화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.125, No.5, 1439-1446, 2021
Spectroscopic and Structural Characterization of Water-Shared Ion-Pairs in Aqueous Sodium and Lithium Hydroxide
The structures of the ion-pairs formed in aqueous NaOH and LiOH solutions are elucidated by combining Raman multivariate curve resolution (Raman-MCR) experiments and ab initio molecular dynamics (AIMD) simulations. The results extend prior findings to reveal that the initially formed ion-pairs are predominantly water-shared, with the hydroxide ion retaining its full first hydration-shell, while direct contact ion-pairing only becomes significant at higher concentrations. Our results confirm previous experiments and simulations indicating greater ion-pairing in aqueous LiOH than NaOH as well as at high temperatures. Our results further imply that NaOH and LiOH ion-pairing free energies have an approximately linear (rather than square-root) dependence on ion concentration (in the molar range), with positive enthalpies and entropies that increase with concentration, thus implying that water-mediated interactions enthalpically disfavor and entropically favor ion-pair formation.