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

Dielectric Behavior of Calcium Oxalate Monohydrate Urinary Stone

Calcium oxalate is the most significant component of urinary stones, usually in its monohydrate form. The mechanisms for the formation of calcium oxalate urinary stones are still not understood, though it is thought that organic macromolecules play a significant role. Calcium oxalate monohydrate (COM) urinary stone was subjected to dielectric studies in order to understand the formation and growth of the renal stones in vivo and use them to help in the treatment procedures for more effective stone fragmentation. The chemical composition and the crystalline nature were verified using Fourier Transform Infrared spectroscopy, X-ray diffraction and thermal analysis. The dielectric parameters for the COM renal stone namely, capacitance, dielectric loss coefficient, impedance, and resistance were measured at room temperature and hence the dielectric constant and the alternating current conductivity were calculated in the frequency range 200 Hz to 5 MHz. The measured values and the dielectric constant showed systematic variations up to 10 kHz. The alternating current conductivity was almost constant up to 2.0 kHz and then showed systematic increase at around 100 kHz and reaches a maximum value at around 5 MHz. The results may be used in further studies of renal stones about their formation and growth.

A Simple Experimental Way of Measuring the Hamaker Constant A(11) of Divided Solids by Immersion Calorimetry in Apolar Liquids

Recent progress in interpretation of immersion calorimetry has shown the link between the immersion enthalpy (Delta(imm)H) value in apolar liquid and the Lifshitz-van der Waals contribution to surface energy (gamma(LW)(S)) of divided solids. In this work we show that a simple relationship can be established between the Hamaker constant (A(11)) of a solid and its immersion enthalpy in a pure apolar solvent. The results are satisfying compared to those already available in the scientific literature. The main interest of this method is the measurement of the Hamaker constants of solids for which contact angle measurements are impossible to carry out and for those for which the complexity of the solid structure hampers the ab initio calculation. Values are given for some clay minerals. Copyright 2000 Academic Press.