Oscillatory Deformation Research Articles

Effect of heat on rheology of gluten fractions from flours with different bread-making quality

Flours from wheat varieties of differing bread-making quality were fractionated using a sequential salt precipitation technique. The gluten fractions in the different varieties varied in the proportion of HMW, LMW glutenins and gliadins. Their rheological behaviour was examined using constant strain (2%) small deformation oscillation tests over frequencies ranging from 0.005 to 10 Hz, before and after heating at 90 °C. The fractions containing a higher proportion of HMW glutenins were associated with a predominantly elastic character, whereas fractions containing mostly gliadins exhibited a viscous-like behaviour. The frequency dependent rheological behaviour of fractions containing HMW proteins was less susceptible to heat, and their elastic character was maintained after heating, whereas the rheology of intermediate fractions and fractions containing mostly gliadins was more susceptible to heating, indicating a rapid change from viscous to elastic behaviour after heating.

Temperature dependence of shear wave attenuation in partially molten gabbronorite at seismic frequencies

Torsion oscillatory deformation experiments have been performed at high temperatures (600–170°C) and over a wide range of low frequencies (20–10−2 Hz) on fine-grained gabbronorite samples from the Oman ophiolite in order to determine the shear wave attenuation as a function of temperature and melt fraction. The specimens have a small and uniform grain size (0.25–0.3 mm) and do not contain secondary, hydrated minerals. Measurements of internal friction (Q−1) were performed using a forced oscillatory torsion apparatus at small strains (∽10−7), and with increasing small temperature steps to reduce thermal microcracking. The general dependence of Q−1 to frequency is Q−1∝ω−α, where ω is the angular velocity of forced oscillations and α is an empirical exponent. Below the melting temperature (∽1050°C), α has average values of ∽0.15 at low frequency (≤ 0.5 Hz) and 0.06 at higher frequency. Above the melting temperature, α has average values of ∽0.22 at low frequency and −0.02 at higher frequency. This frequency dependence of Q−1 is attributed to a viscoelastic behaviour due to the diffusion controlled grain boundary sliding, and partially to the squirt flow of the melt-phase wetting grain boundaries. The onset of melting is associated with a markedly higher Q−1 and a stronger dependence of Q−1 on temperature. The melt-related mechanical dissipation process could be a melt squirt flow. The characteristic frequency for the melt squirt flow is ωm ∽ 0.15–300 Hz when the melt pocket aspect ratio is ∽10‒3–10‒2. Around the melting temperature the internal friction can be approximated by an experimental power law Q−1 = A · [ω‒1 · d‒1 · exp(‒Ea/RT)]α with α ∽0.08, A = 34.72 sαμmα and Eα ∽ 873 kJ mol−1.

Maturation of guinea pig tracheal strip stiffness

Previously, we showed the shortening velocity of guinea pig tracheal strips was the greatest in juvenile (3-wk-old) compared with infant (1-wk-old) and adult animals (3-mo-old). The greatest shortening velocity was associated with the least resistance to shortening calculated from force-velocity curves among the three age groups. It remained to be verified if the stiffness of tracheal tissue, a measure of tissue response to geometrical deformations, is different among the three age groups. We hypothesized that stiffness of intact tracheal strips is lowest in the juvenile group and that this can explain the ontogeny of airway smooth muscle resistance to shortening and shortening velocity. Static stiffness measured through stepwise deformations showed no age-related differences. Evaluation of tissue response to oscillatory deformations showed that the dynamic stiffness of unstimulated tracheal strips was 8.35 +/- 0.88, 4.15 +/- 1.09, and 8.21 +/- 1.57 kPa, and the phase angle was 10.3 +/- 2.93, 2.46 +/- 0.67, and 7.87 +/- 1.77 degrees in infant, juvenile, and adult, respectively. Unstimulated juvenile strips were significantly lower in dynamic stiffness and phase angle compared with unstimulated infant or adult strips. This maturational profile was independent of muscle strip preset length or oscillation mode/amplitude but was abolished at peak of contraction to either carbachol or electric field stimulation. These results suggest that the noncontractile components of tracheal strips are less stiff and contain fewer viscous/frictional elements in juvenile than in other age groups. This may provide a functional basis for reduced resistance to length changes in juvenile airway smooth muscle.

SU-FF-J-58: DMLC Leaf-Pair Optimal Control for Mobile, Deforming Target

Purpose: Tumors in the lung and abdomen tend to move and deform during the course of respiratory cycle. To deliver the intensity modulated therapy, in which intensity map dynamically shifts and deforms in conjunction with the target motion, algorithms have to be developed that control appropriately leaf progression in DMLC IMRT. Description of such algorithms is the purpose of this presentation. Method and Materials: Target motions and deformations are simulated by analytic, periodic functions dependent on position and time. Derived infinitesimal relationships between leaf velocities at all leaf positions assure delivery of the predetermined intensity map. Derived formulas lead to a system of interdependent ordinary, differential equations. When minimization of time of DMLC IMRT delivery is required equations are uniquely defined by scalar fields that are determined by intensity function, target local velocities and target local parameters of deformation, together with constraints on maximum leaf speeds. Integration of differential equations provides trajectories for MLC leaves and thus determines the algorithm for relevant DMLC motion controls. Results: A representative example of DMLC IMRT delivery to deforming target is presented. The example shows the delivery of analytically defined double parabolic intensity function to target undergoing oscillatory type deformation. Target deformation is assumed to be spatially uniform. Deformation of the target, as well as trajectories of leading and following leaves, are calculated and graphically represented for this example. The snapshots of leaf positions at various stages of intensity delivery are also shown. Conclusion: Algorithms are developed for the control of MLC leaf motions that make possible delivery of DMLC IMRT to targets experiencing deforming motions. These realizations of IMRT therapies to deforming targets prevent any discrepancies, rooted in target's dynamic distortions during treatment, between intended and actual intensities delivered to the target.

Elastoplastic Deformation of a Compound Disk under Impulsive Loading

The small elastoplastic deformation theory and the finite-element method are used to analyze the behavior of a compound disk under axisymmetric impulsive loading. Numerical results are presented, which describe the development of plastic deformation, the effect of hardening and the duration of the loading impulse on the oscillatory elastoplastic deformation of the disk

Functional characterisation of potato starch modified by specific in planta alteration of the amylopectin branching and phosphate substitution

Potato starch was modified in planta by antisense of the starch branching enzyme I (SBE I), and the starch branching enzyme II (SBE II) both simultaneously and individually generating B group starches. Another group of starches, G group starches, was generated by over expression of the E. coli glycogen branching enzyme ( E. coli glgB). The content of covalently esterified phosphate increased in the B group starches and decreased in the G group starches. The content of phosphate correlated with length of debranched amylopectin chains measured by HPAEC-PAD, and with gelatinisation mid temperature ( T m) and change in enthalpy (Δ H) measured by differential scanning calorimetry (DSC). Freeze/thaw stability measured by 1H pulse-NMR and cohesiveness measured by texture profile analysis (TPA) was in the same range in all starch samples, whereas gel hardness was inversely correlated to phosphate content. No correlations between the pasting properties measured by rapid visco analysis (RVA), gel strength ( G′) measured by small deformation oscillation testing or any structural parameter could be revealed. The data set was mined using multivariate statistics. Based on this data starch samples could be separated into the two groups B and G, in accordance with their original transformation strategy.

Scaling Behavior of Delayed Demixing, Rheology, and Microstructure of Emulsions Flocculated by Depletion and Bridging

This paper describes an experimental comparison of microstructure, rheology, and demixing of bridging- and depletion-flocculated oil-in-water emulsions. Confocal scanning laser microscopy imaging showed that bridging-flocculated emulsions were heterogeneous over larger length scales than depletion-flocculated emulsions. As a consequence, G' as determined from diffusing wave spectroscopy (DWS) corresponded well with G' as measured macroscopically for the depletion-flocculated emulsions, but this correspondence was not found for the bridging-flocculated emulsions. The heterogeneity of bridging-flocculated emulsions was confirmed by DWS-echo measurements, indicating that their structure breaks up into large fragments upon oscillatory shear deformation larger than 1%. Depletion- and bridging-flocculated emulsions showed a different scaling of the storage modulus with the volume fraction of oil and a difference in percolation threshold volume fraction. These differences will be discussed on the basis of the two types of droplet-droplet interactions studied. Gravity-induced demixing occurred in both emulsions, but the demixing processes differed. After preparation of bridging-flocculated emulsions, serum immediately starts to separate, whereas depletion-flocculated systems at polysaccharide concentrations in the overlap regime usually showed a delay time before demixing. The delay time was found to scale with the network permeability, B; the viscosity, eta, of the aqueous phase; and the density difference between oil and water, Deltarho, as tdelay approximately B(-1)etaDeltarho(-1). The results are in line with the mechanism proposed by Starrs et al. (J. Phys.: Condens. Matter 2002, 14, 2485-2505), where erosion of the droplet network leads to widening of the channels within the droplet networks, facilitating drainage of liquid.

A mathematical model for the dynamics of large membrane deformations of isolated fibroblasts

In this paper we develop and extend a previous model of cell deformations, initially proposed to describe the dynamical behaviour of round-shaped cells such as keratinocytes or leukocytes, in order to take into account cell pseudopodial dynamics with large amplitude membrane deformations such as those observed in fibroblasts. Beyond the simulation (from a quantitative, parametrized model) of the experimentally observed oscillatory cell deformations, a final goal of this work is to underline that a set of common assumptions regarding intracellular actin dynamics and associated cell membrane local motion allows us to describe a wide variety of cell morphologies and protrusive activity. The model proposed describes cell membrane deformations as a consequence of the endogenous cortical actin dynamics where the driving force for large-amplitude cell protrusion is provided by the coupling between F-actin polymerization and contractility of the cortical actomyosin network. Cell membrane movements then result of two competing forces acting on the membrane, namely an intracellular hydrostatic protrusive force counterbalanced by a retraction force exerted by the actin filaments of the cell cortex. Protrusion and retraction forces are moreover modulated by an additional membrane curvature stress. As a first approximation, we start by considering a heterogeneous but stationary distribution of actin along the cell periphery in order to evaluate the possible morphologies that an individual cell might adopt. Then non-stationary actin distributions are considered. The simulated dynamic behaviour of this cytomechanical model not only reproduces the small amplitude rotating waves of deformations of round-shaped cells such as keratinocytes [as proposed in the original model of Alt and Tranquillo (1995, J. Biol. Syst. 3, 905–916)] but is furthermore in very good agreement with the protrusive activity of cells such as fibroblasts, where large amplitude contracting/retracting pseudopods are more or less periodically extended in opposite directions. In addition, the biophysical and biochemical processes taken into account by the cytomechanical model are characterized by well-defined parameters which (for the majority) can be discussed with regard to experimental data obtained in various experimental situations.

Sub‐daily sea ice motion and deformation from RADARSAT observations

We find a persistent level of oscillatory sea ice motion and deformation, superimposed on the large‐scale wind‐driven field, in May 2002 (spring) and February 2003 (mid‐winter), in the high Arctic over a region centered at ∼(85°N, 135°W). At this latitude, the RADARSAT wide‐swath SAR coverage provides 4–5 sequential observations every day, for ice motion retrieval, with a sampling interval at the orbital period of ∼101 minutes. Periodic correlations in ice motion and deformation can be seen in length scales from 10 km and above, and suggest a 12‐hr oscillation that is more likely associated with inertial rather than tidal frequencies. Divergence/convergence of ∼0.1–0.2% peak‐to‐peak or rates of ∼10−7/s is seen in both datasets, with the mid‐winter dataset having smaller values. These observations are remarkable in that short‐period ice motion is previously believed to be inhibited by the strength of the ice pack in the high Arctic during winter. New ice production due to the recurrent openings and closings at these temporal scales, if ubiquitous, could be significant within the winter pack.

Evaluation of the degree of cross‐linking of cellulose‐based superabsorbent hydrogels: a comparison between different techniques

AbstractThree different techniques have been applied to the evaluation of the degree of cross‐linking of superabsorbent cellulose‐based hydrogels obtained from water solutions of carboxymethylcellulose sodium salt (CMCNa) and hydroxyethylcellulose (HEC), chemically cross‐linked with divinyl sulfone. These polyelectrolyte hydrogels are biodegradable and have the same sorption capacity as acrylate‐based superabsorbents on the market. A 13C solid state NMR analysis was carried out on dry samples of hydrogel to obtain the degree of cross‐linking, an important parameter that affects the swelling and mechanical properties of a hydrogel. Dynamic mechanical analysis was performed during the hydrogel cross‐linking using a parallel plate rheometer under oscillatory deformations in order to monitor the evolution of the hydrogel viscoelastic properties during the synthesis. The value of |G*| and the slope of the stress‐deformation ratio plots from uniaxial compression tests were used to evaluate the elastically effective degree of cross‐linking according to classical rubber elasticity theory. Moreover, a dynamic mechanical analysis was carried out on cross‐linked hydrogels at different degrees of swelling in order to investigate the influence of the swelling on the mechanical properties and the application of rubber elasticity theory to swollen hydrogels.

Bubble detachment by diffusion-controlled surfactant adsorption

The effect of the diffusion-controlled adsorption of the surfactant Triton X-100 on detachment of gas bubbles adherent to the wall in pipe flow is studied. Air bubbles of known volume (scaled bubble dimension λ=0.8, 1.0, 1.5) are maintained in tubes inclined at 25°, 45°, 65°, or 90°. Triton X-100 is infused into the bulk flow to achieve a final mixed bulk concentration of either 10% or 100% of the critical micelle concentration. Pressure and flow waveforms are recorded, and video images of bubbles before and during exposure to the surfactant are captured. Surfactant-induced reductions of the surface tension and contact angle lead to distinct regimes of dynamic bubble behavior including static and oscillatory interfacial deformation, deformation with axial displacement, and complete bubble detachment from the wall. The surfactant-mediated responses depend on the interrelated effects of Triton X-100 concentration, bubble size, and tube angle. A high bulk concentration of Triton X-100 produces rapid changes in bubble shape and promotes wetting, increasing the potential for bubble detachment. Bubble detachment occurs more readily with larger bubble volume. For vertical tubes (i.e. no contact forces present) and non-vertical tubes (i.e. contact forces present), the bubble may be displaced axially in either the direction of or opposite to the bulk flow direction following introduction of Triton X-100. Bubble axial motion and detachment result from the surfactant effects on contact line mechanics. For moving contact lines, the contact line velocities corresponding to rates of shrinkage of de-wetted surface area (or, alternatively, rates of gas–liquid interfacial dilation) along with time-dependent contact front length are determined from the experimental data. Potential effects of Triton X-100 on interfacial remobilization are described. Soluble surfactants have the potential to be used for dislodging gas bubbles adherent to a pipe wall by intentional manipulation of interfacial shape and wetting properties.

Gelling property of soy protein–gum mixtures

Gelling properties of soy protein–gum mixtures were determined by small deformation oscillation measurement and the experimental data were analyzed with blending laws of polymers. Gel strength of soy protein–carrageenan mixture was found to follow either upper or lower bounds depending on the concentration of the constituents, suggesting the occurring of phase shift. G′ of soy protein–xanthan mixed gel always followed the upper bound, indicating that soy protein was the continuous phase regardless variations of the gum concentration. Combination of soy protein with propylene glycol alginate (PGA) produced a mixed gel with high gel strength and stayed above the upper bound at all gum concentrations examined. Covalent bonds between PGA and soy protein was suggested to contribute to the rigidity. Storage modulus of the mixture of soy protein–locust bean gum (LBG) was below the lower bound at low gum concentrations due to the limited demixing process of LBG. G′ values of the mixture of soy protein and LBG–xanthan followed the lower bound but approached upper bound on reducing protein concentration, suggesting that the presence of soy protein might inhibit LBG–xanthan mixture from forming continuous networks.

Validity of the Cox–Merz rule for concentrated suspensions

The flow behavior of glass bead, limestone, and powdered quartz suspensions was examined in steady and oscillatory shear tests. The solids content was varied up to a maximum of 25 vol % and the mean particle diameter ranged from 3 to 31 μm. The suspending liquid consisted of one of two silicone oils, which had limiting viscosities at zero shear rate slightly greater than 5×105 and 106 mPa s, respectively. The concept of shear stress equivalent inner shear rate, which describes the response of suspensions in steady shear experiments, was applied here to dynamic tests. Application of this concept yielded uniform descriptions of the flow curves that result from oscillatory deformations. In the region dominated by hydrodynamic forces, a modified Cox–Merz rule was derived. The shear stress function τ(γ) and complex modulus G*(ω) can be expressed as a function of the solid concentration using the parameters in this modified Cox–Merz relation.

Fatigue behaviour of multiblock thermoplastic elastomers. 1. Stepwise increasing load testing of poly(aliphatic/aromatic-ester) copolymers

Fatigue properties of poly(aliphatic/aromatic-ester) (PED) multiblock copolymers were evaluated based on the hysteresis measurement method. This method allows the digitalization of the hysteresis loop and beside the determination of stress and strain-related parameters, stored energy, lost energy, damping and dynamic creep behaviour can be determined. The correlation between hard/soft segment concentration of PED copolymers, and fundamental parameters, which derived during the cyclic loading (using stepwise increasing load testing, SILT), has indicated a good load-carrying performance of polymers containing a high amount of the hard phase. PED copolymers compare very well with commercially available poly(ester–ethers) and show a much better performance than poly(ester–urethanes) when samples are loaded at the same fatigue stress level relative to their ultimate tensile strength. Softer PEDs and poly(ether–urethane) copolymer show much higher values of dynamic modulus than chemically cross-linked silicone elastomer. Therefore, these multiblock copolymers can be considered as good candidates for applications where materials are subjected to oscillatory deformations (for example passive flexor tendon reconstruction).

Characterization of vocal fold scarring in a canine model.

The objective was to assess the histological and viscoelastic shear tissue properties of the scarred vocal fold lamina propria at 2 and 6 months postoperatively in a canine model. Experimental, nonrandomized prospective study. Six canine larynges were injured using a vocal fold stripping procedure. At 2 and 6 months postoperatively, histological analyses of the scarred and control lamina propria samples were completed for collagen, procollagen, elastin, and hyaluronic acid. In canines killed at 2 months, scarred tissue samples contained increased procollagen and decreased elastin. Elastin fibers in the scarred lamina propria were characteristically tangled and disorganized. In canines killed at 6 months, scarred tissue samples showed decreased elastin and increased collagen. Collagen fibers formed thick, disorganized bundles, and elastin fibers were disorganized throughout the entire scarred vocal fold lamina propria. Viscoelastic shear tissue measurements revealed increased stiffness and viscosity in one of three cases at 2 months and in all three cases at 6 months, indicating increased stiffness and resistance to shear flow during oscillatory shear deformation for scarred tissue samples. No differences were observed between the two postoperative times. Results indicated that viscoelastic tissue changes may take place before scar maturation in the scarred vocal fold lamina propria and that, although abundant collagen deposition may influence viscoelastic shear tissue properties, disorganization of collagen and elastin fibers, thick bundle collagen formation, or the interplay of several of these factors might also play a contributing role.

Combined rheometry and small-angle x-ray scattering

We have developed an apparatus to simultaneously monitor rheological parameters with high-resolution small-angle x-ray scattering (SAXS). The device is based on a commercial rheometer coupled to concentric cylindrical shear flow geometry. The shear cell can be operated from 20 °C–180 °C without significant evaporation loss of the sample. The apparatus has wide ranging applications in the field of complex fluids such as colloidal suspensions, surfactant phases, liquid crystals, and polymer solutions. In addition, it allows performing SAXS in combination with a wide variety of rheological tests including simple shear flows, creep, recovery, as well as oscillatory deformation. The performance of the equipment is demonstrated through experiments involving shear-induced ordering of complex fluids.

Internal friction spectroscopy in Li 2O–2SiO 2 partially crystallised glasses

Oscillatory torsion deformation experiments were performed on partially crystallised Li 2O–2SiO 2 glasses in the temperature range 350–480 °C and with frequencies between 20 and 0.002 Hz. The experiments were carried out in a torsion deformation apparatus exerting a small strain on cylindrical samples. Data obtained at varying temperatures and frequency were reduced to master plots using a normalised frequency. The frequency shift factor has been taken as a function of temperature in an Arrhenian form, yielding an activation energy of a background Q −1 close to the activation energy of oxygen defect diffusion (=120 kJ/mol). The master curves of real and imaginary components of shear modulus and internal friction indicate a stretched exponential shear stress relaxation with a an exponent of ≈0.45, characteristic of a broadened relaxation spectrum. The dynamic viscosity was estimated at temperatures of 470 and 480 °C. The extrapolation of dynamic viscosity to zero frequency allowed estimation of the relaxed shear viscosity. The presence of crystals increases the relaxed shear viscosity by ≈ 0.2 log( Pa s) /10 vol.% of crystallinity. Dependence of the relative shear viscosity of partially crystallised lithium disilicate melts on crystal content is discussed.

Effect of Oxidative Enzymes on Bulk Rheological Properties of Wheat Flour Doughs

The use of enzymes such as peroxidases or glucose oxidase instead of chemical oxidants is a very interesting option for improving breadmaking performance of doughs. In this study the effect of such enzymes on bulk rheological properties of dough was quantified and their influence on the polymer network in dough deduced. Small deformation oscillation and relaxation tests (strain 0·001) are not suitable for discriminating between doughs prepared in the presence of the different enzymes. Flow relaxation tests at high deformation and long relaxation times showed a clear distinction between the effect of peroxidase and glucose oxidase. Peroxidase increases only the number or lifetime of transient bonds, whereas glucose oxidase additionally produced cross-links that were permanent on time scales up to 3 h. Peroxidase probably introduced a second, more transient structure (arabinoxylan network) through the gluten network, whereas glucose oxidase may also have strengthened the gluten network. A higher water addition could not compensate for the effect of peroxidase; on longer time scales the stress remained at a higher level. Similar results were obtained in large deformation biaxial and uniaxial extension tests. Peroxidases only increased stress levels. The addition of glucose oxidase resulted in a higher stress and more intense strain hardening. Only in biaxial extension was an influence of pH observed. An increase in stress level was accompanied by a decrease in fracture strain, making predictions of the effects on bread structure complicated.

Rheology and Morphology of Reactively Compatibilized PP/PA6 Blends

This work aims to use the Palierne emulsion type model to describe the relationship between the rheological response to small amplitude oscillatory deformation and morphology of polypropylene/polyamide 6 (PP/PA6) blends compatibilized with maleic anhydride grafted polypropylene (PP-g-MAH). It was found that the Palierne emulsion type model could describe very well the linear viscoelastic responses of binary uncompatibilized PP/PA6 blends and failed to describe the ternary compatibilized PP/PP-g-MAH/PA6 blends. These features could be attributed to the fact that the morphology of the ternary blends was not of the emulsion type with the PA6 particles dispersed in the PP matrix but of an emulsion-in-emulsion type, i.e., PA6 particles dispersed in the PP matrix themselves contained PP or PP-g-MAH inclusions. By consideration of PP-in-PA6 particles as pure PA6 particles, where the volume fraction of the PA6 phase was increased accordingly, the Palierne emulsion type model could work very well for a ternary blending system. Preshear at low frequencies modified the morphology of both binary and ternary blends. The particles of the dispersed phase (PA6) became more uniform. These results suggested that the Palierne emulsion type model could be used to extract information on rheological properties and interfacial tension of polymer blends from known morphology and vice versa.

Experimental observation and matching numerical simulation for the deformation and breakup of immiscible drops in oscillatory shear

This paper describes experimental results on the way immiscible drops of a Newtonian fluid can deform and breakup when subject to oscillatory shear deformation. The paper also reports a matching three-dimensional numerical simulation of corresponding events. Using an optical shearing apparatus and a modified rheometer, experimental observations on the deformation of drops with a viscosity ratio of unity were carried out for a range of strain amplitudes and frequencies. For moderate strain deformations, it was discovered experimentally that the drop deformation oscillates between a maximum and a nonzero minimum deformation parameter and that the numerical simulation was able to capture both this and start up effects. For large strain deformations it was experimentally observed that breakup occurred only by one mechanism; namely, end pinching, and this was successfully matched by the numerical simulation. The results for oscillatory deformation and breakup are compared with those obtained in steady shear.