Aqueous pectin/calcium-ion systems are widely utilized in emulsifiers and food gels. The viscoelasticity and yielding response of these gels depend sensitively on the ratio R of the number of crosslinking ions to the number of binding sites on the pectin polysaccharide chains. Here, we describe a characterization approach using Optimally Windowed Chirps to probe how the linear viscoelastic response evolves during the gelation process. Beyond the gel point we then use Gaborheometry to measure the nonlinear viscoelastic response of mature gels with 0.35≤ R≤ 2.5 . By slowly increasing the oscillatory strain amplitude from γ _0=1% to 200% and computing strain/frequency Gabor spectrograms we monitor the evolution in the nonlinear viscoelastic properties at progressively larger strains. We observe strain stiffening up to the onset of gel failure, followed by yielding and network collapse. We quantitatively connect the measured nonlinear elastic response with the composition- and strain-dependent segmental rigidity through a semiflexible network model.
We consider a certain class of widespread tensorial constitutive equations with structural constraints and introduce two lemmata that reformulate them in terms of unconstrained variables. For trace constraints, the transformation recasts a class of nonlinear evolution equations in terms of an auxiliary linear dynamics, revealing that tube models can reproduce nonlinear rheological behavior using only linear parameters and operations. This yields analytical benchmark solutions for the orientation dynamics of differential reptation models under uniaxial elongation. A determinant-constrained analogue is developed for strain formulations, including the Leonov and Zürich Rheology models. In contrast, this transformation does not eliminate nonlinearities but provides an alternative representation. For the classes considered here, the auxiliary variables exhibit markedly different behavior: trace-based formulations admit analytically tractable auxiliary dynamics, whereas determinant-based formulations remain nonlinear and may exhibit singular behavior.
Rigorous rheological characterization of yield stress food materials is essential for understanding their complex flow behavior and guiding food industrial processing. While cone-plate (CP) and parallel-plate (PP) fixtures are widely used, their performance in long-time, large-deformation measurements can be compromised by solvent evaporation, wall slip, and edge fracture. The cone-partitioned plate (CPP) and plate-partitioned plate (PPP) geometries were developed to mitigate such artifacts by incorporating a non-measuring outer partition that delays fracture propagation into the measuring zone and can partially suppress solvent loss. Although CPP/PPP designs have proven effective for polymer melts, their applicability to yield stress materials remains largely unexplored. In this work, we systematically compare CPP, PPP and vane geometries for the nonlinear rheological characterization of mayonnaise, a representative food emulsion exhibiting yield stress. In addition to the geometry comparison, we applied an iso-deformation shear startup analysis by evaluating the fixed-strain startup stress, σ _10 , at a common accumulated strain of γ = 10 from each shear rate. This approach limits the influence of further structural evolution at larger accumulated strains; breakup-recovery measurements reveal persistent rheological changes after strong deformation, whereas droplet-size measurements after prolonged LAOS show a shift toward larger droplets. The combined results provide practical guidance for geometry selection and shear-history control in the rheological characterization of yield-stress food materials, with roughened PPP fixtures providing the most robust quantitative performance among the configurations examined.
Understanding the mechanical properties of aortic tissue is crucial for improving future medical interventions related to cardiovascular diseases. In this study, we seek to experimentally explore the stress relaxation response of the porcine aorta under constant combined torsional shearing and normal compressive load. Circular samples, measuring 0.5 inches in diameter, were extracted from the side wall of excised porcine thoracic aortas. Experiments were performed on a parallel plate rheometer applying a constant compressive strain ranging from 5 to 25
The morphology of immiscible polymer blends generated during twin-screw extrusion depends on the deformation history of the dispersed phase and on the matrix rheology. Here, this effect is investigated numerically in a two-dimensional, co-rotating, fully intermeshing batch twin-screw extruder. A Newtonian dispersed phase is considered, while the matrix is modeled as Newtonian, a Generalized Newtonian Fluid (GNF) accounting for shear thinning, and a Generalized Newtonian Fluid with Flow-Type dependence (GNFFTy), which combines shear thinning in shear-dominated regions and elongational thickening in extension-dominated regions. Velocity-gradient histories along tracer trajectories are used in a morphology model including droplet deformation, breakup, filament stretching, and coalescence. The three rheologies give similar gross flow structures but different local viscosity fields. The GNF model reduces viscosity in high shear regions, whereas GNFFTy predicts localized viscosity enhancement in extensional screw-screw gaps. These differences affect breakup, showing that shear-rate-based morphology predictions may miss topology-dependent viscosity effects.
