Photoinduced phase transitions

Abstract

Employing actinic light to alter/stabilise a particular thermodynamic phase via the photo-isomerisation of the constituent molecules is an interesting tool to investigate soft matter from a new dimension. This article focuses on our recent results on several aspects of these non-equilibrium phase transitions, which are isothermal in nature. We specifically discuss (i) the influence of different parameters, such as confinement, applied electric field, pressure etc., on the dynamics associated with both the photochemical transition driving the equilibrium nematic to the non-equilibrium isotropic phase and the thermal back relaxation recovering the nematic phase, (ii) unique light-driven disorder–order transition in a reentrant system, (iii) dynamic self-assembly of the smectic A phase, which is stabilised only in the presence of actinic light, (iv) novel temperature-intensity phase diagrams and an example of primary and secondary photo-ferroelectric effects in an antiferroelectric smectic C system. These results highlight the fact that the actinic light can be used as a new tool to study phase transitions and the associated critical phenomena that could also bring about effects that are not seen in equilibrium situations.

Keywords:

• photoisomerisation
• photoinduced transition
• dynamic self-assembly
• high pressure

Acknowledgements

We sincerely appreciate the participation of the students of our Centre Dr. Gurumurthy Hegde, Ms. V. Jayalakshmi, Drs. Chethan Vishal Lobo, K.L. Sandhya and Dr. Vivek Kumar Gupta, P.G. Department of Physics, University of Jammu, Jammu in this programme. Thanks are also due to our colleagues Dr. C.V. Yelamaggad and Dr. Uma S. Hiremath and Dr. Negi (then at Centre for Materials for Electronics Technology, Panchwati, Pune) for providing some of the samples used in these studies. Partial financial support by SERC, DST, New Delhi under a project is gratefully acknowledged.