Evaluation of the calcium oxalate monohydrate Hamaker constant based on static dielectric constant determination and electronic polarization

Knowledge of the static dielectric constant is fundamental to an accurate calculation of the Hamaker constant. However, many materials of interest, particularly biominerals, do not lend themselves to a form amenable to measure dielectric properties readily. In the current work, it is shown that careful preparation of composite samples composed of the biomineral, in the current work, calcium oxalate monohydrate (COM) well-dispersed in a low dielectric constant silicon rubber, permit determination of the static dielectric constant of the biomineral phase. Composite mixing rules were used to deconvolute the dielectric constant of COM from the COM/silicone composite. Utilizing the Lichtenecker dielectric mixing model, the value of the static dielectric constant of COM was determined to be 28.9. Optical and dielectric data were then used in the Tabor-Winterton relationship to calculate the Hamaker constant A₁₃₁ of COM particles interacting in water. The A₁₃₁ for COM as a function of crystallographic habit was also examined. The mean value of A₁₃₁ for COM was calculated to be 13.7(±5.90) × 10^-21 J at 37°C in an aqueous environment, which is about 15% larger than previously published values calculated using only contributions from electronic polarization between interacting materials.