Rheology of thermoreversible gels

This chapter is devoted to the molecular rheology of transient networks made up of associating polymers in which the network junctions break and recombine. After an introduction to theoretical description of the model networks, the linear response of the network to oscillatory deformations is studied in detail. The analysis is then developed to the nonlinear regime. Stationary nonhnear viscosity, and first and second normal stresses, are calculated and compared with the experiments. The criterion for thickening and thinning of the flows is presented in terms of the molecular parameters. Transient flows such as nonhnear relaxation, start-up flow, etc., are studied within the same theoretical framework. Macroscopic properties such as strain hardening and stress overshoot are related to the tension-elongation curve of the constituent network polymers. 

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In general, the small-ampUtude oscillatory shear experiment seems to be the more sensitive method for a safe detection of the gel point, formed by the incipient infinite percolated cluster for thermoreversible systems. Sometimes it is difficult to decide which of the TCFs during a temperature scan has the most linear behaviour in the observed delay time window. As it was shown in (Richter et al. 2004b Richter et al. 2005), the effect in rheology is more pronounced, such that 1-2 K... 

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