Journal of Rheology, Vol.60, No.3, 367-378, 2016
Rheological diagnostic tools for state transitions
Thermodynamic or kinetic state transitions of six polymeric systems were probed using rheology in isothermal and nonisothermal isochronal experiments. The polymeric systems were representative of three different types of transitions: Gelation, macrophase separation, and order-disorder transitions. A phenomenological dimensionless parameter termed the relative elasticity, R, was found to be particularly sensitive to these transitions and was finitely bound by the viscous limit and the elastic limit with values of zero and one, respectively. In addition, the (time or temperature) derivative of R and tan delta (with delta being the phase angle) proved to be more sensitive to transitions as compared to the respective pure values. When compared to other methods found in literature, these new phenomenological protocols are found to be robust while providing a convenient and precise means of detecting transitions. Hence, they may complement existing methods, whereas they are beneficial to industrial or other systems exhibiting multiple transitions due to their high sensitivity. (C) 2016 The Society of Rheology.