Comparisons of Hamaker Constants for Ceramic Systems with Intervening Vacuum or Water: From Force Laws and Physical Properties

Abstract

Van der Waals dispersive forces produce attractive interactions between bodies, playing an important role in many material systems influencing colloidal and emulsion stability, wetting behavior, and intergranular forces in glass–ceramic systems. It is of technological importance to accurately quantify these interactions, conveniently represented by the Hamaker constant,A. To set the current level of accuracy for determiningA, they were calculated from Lifshitz theory using full spectral data for muscovite mica, Al2O3, SiO2, Si3N4, and rutile TiO2, separated by vacuum or water. These were compared to Hamaker constants calculated from physical properties using the Tabor–Winterton approximation, a single oscillator model, a multiple oscillator model, andA’s calculated using force vs separation data from surface force apparatus and atomic force microscope studies. For materials with refractive indices between 1.4 and 1.8 separated by vacuum, all methods produce similar values, but for indices larger than 1.8 separated by vacuum, and any of these materials separated by water, results span a broader range. The present level of accuracy for the determination of Hamaker constants, here taken to be represented by the level of agreement between various methods, ranges from about 10% for the case of SiO2/vacuum/SiO2and TiO2/water/TiO2to a factor of approximately 7 for mica/water/mica.