3.2. Hydrogen bonding between KC and gelatin
For further understanding the interaction of KC and gelatin,
mixing isothermal calorimetry was performed at different temperatures.
Fig. 2a shows the heat flow as a function of time after mixing
of 0.75% KC/0.75% gelatin. The absolute enthalpy value of mixing at
each temperature determined from the area enclosed by the curve
and the baseline is shown in Fig. 2b. At temperatures higher than
40 ◦C, the mixing enthalpy is relatively low, which is contributed
mainly by electrostatic complex coacervation. The mixing enthalpy
becomes increasingly negative (exothermic) when the temperature
is below 40 ◦C. It suggests that a second mechanism comes into play
and reinforces the complexation between KC and gelatin. The transition
of the mixing enthalpy is in line with the turbidity increase
described above.