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Power law gels at finite strains: The nonlinear rheology of gluten gels
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View: Figures


Image of FIG. 1.
FIG. 1.

Mixograph output for of gluten dough at 63% moisture content by weight. After the gluten dough has been fully developed, it is removed from the mixograph at .

Image of FIG. 2.
FIG. 2.

Stress relaxation behavior of a gluten gel. The relaxation modulus approaches a power-law as expected for a critical gel with , over a wide range of time . At short times, an additional Rouse relaxation regime can be observed, with and .

Image of FIG. 3.
FIG. 3.

Deviations from power-law relaxation due to the effects of loading history for various values of sample rest time. Dashed lines represent predictions from the critical gel equation for the apparent modulus [Eq. (5)] with , 1, 10, 100, 1000, and and (dotted line). Open symbols are measured data for gluten gels with , 100, and . The inset illustrates the strain protocol imposed on the sample during the experiment. Note that the rheometer resets or “zeroes” the stress at .

Image of FIG. 4.
FIG. 4.

Expressing the power-law relaxation of a critical gel as a series of Maxwell modes. Deviations can be seen at either end of the spectrum corresponding to the longest and shortest time scales of the summation.

Image of FIG. 5.
FIG. 5.

(a) Storage and loss moduli measured in small amplitude oscillation. Solid lines represent predictions from Eq. (12) and incorporating Rouse modes: , , , and . These parameters were obtained from independent measurements of the relaxation modulus . (b) Comparison between dynamic moduli of vital gluten and native (i.e., “washed”) gluten doughs, showing strong qualitative similarities in the frequency response.

Image of FIG. 6.
FIG. 6.

Creep compliance of a gluten gel. The dashed line represents predictions of the critical gel model from Eq. (17) with gel strength and gel exponent . These parameters are obtained independently from step strain-relaxation experiments. Data at for are included to illustrate the observed “creep ringing.”

Image of FIG. 7.
FIG. 7.

(a) Stress-relaxation function of gluten dough for a range of finite step shear strains with magnitude . (b) Damping function for finite strain amplitude stress relaxation experiments. Lines correspond to algebraic fit to the data set, . Unfilled gluten dough (, ) shows substantially reduced damping compared to highly filled wheat-flour-water dough systems (, ).

Image of FIG. 8.
FIG. 8.

(a) Transient shear stress during start-up of shear flow as a function of time measured for shear rates . The calculated responses from the critical gel component and Rouse modes for are plotted as dashed and dotted lines, respectively. Deviation from Eq. (28) at is a result of the finite rise time of the motor. (b) All curves can be collapsed onto a master strain function (solid line) by factoring out the rate dependence .

Image of FIG. 9.
FIG. 9.

Torsional elastic instability at . (a) Initial conditions. (b) Onset of instability; initially vertical lines drawn on the sample with ink indicate uniform deformation up to this point. (c) The sample becomes asymmetric and is retracted away from point of view while being ejected from the other side of the geometry. (d) The sample rolls up and is ejected from the rheometer.

Image of FIG. 10.
FIG. 10.

(a) Power-law growth in the first normal stress difference as a function of time measured for shear rates . (b) All curves can be collapsed onto a master strain function by factoring out the rate dependence . The solid line is the strain function given in Eq. (33) with determined from linear viscoelastic measurements.

Image of FIG. 11.
FIG. 11.

Schematic of the Sentmanat Extensional Rheometer (SER). The sample of initial cross-section area and gage length is stretched between two counterrotating cylindrical drums.

Image of FIG. 12.
FIG. 12.

Wind-up drum rheometry of a gluten gel using the SER fixture. Deformation and torque measurements were provided by the host ARES rheometer while true strain measurements were made by studying images collected with high-speed digital videography (at ). Initial width of sample is . The solid line is the calculated variation in width under ideal uniaxial elongation given by Eq. (44).

Image of FIG. 13.
FIG. 13.

(a) Tensile stress difference in gluten gels during transient uniaxial elongation at rates of , 0.3, and . At least two runs were performed at each strain rate to ensure reproducibility. (b) Scaled stress function plotted against Hencky strain showing power-law growth at small strains and exponential growth at large strains.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Power law gels at finite strains: The nonlinear rheology of gluten gels