Smart windows devised by fine-tuning properties of "Polymer Network Liquid Crystals" (PNLCs) device by adding tiny flakes of a nanomaterial, hexagonal boron nitride (h-BN) can bring down the load on air conditioners by controlling infra-red light.

In the quest for more energy-efficient homes and devices, controlling how materials interact with light, especially invisible infrared (IR) radiation, is crucial. Infrared light, while essential for life on Earth, can also contribute to unwanted heat, increasing the need for air conditioning and the associated energy consumption. Scientists are constantly seeking innovative ways to manage this radiation.

A research team at the Centre for Nano and Soft Matter Sciences (CeNS), Bengaluru, an autonomous institute of Department of Science and Technology (DST) has brought fascinating new insights in this direction. Their recent work explores how to fine-tune the properties of "Polymer Network Liquid Crystals" (PNLCs) device, using an optimized composite of polymers and liquid crystals, by adding tiny flakes of a nanomaterial, hexagonal boron nitride (h-BN).

Their research highlights two key ways to control the amount of IR light scattered by these materials through nano-level modification of the formed network. In the absence of h-BN, the system forms a course, bead-like network resulting in very little IR scattering and hence essentially no electrical control over. On the other hand, crafted incorporation of h-BN nanoflakes leads to a smooth and continuous network.

Fig: Top panel: Schematic diagram showing (a) the PNLC-BN system polymerized in the disordered phase along with its optical microscopy (left top) FESEM image (right bottom) and that of PNLC-BN system polymerized in the ordered phase with its FESEM image (right).

Bottom panel: Schematic showing that the small sized h-BN flakes are better incorporated into the polymer as their lateral size is comparable to the size of polymer fibre.

 

Consequently, the device with nanoflakes exhibits high-magnitude IR scattering permitting substantial electrical control over the amount of external heat entering the room. From the material design perspective, the “IR-control polymer-LC network” is primarily realized by polymerizing the composite in either the “ordered” or “disordered” state of the LC. Electron microscopy studies show that the accomplished nanoflake disposition creates a large number of local scattering sites, drastically enhancing the IR scattering.

Building on this, the team of the two researchers, Gayathri Pisharody and Priyabrata Sahoo working with faculty supervisors Dr. D.S. Shankar Rao, Dr. Ramakrishna Matte and Dr. S. Krishna Prasad, further explored ways and means of making the h-BN flakes blend seamlessly with the polymer network, a feature that depends on the physical dimension of the nanostructures, their concentration, process temperature and other control parameters.

Optimization of these parameters has led to smart windows driven by electric fields that exhibit a large IR contrast which can be switched between transparent (allowing heat radiation into or from the enclosure) and scattering (blocking IR radiation) states at high operating speeds.  Scaled-up versions of these smart windows could serve as excellent engineering devices, for instance, as specific light/heat management windows, and more importantly for bringing down the load on air conditioners.

The research was published recently as two papers in the Journal of Molecular Liquids.

https://doi.org/10.1016/j.molliq.2025.127809;

https://doi.org/10.1016/j.molliq.2024.126735

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