Molecular Simulation and Analysis of Sorption Process toward Theoretical Prediction for Liquid Permeation through Membranes

Molecular Simulation for Guiding the Design and Optimization of Mixed Matrix Membranes (MMMs) in the Pervaporation Process

Molecular simulation has been used extensively in the study of pervaporation membranes as a new economical and environmentally friendly research method. In this paper, A-SiO₂/PDMS-PTFE mixed matrix membranes (MMMs) were prepared by molecular-simulation-guided experiments to achieve the separation of dimethyl carbonate/methanol (DMC/MeOH)) azeotropes. The interaction energy, X-ray diffraction pattern mean square displacement, and density field between PDMS and inorganic particles were analyzed by molecular dynamics simulations. The dissolution and diffusion processes of the DMC/MeOH azeotropes system in the MMM were simulated, and the surface-silylated silica (A-SiO₂) with relatively better performance was screened. Based on the simulation results, A-SiO₂/PDMS-PTFE MMMs were prepared by the coblending method, and the pervaporation separation performance of MMM membranes for DMC/MeOH azeotropes with different A-SiO₂ loadings was investigated. When the A-SiO₂ loading was 15 wt %, the separation factor of DMC/MeOH azeotropes at 50 °C was 4.74 and the flux was 1178 g m^-2 h^-1, which was consistent with the expected results of the simulation. The MMMs showed good stability in pervaporation over a period of up to 120 h. This study demonstrates that molecular simulations can provide a viable means for pretest screening and validation of experimental mechanisms, and to a certain extent, guide the design and optimization of pervaporation membranes.

Real-Time Measurement of Polymer Brush Dynamics Using Silicon Photonic Microring Resonators: Analyte Partitioning and Interior Brush Kinetics

Polymer brushes are found in biomedical and industrial technologies, where they exhibit functionalities considerably dependent on polymer brush-solvent-analyte interactions. It remains a difficult challenge to quickly analyze solvent-swollen polymer brushes, both at the solvent-polymer brush interface and in the brush interior, as well as to monitor the kinetics of interaction of solvent-swollen brushes with key analytes. Here, we demonstrate the novel use of silicon photonic microring resonators to characterize in situ swollen polymer brush-analyte interactions. By monitoring resonant wavelength shifts, we find that brush-solvent-analyte interaction parameters can be extracted from a single set of data or from successive analyte introductions using a single brush-coated sensor. The partition coefficient of three industrially relevant plasticizers into hydrophobic and hydrophilic brushes was determined and found to be in agreement with known solubility trends. We found that the diffusion coefficient of the plasticizer into the brush decreases as brush thickness increases, supporting a model of a dense inner brush layer and diffuse outer layer. pK_a's of pH-sensitive brushes were determined on the microring resonator platform; upon increasing the dry brush thickness, the pK_a for poly(2-dimethylamino ethyl methacrylate) decreased from 8.5 to approach the bulk material pK_a of 7.3 and showed dependence on the presence and concentration of salt. These proof-of-concept experiments show how the surface-sensitive nature of the microring resonator detection platform provides valuable information about the interaction of the polymer brushes with the solvents and analytes, not easily accessed by other techniques.