Free volume changes on optical switching in azobenzene-polymethylmethacrylate blends studied by a pulsed low-energy positron beam
✍ Scribed by Stephan Harms; Klaus Rätzke; Christina Pakula; Vladimir Zaporojtchenko; Thomas Strunskus; Werner Egger; Peter Sperr; Franz Faupel
- Book ID
- 105339530
- Publisher
- John Wiley and Sons
- Year
- 2011
- Tongue
- English
- Weight
- 228 KB
- Volume
- 49
- Category
- Article
- ISSN
- 0887-6266
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✦ Synopsis
Abstract
Polymers including chromophores, which can be switched by light, have been studied extensively during the last years due to a host of potential applications which arise from the marked changes in physical properties on switching. Even though there is clear evidence that the free volume has a significant influence on the isomerization kinetics, the question of free volume changes on switching was only addressed recently. Using a pulsed low‐energy positron beam the ortho‐positronium lifetime τ~3~ was taken as a very sensitive free volume probe, and no change in free volume was detected on isomerization in an azobenzene‐polymethylmethacrylate (PMMA) copolymer containing about 8 wt % of the azobenzene moiety. Here, we report for the first time on free volume changes in an azobenzene‐PMMA blend with an azobenzene moiety concentration as high as 40 wt %. Using the same pulsed low‐energy positron beam, small but significant changes of τ~3~ were observed between the structurally relaxed dark and the UV‐illuminated states suggesting a decrease in free volume of the order of 10%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011