Temperature effects on alcohol aggregation phenomena and phase behavior in n-butanol aqueous solution

Abstract

Liquid-liquid phase separation is an important phenomenon that prevails from simple to complex molecular systems where temperature plays a crucial role in the fundamental understanding of phase behavior in a theoretical and industrial perspective. The n-butanol aqueous solutions have two separate liquid phases of alcohol-rich and water-rich formed at room temperature. The change in phase behavior occurs from two phases to one with an increase of temperature, exhibiting an upper critical solution temperature (UCST) behavior. We carried out molecular dynamics simulations and graph theoretical analysis to understand how temperature regulates n-butanol aggregation and the network properties of water at various concentrations. The theoretical studies suggest that the n-butanol molecules form two distinct alcohol aggregates, water-compatible or water-incompatible, determined by the interactions between alcohol and solvent molecules. Moreover, the proposed bifurcating aggregation pathway is sensitive to the temperature and composition of the n-butanol aqueous solution. The current study shows how temperature is significant in modulating the alcohol aggregation behavior and affects water structure which determines the phase behavior of aqueous solution systems. The effect of temperature on the alcohol aggregation pattern and water structure in n-butanol/water mixtures provides a critical clue in the fundamental understanding and determining the phase behavior of binary water mixtures. The current study also provides a molecular framework to examine and govern the UCST behavior of aqueous solution systems.