Characteristic length of glass transition from calorimetry in different confinements

Abstract
The characteristic length ξ_α from calorimetry describes the size of subsystems which are statistically independent from environment with respect to Fourier components of entropy fluctuation relevant for the α relaxation [l]. This paper is a review of our results in confined geometries. The lengths are determined for three different geometric situations. 1. Self-organized amorphous mobile layers between crystalline layers in semicrystalline polyethylene terephthalate PET. Parameter : layer thickness [2]. 2. Temperature modulated DSC (TMDSC) of the glass former benzoin isobutyl ether (BIBE) in coated pores of different glasses. Structural effects can be separated from the glass transition. Parameter : pore size from 2.0 to 7.5 nm [3]. The characteristic lengths in confined geometries are smaller than in bulk and decrease systematically for decreasing confinement sizes. 3. Determination of the thickness of immobilized layers on spherical fillers in SBR rubbers. This experiment is twofold complementary to the usual experiment in pores : particles instead of pores, and immobilization instead of active response. Parameters : filler size and content, related by a scaling method [4].