Temperature dependence of the activation volume in a nonlinear optical polymer: Evidence for chromophore reorientation induced by sub-Tg relaxations
✍ Scribed by Shane J. Strutz; Shane C. Brower; L. Michael Hayden
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 240 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0887-6266
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✦ Synopsis
Second harmonic generation (SHG) was used to measure the temperature dependence of the reorientation activation volume of 4-(diethylamino)-4-nitrotolane (DEANT) in poly(methyl methacrylate) (PMMA). The decay of the SHG signal from films of DEANT/PMMA was recorded at hydrostatic pressures up to 3060 atm and at different temperatures between 25ЊC below the glass transition temperature to 35ЊC above it. The activation volume, DV * ab associated with the long range a-type motion of the polymer remained constant at 213 { 10 A ˚3 between T g 0 25ЊC and T g / 10ЊC. At higher temperatures, DV * ab decreased linearly with increasing temperature. The activation volume, DV * b , associated with short range secondary relaxations was constant over the entire temperature range with a value of 77 { 10 A ˚3. The data suggest that above T g chromophore reorientation is coupled to both the long range and local motions of the polymer; whereas, well below T g chromophore reorientation is closely coupled to the local relaxations of the polymer.