(318h) The Sequencing of Dynamic Rheological Measurements

A new quantitative analysis scheme is presented that is commensurate with recent studies [1, 2] suggesting that nonlinear rheological responses to large amplitude oscillatory shear (LAOS) are due to sequences of physical processes. In addition to two ‘regular’ viscoelastic material parameters (moduli, viscosities, compliances, or fluidities), the new scheme includes a third term that is an entirely new concept for viscoelastic analysis. The new term accounts for yield strains and stresses, shifting equilibria, and irreversibly-acquired strain.

The new technique is used to analyze the nonlinear rheological response to LAOS of a series of mixed cationic/anionic surfactant (CTAT/SDBS) WLMs in which the level of branching is controlled via the addition of the hydrotropic salt sodium tosylate [3]. By providing temporal resolution to the analysis of viscoelastic responses, this research provides a rational pathway toward a more complete understanding of results from all oscillatory rheological tests as well as hybrid flow-microstructure experiments.

[1] S. A. Rogers et al., J. Rheol. 55, 435 (2011).

[2] C. R. Lopez-Barron et al., Phys. Rev. Lett. 108 (2012).

[3] B. A. Schubert et al., Langmuir 19, 4079 (2003).