A novel protocol for confinement of liquid crystals in an architecture called hierarchical double networks of polymers can give next-generation solutions for low-energy consuming on-demand switchable smart windows operating between low and high transmittance.

Interpenetrating polymer networks are soft matter systems that innovatively optimise different functionalities such as mechanical, optical, and electrical properties to provide novel solutions in engineering and biomedical applications. A specific class of these architectures, labelled hierarchical double networks, synergistically combining rigid and soft networks to realize thermal, electrical, and optical properties are currently attracting much attention.

The research team of Dr. D S Shankar Rao, Dr. S Krishna Prasad, and Dr. Varshini G V, at the Centre for Nano and Soft Matter Science, Bengaluru have added a new dimension to this field by introducing double networks which are superimposed on liquid crystals. These networks are realized by two different and independently controlled & on-demand stimuli-- light and temperature. While the former creates an orientationally self-assembled polymer network, the organogelation (converting to semi-solid material composed of gelling molecules organized in the presence of an appropriate organic solvent) of the second active component driven by temperature provides the second network which effectively traps the first one. The overall result is a well-controlled porous hierarchical network that confines the liquid crystal while allowing it to be electrically switched between its direction-dependent states and governing the dynamics through the created virtual surfaces of polymeric and gel nature. 

Fig 1: Schematic illustration of the scope of the network and the morphology of the system as imaged through an electron microscope

While exhibiting interesting physics in terms of the thermodynamic characteristics, these hierarchical physical networks also help in realizing the next-generation solution for low-energy consuming privacy windows which are on-demand switchable between high and low haze states with very high spatial resolution achievable by present-day techniques of lithography. 

The work is published in the Journal of Material Chemistry C, 11, 7682-7696 (June 2023).  DOI: 10.1039/d3tc00991b

For further details, Dr. D S Shankar Rao(Email:shankar[at]cens[dot]res[dot]in) can be contacted.

Figure 2: Smart window device fabricated using the hierarchical networks in voltage on and off states