Small characteristic length at the glass transition cooperativity onset

  • Donth E
  • Kahle S
  • Korus J
 et al. 
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Abstract

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 (Delta epsilon, Delta C-p) and of square root of cooperativity (N-alpha(1/2)) as function of temperature below the onset. A quasi continuous description is derived from kinetic molecular 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 N-alpha(min) approximate to 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 N-alpha(T-g) approximate to 100 molecules. A new interpretation of the WLF asymptote Ig Omega is suggested.

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Authors

  • E Donth

  • S Kahle

  • J Korus

  • M Beiner

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