2008 Volume 34 Issue 6 Pages 587-593
Ripplon surface laser-light scattering (the ripplon method) is a powerful and extremely appealing measurement tool for measuring surface properties, because it can quickly extract information about the surface of liquid films without contact and without the need for external disturbances such as induced excitations. In this research, a newly developed ripplon surface laser-light scattering measurement instrument was used to conduct measurements of the surface properties of cellulose acetate butyrate (CAB) polymer dissolved in methyl ethyl ketone (MEK) with the goal of measuring a polymer–organic solvent system that is widely used in the fabrication of functional films and other areas. Although no variation in surface tension with polymer concentration was observed by a contact measurement method (the Wilhelmy Plate method), the surface tension decreased as the polymer concentration increased when observed by the ripplon method in the frequency range of several tens of kHz. When the model of adsorption of polymer onto the liquid film surface was examined in the measured ripplon frequency range, it was inferred that the ripplon wave modulation speed was significantly greater than the time required for the CAB polymer to adsorb onto and desorb from the liquid film surface. Consequently, there was not enough time for the CAB polymer to adsorb onto and desorb from the surface, and the film behaved like an insoluble molecular film. It is therefore clear that differences in the amount of polymer adsorbed onto a liquid film surface due to differences in the CAB polymer concentration and molecular mass correspond to a reduction in surface tension and are observed as changes in surface elasticity. By focusing on this variation in surface elasticity, it is expected that this method can be used as a new tool for measuring and evaluating the ease of adsorption and desorption of polymer onto the liquid film surface of low density polymer–organic solvent systems having low surface tension and low viscosity, which had previously been difficult to measure.
