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Research Article

Light-triggered thermal conductivity switching in azobenzene polymers

View ORCID ProfileJungwoo Shin, Jaeuk Sung, Minjee Kang, Xu Xie, Byeongdu Lee, Kyung Min Lee, Timothy J. White, Cecilia Leal, Nancy R. Sottos, Paul V. Braun, and David G. Cahill
  1. aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
  2. bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
  3. cBeckman Institute for Advanced Science and Technology, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
  4. dX-ray Science Division, Argonne National Laboratory, Argonne, IL 60439;
  5. eMaterials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, OH 45433

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PNAS March 26, 2019 116 (13) 5973-5978; first published March 8, 2019; https://doi.org/10.1073/pnas.1817082116
Jungwoo Shin
aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
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  • ORCID record for Jungwoo Shin
Jaeuk Sung
aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
cBeckman Institute for Advanced Science and Technology, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
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Minjee Kang
aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
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Xu Xie
aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
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Byeongdu Lee
dX-ray Science Division, Argonne National Laboratory, Argonne, IL 60439;
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Kyung Min Lee
eMaterials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, OH 45433
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Timothy J. White
eMaterials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson Air Force Base, OH 45433
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Cecilia Leal
aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
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Nancy R. Sottos
aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
cBeckman Institute for Advanced Science and Technology, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
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Paul V. Braun
aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
cBeckman Institute for Advanced Science and Technology, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
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  • For correspondence: pbraun@illinois.edu d-cahill@illinois.edu
David G. Cahill
aDepartment of Materials Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
bMaterials Research Laboratory, University of Illinois at Urbana–Champaign, Urbana, IL 61801;
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  • For correspondence: pbraun@illinois.edu d-cahill@illinois.edu
  1. Edited by Timothy M. Swager, Massachusetts Institute of Technology, Cambridge, MA, and approved February 12, 2019 (received for review October 19, 2018)

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Significance

Heat is carried as diffusion of vibrational modes in insulating polymers, a process that is highly dependent on the macromolecular ordering of a polymer. As a result, changes in macromolecular ordering have potential to significantly change the thermal transport property of a polymer. Here, we design and synthesize a thermally switchable azobenzene polymer that exhibits a reversible crystal-to-liquid transition in response to UV and visible light. By driving a transition between the planar (trans) and nonplanar (cis) conformational states of azobenzene moieties attached to the polymer, we modulate interchain π-π bonding, resulting in fast and reversible thermal and structural transitions. This work unravels the pathway of crystal-to-liquid transitions of the azobenzene polymer and the resulting thermal and physical property changes.

Abstract

Materials that can be switched between low and high thermal conductivity states would advance the control and conversion of thermal energy. Employing in situ time-domain thermoreflectance (TDTR) and in situ synchrotron X-ray scattering, we report a reversible, light-responsive azobenzene polymer that switches between high (0.35 W m−1 K−1) and low thermal conductivity (0.10 W m−1 K−1) states. This threefold change in the thermal conductivity is achieved by modulation of chain alignment resulted from the conformational transition between planar (trans) and nonplanar (cis) azobenzene groups under UV and green light illumination. This conformational transition leads to changes in the π-π stacking geometry and drives the crystal-to-liquid transition, which is fully reversible and occurs on a time scale of tens of seconds at room temperature. This result demonstrates an effective control of the thermophysical properties of polymers by modulating interchain π-π networks by light.

  • polymer
  • thermal conductivity
  • phase transition
  • thermal switch
  • azobenzene

Footnotes

  • ↵1J. Shin and J. Sung contributed equally to this work.

  • ↵2To whom correspondence may be addressed. Email: pbraun{at}illinois.edu or d-cahill{at}illinois.edu.
  • Author contributions: J. Shin, J. Sung, K.M.L., and T.J.W. designed research; J. Shin, J. Sung, M.K., and B.L. performed research; J. Shin, X.X., and D.G.C. contributed new reagents/analytic tools; J. Shin, J. Sung, M.K., B.L., C.L., N.R.S., P.V.B., and D.G.C. analyzed data; and J. Shin, J. Sung, P.V.B., and D.G.C. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • Data deposition: The raw synchrotron X-ray scattering datasets of the 2D diffraction images reported in this paper have been deposited in Globus MDF Open, dx.doi.org/doi:10.18126/M2VH2X.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1817082116/-/DCSupplemental.

Published under the PNAS license.

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Light-triggered thermal conductivity switching in azobenzene polymers
Jungwoo Shin, Jaeuk Sung, Minjee Kang, Xu Xie, Byeongdu Lee, Kyung Min Lee, Timothy J. White, Cecilia Leal, Nancy R. Sottos, Paul V. Braun, David G. Cahill
Proceedings of the National Academy of Sciences Mar 2019, 116 (13) 5973-5978; DOI: 10.1073/pnas.1817082116

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Light-triggered thermal conductivity switching in azobenzene polymers
Jungwoo Shin, Jaeuk Sung, Minjee Kang, Xu Xie, Byeongdu Lee, Kyung Min Lee, Timothy J. White, Cecilia Leal, Nancy R. Sottos, Paul V. Braun, David G. Cahill
Proceedings of the National Academy of Sciences Mar 2019, 116 (13) 5973-5978; DOI: 10.1073/pnas.1817082116
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