Electric-Field-Induced Structure and Dynamics of Ethanol-Water Mixture in Hydrophobic-hydrophilic Nanochannels

Abstract

Understanding the behavior of confined fluid mixtures under external electric fields is essential for advancing scientific knowledge and improving a wide range of technological applications, from energy systems to biological processes. The electric field widely used to investigate the phase transition of water and modification of interfacial water at the nanoscale. However, a molecular-level understanding of the interfacial layer of a confined fluid mixture under an electric field remains unexplored. In this study, we explore the structural and dynamic behavior of binary ethanol-water mixtures confined within slit like hydrophilic (mica) and hydrophobic (graphene) nanochannels under an external electric-field using classical molecular dynamics (MD) simulations. We find two distinct interfacial water layers near the hydrophilic mica surface, and a more pronounced sharp peak appears near the hydrophobic graphene sheet with increasing electric field. The density maxima of the -OH and -CH3 groups of ethanol shift towards and away from the graphene surface with an increasing electric field. Our simulations reveal that the electric field strongly impacts the inter and intralayer hydrogen bonding among water and ethanol molecules. The diffusion coefficient of water slightly increases with the electric field and then reduces with an electric field for a lower concentration of ethanol. This finding reveals that the electric field influences the desorption of interfacial water near the hydrophilic mica surface, which can be an implication for diverse technological applications like modifying surface wettability.