Strain-Dependent Kinetics in the Cis-to-Trans Isomerization of Azobenzene in Bulk Elastomers

• Published in: The journal of physical chemistry. B Vol. 123; no. 40; pp. 8492 - 8498
• Main Authors: Lin, Yangju, Hansen, Heather R, Brittain, William J, Craig, Stephen L
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 10.10.2019
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/acs.jpcb.9b07088

The cis-to-trans isomerization of azobenzene is accelerated in a bulk PDMS elastomer under uniaxial tension. The kinetics are cleanly described by a single-exponential first-order process (k = 2.7 × 10–5 s–1) in the absence of tension but become multiexponential under constant strains of 40–90%. The complex kinetics can be reasonably modeled as a two-component process. The majority (∼92%) process is slower and occurs with a rate constant that is similar to that of the unstrained system (k = 2.3–2.7 × 10–5 s–1), whereas the rate constant of the minority (∼8%) process increases from k = 10.1 × 10–5 s–1 at 40% strain to k = 21.3 × 10–5 s–1 at 90% strain. Simple models of expected force–rate relationships suggest that the average force of tension per strand in the minority component ranges from 28 to 44 pN across strains of 40–90%.