Large amplitude oscillatory shear flow of gluten dough: A model power-law gel

Abstract

SYNOPSISIn a previous paper [Ng and McKinley (2008)], we demonstrated that gluten gels can best be understood as a polymeric network with a power-law frequency response that reflects the fractal structure of the gluten network. Large deformation tests in both transient shear and extension show that in the absence of rigid starch fillers these networks are also time-strain factorizable up to very large strain amplitudes ( ). In the present work, we further explore the non-linear rheological behavior of these critical gels by considering the material response obtained in large amplitude oscillatory shear (LAOS) over a wide range of strains and frequencies. We use a Lissajous representation to compare the measured material response with the predictions of a network theory that is consistent with the proposed molecular structure of gluten gels. In the linear viscoelastic regime, the Lissajous figures are elliptical as expected and can be quantitatively described by the same power-law relaxation parameters determined independently 2 from earlier experiments. In the non-linear regime, the Lissajous curves show two prominent additional features. Firstly a gradual softening of the network indicated by the rotation of the major axis. This feature is accounted for in the model by the inclusion of a simple non-linear network destruction term that reflects the reduction in network connectivity as the polymer chains are increasingly stretched. Secondly, a distinct upturn in the viscoelastic stress is discernable at large strains. We show that this phenomenon can be modeled by considering the effects of finitely extensible segments in the elastic network. We apply this model to other large amplitude transient flows such as the start-up of steady shear and extension. In addition to quantitative prediction of the evolution of stress in the gluten gel, we find that the onset of strongly non-linear unsteady phenomena such as edge instability in shear and sample rupture during extension can be understood as consequences of the finite extensibility and increased dissociation of the network filaments. (2008)] have shown that under small amplitude oscillatory conditions, as well as in large deformations in either shear or extension, the gluten gel can best be understood as consisting of flexible/semi-flexible segments that are interconnected to form a gel network. The interstitial spaces are filled with water but have minimal direct effect on the rheology as little or no solvent contribution to the total stress can be detected. For time scales that are greater than the Rouse relaxation time of the polymeric network segments, we also demonstrated that the quasi-linear behavior in an unfilled gluten gel is time-strain separable up to large strains and can be welldescribed by the generalized gel equation: 3 I INTRODUCTIONwhere is the finger strain tensor. The expression can also be rewritten in terms of the finite strain rate tensor in the following way:( 2) where [Bird et al. (1987a)].Our previous studies also showed that in start-up ...

Effect of mixing on LAOS properties of hard wheat flour dough

“…LAOS parameters (e 3 /e 1 , v 3 /v 1 , G L , G M , h L , h M , S and T) showed that, the gluten network has time to stretch and reaches its limit in terms of its ability to elastically deform at the lower frequencies. These findings are consistent with Ng et al (2011) 0 s findings on gluten gels. We then studied Lissajous curves and we saw the previously observed intracycle strain thickening to occur with dough as well at all phases of Farinograph mixing.…”

“…Examples include gluten gels (Ng et al, 2011), polysaccharide dispersions i.e. carrageenan or starch (Klein et al, 2008), whey protein isolate and к-carrageenan gels (Melito et al, 2013a), tuna myofibrillar protein (Liu et al, 2014), commercial cheese (Melito et al, 2013b), and tomato paste (Duvarci et al, 2016).…”

A review of nonlinear oscillatory shear tests: Analysis and application of large amplitude oscillatory shear (LAOS)

“…The LAOS decoupling of simultaneous overall softening with local stiffening was also reported recently for a filled elastomer system [154]. Such physical insight may be able to inform constitutive models of this and other materials tested with LAOS, as recently demonstrated with nonlinear constitutive models to capture the biomechanics of hagfish gel [155] and gluten dough networks [156]. …”

Describing and prescribing the constitutive response of yield stress fluids using large amplitude oscillatory shear stress (LAOStress)

“…There have already been several examples in the rheology literature of studies focused on using LAOS to determine model parameters and test the predictive performance of constitutive models (Giacomin et al, 1993;Zhou et al, 2010;Calin et al, 2010;Ng et al, 2011;Giacomin et al, 2011;Gurnon and Wagner, 2012). Similarly, in the solid mechanics and plasticity community, experiments very similar to LAOS are frequently used to probe material behavior.…”