Analysis of the molecular mobility of polymers in the bulk state by the fluorescence anisotropy decay technique

Abstract

The basic phenomena of fluorescence and fluorescence anisotropy decay (FAD) are briefly presented. The FAD technique is first applied to polybutadiene labelled with anthracene in the middle of the chain and embedded in a matrix of unlabelled polybutadiene; experiments are performed in the temperature range −50°C- +80°C. It is shown that the experimental data can be very well accounted for using the orientation autocorrelation function proposed by Hall and Helfand (6) for polymer chains. Studies performed on 9,10-dialkylanthracene probes (with various lengths of the alkyl substituents) molecularly dispersed in a polybutadiene matrix, have shown that the dynamic behavior of the 9,10-dihexadecylanthracene probe is very close to that of the labelled polybutadiene chain. This indicates that the 1-dimension diffusion of orientation correlation along the chain, observed by FAD on labelled polybutadiene in bulk, involve rather short chain portions (about 6 monomer units). Furthermore, the temperature dependence of the correlation times of both anthracene labelled chains and anthracene probes with long alkyl substituents, is in agreement with the WLF equation used to describe the glass-transition phenomena. Thus, these local reorientation processes observed in FAD correspond to segmental motions of polybutadiene chains which are involved in the macroscopic phenomenon of the glass transition.