Photo‐Responsive Water Filtration Membranes Based on Polymerizable Columnar Liquid Crystals with Azo Moieties

Abstract

New materials developed in the last years promise to contribute significantly to the preparation of membranes with improved performance in water filtration. Specifically, the use of dynamic‐responsive systems provides reversibility of the membrane properties. In this work, a reversible photo‐switchable membrane based on templated liquid crystals is presented. Crosslinking of a columnar network, formed by the self‐assembly of a discotic supramolecular complex with a photo‐responsive moiety, results in a switchable filtration membrane. The azo groups in the membrane undergo a photoinduced trans‐cis isomerization by irradiation with 365 nm light and relax back to the cis isomer with a lifetime of 5.7 h or within a few minutes by irradiation at 455 nm. The membranes have a light‐induced reversible change in the water permeability and molecular weight cut off of poly (ethylene glycol). The effective pore size of the trans isomer (1.2 nm) increases to 1.4 nm for the cis isomer. Rejection of the organic dye Rhodamine B is reversibly switched between 50 and 85% by alternating irradiation at 365 nm and 455 nm. The reversible and specific switching demonstrates the potential of this system for light‐controlled separation in nanoporous membranes.

Adaptive 2D and Pseudo-2D Systems: Molecular, Polymeric, and Colloidal Building Blocks for Tailored Complexity

“…Photo-isomerization may be considered a form of mechanical motion that can be exploited to manipulate chemical systems to perform mechanical work [194]. The reversibility of photo-isomerization brings about a plethora of possibilities, such as back and forth movement of molecular machines/motors [195][196][197], smart self-cleaning membrane filters with tunable porosity [198,199], catalysis on demand [200], and remotely-controlled drug-release [201].…”

Light-Powered Liquid Crystal Polymer Network Actuator Using TiO2 Nanoparticles as an Inorganic Ultraviolet-Light Absorber

“…For this reason, the use of light-sensitive materials is aimed in this work. Among different aspects of selecting the suitable material, the degree of flexibility and the capacity to change shape with a reasonable response time should be considered. , These features help us to overcome rigid actuator issues such as finite freedom and relatively complex control systems . The liquid crystal polymer network (LCN), which combines the mechanical capabilities of polymers with the anisotropic nature of LC, has been prioritized as a candidate among the materials employed in this discipline.…”

Hydrogen-Bonded Structures of Water Molecules in Hydroxy-Functionalized Nanochannels of Columnar Liquid Crystalline Nanostructured Membranes Studied by Soft X-ray Emission Spectroscopy

“…Nanostructured materials based on nanosegregated liquid crystals have attracted attention as transport and separation materials. − Water treatment using polymer membranes that transport water molecules selectively is an essential technology in recent years for obtaining safe water with lower cost and lower energy consumption. − We expect that ordered nanochannels with homogeneous channel sizes in water treatment membranes may contribute to a more accurate selective separation. Liquid crystalline (LC) nanoporous membranes are considered as a new type of membrane material that utilizes the nanosegregation process of amphiphilic molecules. − …”