FINITE-SIZE EFFECTS ON THE GLASS-TRANSITION TEMPERATURE

An expression for the activation energy of the viscosity in the percolative transport regime demonstrates its proportionality to the peak in a distribution of barrier heights as well as to the width of the distribution. Such an expression implies that a ''blocking'' (slower than average) rate is responsible for the macroscopic relaxation time. This concept has recently been shown to account for a large number off phenomena related to the glass transition. Here it is shown that the average of a glass transition temperature over a large number of very small systems must correspond to an average barrier height; consequently the average glass temperature is reduced by confinement in pores because the average barrier height is smaller than the ''blocking'' barrier.