The calculation of dispersion forces for engineering applications

The design and operation of industrial processes for colloidal materials is dependent upon predictive methods for the quantitative description of the fundamental interactions operating. This will include the requirement to calculate the attractive van der Waals interaction energy as a function of distance. The paper provides a systematic and critical review and reassessment of the various methods of calculating the van der Waals interaction energy with the specific purpose of developing and recommending the method of calculation most suitable for engineering applications. The problem of the interaction between like spheres is specifically addressed. The paper describes an extensive comparison of exact, sophisticated and simplified treatments for such calculations. In developing and recommending a method of calculation of the interaction energy for engineering applications, the most important features to be considered are accuracy, the amount and availability of physical properties data required, and the demand on computing time. It is shown that these requirements are met by the combination of an analytical approximation for the effective screened, retarded Hamaker constant and a Hamaker geometrical factor. If appropriate refractive index data is available, this approach may be readily applied to any material.