Glasses with strong calorimetric β-glass transitions and the relation to the protein glass transition problem

We describe the heat capacity manifestation of the glass transition in two salts of asymmetrical organic cations in which the glass transition on heating occurs in two distinct stages with roughly equal thermodynamic strengths, ΔC_p. The first of these appears to involve side chain motions since it freezes out at the temperature at which a plastic crystal phase of the same compound exhibits the plastic crystal glass transition. The latter is weaker than the liquid-to-glass transition because it involves the loss of fewer degrees of freedom. The behavior is unusual because secondary relaxation in glasses usually has only small excess heat capacity. The behavior is reminiscent of that in proteins in which the glass transition is smeared out over a very wide range of temperatures.