Logistic gate-like permeable property of gating membrane with ion-recognition polyampholyte

A new gating membrane was developed by grafting an ion-recognition polyampholyte onto the pore surface of a porous substrate. The grafted polymer is composed of acrylic acid as a negative charge, which depends on the pH, and a pendent crown ether receptor that captures specific ions, such as K+ or Ba2+, to behave as a fixed positive charge. While the gating membrane shows monotonic permeability with pH without specific ion signals, it expresses maximum permeability at certain pHs in the presence of specific signals the feature of polyampholyte-grafted membranes. The membrane expresses a logistic gate-like property. It is permeable only in the absence of specific signals and in certain pH ranges; it is non-permeable under other conditions. This interesting phenomenon can be reasonably explained by there being an association between the membrane pore opening state and the swelling state of the grafted ionrecognition polyampholyte, determined by its intramolecular electrostatic interaction. (C) 2013 Elsevier Ltd. All rights reserved.