhelmy plate method, pendant drop analysis, and the maximum bubble pressure method) are compared here for the measurement of non-equilibrium tensions for various applications.
Wettability of Swellable Nonwovens
Determination of Contact Angle Against Swellable Nonwoven Material
A variety of different experimental methods are available for the determination of contact angles for liquids against solid samples. Standard optical and Wilhelmy methods become difficult or impossible to solve if a sample swells when exposed to the liquid of interest. For many samples, the Washburn method becomes the experiment that can be performed with the best reproducibility. Although the Washburn results may be reproducible, the results can still be erroneous when the solvent of interest swells the sample. This is often the case with water contact angles measured against many super absorbers, natural products, and personal care products. A method is shown below for extracting accurate contact angles for samples that swell in the presence of the liquid of interest.