Flow behaviour and implications of dissipation energy during the thermomechanical process
The BSA solution was subjected to linear shear ramp flow from 1-1000 s-1 to determine the flow curves at 55°C, 60°C and 65°C. The flow curves for thermomechanical treatments at three different temperatures (55, 60 and 65 °C) are shown in Figure 6 (a). The obtained shear stress (\(\tau,\ \ Pa\)) and shear rate (\(\gamma,\ \text{\ s}^{-1}\)) were fitted to the model power law as\(\tau=K\gamma^{n}\) (Manoi and Rizvi 2008). Here K is the consistency coefficient, which describes the texture or flow behaviour of a fluid, and “n” is the performance index, which describes Newtonian or non-Newtonian fluid. There was only one slope at 55 °C, while two different slopes were observed at higher temperatures. The value of “n ” at 55 °C was found to be 0.95, which indicated Newtonian behaviour of the solution and the absence of aggregates. This agreed with the Th-T fluorescence and CD data (Figures 3 and 4). However, the values of “n ” at 60 and 65 °C were greater than 1, which indicated the shear thickening behaviour of the solution due to the aggregation. The “n ” values were higher at 65 °C than 60 °C, which corresponded to the greater aggregation (enhanced rate and larger aggregate sizes) at 65 °C. The values of first slopes were higher than the second slopes. This indicated the formation of aggregated during the initial shearing and a shear thickening (“n ”=1.97 and 3.23) behaviour was observed. Further the exposure of greater magnitude of shear force broke the larger aggregates at higher shear rates (Hill et al. 2006), which resulted into lower values of “n ” (1.52 and 2.03).