Gating Characteristics of Thermo‐Responsive Membranes with Grafted Linear and Crosslinked Poly(N‐isopropylacrylamide) Gates

Abstract

Thermo-responsive porous membranes with grafted linear and crosslinked poly(N-isopropylacrylamide) (PNIPAM) gates are successfully prepared at temperatures above and below the lower critical solution temperature (LCST) of PNIPAM by using a plasma-induced grafting polymerization method, and the effects of operation pressure and grafting temperature on the thermo-responsive gating characteristics of the prepared membranes are investigated systematically. The fluxes of water through the grafted membranes increase simply with increasing the operation pressure no matter whether the environmental temperature is 40°C or 25°C. Under high operation pressure (e.g., higher than 0.14 MPa), the grafted linear PNIPAM gates deform to a certain extent, whereas the grafted crosslinked PNIPAM gates do not deform. For both membranes with grafted linear and crosslinked PNIPAM gates, the membranes prepared at 25°C (below the LCST of PNIPAM) show larger thermo-responsive gating coefficients than those prepared at 40°C (above the LCST of PNIPAM), which results from different distributions of grafted PNIPAM gates in the membrane pores. When the PNIPAM gates are grafted at 25°C, the grafted layer near the membrane surface is much thicker than that inside the membrane pores; on the other hand, when the PNI-PAM gates are grafted at 40°C, the grafted layer is homogeneously formed throughout the whole pore length. Both linear and crosslinked grafted PNIPAM gates in the membrane pores exhibit stable and repeatable thermo-responsive "open-close" switch performances under the operation pressure of 0.26 MPa. The results in this study provide valuable guidance for designing, fabricating, and operating thermo-responsive gating membranes with desirable performances.

Ethanol‐responsive characteristics of polyethersulfone composite membranes blended with poly(N‐isopropylacrylamide) nanogels

“…For example, the maximum thermo‐responsive factor R 45/15 of blank membrane in water is 1.7 calculated by the measured water flux. This value is quite close to 1.8 that obtained by substituting the solution viscosity values at different temperatures into the Hagen–Poiseuille's Equation . The result shows that the blank membrane without blended PNIPAM nanogels has no thermo‐responsive characteristics.…”

“…The efficiency of ethanol fermentation will be lowered when the membranes are not operated at the optimal ethanol concentration and temperature. Fortunately, the developing smart membranes have the capability to autonomously adjust the permeation performance according to the external environmental stimuli, such as temperature, pH, and ion signal . Act as smart valves, the ethanol‐responsive smart membranes are developed to self‐regulatively adjust the trans‐membrane permeability responding to the ethanol concentration.…”

Biomimetic Smart Interface Materials for Biological Applications

“…Most smart gating materials are prepared by grafting linear stimuli‐responsive polymer chains onto the substrate membranes. For example, grafting PNIPAAm onto porous materials or meshes is a common way to prepare thermoresponsive smart gating membranes 80. In 2007, our group reported the grafting of pure PNIPAAm on a nanostructured copper‐mesh film obtained by treatment with aqueous ammonia and evaluated its water‐permeation properties at different temperatures 81.…”

Thermo‐Responsive Polyethersulfone Composite Membranes Blended with Poly(N‐isopropylacrylamide) Nanogels

“…Among the environmental stimuli, temperature fluctuations can be easily achieved and controlled artificially, so thermo-responsive membranes are attracting an ever-increasing interest [1][2][3]. Thermo-responsive membranes are highly potent in a myriad of applications, including controlled-release systems [2,3,[5][6][7][8], separations [2,3,[9][10][11][12][13], switching valves [14][15][16], and tissue engineering [17][18][19].…”