Large amplitude oscillatory shear (LAOS) behavior of chocolates of different compositions

Abstract

The complex rheological response of chocolates of different compositions was analyzed in depth from stationary shear flow curves and large amplitude oscillatory shear tests. The samples have a wide range of cocoa content that controls the rheological behavior characterized by a yielding response. The strain amplitude at which the chocolates changed from elastic-dominated to viscous-dominated behavior ranged from 0.2 to 0.4%. In this region, the stress response to the applied sinusoidally oscillating shear strain showed transient overshoots whose values were similar to yield stress calculated using the Casson equation in continuous flow. The nonlinear response at the steady-state was analyzed. The Q0nonlinearity parameter, obtained from Fourier Transform analysis, increases as the concentration of the solids conferring bimodality to the particle size distribution increases. In the study of intracycle nonlinearities, the analysis of the third-order Chebyshev elastic and viscous coefficients showed that the sample which contains the highest amount of solids different from cocoa exhibited the lowest strain-stiffening and the highest shear-thinning behaviors. Stress bifurcation analysis identified the beginning of the yielding transition and evidenced a nonlinear solid-like behavior before the solid-liquid transition. Analysis of Lissajous–Bowditch curves allowed the static and dynamic contributions of the yielding transition to be identified, and the full Sequence of Physical Process quantitative analysis captures the time-dependent nonlinear response of chocolates over the history of applied deformations.