Influence of polymerisation parameters on the electro-optical properties of polymer-stabilised liquid crystals for smart glass application

ABSTRACT

Smart windows are an important application of liquid crystal/polymer nanocomposites. Recently, an original design has been proposed for a window that switches from a scattering to a transparent state under an electric field. By polymerisation, the topological defects of the smectic A phase under hybrid anchoring conditions are stabilised in the nematic phase, making them addressable by the field. Here, we report the impact of the polymerisation parameters on the electro-optical properties and microstructure of the nanocomposites. We have first estimated the polymerisation kinetics and then investigated the influence of the UV-light intensity, monomer concentration, and photoinitiator concentration. UV-light intensity has little effect on the electro-optical properties of the device, although microstructural changes were observed. The monomer concentration has a strong impact on the scattering power in both the on- and off-states. A model is proposed to describe the dependence of the response times on the monomer concentration. Finally, no influence of the photoinitiator concentration on the electro-optical properties was observed. Polymerisation could occur even in the absence of photoinitiator, possibly due to the presence of impurities that could generate radicals under irradiation. Our study should help optimising the formulation of polymer-stabilised liquid crystal nanocomposites for industrial applications.

Graphical abstract

KEYWORDS:

• Smectic A
• nematic
• polymer
• focal conic domains
• smart glass
• PSLC

Acknowledgments

We would like to thank Emmanuel Garre for his invaluable help with the experimental work and his many suggestions on sample preparation and characterisation. We thank Hanane Belghit for discussions on photoinitiators and LC-HRMS experiments, Anaïs Verron for SEM experiments, Bertrand Heurtefeu and Stéphane Lohou for discussions on polymer chemistry, Cécile Ozanam, Iryna Gozhyk and Laurent Maillaud for discussions on optical measurements, Axel Fouques for discussions on material characterisation, and Olivier Delrieu for measurements of the intensity of UV-lamps. This work was funded by a joint Ph.D. grant from Agence Nationale Recherche et Technologie and Saint-Gobain Research Paris. The authors thank the French Agence Nationale de la Recherche (grant number ANR-23-CE24-0006-03, project DISPLAY) for financial support.

F.M., I.D., C.M. and P.D. designed the project, I.D., C.M. and P.D. supervised it, and C.N.M. performed the experiments and analysed the data which was interpreted by all the authors. C.N.M. prepared the figures and wrote the initial draft of the manuscript which was edited and reviewed by all the authors.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/02678292.2024.2374952

Additional information

Funding

The work was supported by the Association Nationale Recherche Technologie (ANRT), Saint-Gobain Research Paris and the Agence Nationale de la Recherche (ANR, grand number: ANR-23-CE24-0006-03, project DISPLAY).