Local movements in amorphous polymers around the glass transition temperature studied by fluorescence correlation spectroscopy

BEATRIZ ARAOZ; PEDRO F. ARAMENDIA

Buenos Aires

Workshop; 1st Workshop on Advanced Fluorescence Microscopy; 2007

-Glass transition temperature (Tg) is one of the fundamental properties of the amorphous polymeric matrix. Around Tg a great increase of mobility in atomic scale takes place and the length correlation of these movements enhance quickly. Several studies are focused on the dynamics of glass transition but its nature has not been solved. The origin of glass transitions has been determined to be dynamical events rather than phase transitions. Below the Tg, the system fluctuate at a very low speed and the lapse in which the different surroundings/environments are equaled can be of several hundreds of seconds, consequently the system is heterogeneous at micro scale and is observed one speeds or frequencies distribution of the dynamic processes. Over Tg, the system fluctuate faster and the behavior of the environments are similar to the fluids. By this way, the dynamic behavior becomes homogeneous and tends to show a single characteristic time (monoexponential kinetic regimen). The interactions probe-environment allows studying the local movements and diffusion in heterogeneous systems and their local temporal evolution. We propose the study of local movements in polymeric matrix around Tg by the observing of polarized fluorescence intensity and lifetime of single molecules using polarized fluorescence correlation spectroscopy (FCS) applied to fluorescent probe-polymer systems. When domain size became comparable with the distance characteristics of the fluctuations, the Tg is influenced by nanoconfinement effects; because of this, we propose to measure the influence of the thickness of polymeric films on Tg, which is easily tuned by spin-coating. The FCS has great spatial resolution and very low detection limits at the time that allows to make measures in equilibrium conditions and to cover more than 5 orders of magnitude in the time scale with one single determination. From this point of view it is a very adequate technique to make measurements in systems that have a great spectrum of characteristics times, like the amorphous polymers.