Free-standing thin film interactions with small particles

Abstract

In order to investigate foam stability and coating ability via interactions with particles a free-standing film of initial thickness 150 μm to 350 μm was created within a metallic ring of 16 mm diameter. The weight change of the film is monitored and attributed to water loss with time. The effects of film drying are investigated with respect to the film′s interaction with a solid, spherical, 3 mm diameter glass bead. This particle was dropped onto the film and high-speed camera imaging was used to examine the moment it interacts with the film. In addition to the water content of the film, the relative humidity of the environment, the initial film thickness of the film and the moment the bead interacts with the film are all factors that influence the quality of the film and hence how it interacts with the glass bead. The bead would cause defect points in the film to turn into tears. Films with a higher final water content presented with less tears and gave the particle a more homogeneous coating. Thin films are often used in experimental and theoretical studies as a basis to investigate foam behavior (Bergeron & Radke, 1992; Myers, 1998, Stubenrauch and Von Klitzing, 2003, Weaire and Kermode, 1983). The importance of foam interaction with small solids spans a wide range of industrial and scientific fields such as agriculture, food science, pharmaceuticals, drilling fluids, household & personal care products (Dickinson, 2010, Eisner et al., 2007, Hunter et al., 2008, Mason et al., 2006, Murray, 2007, Quebaud et al., 1998). Liquid coatings are often used within the food industry, most notably for snack foods and animal feeds (Baldwin et al., 2011, Beckett, 2008, Rockey et al., 2010). What is under investigation here is how a foam, represented via a liquid thin film, can be used to coat a small spherical particle. In addition the drying of the thin, surfactant-based films is taken under consideration with respect to the interaction of such films with solid particles.