Surface Energetics of Calcium Carbonate Powders by Inverse Gas Chromatography (IGC) and Cleaved Crystals by Contact Angle Measurement

Abstract

Inverse gas chromatography (IGC) and sessile drop contact angle measurement were used to study the surface energetics of calcium carbonates from different sources and the effects of surface conditioning . A compilation of the results using these two methods to determine the apolar and polar nature of the surface is given . The results of the two analytical methods are summarized individually . IGC analysis provided a sensitive tool for detecting differences in surface energy attributed to variation in surface water, or by contamination with other chemisorbed species. Basic probes were used to characterize surface acidic sites. Acidic probes, however, were found too reactive with the calcium carbonate to enable a quantification of the surface basicity. Strong adsorption of acidic probes indicates the presence of a strong basic component at the surface. The susceptibility of the IGC method to misinterpretation retention data obtained from chemisorbed probes was also identified . Contact angle experiments were conducted on cleaved calcite samples using multiple wetting liquids and two techniques to separate the polar and apolar contributions of surface energy. The results demonstrate a strong interaction of water with the calcite surface and the reduction of total surface energy when the surface is treated with alkylketene dimer. A comparison of results from both methods is provided . Differences in the application of the results of the two methods to access the surface energetics are addressed. The importance of distinguishing between the thermodynamics of gas/condensed and condensed/condensed phase interactions when comparing the results from IGC and wetting experiments is also discussed . For calcium carbonate, the trends observed by the two approaches are consistent, although a defining link between the two was not established.