D1 Differential Scanning Calorimetry (DSC)

Topic

Differential scanning calorimetry (DSC)—the experimental method described by this model—records the heat flow exchanged between the polymer and its surroundings as its temperature rises in a controlled manner; the integral of this heat flow across the melting peak exhibited in the recording determines the polymer's enthalpy of fusion—the same type of transformation enthalpy quantified for a different material by another model in a separate set, using this same principle of integrating a calorimetric peak. If the polymer's melting peak is broader or more intense in the recording, the resulting integral—and thus the enthalpy of fusion it determines—is correspondingly higher.

Once determined, this enthalpy of fusion dictates the polymer's crystallinity—the volume fraction corresponding to ordered phases rather than amorphous phases, a concept detailed by another model in this set: the closer the measured enthalpy of fusion is to the reference value for a fully crystalline version of the same polymer, the higher the resulting crystallinity. Conversely, if the measured enthalpy of fusion is lower than the reference value, the crystallinity is proportionally lower. For this reason, this model—utilizing the differential scanning calorimetry and enthalpy of fusion with which it began—also determines the polymer's glass transition temperature from that same heat flow trace (a temperature described in greater detail by another model in this set). This value corresponds to the midpoint of the step-like change in heat capacity shown in the trace—a shift that is more gradual and less pronounced than the sharp melting peak, and distinct from the dilatometric determination used for the same purpose by a model from a different set. Consequently, if this heat capacity step appears at a higher or lower temperature within the heat flow trace, the glass transition temperature defined by its midpoint shifts in the same direction.

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