Putative role of attractive and repulsive forces in the glass transition

Publication date: 17 January 2018
Source:Polymer, Volume 135
Author(s): Isaac C. Sanchez, Sean P. O'Keefe, Jeffrey P. Thompson
At a given temperature a balance between repulsive and attractive molecular forces determines liquid density. As temperature is lowered, attractive forces increase, but eventually saturate and asymptote to a near fixed value. At saturation, the attractive/repulsive force balance stabilizes the liquid density, which thereafter becomes effectively temperature independent. Configurational entropy also saturates, but at a much lower temperature. Once entropy begins to saturate, it converges to zero at absolute zero. There is no second order phase transition nor is there a divergent temperature above absolute zero predicted for glass relaxation phenomena. Using a phenomenological argument, it is shown that the relaxation time for volume relaxation varies inversely with configurational entropy. Stoichiometric electron density is proposed as a metric for repulsive force strength, which was determined at Tg and averaged 0.61±0.03 mol/cc for 15 polymers that contain oxygen and 0.53±0.02 mol/cc for 7 hydrocarbon polymers. Qualitatively, similar polymer liquids that pack to higher electron densities at a given temperature are expected to experience a glass transition earlier as temperature is lowered. For certain polymer types, the glass transition appears to be an isoelectronic state.

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