Understanding the Antifouling Mechanism of Zwitterionic Monomer-Grafted Polyvinylidene Difluoride Membranes: A Comparative Experimental and Molecular Dynamics Simulation Study

Abstract

The antifouling process of the membrane is very vital for the highly efficient treatment of industrial wastewater, especially high salinity wastewater containing oil and other pollutants. In the present work, the dynamical antifouling mechanism is explored via molecular dynamics simulations, while the corresponding experiments about surface properties of the zwitterionic monomer-grafted polyvinylidene difluoride membrane are designed to verify the simulated mechanism. Water can form a stable hydration layer at the grafted membrane surface, where all the simulated radial distribution function of water/membrane, hydrogen bond number, water diffusivity, and experimental oil contact angles are stable. However, the water flux across the membrane will increase first and then decrease as the grafting ratio increases, which not only depends on the reduced pore size of the zwitterionic monomergrafted membrane but also results from water diffusion. Furthermore, the dynamical fouling processes of pollutants (taking sodium alginate as an example) on the grafted membrane in water and brine solution are investigated, where both the high grafting ratio and electrolyte CaCl 2 can enhance the fouling energy barrier of the pollutant. The results show that both the enhanced hydrophilic property and the electrostatic repulsion can affect the antifouling capability of the grafted membrane. Finally, the ternary synergistic antifouling mechanisms among the zwitterionic membrane, electrolyte, and pollutant sodium alginates are discussed, which could be helpful for the rational design and preparation of new and highly efficient zwitterionic antifouling membranes.

Investigation of Surfactant–Membrane Interaction Using Molecular Dynamics Simulation with Umbrella Sampling

“…67−69 On one hand, for the same foulant, because of the similar extents of hydration in different environments, the flux trend can be directly correlated with foulant−membrane interaction energy. 67,68 On the other hand, when different foulants are compared, the more significantly different extents of hydration have non-negligible influences on the overall free energy, and thereby the foulant−membrane energy is not directly correlated with the flux trends. 69 In this study, three surfactants have distinctly different hydrations (Figure 7a), which necessitates the consideration of the overall free energy.…”

Analysis of zwitterionic membrane fouling mechanism caused by HPAM in the presence of electrolytes

“…The details about the building method were modeled according to the previous work. 22 The grafted degree in the simulation part is described as R DMAPS ( R DMAPS = 0%, 15%, 30%).…”

“…The water permeability test, the contact angles 31 of prepared zwitterionic membranes graed with different DMAPS concentrations (C DMAPS ) and the anti-oil-adhesion property 32,33 of the zwitterionic membrane have been reported in our previous work. 22 The obvious change of the wetting ability and oil adhesion force shows that the dominative role of graed DMAPS on the zwitterionic membrane. 1% PVDF-g-DMAPS membrane are selected to make a further investigation as hydrophilic performance is stable.…”

“…As an effective means to explain the microscopic mechanism, molecular dynamics simulations can illustrate the interactions between the membrane and foulants from a molecular perspective. 20,21 Liu et al 22 explored the effect of the hydration layer on the surface of zwitterionic membrane and the dynamic antifouling mechanism of the membrane for sodium alginate by molecular dynamics simulations. Talati et al 23 investigated the separation performance of carbon nanotube membranes for different heavy metal ions (Zn 2+ , Ni 2+ , Cd 2+ ) in aqueous solutions using molecular dynamics simulations.…”

Computational Investigation of Antifouling Property of Polyacrylamide Brushes

“…Furthermore, more advanced steered MD (SMD) simulations were proposed and developed to study the adsorption of a foulant or protein on different polymer-grafted surfaces. Liu et al studied molecular structure and water diffusion at PVDF- g -DMAPS membranes using both conventional MD and SMD simulations. They observed the existence of the hydration layer at the water–membrane interface, where the enhanced HB strength and electrostatic repulsion dominate the antifouling capability.…”