Interaction between low molecular weight carboxylic acids and muscovite: Molecular dynamic simulation and experiment study

Interface phenomena between low molecular weight (LMW) carboxylic acids and muscovite was investigated through molecular dynamic simulation and experiment, where the typical monocarboxylic acids including formic acid (C-1), acetic acid (C-2), propionic acid (C-3) and butyric acid (C-4) were used as models. Density distribution, adsorption energy, root mean square dynamic (RMSD) of carboxylic acids on water-muscovite interface were calculated through molecular dynamic simulation, and the advanced characterization methods, such as ATR-FTIR spectra, AFM images and contact angle were performed to test and verify the relative simulation findings. The molecular simulation showed that carboxylic acids adsorbed on surface of muscovite through hydrogen bond between H atom of -COOH functional group of carboxylic acid and O atom of muscovite, belong to outer sphere adsorption, and ATR-FTIR spectra and AFM images confirmed this finding. Adsorption energy for long carbon chain carboxylic acid (C-4) was higher than that for short carbon chain carboxylic acid (C-1, C-2 and C-3) due to the effect of carboxylic acid diffusion on water-muscovite interface. The hydrophilic functional group -COOH of carboxylic acids preferably adsorbed on muscovite surface, while the hydrophobic functional groups -CH3 and -CH2 of carboxylic acids were far from the muscovite surface. So, the hydrophobicity on muscovite surface increased due to the adsorption of carboxylic acids, which resulted in the increase of contact angle of water on muscovite surface.