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).