Responsive Polyelectrolyte Gel Membranes

Abstract

In the past two decades, synthesis of responsive membranes with pores that could be opened and closed by changing chemical or physical properties of their environment has been the subject of many publications (see Ulbricht's work for a recent review). [1][2][3][4][5][6][7][8] In most studies the variable pore permeability was attained by the surface modification of commercial microfiltration membranes using polymers that expand or contract in response to external stimuli. Radiation-and plasma-induced graft polymerizations were employed to immobilize a monolayer of surface-attached responsive polymer chains (brushlike layers) or crosslinked polymer networks (gels) on the membrane and/or pore surfaces. Stimuli-induced changes of the conformation of the grafted-polymer chains affected the permeability of nanometer-sized pores in the membranes. Responsive gels were used to fill the interior of larger submicrometer/micrometer pores and regulate the membrane permeability. Membranes sensitive to changes in temperature, pH, ionic strength, light intensity, reduction-oxidation state of functional groups, and concentration of various substances have thus been fabricated based on the above-mentioned principles. The application of such stimulus-responsive membranes or "chemical valves" (functional gates) includes flow control, size-selective filtration, chemical and bioseparation, controlled release of chemical substances and drugs, and chemical sensors.In the present study, we report on a novel method for the fabrication of flexible stimulus-responsive polymer gel (PG) membranes. These membranes are thin porous films made of a crosslinked polyelectrolyte. Past research has focused on porous thin-film membranes made of polyelectrolyte complexes. [9,10] In our approach the porous films are formed via phase separation of a polyelectrolyte and a volatile additive. This approach provides a broad possibility to regulate pore sizes and the membrane responsiveness. In our method, the PG membranes can be prepared on any flat substrate with a low surface roughness (e.g., Si wafer); afterward, the membrane can be transferred (and attached chemically, if necessary) onto various porous or nonporous supports (with flat, profiled, and even curved surfaces, e.g., membrane filter, fabrics, chemical sensor, or human skin). The fabrication of these membranes consists of three very simple steps, described in detail below.The PG membranes operate in a similar manner to those prepared by the grafting of polymers on the surface of porous substrates. That is, 3D swelling of the PG upon an external stimulus leads to shrinkage of the pores and, consequently, to the regulation of the membrane permeability. However, the PG membranes, unlike the membranes reported in literature, respond via swelling and shrinking of the entire body of the membrane. The shrinking allows for the stimuli-responsive mechanism of pore-size regulation in a very broad range, from completely closed pores (pore opening size = 0) to large open pores (pore opening size = 0.3 lm)....

Electrochemical Nanotransistor from Mixed‐Polymer Brushes

“…Their applications for controlled surface wettability, [6,7] thin-films permeability, [8,9] catalysis, [10] and particularly for assembling modified electrodes, [11] used in switchable sensors, [12] fuel cells, [13] and memory units, [14] resulted in novel materials, devices, and systems. [15,16] Recent integration of signal-responsive materials, functionalized switchable interfaces and biocomputing systems processing biochemical information resulted in the novel concept of biochemically controlled ''smart'' materials with built-in Boolean logic.…”

Gold‐Nanoparticle‐Enhanced Plasmonic Effects in a Responsive Polymer Gel

“…The membrane preparation and the mechanism responsible for pore formation are described in detail in our previous papers. [29,30] It has been previously demonstrated that only one-fifth of the pyridine groups were involved in the crosslinking, while the remaining groups could serve as pH-responsive units. [30] Two different kinds of gold particles were associated with the gel material to enable optical detection of changes in its swelling degree induced by an external signal (pH): gold NPs dispersed throughout in the gel and a layer of gold islands prepared on a glass substrate.…”

Nanomembrane Materials Based on Polymer Blends

“…Thin films with well-controlled nanoscale porosity-most interesting from the point of view of practical applications-are primarily from the multiphase materials through the selective removal of one of the polymeric phases or a sacrificial colloidal component in hybrid films. Some researchers proposed self-assembly methods based on liquidliquid phase separation in multi-component solutions comprising a stimuli-responsive cross-linkable polymer and a pore-forming component [102][103][104]. The phase separation occurred during spin-cast deposition of polymeric films.…”

“…The phase separation occurred during spin-cast deposition of polymeric films. Tokarev et al [102] used monovalent salt to disrupt a polyelectrolyte complex of two biopolymers (alginate and gelatin), thus triggering their phase separation in spin-cast films. Hydrogen bonding between two water-soluble polymers can be also used to delay phase separation, as was demonstrated for the system composed of alginate and poly(vinyl alcohol) (PVA) [104].…”