Migration of water and ions in nanopores under different ion-ion correlation strength condition

Abstract

Migration of moisture and ions in C-S-H nanopores is restricted due to the prominence of interfacial effect and intermolecular forces. This paper provided a migration model of water and chloride ions considering ion correlation, dual interface slip and time-varying characteristics of Electrical Double Layer (EDL), which based on governing equations and boundary conditions of nano-flow as well as the hierarchical structure and transport mechanism of restricted liquids. In the paper, the wettability of the C-S-H surface was investigated by conducting contact angle experiments on the synthesized single-phase C-S-H, then the distribution characteristics of water and ions were described in combination with the properties of restricted liquids. By introducing slip length and velocity, the slip between solid-liquid interfaces and the slip between liquid layers near the wall were described. The time-varying properties of the double layer are described by introducing Einstein-Stokes equation and Modified Poisson-Boltzmann equation. Based on AFM, wedge coefficient was introduced into the model to characterize the pore morphology. The results show that the contribution ratio of slip and time-varying of EDL can reach about 70% and 20%, respectively and this phenomenon is more significant in smaller pore size. There are large differences in small and large pore sizes for the phenomena caused by different ion correlation strength conditions. Under strong ion correlation, the influence of water film slip is weakened by 8–10% due to the existence of strong adhesion between solid-liquid interface. The findings provided a systematic insight into the micro-and nanoscale flow.