Techniques for the measurement of forces between solids

Abstract

Techniques for the direct measurement of forces between solids as a function of the distance of separation of their surfaces are reviewed. If the solids are separated by gas or a vacuum, then thee forces are generally identified as macroscopic van der Waals forces. The impetus for their measurement has been the verification of the Lifshitz theory. Ine ron-ire charactter of these forces means that the measuring system has very ??? chanical properties. The exploitation of these properties in measured ??? collection, dynamic and jump methods is discussed. Particular attention ??? to a completely novel techniques the dynamic-jump method. The ??? ??? have dictated the choice of solids are summarized. The measurements of forces between sheets of ??? probably represent the most comprehensive ??? experimental studies; the forces have been measured by both direct and incorrect methods. The comparison or the results with Lifshitz theory is given a critical assessment. The existence of repulsive forces between solid particles dispersed iin liquid phases has been known for a long time in colloid science. In ionic solutions, the measurement of forces between solids has reproduced the effects predicted by simple electrical double-layer theory. In polymer solutions forces have been detected that may be attributed to steric stabilization forces. However, the nature of forces due to liquid structure has not been so well know. Recently liquid-structure forces of an oscillatory character have been measured between ??? ???. Forces measured between hydrophobic surfaces in aquaous systems under certain conditions exhibit significant departures from DLVO theory.