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Query: UMLS:C0220723 (PCA)
 4,687 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rotational motions of probe molecules in poly(cyclohexyl acrylate) (PCA) were investigated by both ensemble fluorescence recovery after photobleaching (FRAP) and single-molecule spectroscopy at temperatures near the glass transition temperature (Tg) of the polymer host. FRAP measurements of the ensemble anisotropy decay show a nonexponential decay with beta values of 0.5-0.6 when fit by a stretched exponential function. The relationship between the average relaxation time and temperature follows the Williams-Landel-Ferry equation, whereas beta shows no temperature dependence over this range. The same system was also studied by single-molecule spectroscopy at 2 degrees C above the Tg of PCA. The rotational dynamics of the probe molecule can be measured by the autocorrelation function of the linear dichroism signals. Each single-molecule correlation function was fit to the stretched exponential function. The results from all single-molecule data yield broad distributions of both the correlation times (tau) and beta values. The average of the single-molecule correlation times agrees with the ensemble relaxation time, and the sum of all single correlation functions has a nonexponential decay that is almost identical to the ensemble anisotropy decay. The ensemble beta values are smaller than the average beta values in the single-molecule experiments, demonstrating that the system exhibits heterogeneous dynamics. However, the dynamics are not described by an ensemble of molecules that all have single-exponential correlation functions with different time constants.
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PMID:Nonexponential relaxation of poly(cyclohexyl acrylate): comparison of single-molecule and ensemble fluorescence studies. 1919 99