Switchable gas permeability of a polypropylene‐liquid crystalline composite film

Abstract

The development of functionalized polyolefins for use as stimuli‐responsive commodity polymers has recently received much attention. In this work, a microporous polypropylene (PP) scaffold is used to align and fortify a smectic liquid crystalline network (LCN) which can switch its gas permeability upon pH changes. The LCN is a photopolymerized liquid crystalline mixture of a dimerized benzoic acid derivative monoacrylate and a diacrylate crosslinker. In the hydrogen‐bonded state, the composite membrane shows a high‐molecular order and a low permeability for He, N2, and CO2 gases. By pH switching from the hydrogen‐bonded state to the salt form, the molecular order is reduced, and the gas permeability is increased by one order of magnitude. This increase is mainly attributed to a loss in order of the system, increasing the free volume, resulting in an increased diffusibility. By exposing the composite film to basic or acidic environments, reversible switching between low and high gas permeability states is observed, respectively. The physical constraints imposed by the PP scaffold strengthens the membrane while the reversible switching inside the liquid crystalline polymer is maintained. This switching of gas permeation properties is not possible with the fragile freestanding LCN films alone.

A pH-Responsive Liquid Crystal Hydrogel Actuator with Calcium-Induced Reprogrammable Shape Fixing

“…Fabrication of the Composite Soft Actuators. 29,37 Two LC mixtures were made consisting of either 60 wt % monoacrylate (I) and 40 wt % diacrylate (II) (40% Cl) or 90 wt % monoacrylate I and 10 wt % diacrylate II (10% Cl), with the addition of 1 wt % photoinitiator and 0.1 wt % inhibitor. The LC mixture was dissolved in THF (20 wt %) and subsequently bar-coated with a wet film thickness of 6 μm onto a PVP-coated glass substrate.…”

Tuning the Gas Separation Performances of Smectic Liquid Crystalline Polymer Membranes by Molecular Engineering

“…Subsequent crosslinking of the LC monomers to fixate the nanostructures is necessary to provide sufficient mechanical strength to obtain robust free-standing LC polymer membranes. So far, LC polymer membranes have mainly been investigated for water separations [13][14][15][16][17][18][19][20][21][22][23][24], but hardly for gas separations [25][26][27]. Studies show the importance of molecular order and orientation in LC polymer membranes, see, for example, our previous work [26].…”