Control of Spatial Periodicities of Dewetting Structures of Oleo-Liquid Films

Thin liquid films containing octyl p-methoxycinnamate (OPMC) and octylsilyl titanium dioxide particle having average diameter of 35 nm (OSI-TIO2-35) were prepared on glass plates. The content of OSI-TIO2-35 to OPMC was varied from 8:2 to 2:8 and the film thickness was from 0.050 to 0.200 mg/cm². The liquid films underwent dewetting when immersed into water at 35 °C for 10 min to form long cylindrical ridged patterns or droplet patterns. The dewetting patterns were confirmed to be spatially periodic by two-dimensional fast Fourier transform indicating that the first stage of the dewetting was spinodal dewetting, i.e., formation of holes by amplification of surface fluctuation followed by growth and coalescence of holes. Both thickness and content of the films influenced on the dewetting pattern formation. Dewetting occurred more easily as decreasing the film thickness. Droplet patterns tended to be formed as increasing the content of OPMC. Characteristic length of the dewetting patterns decreased as increasing the content of OSI-TIO2-35 and decreasing the film thickness. Wave vector of fluctuation having the highest growth rate is influenced by film thickness and interfacial tension. Interfacial tension and viscosity of the liquid film are easily adjusted by changing the ratio of OPMC to OSI-TIO2-35. Spatial periodicities of dewetting structures of the oleo-liquid films are thus easily controlled.