The role of surface wettability on water transport through membranes

Preparation and Characterization of PVDF-TiO2 Mixed-Matrix Membrane with PVP and PEG as Pore-Forming Agents for BSA Rejection

Polymeric membranes offer straightforward modification methods that make industry scaling affordable and easy; however, these materials are hydrophobic, prone to fouling, and vulnerable to extreme operating conditions. Various attempts were made in this study to fix the challenges in using polymeric membranes and create mixed-matrix membrane (MMMs) with improved properties and hydrophilicity by adding titanium dioxide (TiO₂) and pore-forming agents to hydrophobic polyvinylidene fluoride (PVDF). The PVDF mixed-matrix ultrafiltration membranes in this study were made using the non-solvent phase inversion approach which is a simple and effective method for increasing the hydrophilic nature of membranes. Polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) as pore-forming chemicals were created. Pure water flux, BSA flux, and BSA rejection were calculated to evaluate the mixed-matrix membrane's efficiency. Bovine serum albumin (BSA) solution was employed in this study to examine the protein rejection ability. Increases in hydrophilicity, viscosity, and flux in pure water and BSA solution were achieved using PVP and PEG additives. The PVDF membrane's hydrophilicity was raised with the addition of TiO₂, showing an increased contact angle to 71°. The results show that the PVDF-PVP-TiO₂ membrane achieved its optimum water flux of 97 L/(m²h) while the PVDF-PEG-TiO₂ membrane rejected BSA at a rate greater than 97%. The findings demonstrate that use of a support or additive improved filtration performance compared to a pristine polymeric membrane by increasing its hydrophilicity.

A Facile Strategy toward the Preparation of a High-Performance Polyamide TFC Membrane with a CA/PVDF Support Layer

In this study, polyamide (PA) thin-film composite (TFC) nanofiltration membranes were fabricated via interfacial polymerization on cellulose acetate (CA)/poly(vinylidene fluoride) (PVDF) support layers. Several types of CA/PVDF supports were prepared via the phase inversion method. With increasing CA, the PVDF membrane surface pore size decreased and hydrophilicity increased. The effect of the support properties on the performance and formation mechanism of PA films was systematically investigated via an interfacial polymerization (IP) process. The permselectivity of the resulting TFC membranes was evaluated using a MgSO4 solution. The results show that the desired polyamide TFC membrane exhibited excellent water flux (6.56 L/(m2·h·bar)) and bivalent salt ion rejection (>97%). One aim of this study is to explore how the support of CA/PVDF influences the IP process and the performance of PA film.

Poly(ionic liquid)‐Armored MXene Membrane: Interlayer Engineering for Facilitated Water Transport

Two‐dimensional (2D) MXene‐based lamellar membranes bearing interlayers of tunable hydrophilicity are promising for high‐performance water purification. The current challenge lies in how to engineer the pore wall's surface properties in the subnano‐confinement environment while ensuring its high selectivity. Herein, poly(ionic liquid)s, equipped with readily exchangeable counter anions, succeeded as a hydrophilicity modifier in addressing this issue. Lamellar membranes bearing nanochannels of tailorable hydrophilicity are constructed via assembly of poly(ionic liquid)‐armored MXene nanosheets. By shifting the interlayer galleries from being hydrophilic to more hydrophobic via simple anion exchange, the MXene membrane performs drastically better for both the permeance (by two‐fold improvement) and rejection (≈99 %). This facile method opens up a new avenue for building 2D material‐based membranes of enhancing molecular transport and sieving effect.

Upstream events dictate interfacial slip in geometrically converging nanopores

Continuum computations of fluid flow in conduits approaching molecular scales are often executed with a certain level of abstractions via the imposition of a pre-defined slip condition at the wall. However, in reality, the interfacial slip may not be affixed a priori as a direct one-to-one mapping with the surface wettability and charge but is implicitly interconnected with the concomitant dynamical events that may be effectively captured only under flow conditions. The flow in nanofluidic channels with axially varying cross sections hallmarks such situations in which the effective slip at the wall gets dynamically modulated by upstream flow conditions and cannot be trivially stamped as guided by localized intermolecular interactions over interfacial scales alone. In an effort to capture such flows without resorting to full-domain molecular dynamics simulations, here we bring out advancements on hybrid molecular-continuum simulations and report predictions that closely capture molecular dynamics based predictions of water transport through converging nanopores. Our results turn out to be of significant implications toward designing of emerging nanoscale devices of multifarious applications ranging from miniaturized reactors to highly targeted drug delivery systems.

Thermodynamic Barrier for Nanoparticle Penetration into Nanotubes

It is promising yet challenging to develop efficient methods to separate nanoparticles (NPs) with nanochannel devices. Herein, in order to guide and develop the separation method, the thermodynamic mechanism of NP penetration into solvent-filled nanotubes is investigated by using classical density functional theory. The potential of mean force (PMF) is calculated to evaluate the thermodynamic energy barrier for NP penetration into nanotubes. The accuracy of the theory is validated by comparing it with parallel molecular dynamics simulation. By examining the effects of nanotube size, solvent density, and substrate wettability on the PMF, we find that a large tube, a low bulk solvent density, and a solvophilic substrate can boost the NP penetration into nanotubes. In addition, it is found that an hourglass-shaped entrance can effectively improve the NP penetration efficiency compared with a square-shaped entrance. Furthermore, the minimum separation density of NPs in solution is identified, below which the NP penetration into nanotubes requires an additional driving force. Our findings provide fundamental insights into the thermodynamic barrier for NP penetration into nanotubes, which may provide theoretical guidance for separating two components using microfluidics.