Daniel Kuo

To obtain high quality of drinking water free from biocontaminants is especially important issue. A new strategy employing smectic liquid‐crystalline ionic membranes exhibiting 2D structures of layered nanochannels for water treatment is proposed for efficient virus removal and sufficient water flux. The smectic A (SmA) liquid‐crystalline membranes obtained by in situ polymerization of an ionic mesogenic monomer are examined for removal of three distinct viruses with small size: Qβ bacteriophage, MS2 bacteriophage, and Aichi virus. The semi‐bilayer structure of the SmA significantly obstructs the virus penetration with an average log reduction value of 7.3 log₁₀ or the equivalent of reducing 18 million viruses down to 1. Furthermore, the layered nanochannels of the SmA liquid crystal allow efficient water permeation compared to other types of liquid‐crystalline membrane consisting of nanopores.

Switching one-dimensional ion conductivities in organic materials is a challenging task. Recently we found that a liquid-crystalline (LC) N,N,N-trimethyl-3,4,5-tridodecyloxy-anilinium salt showed a remarkable change in the conductivities of about four orders of magnitude, which was triggered by a thermotropic LC phase transition between rectangular (Col_r) and hexagonal (Col_h) columnar phases. In the present study, we have succeeded in tuning the switching temperature by changing the length of the alkyl chains attached to the anilinium ring of LC materials. The size of the N,N,N-trialkylanilinium cations, that is, trimethyl, dimethylethyl and diethylmethyl, and the counterion (BF₄, PF₆ or CF₃SO₃) play a crucial role in the formation of successive Col_r and Col_h LC phases, which affect the switching behaviour. We have found that the temperature of the Col_r–Col_h phase transition and the switching of ion conductivity are tuned in N,N,N-trimethylanilinium tetrafluoroborates by changing the length of the alkyl chains. These results give new insights into the design of ion-conductive self-assembled molecular materials.

Here we report columnar liquid-crystalline (LC) nanostructured membranes that highly remove viruses and show sufficient water permeation. These membranes were prepared by employing two-component liquid crystals that exhibit tetragonal columnar phases. The membranes exhibited virus rejection values of >99.99% (log₁₀ reduction value (LRV) > 4) and water flux ranging from 19 to 61 L m^–2 h^–1 (operation pressure: 0.3 MPa). These membranes were fabricated by photopolymerization of a fan-shaped diol molecule and imidazolium ionic liquid mixture, followed by subsequent removal of the ionic liquid. The rejection values and water flux depend on the fraction of ionic liquid. These results show new design strategies of materials for the water treatment nanostructured membranes that remove pathogens and contaminants.

To remove viruses from water, the use of self‐assembling liquid crystals is presented as a novel method for the synthesis of membranes with a regular pore size (below 1 nm) and controlled pore structures. Nanostructured bicontinuous cubic liquid‐crystalline (LC) thin films are photopolymerized onto a polysulfone support layer. It is found that these membranes reject the virus, Qβ bacteriophage (≈20 nm diameter) by >99.9999%. Prepressurization of the membrane appears to enhance their virus rejection properties. This is the first example of nanostructured LC membranes that are used for virus rejection, for which they show great potential.