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

balanced by repulsive forces, as found in liquid phase sinVan der Waals dispersive forces produce attractive interactions tered Si3N4 (2–4) and thick film resistor materials (5) . It between bodies, playing an important role in many material sysis obviously of interest to be able to quantify these interactems influencing colloidal and emulsion stability, wetting behavior, tions in order to understand how to manipulate relevant maand intergranular forces in glass–ceramic systems. It is of technoterial properties. The Hamaker constant is a convenient logical importance to accurately quantify these interactions, convequantity with which to represent these interactions. For the niently represented by the Hamaker constant, A . To set the current vast number of systems composed of particles suspended level of accuracy for determining A , they were calculated from in aqueous media, there have been only a few attempts to Lifshitz theory using full spectral data for muscovite mica, Al2O3, experimentally quantify these interactions, perhaps largely SiO2, Si3N4, and rutile TiO2, separated by vacuum or water. These were compared to Hamaker constants calculated from physical due to experimental difficulty in obtaining accurate data. At properties using the Tabor–Winterton approximation, a single present, there are several techniques in use for the quantifioscillator model, a multiple oscillator model, and A’s calculated cation of these phenomena. using force vs separation data from surface force apparatus and In this work, the Hamaker constant is viewed as a systematomic force microscope studies. For materials with refractive indispecific physical constant whose value for a given system ces between 1.4 and 1.8 separated by vacuum, all methods produce and geometry must be independent of the method of measimilar values, but for indices larger than 1.8 separated by vacuum, surement. Therefore, the value of the Hamaker constant meaand any of these materials separated by water, results span a sured by any accurate technique will agree well with that broader range. The present level of accuracy for the determination from any other accurate measurement technique. To date of Hamaker constants, here taken to be represented by the level there has been no comparison of the results of all the techof agreement between various methods, ranges from about 10% niques currently in use for any system to determine how for the case of SiO2/vacuum/SiO2 and TiO2/water/TiO2 to a factor of approximately 7 for mica/water/mica. q 1996 Academic Press, Inc. well the values may agree. The purpose of this work is to