The Interplay between Dynamics and Structure on the Dielectric Tensor of Nanoconfined Water: Surface Charge and Salinity Effect

Author(s)

Coelho, Felipe Mourao ; Franco, Luis Fernando Mercier

• Document type: Journal article
• Source: Journal of Physical Chemistry B; v. 128, n. 47, p. 9-pg., 2024-11-16.

Abstract

Under confinement, the water dielectric constant is a second-order tensor with an abnormally low out-of-plane element. In our work, we investigate the dielectric tensor of an aqueous NaCl solution confined by a quartz slit-pore. The static dielectric constant is determined from local polarization density fluctuations via molecular dynamics simulations. In a pioneering investigation, we evaluate not only the effect of salinity but also surface charge. The parallel dielectric constant decreases with salinity due to dielectric saturation. From a dynamic perspective, the relaxation of water dipoles is slower within the hydration shells of ions. An anisotropic arrangement on the quartz surface results in preferred orientations of interfacial water molecules. By embedding charge, the surface structure changes, and extra dipole fluctuations in one direction may develop anisotropy in the parallel dielectric constant at the interface. Both surface charge and salinity increase the perpendicular dielectric constant. Nevertheless, the surface charge effect is more pronounced and may even recover the bulk dielectric constant value. The electric field established by the charged surface may disturb the planar hydrogen bond network at the interface, increasing out-of-plane dipolar fluctuations. Our work advances the knowledge of confined dielectric behavior, shedding light on the key role that charged surfaces play. (AU)

• FAPESP's process: 20/13300-6 - Molecular dynamics simulations for studying equilibrium properties of confined mixtures
• Grantee: Felipe Mourão Coelho
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• FAPESP's process: 21/13068-9 - Thermodiffusion of CO2 in water: the Impact of the geothermal gradient in the carbon sequestration within deep saline aquifers via molecular simulation
• Grantee: Felipe Mourão Coelho
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)
• FAPESP's process: 18/02713-8 - Molecular dynamics of confined fluids: equilibrium and transport properties
• Grantee: Luís Fernando Mercier Franco
• Support Opportunities: Research Grants - Young Investigators Grants