Local movements in amorphous polymers around the glass transition temperature studied by steady state anisotropy

BEATRIZ ARAOZ; PEDRO F. ARAMENDIA

Bariloche

Workshop; US. Argentina Workshop on Nanomaterials; 2009

CONICET

The glass transition temperature (Tg) is one of the fundamental properties of an amorphous polymeric matrix. Around Tg a great increase of mobility at the atomic scale takes place and the correlation length of these movements rises quickly. Several studies were focused on the dynamics of glass transition but its nature has not been solved yet. When domain size becomes comparable to the characteristic distance of the fluctuations, the Tg is influenced by nanoconfinement effects; because of this, we propose to monitor the variation of Tg with polymer thickness by fluorescence anisotropy of embedded probes. Thickness control and preparation is easily performed by spin-coating. In this work, we study local movements in thin films of polyalkyl methacrylates (butyl, PBMA; ethyl, PEMA and propyl, PPMA) doped with Rhodamine 6G and with Nile Red, around Tg by steady state anisotropy. Our experiments show a temperature dependence of anisotropy in films of 200 nm, 100 nm and 50 nm thickness, the change in the anisotropy is remarkable well over the Tg measured by differential scanning calorimetry (DSC). These results could be explained in terms of the high frequency (~GHz) in which fluorescence measures the relaxation, which depends on the dye lifetime. This phenomenon is independent of the alkyl chain length. Referencias: 1 R. D. Priestley et al., Aust. J. Chem. 2007, 60, 765–771. 2 Mc Crum, Read and Williams. Dover publications, Inc, 1967.