Hydrophobic radiofrequency plasma-deposited polymer films: dielectric properties and surface forces

Abstract

Advancing and receding contact angles for various liquids placed on the surface of thin n-hexane plasma polymer films have confirmed that the surface is hydrophobic; comparable to polyethylene. A waveguide technique has been employed to determine the refractive indices of the plasma polymer films in the visible and near infrared regions of the dielectric spectrum. Along with ESCA data that provide polymer group functionality, this information has been used to estimate the n-hexane plasma polymer density and to construct a simple dielectric permeability function (ϵ(iξ), the dielectric constant at imaginary frequency iξ) for the polymer. The dielectric permeability function and Lifshitz theory have been used to calculate the Hamaker function (including non-retarded Hamaker constants) which should characterise the van der Waals interaction in systems that contain n-hexane plasma polymers. The atomic force microscope (AFM) has been employed to measure the force of interaction between n-hexane plasma polymer films deposited on muscovite mica flat plates and either uncoated silicon nitride AFM tips or n-hexane plasma polymer coated glass spheres. The force versus separation curves have been compared with DLVO theory. The homointeraction between n-hexane plasma polymer coatings in water initially displays a long-range attraction additional to van der Waals interaction. There is evidence that after prolonged immersion in water the thin n-hexane plasma polymer films swell.