Insight into the Structure and Dynamics of Ethanol–Water Binary Mixture Confined in Nanochannel by Mica and Graphene

Abstract

Investigation of the structural properties and dynamics of fluid mixture confined in nanochannels has become an essential topic in many fields due to potential applications in nanofluidic devices and biological systems. Here, we study the ethanol–water blend confined between the mica and single or multilayer graphene for different slit pore widths, ethanol content, and temperatures. Our molecular dynamics simulation indicates that water molecules are adsorbed at the mica surface, while ethanol molecules prefer to be adsorbed near the graphene surface. We find that distinct layers of ethanol molecules form as the channel width and ethanol content in the mixture are increased. The diffusion of confined ethanol and water molecules depends on the nanopore widths, concentrations, and temperatures. Interestingly, at nanopore widths of 1.0 and 1.3 nm, the mobility of confined ethanol molecules is greater than that of water molecules for all ethanol concentrations. In contrast, at pore width of 0.7 nm, the opposite behavior is observed at lower concentrations of ethanol (x EtOH = 0.1 and 0.3) in the mixture. Furthermore, the diffusivity of ethanol and water in the mixtures increases with increasing the temperatures. The hydrogen bond and cluster analysis imply the segregation of water molecules near the mica surface, while ethanol molecules are near the opposite pore wall (graphene).

Enhanced Pervaporation of the Poly(dimethylsiloxane) (PDMS) Mixed Matrix Membrane Based on the Self-Assembly of Multidimensional Carbon Nanomaterials

“…The separation factor of both the rGO/PDMS and P-CNT/PDMS membranes decreases with the increase of the rGO or P-CNT content. The incorporation of the hydrophobic rGO and P-CNT nanoparticles into the PDMS matrix enhances the hydrophobicity and the ethanol affinity of the membranes. , However, when the rGO or P-CNT content exceeds 0.8 wt %, the large aggregates of the rGO or P-CNTs create defects in the membrane matrix and on its top surface, resulting in an increase in the total flux but a decrease in the separation factor of the membrane. Moreover, the rGO/PDMS MMM has a higher flux and separation factor than those of the P-CNTs/PDMS MMM at the same content level.…”

“…As shown in Figure b, the swelling of all of the membranes in ethanol is greater than that in water, indicating that the PDMS had a strong affinity of ethanol. The PDMS MMMs exhibit higher ethanol swelling than that of the pure PDMS membrane, indicating that the MMMs have enhanced ethanol affinity due to the adsorption sites of the nanoparticles. , The ethanol swelling of the rGO/PDMS membrane is slightly higher than those of P-CNTs/PDMS and P-CNTs@rGO/PDMS. It may come from the surface agglomerations of the rGO nanoparticles (Figure c).…”

“…With increasing temperature, the free volume of the PDMS expands, causing more ethanol and water to dissolve in the matrix. At the same time, due to the affinities among the CNTs, rGO, and ethanol molecules, more ethanol molecules are transported through the permeation channels (the interfaces) formed by the P-CNTs@rGO nanoparticles, resulting in the increase of the ethanol flux. , The main resistance affecting ethanol permeation comes from the PDMS matrix. Therefore, the permeation channels formed by the P-CNTs@rGO nanoparticles have the advantages of rapid transport and good selectivity of ethanol molecules.…”

“…The tubular and lamellar structures of the CNT or rGO containing polymeric materials endow them with many superior characteristics and performance, such as high mass transfer efficiency, strong hydrophobicity, permselectivity, and excellent mechanical properties. Researchers have proved that both CNTs and rGO can provide more preferential adsorption sites for the ethanol molecules, thus enhancing the selectivity of the PDMS membrane’s matrix. , Meanwhile, the interface between the PDMS matrix and carbon materials can be tuned to form permeable nanochannels. These nanochannels may improve the fluxes of all of the PDMS-based membranes.…”

“…Researchers have proved that both CNTs and rGO can provide more preferential adsorption sites for the ethanol molecules, thus enhancing the selectivity of the PDMS membrane's matrix. 21,22 Meanwhile, the interface between the PDMS matrix and carbon materials can be tuned to form permeable nanochannels. These nanochannels may improve the fluxes of all of the PDMS-based membranes.…”