Shear-thickening Behavior Research Articles

Effect of Dispersion Media Composition on the Structure and Rheology of the Short-Sidechain Perfluorosulfonic Acid Ionomer Dispersions

Perflourosulfonic acid (PFSA) ionomers are used in many applications including polymer-electrolyte membrane fuel cells and electrolysers owing to their many attractive properties such as excellent ion-conductivity, chemical resistance, mechanical properties, and thermal stability. In polymer-electrolyte membrane fuel cells and electrolysers, they are used as the membrane and as a component in the catalyst layers, to provide proton conductivity and serve as a binder for the catalyst particles, which are two key components of these devices. Understanding the structure and rheological properties of the ionomer dispersions is important for solution-processed fabrication of the membranes and the catalyst layers, and will enable better control their final structure/morphology, and improve the device performance. A water-alcohol solvent mixture is a common dispersion media for ionomer dispersions as well as the catalyst inks. While significant efforts exist on the structure of ionomer dispersions in water-alcohol solvent mixtures, their rheological properties, particularly the effect of solvent composition at non-dilute concentrations remain less explored. In this talk, the effect of water-alcohol (isopropanol) composition of the dispersion media on the rheological properties of ionomer dispersions will be presented. The results of small-angle x-ray scattering characterization of the ionomer dispersions will be also discussed. As a model ionomer, a short sidechain perfluorinated ionomer (PFSA), produced by 3M, was used. In dispersions with low ionomer concentrations, the zero-shear viscosity scaling with concentration was found to be similar for all alcohol fractions in the solvent mixture, following Fuoss’s law for polyelectrolytes. Whereas at higher concentrations, beyond the semi-dilute unentangled regime, their scaling was strongly dependent on alcohol fraction, where the scaling exponent increasing with increasing the alcohol fraction. Furthermore, the dispersions showed dramatic shear-thickening and strain-stiffening behaviors at higher alcohol fractions. The rheological observations suggest water-alcohol composition significantly alters the interactions between ionomer, and consequently their structure, and has strong implications in processing as well as on the morphology/structure of the membranes and the catalyst layers.

Rheological behavior and solution pH response properties of nanoparticle-regulated low surface tension systems.

Regarding the rheological properties of fluids, certain nanoparticles can markedly modify the rheological behavior of low surface tension solutions by interacting with surfactant molecules. In this work, a low surface tension fluid with cetyltrimethylammonium chloride was prepared, and the silica nanoparticles were uniformly dispersed into it by ultrasonic dispersion. By adjusting the size, shape, and concentration of nanoparticles, the fluid behavior can be changed from Newtonian to non-Newtonian with finely tuned viscosity and characterized by a shear-thinning rheological behavior. In addition, this work explored how variations in environmental temperature and solution pH affect the rheological responses of the low surface tension suspension system. The experimental findings revealed that increasing the temperature substantially decreases the system's viscosity and induces a shear-thickening behavior. It is particularly significant that, under extreme pH conditions (either strongly acidic or alkaline), the viscosity of the nanoparticle suspensions was markedly enhanced at a particle concentration of 10 000 ppm. This interesting result coincided with a notable reduction in the zeta potential and an increase in the average particle size, suggesting an intensified aggregation of particles within the suspension system. A mechanism detailing the interaction between silica nanoparticles and surfactant micelles was proposed. This work indicates that the incorporation of nanoparticles into surfactant solutions offers a powerful approach to modulating fluid rheology across various conditions.

Micro-encapsulated phase change material suspensions for heat and mass transfer: A thermo-physical characterization

Despite the growing popularity of phase change materials (PCM) and suspensions of micro-encapsulated phase change materials (mPCM) in both industrial and scientific applications, their properties characterization remains partial and mainly limited to thermal properties. The characterization of such suspension is a crucial aspect for comprehending their behavior and optimizing their performance. This paper is dedicated to a wide characterization of two suspensions containing micro-encapsulated phase change material. In pursuit of a thorough understanding, we also extend our characterization efforts to the bulk PCM encapsulated within the particles.Our primary focus is on determining the materials thermal properties such as latent heat and specific heat capacity using differential scanning calorimetry. Different cooling and heating rates have been employed in our measurements. Regarding our experiments, the bulk phase change material is predominantly identified as octadecane. Results obtained from calorimetry are then compared between the bulk PCM and the mPCM suspensions. By comparing the magnitudes of latent heat obtained for suspensions with the bulk material, we can accurately determine the mass fraction of PCM within each suspension. Noteworthy, during the solidification process an additional latent heat peak is observed only for the encapsulated PCM.The density of the materials is also measured. The phase change of PCM included in the capsules can be observed in densimetry: within the studied temperature range (283.15–306.15 K), the most significant density variations occur during intervals associated with phase change transitions. In ranges where the PCM, included in the capsules, is in a single-phase state (solid/liquid), we provide linear laws that account for density variations with temperature.Finally, our characterization work focuses on the rheological properties of the materials. While the bulk PCM in liquid phase exhibits a Newtonian viscosity, mPCM suspensions present a non-Newtonian viscosity. Both shear-thinning and shear-thickening behaviors are observed depending on the suspension particle volume fraction ϕ of mPCM. This paper concludes with a full comparison of our characterization results with models and correlations proposed in the literature.

Clove leaf essential oil Pickering emulsion stabilized by octenyl succinic anhydride modified waxy maize starch: An eco-friendly alternative

Clove leaf essential oil (CEO) is renowned for its well-established bioactive properties, which makes it an element with high added-value, especially for the food and pharmaceutical industries. Nevertheless, its use is hindered by instability and limited water solubility. Therefore, this study aimed to overcome these challenges by developing a stable Pickering emulsion of clove leaf essential oil using octenyl succinic anhydride modified waxy maize starch (OSA starch) particles as stabilizing agent, providing an eco-friendly alternative to conventional surfactants. First, the experimental conditions for the development of two distinct emulsion were optimized using a Response Surface Methodology (RSM). As a result, slightly shear-thickening behavior emulsions were obtained, with droplet size from 1 to 6 μm, absolute zeta potential values above 30 mV, and an exceptional stability for more than a month. These aspects can be linked to the synergistic effect of chemical/electrostatic interaction between essential oil and OSA starch. Finally, both samples exhibited an outstanding antibacterial efficacy, with MBC/MIC values below 4, classifying them as bactericidal agents against some typical foodborne pathogens. Our results indicate that these Pickering emulsions have noteworthy properties that make them an additive with promising potential for application in the food industry.

Synthesis and rheological performance of shear-thickening waterborne polyurethane

Shear-thickening fluids (STFs) are a new type of intelligent material with excellent performance whose viscosity increase sharply with the increase of shear rate or shear stress. However, the synthesis yield of dispersed phase particles is low, and the particle re-dispersion process is challenging for the industrial production of STFs. In this work, through structural design, a waterborne polyurethane (WPU) with typical shear-thickening properties was synthesized for the first time. This synthesis process is conducive to industrial production. The rheological properties of the synthesized WPU at different concentrations, temperatures, and pH were studied using a rheometer. The results showed that the WPU exhibited typical shear-thickening behavior. However, due to the special core–shell structure of the WPU particles, the shear rate has two transition responses to the shear-thickening behavior. With increasing concentration, the shear-thickening performance of the WPU is enhanced, and the critical shear rate is decreased. For the coexistence of Brownian motion and solvation, the rheological curve of the WPU exhibits a complex response to temperature increase; its shear-thickening behavior decreases with rising temperature, but the viscosity first decreases and then increases with temperature. Due to the presence of carboxyl groups on the surface of the WPU particles, its shear-thickening performance shows a strong response to pH. By appropriately adjusting the pH, the viscosity and particle size of the WPU can be increased through the ionization of carboxyl groups, thereby enhancing the shear-thickening behavior.

Identifying rheological regimes within pyroclastic density currents

Pyroclastic density currents (PDCs) are the most lethal of all volcanic hazards. An ongoing challenge is to accurately forecast their run-out distance such that effective mitigation strategies can be implemented. Central to this goal is an understanding of the flow mobility—a quantitative rheological model detailing how the high temperature gas-pyroclast mixtures propagate. This is currently unknown, yet critical to accurately forecast the run-out distance. Here, we use a laboratory apparatus to perform rheological measurements on real gas-pyroclast mixtures at dynamic conditions found in concentrated to intermediate pumice-rich PDCs. We find their rheology to be non-Newtonian featuring (i) a yield stress where deposition occurs; (ii) shear-thinning behavior that promotes channel formation and local increases in velocity and (iii) shear-thickening behavior that promotes decoupling and potential co-PDC plume formation. We provide a universal regime diagram delineating these behaviors and illustrating how flow can transition between them during transport.

Rheology of a crowd: from faster-is-slower to shear thickening

The evacuation speed of pedestrians through bottlenecks usually leads to the faster-is-slower (FIS) phenomenon, which relies on frictional clogging and clusters’ size. However, less attention is given in literature to the rheology of pedestrian crowds and the forces ruling their dynamics. Here, we establish a link between the faster-is-slower phenomenon (FIS) in pedestrian crowds and the shear-thickening rheological behavior of (non)Brownian suspensions. We analyze pedestrian room egress through particle-based simulations using the Social Force Model, revealing an S-shaped shear rate dependency characteristic of discontinuous shear thickening (DST). At the same time, the crowd flow viscosity near the exit exhibits a steep increase coinciding with FIS occurrence, establishing a correlation between FIS and shear thickening. Our results prove that crowd evacuations are governed by two distinct critical jamming densities, one frictional and another frictionless, and that contact forces alone cannot lead to FIS, but social force interactions are necessary to avoid contacts at low desired speeds. Our results point at the suitability of (non)Brownian suspensions as models that provide an original rheological perspective to pedestrian dynamics.

Investigation of entropy generation in power law fluid-filled bulging enclosures: effects of flow and heat transfer

This paper presents a complete investigation into the phenomenon of dual convection flow within a bulging enclosure along with non-Newtonian power-law fluids and employs the Galerkin finite element method for simulation. The main objective is to study the heat and mass transfer and entropy generation within the enclosure. Various factors, such as the Rayleigh number, power law coefficient, Lewis number, and effects of magnetic inclination are evaluated for their influence on flow dynamics and heat distribution. The study also investigates the relationship between these parameters and entropy generation, providing insights into the irreversible processes within the system. A comparative analysis of averaged Nusselt and Sherwood coefficients reveals distinct thermal and fluidic behaviours across varying power-law indices, emphasizing differences between shear thickening, shear thinning, and Newtonian fluid behaviours. The findings provide valuable insights into non-Newtonian power-law fluids in complex flows, enhancing our understanding of flow and heat transfer in bulging enclosures.

Shear thickening of dilute suspensions of fractal silica aggregates

The increase in viscosity under shear known as shear thickening (ST) is an inherent property of a wide variety of dense particulate suspensions. Recent studies indicate that ST systems formed by fractal particles are promising candidates for various practical applications. However, ST in fractal systems remains poorly explored. Here we experimentally study the ST behavior in suspensions of hydrophilic fumed silica (FS) particles in glycerol. Remarkably, unlike non-fractal systems, we observe a strong dependence of the onset stress for ST on the volume fraction of fractal objects and a reversible weakening of the ST response that depends strongly on the particle volume fraction as well as the properties of the FS system. Using in-situ boundary imaging, we map out the spatio-temporal flow properties during ST for different FS systems. We find that the fractal nature and structural properties like the internal branching of the particles can qualitatively explain the complex ST phase diagram of these systems.

Effect of topographical pattern on vortex shedding and heat transfer phenomena in power-law fluid flow around a rotating cylinder

The present numerical investigation studies the momentum and heat transfer phenomena from a heated rotating patterned cylinder in the vortex shedding regime. In particular, the effect of surface patterns ( ω , δ ), fluid behavior ( 0.4 ≤ n ≤ 1.6 ), cylinder rotation speed ( 0.5 ≤ α ≤ 2 ), and Prandtl number ( 1 ≤ Pr ≤ 100 ) at Reynolds number 100 on the force coefficients and Nusselt number are studied. Vorticity and isotherm profiles demonstrate the flow dynamics and heat transfer characteristics. According to the findings of this study, the formation of the vortex (including its size, shape, and number of vortices) and the time period during which the vortex shedding pattern repeats itself demonstrates a dependency on the shape of the cylinder, fluid behavior, and rotating speed. It has been noted that a significant decrease in the frequency of vortex shedding occurs on adding topographical patterns. Additionally, it has been noticed that on increasing rotational speed, vortex shedding can be suppressed for all fluid behaviors. Numerical simulation results reveal that the average drag coefficient ( C ¯ D ) for a rotating patterned cylinder decreases with increasing rotational speed ( α ), and it further reduces on increase in pattern frequency ( ω ) and amplitude ( δ ) compared to a smooth circular cylinder. The shear-thinning fluid behavior helps to dissipate the heat from the cylinder to the surrounding fluid. Conversely, shear-thickening fluid behavior exhibits the opposite trend.

Glass Transition Temperature and Mechanical Properties of Poly(Ethylene Carbonate)/Organoclay Composites

Poly(ethylene carbonate) (PEC) is a form of aliphatic polycarbonate, a biodegradable polymer made via the copolymerization of carbon dioxide and epoxides. The poor thermal stability and mechanical properties of these aliphatic carbonates are attributed to the carbon structure's flexibility, which restricts their applications. By combining PEC with organoclay CP180, this study addressed the weaknesses of PEC with organoclay addition. A physical blending technique was employed to generate PEC/organoclay composites with a 10-50 wt.% ratio of organoclay. The blended material's thermal characteristics were analyzed using differential scanning calorimetry (DSC), and the mechanical characteristics were measured using a universal tensile machine. The Field Emission Scanning Electron Microscopy (FESEM) analysis determined the blends' morphology. Before the torque value for all curves grew with the addition of CP180 material to the PEC matrix, it became constant. It reached a high value due to the shear-thickening behavior of the PEC matrix with organoclay addition. Tg of PEC increased by more than 7°C by 40 wt.% organoclay addition, as evident in the hindrance of PEC flexibility, significantly increased the toughness of this PEC. From the FESEM images, the formation of large silicate starts to aggregate effectively, lowering the interfacial area between organoclay and PEC as the clay content continues to rise, as shown by 50 wt.% organoclay addition.

Study of the Carreau fluid over a linearly curved stretching sheet: A numerical approach

Carreau fluid flow over a linearly curved stretching surface has significant applications in manufacturing industries. This study focuses on the impact of various parameters on the velocity, temperature, pressure skin friction, and heat transfer coefficient of a 2D Carreau flow. Both shear thinning (pseudoplastic) and shear thickening (dilatant) behaviors are considered. The parameters include suction, non-dimensional radius of curvature, Weissenberg number, magnetic parameter, power-law index, Eckert number (viscous dissipation parameter), and Prandtl number. The effects of viscous dissipation, magnetic field, convective boundary conditions, and suction are also taken into account. The study reveals that the flow velocity decreases with increasing magnetic parameter, curvature factor, and suction, but increases with the Weissenberg number and power law index. The heat transfer rate is reduced by the curvature factor, Weissenberg number, suction, power-law index, and Prandtl number, while the magnetic parameter has the opposite effect. The boundary value problem is simplified through appropriate similarity transformation and solved numerically using the shooting method and Matlab’s built-in function bvp4c. The results obtained from these two methods show good agreement. The findings also align well with existing literature in some limiting cases, confirming the validity of the study.

Microstructural smoothed particle hydrodynamics model and simulations of discontinuous shear-thickening fluids

Despite the recent interest in the discontinuous shear-thickening (DST) behavior, few computational works tackle the rich hydrodynamics of these fluids. In this work, we present the first implementation of a microstructural DST model in smoothed particle hydrodynamic (SPH) simulation. The scalar model was implemented in an SPH scheme and tested in two flow geometries. Three distinct ratios of local to non-local microstructural effects were probed: zero, moderate, and strong non-locality. Strong and moderate cases yielded excellent agreement with flow curves constructed via the Wyart–Cates (WC) model, with the moderate case exhibiting banding patterns. We demonstrate that a local model is prone to a stress-splitting instability, resulting in discontinuous stress fields and poor agreement with the WC model. The mechanism of stress splitting has been explored and contextualized by the interaction of local microstructure evolution and the stress-control scheme. Analytic solutions for a body-force-driven DST channel flow have been derived and used to validate the SPH simulations with excellent agreement in velocity profiles. Simulations carried out at increasing driving forces exhibited a decrease in flow. We showed that even the simple scalar model can capture some of the key properties of DST materials, laying the foundation for further SPH study of instabilities and pattern formation.

Non-linear electro-rheological model of a membrane immersed in Tanner-Power law fluids applied to outer hair cells: Shear-thinning mechanisms

Flexoelectric actuation employs an applied electric field to induce membrane curvature, which is the mechanism utilized by the outer hair cells (OHC) present in the inner ear. The model developed for this study, representing the OHC, integrates two key components: (i) an approximation of the flexoelectric membrane shape equation for circular membranes attached to the inner surface of a circular capillary, and (ii) the coupled capillary flow of contacting liquid viscoelastic phases characterized by the Tanner-Power law rheological equation of state. A second-order non-linear differential equation for average curvature has been derived, and a robust numerical method has been programmed. This model simplifies to a linear model used previously. The main challenge involves identifying and describing the enhancement in curvature change rate. It was observed that low symmetry, low viscosity, and soft membrane and shear-thickening behavior of the phases enhance the curvature change rate. Additionally, there exists a critical electric field frequency value that maximizes the curvature change rate (resonance effect). The current theory, model, and computational simulations add to the ongoing development comprehension of how biological membrane shape actuation through electromechanical couplings.

Effects of particle properties, intermolecular forces, and molecular structure on the shear-thickening behavior of waxy starch dispersions

The shear-thickening phenomenon in waxy starch dispersions has been reported; however, the influence of starch properties on it remains unclear. Herein, the shear-thickening behavior of five waxy starch dispersions at different concentrations is investigated, and two shear-thickening areas are identified for the first time. Waxy potato and cassava starch dispersions present two shear-thickening areas, waxy maize and wheat starch dispersions exhibit one shear-thickening area, and waxy rice starch dispersion exhibits no shear-thickening behavior. Starches with high degree of polymerization (DP > 12 and > 37 chains), short-range order, relative crystallinity, melting enthalpy (ΔH), and low molecular weight easily form large particle fragments and strong intermolecular forces, thereby resulting in double shear-thickening areas. Starches with relatively high DP > 12 chains, short-range order, relative crystallinity, and ΔH form one shear-thickening area. Starches with no shear-thickening area have high molecular weight, degree of branching, and DP < 12 chains, and low short-range order, relative crystallinity, and ΔH. It can be speculated that the first shear-thickening area (2–5 s−1) is due to the presence of large particle fragments, whereas the second (10–15 s−1) is due to the interaction between the side chains of the starch molecule.

Shear thickening of cementitious suspensions: effect of high-volume fraction and hydration

The lubrication layer (LL) formed at the concrete–pipe interface plays a crucial role in facilitating concrete pumping. Shear thickening in this layer significantly affects concrete pumping. However, very few studies are available for understanding the onset and intensity of shear thickening of the LL. In this study, the effect of solid volume fraction (SVF), superplasticiser dosage, supplementary cementitious materials and hydration on the shear thickening (continuous and discontinuous) behaviour of cementitious suspensions were investigated. Results show that an increase in SVF reduces the shear thickening intensity for systems using ordinary Portland cement (OPC), whereas the intensity is amplified for systems with fly ash (FA) or ground granulated blast furnace slag (GGBS). An increase in superplasticiser dosage results in an early onset of shear thickening and increases the shear thickening intensity, regardless of the binder used. Systems including GGBS exhibit the highest shear thickening intensity, followed by OPC- and FA-based systems. Based on these results, it is evident that the superplasticiser dosage for OPC-based systems needs to be optimised based on the structural buildup, while, for FA- or GGBS-based systems, the superplasticiser dosage needs to be optimised based on shear thickening behaviour with respect to hydration.

On the use of time-dependent fluids for delaying onset of transition to turbulence in the flat plate boundary-layer flow: A passive control of flow

Inelastic time-dependent fluids display continuous and reversible changes in viscosity when subjected to a constant shear-rate. These alterations arise from the gradual modification of the material’s microstructure due to shear-induced effects, known as shear rejuvenation. When this process generates smaller structural units, it is termed thixotropy; conversely, if it produces larger units, it is labeled anti-thixotropy. Aging is another characteristic of such fluids, denoting the capacity of the material to regain its original structure in the absence of shear, thus reversing the initial time-dependent change. This phenomenon often results from thermally activated Brownian motion prompting the reorganization of the material’s microconstituents. Consequently, attractive forces between these components can instigate the reconstruction of a network-like structure within the material. This study centers on investigating how variations in fluid microstructure impact the onset of transition to turbulence in a flat plate boundary-layer flow. Specifically, the focus is on cases where larger structural units emerge during the breakdown process (anti-thixotropy). To represent such fluids, the Quemada model, an inelastic structural-kinetic model, is employed. This model effectively captures thixotropy and anti-thixotropy by appropriately configuring model parameters. The analysis begins with obtaining a local similarity solution for the generalized Blasius equation, representing the base flow. Subsequently, the stability of this flow is assessed using linear temporal stability theory. This involves introducing infinitesimally-small normal-mode perturbations to the base flow, yielding the generalized Orr–Sommerfeld equation. Solving this equation using the spectral method provides insights into stability. Results from this study indicate that for low Deborah numbers, the shear-thickening behavior prevails, causing destabilization. In contrast, higher Deborah numbers lead to stability. This implies that anti-thixotropy effectively delays the onset of transition to turbulence and could hold practical applications for flow control.

Does harvesting age matter? Changes in structure and rheology of a shear-thickening polysaccharide from Cyathea medullaris as a function of age

A shear-thickening polysaccharide from the New Zealand Black tree fern (Cyathea medullaris, commonly known as mamaku) extracted from different age fronds (stage 1: young, stage 2: fully grown and stage 3: old) was characterised in terms of structure and rheological properties. Constituent sugar analysis and 1H and 13C NMR revealed a repeating backbone of −4)-β-D-GlcpA-(1 → 2)-α-D-Manp-(1→, for all mamaku polysaccharide (MP) samples from different age fronds without any alterations in molecular structure. However, the molecular weight (Mw) was reduced with increasing age, from ~4.1 × 106 to ~2.1 × 106 Da from stage 1 to stage 3, respectively. This decrease in Mw (and size) consequently reduced the shear viscosity (ηs-Stage 1 > ηs-Stage 2 > ηs-Stage 3). However, the extent of shear-thickening and uniaxial extensional viscosity of MP stage 2 was greater than MP stage 1, which was attributed to a greater intermolecular interaction occurring in the former. Shear-thickening behaviour was not observed in MP stage 3.

Dynamics of a self-interacting sheet in shear flow.

Solution processing of 2D materials such as graphene is important for applications thereof, yet a complete fundamental understanding of how 2D materials behave dynamically in solution is lacking. Here, we extend previous work by Silmore et al., Soft Matter, 2021, 17(18), 4707-4718 by adding short-ranged Lennard-Jones interactions to 2D sheets in shear flow. We find that the addition of these interactions allows for a rich landscape of conformations which depend on the balance between shear strength, bending rigidity, and interaction strength as well as the initial configuration of the sheet. We explore this conformational space and classify sheets as flat, tumbling, 1D folded, or 2D folded based on their conformational properties. We use kinetic and energetic arguments to explain why sheets adopt certain conformations within the folded regime. Finally, we calculate the stresslet and find that, even in the absence of thermal fluctuations and multiple sheet interactions, shear-thinning followed by shear-thickening behavior can appear.

Process-structure-function relationship for mamaku suspension: Effect of drying methods on powder functionality

The pith from mamaku tree fern entraps a unique shear-thickening biomacromolecule called mamaku polysaccharide (MP) that may alter the rheological profile in the gut. Here we examined the potential of using the whole pith—natural entrapment of MP in the tissue of pith—to develop a food ingredient with shear-thickening behaviour as an alternative to MP extract. In this study, fresh mamaku pith was collected and dried using an oven-dryer or freeze-dryer, and ground into a powder (ODP: oven-dried powder; FDP: freeze-dried powder). Both the ODP and FDP were characterised for their physical properties (colour, densities, surface morphology), rehydration in water, rheological behaviour and in vitro starch digestion. Freeze-drying resulted in a porous structure, while after oven-drying, the structure collapsed and an increase in density was observed. Upon rehydration with water, both FDP and ODP absorbed water, causing the powder particles to swell and release the water-soluble compounds into the continuous phase. The ability of FDP to release water-soluble MP into the continuous phase resulted in a rheological behaviour of a suspension similar to MP extract solution (shear-thickening behaviour). No shear-thickening was observed in ODP suspension because not enough MP was available in the continuous phase to form polymer-polymer interactions. In-vitro digestion of wheat biscuits mixed with rehydrated FDP suspension reduced starch digestion by ∼35% after 10 min, but starch digestion was unaffected by ODP suspension. This was due to the changes in the rheological behaviour resulting from the alteration in structural characteristics of the powder samples by the different drying methods.