pH-Sensitive Bipolar Ion-Permselective Ultrathin Films

Abstract

pH-Sensitive bipolar ion-permselective films of polyelectrolyte multilayers were prepared by layer-by-layer (LbL) assembly and photo-cross-linking of benzophenone-modified poly(acrylic acid) (PAA-BP) and poly(allylamine hydrochloride) (PAH-BP). The multilayer structure and ionizable group composition was finely tuned by changing the pH of the dipping solution. This structure and composition was in turn "preserved" by photo-cross-linking, forming highly stable membrane films. Since PAA-BP and PAH-BP are weak polyelectrolytes, it is possible to control the number of unbound, un-ionized -COOH or -NH2 groups in the multilayer by changing the pH. Moreover, the pH of the deposited film also plays an important role in determining selective latter permselectivity. For example, PAA-BP/PAH-BP multilayers deposited from two pH conditions, pH = 3 (PAA-BP) and pH = 6 (PAH-BP), showed pH-switchable permselectivity for both cationic (pH = 10) and anionic (pH = 3) probe molecules in a single film. The system offers advantages in film stability and introducing reversible selective ion permeability over previous multilayer film and cross-linking methods.

A Smart Nanofiber Web That Captures and Releases Cells

“…[30] In general, BP is excited indirectly to the lowest triplet state (p-p*) by direct absorption into singlet state (p-p*) upon irradiation with UV light. [31] The BP ketyl radical and an on-chain polymer radical readily recombine to generate a new CÀC bond, [32] thereby resulting in cross-linking within the nanofibers (Figure 1 b). UV/Vis spectroscopy was used to monitor the cross-linking with BP.…”

Challenges and breakthroughs in recent research on self-assembly

“…These attributes are useful for controlled release and drug delivery [856,857]. For example, Rubner, Cohen, and coworkers introduced soft LbL films within the pores of a polymer support to prepare a pH-sensitive permeation valve (figure 100) [858].…”

Multiresponsive, Hierarchically Structured Membranes: New, Challenging, Biomimetic Materials for Biosensors, Controlled Release, Biochemical Gates, and Nanoreactors

“…Responsive LBL films deposited on the electrode surface are used as membrane-based sensors, where the membrane controls the transport of the redox species to a working electrode. [13,14] Weak PEs can be deposited with a high percentage of segments comprising loops and tails, by adsorbing under pH conditions of incomplete charge, and allowing for further large-scale reorganization and phase separation regulated by pH changes. It has been shown that such a reorganization causes phase separation in the LBL films, and results in the formation of a microporous membrane.…”