Smart membranes
A research group from the Graduate School of Engineering at Tohoku University (Japan; www.tohoku.ac.jp) has developed an ion-selective, smart porous membrane that can respond to external stimuli for controlling permeation. The technology has potential applications in molecular separation and sensing applications.
Nanostructure properties, such as pore size, thickness and film density, affect molecular selectivity and molecular permeability. Surface properties also have a significant impact on molecular selectivity. Therefore, it is important to be able to control both the 3-D nanostructures and surface properties of ultrathin porous films.
“In our study, we succeeded in developing responsive porous SiO2 thin films with an extremely thin film thickness of 8 nm with a uniformly covered surface in a pH-responsive silane coupling agent,” says Yuya Ishizaki, a co-author of the study published in Langmuir. “The responsive porous thin film can adjust the surface charge depending on the pH change in the solution, resulting in selective ion permeation.”
To prepare the porous films with a controlled structure to nanometer-scale accuracy, the research group focused on polymer thin films containing silsesquioxanes, which have unique cage structures. The polymer films were fabricated using the Langmuir-Blodgett technique, chosen because it provides molecular-scale controllability in the film thickness. Langmuir-Blodgett polymer nanosheets also make it possible to fabricate porous SiO2 thin films with controlled nanostructures by simple ultraviolet (UV) light irradiation under ambient conditions.