Electronic Resource
College Park, Md.
:
American Institute of Physics (AIP)
The Journal of Chemical Physics
92 (1990), S. 2603-2613
ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Laser induced holographic grating relaxation studies of thymoquinone dissolved in amorphous poly(α-methyl styrene) have been carried out. The Onsager theory of mutual diffusion for binary and tertiary systems are utilized to analyze the shape of the diffraction intensity curve. Different line shapes that are associated with the relaxation of the diffraction intensity are interpreted in terms of the diffusion processes. Diffusion coefficients are obtained as a function of thymoquinone concentration from 0.3 to 20 wt. % at various temperatures. It is shown that at very low concentrations (less than 0.5%), the self-diffusion coefficients of the dye molecule and its photoproduct are obtained. Above 0.5% concentrations the diffusion coefficient rapidly increases with increasing dye concentration. The temperature dependence of the self-diffusion coefficient follows the Williams–Landel–Ferry equation, whereas the mutual diffusion coefficient at higher dye concentrations follows the Arrhenius equation. The self-diffusion coefficient rapidly decreases as the sample temperature is traversed across the glass transition temperature (Tg). However at finite dye concentrations there is no detectable effect owing to the onset of Tg on the mutual diffusion coefficient. The difference is attributed to the plasticizing effect of the dye molecules.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.457954
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