New techniques and surfaces for direct force measurements

Abstract

New techniques for the production of surfaces suitable for direct force measurement and a new apparatus for performing the measurements are presented. The surface of mica was modified by adsorption of a bilayer from surfactant solution . The effect of interbilayer adhesion is to cause multilayer formation. Bilayers containing charged glycolipids were also deposited onto mica and with this system no adhesion was measured between the bilayers. Silver films on mica were prepared by vacuum evaporation and and by a new surface modification technique which uses mica as a template to mould the silver film. Mica was also covalently modified by a two step process. Firstly, the surface is treated with low temperature water vapor plasma. A combination of reaction and sputtering in the plasma environment alters the surface properties of mica. Unlike untreated mica the treated surface h as exposed hydroxyl groups and this allows the treated surface to be altered by reaction with chlorosilanes. The plasma treatment technique causes minimal alteration to the surface smoothness and oscillatory solvation forces were measured in octamethyltetrasiloxane (OMCTS). Reaction of the plasma treated mica with (Tridecafluoro-1,1,2,2-T etrahydro octyl)-1- Dimethylchlorosilane renders the surface hydrophobic and the force between these surfaces at short range is an exponential attraction- the hydrophobic attraction. The new surface force apparatus is a simplified yet improved version of the surface force apparatus first developed by Israelachvili and Adams, J. Chem. Soc. Faraday Trans 1, 74,975(1978). It gives the same measurement resolution and has the same possibilities of studying various phenomena in thin films such as friction, viscosity, adhesion and phase transitions. It offers improved performance with regard to control of surface separation and increased versatility by virtue of variable chamber dimensions and geometry. Show more