Tetra-n-butyl ammonium chloride (TBAC) is known to form semi-clathrate cages and exhibits osmotic coefficients and anomalous activity, which has a dependence on concentration and temperature. Specifically, the concentration dependence of the osmotic and activity coefficients of the TBAC-H2O system are found to exhibit maxima (which is anomalous) around 2 molal, which is believed to be due to semi-clathrate formation. However, the maxima are then found to gradually disappear with increasing temperature. Experimental studies of the activity and computer simulations were performed on TBAC, ranging from 300K to 360 K over varying TBAC molar concentrations from 0.25 molal to 8 molal. The varying concentrations allowed for different spatial arrangements of the TBA, Chloride, and the water molecules that surrounded them, the free energy, enthalpy, and entropy of the non-ideal portion were calculated and broken down due to solvent and solute to find the significant contribution of each component. The 3D structural analysis confirms that different clathrates are formed at different concentrations, which is consistent with the anomalous activity coefficients observed in experiments. An understanding of these solutions on an atomic level should be capable of being generalized to a broad class of electrolyte solutions with applications to biological, petroleum chemical, and energy storage systems.

Structure and activity coefficients of tetra-n-butyl ammonium chloride (TBAC) at varing concentrations and temperature

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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