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Photochemical-induced phase transitions in photoactive semicrystalline polymers

Bai, Ruobing and Ocegueda, Eric and Bhattacharya, Kaushik (2021) Photochemical-induced phase transitions in photoactive semicrystalline polymers. Physical Review E, 103 (3). Art. No. 033003. ISSN 2470-0045. doi:10.1103/PhysRevE.103.033003.

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The emergent photoactive materials obtained through photochemistry make it possible to directly convert photon energy to mechanical work. There has been much recent work in developing appropriate materials, and a promising system is semicrystalline polymers of the photoactive molecule azobenzene. We develop a phase field model with two order parameters for the crystal-melt transition and the trans-cis photoisomerization to understand such materials, and the model describes the rich phenomenology. We find that the photoreaction rate depends sensitively on temperature: At temperatures below the crystal-melt transition temperature, photoreaction is collective, requires a critical light intensity, and shows an abrupt first-order phase transition manifesting nucleation and growth; at temperatures above the transition temperature, photoreaction is independent and follows first-order kinetics. Further, the phase transition depends significantly on the exact forms of spontaneous strain during the crystal-melt and trans-cis transitions. A nonmonotonic change of photopersistent cis ratio with increasing temperature is observed accompanied by a reentrant crystallization of trans below the melting temperature. A pseudo phase diagram is subsequently presented with varying temperature and light intensity along with the resulting actuation strain. These insights can assist the further development of these materials.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bai, Ruobing0000-0002-5847-0502
Ocegueda, Eric0000-0001-7845-6890
Bhattacharya, Kaushik0000-0003-2908-5469
Additional Information:© 2021 American Physical Society. Received 1 December 2020; accepted 26 February 2021; published 16 March 2021. This work was motivated by the experimental work of Alexa S. Kuenstler, Hantao Zhou, and Ryan Hayward, and we are grateful to them for numerous interesting discussions. We are also grateful for the support of the Office of Naval Research through the MURI on Photomechanical Material Systems (Grant No. ONR N00014-18-1-2624).
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-18-1-2624
Subject Keywords:Photochemistry; Photomechanical; Phase transition; Phase field model; Semi-crystalline polymers
Issue or Number:3
Record Number:CaltechAUTHORS:20210106-131335150
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107352
Deposited By: George Porter
Deposited On:12 Jan 2021 15:16
Last Modified:06 Apr 2021 20:18

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