An historical review of surface force measurement techniques

The measurement of surface forces has developed from a pursuit to test the theories of van der Waals and colloidal interactions to a field which encompasses issues as varied as cell interactions, lubrication, rheology, phase transitions, DNA binding and materials science. The desire to continually improve the accuracy and the applicability of surface force measurements has driven consistent improvements in the instrumentation employed. Until recently, macroscopic surfaces were required to enable accurate measurement of surface forces to be performed. These measurements are found to describe accurately the behaviour of a wide variety of colloidal systems. With the advent of the techniques of atomic force microscopy, total internal reflection microscopy and colloidal particle scattering and their application to force measurement, the sensitivity of force measurement has increased sufficiently to enable microscopic surfaces to be studied. It now seems possible that the next generation of instrumentation may be used to investigate interactions on a molecular scale. Here the techniques of measuring surface forces, both direct and indirect, are illustrated, from early measurements to the present. Further, recent developments and techniques which may be applied to the measurement of surface forces in the future are discussed. (C) 1997 Elsevier Science B.V.