text: One parameter characterizing this phenomenon is the fragility index, which is the slope of an Angell plot.
full_question: One parameter characterizing this phenomenon is the fragility index, which is the slope of an Angell plot. One theory describing this phenomenon states it takes place when the configurational entropy is zero, while another theory states it occurs at a precise value of the free volume. The Gibbs-DiMarzio theory describes this phenomenon. Extrapolating the entropy curve for this phenomenon paradoxically yields a zero change in entropy below a critical temperature, a result derived by Kauzmann. The temperature dependence of viscosity in this phenomenon can be measured by the Vogel-Fulcher-Tammann equation, the Doolittle equation, or the Williams-Landel-Ferry equation. In general, the temperature at which this process occurs tends to be low for an elastomer and high for a thermoplastic. It's not melting, but this process can be studied by performing either dilatometry or differential scanning calorimetry on a polymer. For 10 points, name this process in which an amorphous material reversibly transitions between a brittle and a rubbery state.
first_sentence: One parameter characterizing this phenomenon is the fragility index, which is the slope of an Angell plot.
raw_answer: glass transition