Controlling thin liquid film viscosity via modification of substrate surface chemistry

The viscosity of thin films of liquid poly(dimethylsiloxane) have been studied on silicon and fluoropolymer-coated silicon by means of a perturbation technique applied using colloid probe atomic force microscopy. The liquid film supported by a silicon substrate exhibited a greater viscosity than the bulk liquid, due to the strong interaction between the molecules near to the liquid/solid interface. In comparison, the liquid film supported by a fluoropolymer-coated substrate exhibited a similar viscosity to the bulk liquid, due to the weak interaction between the liquid and the fluoropolymer surface. This demonstrates the possibility to control the viscosity of thin liquid films via selection of the substrate chemical properties.