CONICET | Buscador de Institutos y Recursos Humanos

One of the most important properties of glassy polymers is the glass transition temperature , Tg. Several studies showed that Tg is influenced by confinement effect(1-2). Poly n-alkyl methacrylate films of thickness below 100 nm show changes in Tg up to 20 ºC compared to bulk films. This result might have an impact on systems like Oleds where thin films are employed. For these reasons, we are interested on monitoring local cage changes near a fluorescent probe (Nile Red, NR) in poly (n-alkyl) methacrylates (n-butyl, PBMA, n-propyl, PPMA, and methyl, PMMA) films of nanometer scale. Studies were performed by single molecule fluorescence spectroscopy as a function of temperature and film thickness Three types of NR emission spectra with different emission maximum were found in all the polymers (middle figure). Analysis of time traces of spectral fluctuations for every molecule was performed by using the energy difference between successive emission spectra (2E). We observe large jumps and small fluctuations of spectrum maximum position (upper and middle figures). Statistical analysis was performed using the complementary cumulative distribution function of the energy difference (Φc(2E)), which gives the probability of observing a spectral change with absolute energy greater than a given value (lower figure). The analysis allows the estimation of transition probability and amplitude of the spectral changes. In PBMA films, both of them increase with temperature and are always greater in 200 nm films than in 25 nm ones. This can be related to a decrease of NR local environments dynamics with film thickness (higher rigidity of 25 nm films). (1) Priestley, R. D.; Mundra, M. K.; Barnett, N. J.; Broadbelt, L. J.; Torkelson, J. M. Australian Journal of Chemistry 2007, 60, 765. (2) Ellison, C. J.; Torkelson, J. M. Nat Mater 2003, 2, 695.