Using flash DSC for determining the liquid state heat capacity of silk fibroin

• We studied 19 silk protein samples by fast scanning calorimetry using a Flash DSC1.
• Samples were non-crystalline as-cast, or made non-crystalline after first melting.
• Mass was evaluated one way, by using the known glassy state heat capacity.
• Mass was evaluated another way, by using the known heat capacity increment at Tg.
• We find (for T in K): Cpliquid(T) = (1.98 ± 0.06) J/g K + T·(6.82 ± 1.4) × 10−4 J/g K2.

In this technical note, we report a study of the heat capacity of amorphous silk fibroin protein evaluated using the Flash DSC1 for fast scanning calorimetry. Nineteen amorphous thin films were obtained either after casting directly from water solutions, or after melting of previously crystalline films. Fibroin films were mounted onto Flash DSC1 sensors, dried free of bound water, relaxed just above the glass transition, Tg, then scanned in heating and cooling at ±2000 K/s. The heat flow rate data were analyzed by finding the symmetry line between the heating and cooling scans, and by subtraction of the empty sensor heat flow rate, similarly corrected for its symmetry line. To evaluate the sample mass, two approaches were compared. First, the mass was obtained from known solid state heat capacity, Cpsolid(T), at a temperature below Tg. Second, the mass was obtained from the known heat capacity increment at the glass transition, ΔCp(Tg). The Cpsolid(T) and ΔCp(Tg) had been obtained previously from slow scanning differential scanning calorimetry. The use of either method for mass determination necessitated additional corrections to the heat capacity data to bring them into agreement with the literature values. After these corrections, the heat capacity of silk fibroin in the liquid state was evaluated over a wide temperature range above Tg. We find Cpliquid(T) = (1.98 ± 0.06) J/g K + T·(6.82 ± 1.4) × 10−4 J/g K2 in the temperature interval from 510 to 570 K with an uncertainty of about ±5%.

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