Electrically Mediated Membrane Pore Gating via Grafted Polymer Brushes

Abstract

Stimuli-responsive membranes that enable the smart control of membrane transport properties represent an interesting class of materials for a wide range of separation processes. In this work, surface-initiated, electrochemically mediated atom transfer radical polymerization was used to grow poly(acrylic acid) brushes from the surface of a percolating network of carbon nanotubes coating an ultrafiltration membrane. Brush molecular weights as high as 930 kDa were achieved, with very low dispersivity. When no potential was applied, the material was able to reject 88% of 12 kDa dextran in 50 mM NaCl solution. Membrane rejection and flux were readily changed upon the application of electrical potentials, with positive potentials increasing flux by 85% and reducing rejection by 56%, while negative potentials reduced flux by 30% and increased rejection by 5%. We show evidence that counterion migration, moving in response to the applied electric field, is responsible for the expansion or collapse of the grafted charged polymer brushes, which induced or eliminated pore gating. In addition, atomic force microscopy was used to probe the forces exerted by brush conformational changes in response to the applied field. These materials can find applications in industrial separations where gating is needed and may possess interesting anti-fouling properties.

Voltage-Gated Membranes Incorporating Cucurbit[n]uril Molecular Containers for Molecular Nanofiltration

“…Precise assembly with smart materials is essential in designing next-generation membranes to meet harsh and complex separation challenges . Voltage, like other external stimuli such as pH, temperature, and light, is expected to endow NF membranes with an intelligent gating function to achieve on-demand and precise separation. − Currently, only a limited number of conductive materials have been used in the preparation of electroresponsive NF membranes, including conductive polymers and nanomaterials such as polyaniline, polypyrrole, carbon nanotubes, and graphene derivatives. − However, the processes required to load the abovementioned materials into the membrane to achieve the removal of small molecular pollutants are often complicated and excessive, which diminishes the prospects for scalable manufacture. Redox-active small molecules can be tuned by synthetic chemistry and possess excellent electrical conductivity.…”

Visualization of the pH Response through Autofluorescent Poly(styrene-alt-N-maleimide) Polyelectrolyte Brushes

“…4 These reversible transitions between two states can be induced by changes in pH, ion content, temperature, solvent, and mechanical force and thus render them as suitable materials for the design of stimuli-responsive ("smart") surfaces. 5−7 Polyelectrolyte brushes (PEBs), which contain charged groups in their repeating units, have attracted considerable attention for the design of smart polymer interfaces, and many applications have been described for PEBs, including smart membranes, 8 enzyme immobilization supports, 9,10 smart actuators, 11 and responsive interfaces. 12 Specifically, weak polyelectrolyte brushes establish a versatile platform for responsive coatings since they can undergo dynamic changes in accordance with their degree of ionization and protonation, depending on the local pH.…”

Redox- and Enzyme-Responsive Macrospheres Gatekept by Polysaccharides for Controlled Release of Agrochemicals

“…3,4 Recently, much attention has been paid to the carriers for the controlled release of agrochemicals. 5,6 In particular, stimuli-responsive carriers such as pH-, 7 thermal-, 8 UV light-, 9 magnetic field-, 10 electric field-, 11 redox-, 12,13 and enzyme-responsive 14 carriers have been developed for targeted and controlled release. The agrochemical released by the stimuli-responsive controlled technology has great potential to tackle the defects of conventional procedures, and the stability of agrochemical properties can be significantly improved.…”

“…However, less than 10% of agrochemicals exert effect on their target by conventional procedures, thus agrochemicals need to be applied repeatedly for maintaining their effective concentrations. Therefore, the abuse and improper application technology of agrochemicals have led to serious soil and groundwater pollution. , Recently, much attention has been paid to the carriers for the controlled release of agrochemicals. , In particular, stimuli-responsive carriers such as pH-, thermal-, UV light-, magnetic field-, electric field-, redox-, , and enzyme-responsive carriers have been developed for targeted and controlled release. The agrochemical released by the stimuli-responsive controlled technology has great potential to tackle the defects of conventional procedures, and the stability of agrochemical properties can be significantly improved.…”