Interaction Forces between Mica Sheets at Small Separations

Abstract

WHEN thin sheets of mica are brought very near to each other they deform; we decided that this deformation could be used to investigate the strength of the intermolecular attraction. The system we used in this study consisted of two narrow strips ∼5 µm thick, in contact over part of their length and held apart by external forces at one end, thus forming a double cantilever. Near the line of bifurcation, the attractive forces deflect the sheets towards each other and a non-uniform loading applied to the cantilevers has been used to simulate the attraction. We measured the deflection by multiple-beam interferometry. At the same time the surface energy γ, required to overcome the forces of attraction, was determined as described previously1,2. The result is shown as curve a in Fig. 1; curve b is the calculated shape of a similar cantilever which carries no distributed load. Suitable mathematical functions containing a number of adjustable parameters may be used to represent the loading and the beam equation solved for particular values of the parameters.