Capacitance Dilatometry Attachment for a Surface-Force Apparatus

Abstract

An application of capacitance dilatometry to a surface-force apparatus is described. The distance between the surfaces is obtained from the capacitance of a cylindrical parallel-plate capacitor measured with a variable-ratio transformer bridge; the surface separation is made to vary with a magnetic force transducer. The method permits measurements of forces between opaque surfaces over periods of time ranging from tens of milliseconds to, in principle, an indefinite period. A new method of signal analysis that allows linear and accurate measurement of displacement over a large fraction of the separation between the plates of the capacitor is described.