Small Characteristic Length at the Glass Transition Cooperativity Onset

E. Donth , S. Kahle , J. Korus , M. Beiner

A fluctuation theory approach to a cooperativity onset of the dynamic glass transition is described. Recent dielectric and heat capacity spectroscopy (HCS) experiments for several random copolymers of n-butyl methacrylate with styrene indicate a steep linear increase of relaxation intensities (Δε,ΔCp) and of square root of cooperativity (Nα1/2) as function of temperature below the onset. A quasi continuous description is derived from kinetic molelcular randomness. This description can be applied to small cooperativity near the onset. The experimental indications can analytically be reproduced by means of a Landau order parameter expansion adapted to dominance of fluctuation in a free volume approach to the dynamic glass transition. An important parameter of the approach is the minimal cooperativity of order Nαmin≈1. The sharp onset obtained in the extrapolation is associated with the construction of a large conditionality raster. Far below the onset, the size of cooperativity at the glass temperature is theoretically estimated to be of order Nα(Tg)≈100 molecules. A new interpretation of the WLF asymptote lg Ω is suggested.

Domaines: Articles anciens

E. Donth, S. Kahle, J. Korus, M. Beiner. Small Characteristic Length at the Glass Transition Cooperativity Onset. Journal de Physique I, 1997, 7 (4), pp.581-598. ⟨10.1051/jp1:1997177⟩. ⟨jpa-00247346⟩