Measurement of forces of molecular attraction of crossed fibres as a function of width of air gap

Abstract

DERJAGUIN and Abrikosova1 were the first to measure molecular forces as a function of the distance between macro-objects, using negative feedback. The results coincided, within the limits of experimental error, with the conclusions of the theory of retarded molecular forces (which was subsequently developed by Lifshits2,3). In the earlier research work1, as in a number of subsequent experiments, the width of an air gap was measured by optical methods (using the interference of light). The research work was therefore limited to transparent bodies. Moreover, test bodies had to possess a sufficiently large radius of curvature. The latter condition meant that the quality of the surfaces had to meet stringent requirements; it was also difficult to ensure the absence of dust particles in the gap between interacting bodies with large radius of curvature. As a result, only in two cases4,5, owing to the use of molecular-smooth surfaces of mica, did researchers succeed in measuring, not only the retarded, but also non-retarded molecular forces.