Small Amplitude Oscillatory Rheometry Research Articles

Trends in the temperature dependence of dynamical heterogeneity in strong and fragile supercooled liquids

The temperature dependence of the Kohlrausch-Williams-Watts (KWW) stretching exponent β of shear relaxation kinetics is determined for a wide variety of deeply supercooled glass-forming liquids with fragility index m ranging between ∼ 30 and 90 using small amplitude oscillatory shear parallel plate rheometry. Intriguingly, and contrary to conventional wisdom, β and m are observed to be uncorrelated at temperatures close to the glass transition Tg. However, a clear pattern emerges when the variation of β is considered as a function of the α-relaxation timescale τα. In particular, β is observed to increase rapidly (slowly) for relatively strong (fragile) liquids with decreasing τα upon increasing temperature above Tg. Consequently dβ/d(log τα) is found to be negatively correlated with m near and above Tg. A possible origin of this intriguing trend is discussed within the frameworks of the energy landscape and the elastic facilitation models of relaxation of supercooled liquids.

Upcycling Lactobacillus casei culture waste into vegan cheese analogue using inulin, locust bean gum, and κ-carrageenan

The growing popularity of probiotics has led to the generation of substantial by-products. Among these, cell-free supernatant is recognized for containing beneficial postbiotics. Here, we upcycled Lactobacillus casei-free supernatant (LFS) into cheese analogues using inulin (INU), locust bean gum (LBG), and kappa-carrageenen (kCG). In this system, LBG/kCG established the primary structure, while interstitial spaces were progressively filled by INU. Despite the absence of milk proteins and fats, the cheese analogue with 35% w/w INU, 0.2% w/w LBG, and 0.8% kCG exhibited a texture and appearance resembling commercial processed cheese, as determined by texture profile analysis and dynamic small amplitude oscillatory rheometry technique. This can be attributed to the effective fat-replacing activity of INU regarding texture and rheology. Furthermore, the potassium-dominated salt composition of LFS proved advantageous for the LBG/kCG-derived structure-forming. These findings hold significant promise for upcycling probiotics wastewater into low-fat vegan cheese analogues, enriched with both prebiotics and postbiotics.

Artificial neural network investigation of injectability and percolation of highly filled β -Tricalcium phosphate suspensions

Over the past few decades, calcium phosphate cement has been used successfully for bone reconstruction applications. As percutaneous surgical methods have developed, there is an increased interest in calcium phosphate cement injection behavior. The aim of this study is to minimize percolation (liquid phase migration under pressure) and maximize injectability (ratio of the extruded part to whole) of highly filled β-tri calcium phosphate (β-TCP) suspensions by varying capillary flow process parameters with an artificial neural network (ANN) approach. The effects of hydroxyethyl cellulose (HEC) and polyethylene glycol (PEG-400) were also studied as binder additives for injectable β-tri calcium phosphate pastes. Prepared suspensions were investigated by capillary and small amplitude oscillatory rheometry. The study predicted experimental input and output data by using Backpropagation Neural networks via the Levenberg-Marquardt algorithm. The ANN model was developed by feed-forward back propagation network and predict percolation (%) and injectability (%). A great agreement was observed between the predicted values by the ANN model and the experimental data for injectability (%) and percolation (regression coefficients) of 0.9984 and 0.9982 respectively. The results depict that ANNs can improve the accuracy of injectability and percolation results which can be used to optimize process and additive parameters for injectable bone cements and pastes. 2 wt% HEC was determined as the most effective factor to improve the rheological properties of highly filled β-TCP pastes which could be injected as much as 99.21 % at a rate of 15 mm/min through dies with L/D ratio of 15. Their percolation value was calculated as 0.82 %. Lubricative effect of PEG-400 additive with 2 wt% HEC to reduce injection force was also demonstrated.

Rheological and clot microstructure evaluation of heparin neutralization by UHRA and protamine

The current study reports the use of small amplitude oscillatory rheometry to investigate the dynamics of blood clot formation upon heparin neutralization under three different oscillatory frequencies, two of which were mimicking physiological heart rates. We utilized two different heparin antidotes, namely protamine and newly developed universal heparin reversal agent (UHRA-7), at different concentrations to determine the quality of blood clot formed upon heparin neutralization by analyzing several key rheological parameters. Scanning electron microscopy (SEM) was used to determine the morphology and microstructure of the blood clot after heparin neutralization to support the rheological observations. The current study revealed that the structure of blood clots formed had significant differences when an oscillatory frequency that mimicked the physiological heart rate was used in comparison to a lower frequency commonly used in current clinical measurements. The limited working dose range for protamine and its intrinsic anticoagulation behaviour was observed. The neutralization profile of UHRA-7 showed a large window of activity. The global assessment of rheological parameters and microstructure of the clot together revealed additional details describing anticoagulant reversal and blood coagulation dynamics by relating the blood clot's fiber thickness and the oscillatory measurements, including storage modulus and blood clot's contractile force. Additionally, a mechanical characterization was conducted to provide a further assessment of blood coagulation using the rheological data.

Rheological characterization of complex dynamics in Na-Zn metaphosphate glass-forming liquids.

The viscoelastic behavior and shear relaxation in supercooled [NaPO3]x[Zn(PO3)2]1-x metaphosphate liquids with 0.2 ≤ x ≤ 1.0 are investigated using a combination of small amplitude oscillatory and steady shear parallel plate rheometry, resonant ultrasound spectroscopy, and differential scanning calorimetry. The results demonstrate that these liquids are thermorheologically complex with the coexistence of a fast and a slow relaxation process, which could be attributed to the segmental motion of the phosphate chains and the Zn-O bond scission/renewal dynamics, respectively. The segmental motion of the phosphate chains is found to be the dominant process associated with the shear relaxation for all metaphosphate liquids. The compositional evolution of the calorimetric fragility of these liquids is shown to be related to the conformational entropy of the constituent phosphate chains, which is manifested by the width of the relaxation time distribution for the segmental chain motion. This entropy decreases and the temporal coupling between the chain dynamics and Zn-O bond scission-renewal increases with the increasing Zn content as the higher field strength Zn modifier ions provide more effective cross-linking between the phosphate chains.

Rheological behavior of molecular vs network chalcogenide supercooled liquids.

The viscoelastic behavior of supercooled glass-forming liquids along the binary join As4S3-GeS2 with As4S3 contents varying from 81.25 to 9 mol. % and correspondingly with structures varying from predominantly molecular to a three-dimensional tetrahedral network is studied by small-amplitude oscillatory shear parallel plate rheometry. The storage shear modulus G' shows a scaling behavior of G'(ω) ∼ ωn in the terminal (low-frequency) regime, where n varies between 1 and 2 and shows an increasingly anomalous departure from the expected value of 2 (Maxwell scaling) with increasing molecule content. A concomitant departure from the Maxwell scaling is also observed for the loss modulus G″ at frequencies above the G'-G″ crossover. On the other hand, the variation in the phase angle δ with the complex modulus indicates that the molecular liquid does not display a purely viscous response even at the lowest frequencies. These results, combined with an analysis of the relaxation spectra of these liquids, suggest that the anomalous behavior of molecular liquids may be linked to their rather broad relaxation spectrum and the presence of slow relaxation processes associated with molecular clusters. Additionally, these liquids are also characterized by a wide high-frequency plateau in the relaxation spectral density that can be linked to the rotational dynamics of the constituent molecules. Such fundamental differences between the rheological behavior of molecular and network liquids may explain the significantly higher fragility of the former.

Investigation of the shear relaxation behavior of As-Se liquids within the framework of entropic and elastic models of viscous flow

The shear relaxation behavior of supercooled arsenic selenide liquids is studied using small amplitude oscillatory parallel plate rheometry. Compositions with >80% Se, characterized by a low-dimensional network of selenium chain segments cross-linked by threefold coordinated arsenic atoms, display the coexistence of a nearly-Arrhenius, slow relaxation process and a strongly non-Arrhenius, fast relaxation process corresponding to bond scission/renewal and chain segmental motion, respectively. The coupling between the weakly non-Arrhenius bond scission and the strongly non-Arrhenius viscosity is achieved near Tg due to the pronounced temperature-dependence of the modulus corresponding to this relaxation process. The temperature dependence of this relaxation modulus is related to the conformational entropy of the chain segments. The large difference between the activation energy of viscous flow and that of the timescale of the relaxation associated with bond scission/renewal implies the need for a revision of the existing models of viscous flow in the literature.

Comparison of hardening kinetics by small amplitude oscillatory rheometry in the case of alkali activated kaolinitic clays

In this study, the rheological behaviour of geopolymeric inorganic binders were determined. These binders were synthesized by alkaline activation of aluminosilicate material. Five kaolinite clays were chosen for investigation and as an alkaline activator of hardening process, the potassium silicate solution with silicate module of 1.61 was used. For increase of reactivity, the kaolinite clays were calcined by heat treatment at 600 °C for 4 hours and converted to metakaolin state. The particle size of individual materials was determined by measurement of laser light scattering. The rheological properties were determined in accordance to flow properties by measurements on Ford viscosity cup and by strain controlled small amplitude oscillatory rheometry measurements at 30 °C isotherm and the hardening process evolution was documented by measurement of complex viscosity. The effects of granularity and accessory minerals on flow and hardening properties are discussed.

The effect of milled basalt fibers addition on rheological and mechanical properties of alkali activated binder

In this study, the effects of milled basalt fibers addition on rheological behaviour of alkali activated geopolymer binder were determined. This binder was synthesized by alkaline activation of calcined clay stone powder and milled blast furnace slag by potassium silicate solution. Milled basalt fibers as filler were used in range of 0-20 wt% addition to powder part of binder and the effects on rheological and mechanical properties were evaluated. The rheological properties were determined in accordance to flow properties by measurements on Ford viscosity cup and by strain controlled small amplitude oscillatory rheometry measurements of hardening process. The final properties were documented by measurements of flexural strength after 28 days and by scanning electron microscopy. The results indicate that milled basalt fibers addition has effect on flow properties of binder. The flow time increased three times and the complex viscosity is also coherently increased. The reinforcement led to two times higher values of flexural strength and the best figure of merit lied in the range of 1-5 wt% addition of milled basalt fibers.

Rheology, thermal properties, and microstructure of heat-induced gel of whey protein-acetylated potato starch

The objective of the present work was to investigate the effects of acetylated potato starch (APS) on the rheological and thermal properties and the microstructure of a heat-induced gel of whey protein isolate (WPI) using small-amplitude oscillatory rheometry, differential scanning calorimetry (DSC), dynamic light scattering (DLS) and scanning electron microscopy (SEM). The rheological results indicated that the elastic (G’) and viscous modulus (G”) of the WPI-APS systems increased as the concentrations of APS increased. During heating and cooling, the rheological profiles of the WPI-APS systems exhibited continuous increases in G’ at temperatures more closely related to those observed for WPI rather than APS. DSC results indicated that increasing APS concentration had no influence on the individual phase transition of WPI and APS. An analysis of the Flory–Huggins parameter χ12 suggested an obvious phase separation between WPI and APS in the WPI-APS system. The comprehensive analytical results indicated that the gelatinization for APS was earlier than the denaturation for WPI, contributing to the formation of larger-sized WPI-APS aggregates. The results could provide a theoretical foundation for food preparation containing WPI and APS.

Ceramic-like open-celled geopolymer foam as a porous substrate for water treatment catalyst

This paper presents results from experimental study on microstructural and mechanical properties of geopolymer-based foam filters. The process for making porous ceramic-like geopolymer body was experimentally established, consists of (a) geopolymer paste synthesis, (b) ceramic filler incorporation, (c) coating of open-celled polyurethane foam with geopolymer mixture, (d) rapid setting procedure, (e) thermal treatment. Geopolymer paste was based on potassium silicate solution n(SiO2)/n(K2O)=1.6 and powder mixture of calcined kaolin and precipitated silica. Various types of ceramic granular filler (alumina, calcined schistous clay and cordierite) were tested in relation to aggregate gradation design and particle size distribution. The small amplitude oscillatory rheometry in strain controlled regime 0.01% with angular frequency 10 rad/s was applied for determination of rheology behavior of prepared mixtures. Thermal treatment conditions were applied in the temperature range 1100 – 1300 °C.The developed porous ceramic-like foam effectively served as a substrate for highly active nanoparticles of selected Fe+2 spinels. Such new-type of nanocomposite was tested as a heterogeneous catalyst for technological process of advanced oxidative degradation of resistive antibiotics occurring in waste waters.

The influence of metakaolin substitution by slag in alkali-activated inorganic binders for civil engineering

In this study the effect of metakaolin replacement by milled blast furnace slag in alkali-activated geopolymeric binder was investigated in accordance to their rheological and mechanical properties. It was demonstrated that slag addition into the metakaolin binder can improve mechanical properties of final products. Our investigation was focused on broad interval of metakaolin substitution in the range from 100 to 40 volume per cents of metakaolin so that the volume content of solids in final binder was maintained constant. Prepared binders were activated by alkaline solution of potassium silicate with silicate module of 1.61. The particle size analyses were performed for determination of particle size distribution. The rheological properties were determined in accordance to flow properties by measurements on Ford viscosity cup and by oscillatory measurements of hardening process. For the investigation of hardening process, the strain controlled small amplitude oscillatory rheometry was used in plane-plate geometry. For determination of applied mechanical properties were binders filled by ceramic grog in the granularity range 0-1 mm. The filling was maintained constant at 275 volume per cents in accordance to ratio of solids in dry binder. The mechanical properties were investigated after 1, 7 and 28 days and microstructure was documented by scanning electron microscopy. The results indicate that slag addition have beneficial effect not only on mechanical properties of hardened binder but also on flow properties of fresh geopolymer paste and subsequent hardening kinetics of alkali-activated binders.

Hardening kinetics investigation of alkali-activated binder by small amplitude oscillatory rheometry

In this study, the rheological behavior of geopolymeric inorganic binder was determined. This binder was synthesized by alkaline activation of mixture, comprising calcined claystone powder and milled blast furnace slag. As an alkaline activator of hardening process, the potassium silicate solution was used. For the investigation of hardening kinetics, the strain controlled small amplitude oscillatory rheometry was used with strain of 0.01%. The reproducibility and versatility of this method is demonstrated for determination of hardening process evolution. The changes of loss tangent shape were studied in this experiment and applied for determination of gelation time. All experiments were conducted at isothermal conditions in temperature range 27-70°C and parallel plate geometry. The results indicate that reaction kinetics is directly depending on temperature. The hardening kinetics was mathematically described and these calculations were compared with self-contained experiment conducted at 2°C. This experiment is described in details and the results of gelation time measurements confirmed calculated data.

Mechanically activated fly ash as a high performance binder for civil engineering

This study is aimed for investigation of fly ash binder with suitable properties for civil engineering needs. The fly ash from Czech brown coal power plant Prunerov II was used and mechanically activated to achieve suitable particle size for alkaline activation of hardening process. This process is driven by dissolution of aluminosilicate content of fly ash and by subsequent development of inorganic polymeric network called geopolymer. Hardening kinetics at 25 and 30 °C were measured by strain controlled small amplitude oscillatory rheometry with strain of 0.01 % and microstructure of hardened binder was evaluated by scanning electron microscopy. Strength development of hardened binder was investigated according to compressional and flexural strength for a period of 180 days. Our investigation finds out, that mechanically activated fly ash can be comparable to metakaolin geopolymers, according to setting time and mechanical parameters even at room temperature curing. Moreover, on the bases of long time strength development, achieved compressional strength of 134.5 after 180 days is comparable to performance of high grade Portland cement concretes.

Predicting coagulation and syneresis parameters of milk gels when inulin is added as fat substitute using infrared light backscatter

Production of reduced fat cheeses often requires modification of the manufacturing procedure using fat substitutes such as inulin, in order to achieve acceptable sensory properties. Nowadays the use of optical sensors in cheese making justify developing prediction algorithms for coagulation and syneresis parameters in milk gels with inulin with the goal of improve cheese yield, quality and homogeneity. A randomized factorial design was used to test the effect of inulin concentration (0%, 3%, and 6% w/w), temperature (27, 32, and 37°C), and fat (<0.2%, and 1.5% w/w) on light backscatter parameters typically used for predicting significant coagulation and syneresis indexes. The coagulation process was monitored using near infrared spectrometry, small amplitude oscillatory rheometry and visual coagulation indexes. The extent and kinetics of syneresis was evaluated by volumetric methods. Prediction models with one, two and three-parameter were determined for the whey drainage kinetic rate constant (k), curd yield (cy), clotting time (tclot), visual cutting time (tcut), as well as the rheologically-determined gelation (tG′1) and cutting times (tG′30). The results demonstrated that it is possible to obtain models for the prediction of coagulation and syneresis parameters in milk gels when inulin is added as a fat substitute using a fiber optic light backscatter sensor.

Rheological and Microstructural Characteristics of Thermally Produced Flaxseed Gum–Whey Protein Isolate Mixed Solutions and Gels

The rheological, thermal gelation, and microstructural properties of flaxseed gum–whey protein isolate (WPI) mixtures were studied using steady shear viscometry, small amplitude oscillatory rheometry, differential scanning calorimetry (DSC), and confocal laser scanning microscopy (CLSM). The concentration of flaxseed gum was varied from 0.1%–0.5% (w/w) while the concentration of WPI was maintained at 20% (w/w). The addition of flaxseed gum increased the viscosity of flaxseed gum–WPI solutions and the strength of the mixed gels. The degree of increase in gel strength was found to depend on the concentration of flaxseed gum. The gel strength of the flaxseed gum–WPI mixed gels increased with the increase of flaxseed gum at low gum concentrations (0.1%–0.3% w/w). The gel strength of these mixed gels decreased (but it was still higher than WPI only gel) at high flaxseed gum concentration (0.5% w/w) due to excessive phase separation caused by thermodynamic incompatibility. This phase separation was clearly visible in micrographs obtained from CLSM.

Using a fiber optic sensor for cutting time prediction in cheese manufacture from a mixture of cow, sheep and goat milk

NIR light backscatter technology has been proven successful for monitoring cow milk coagulation and predicting cutting time but has never been tested with milk mixtures. In Spain ∼40% of the cheese produced is made from cow, sheep and goat milk mixtures. The aim of this study was to evaluate if the proposed optical technology could be used to monitor milk coagulation and predict cutting time in milk mixtures. A randomized factorial design with three factors and three replicates was employed. Cow, goat and sheep milk was mixed in two different proportions. Milk mixtures were coagulated at constant calcium chloride addition level, pH and fat concentrations using two different enzyme concentrations and three coagulation temperatures (N=36 tests). Milk coagulation was monitored using small amplitude oscillatory rheometry and a NIR fiber optic light backscatter sensor. Simultaneously, clotting time was visually evaluated. Optical parameter tmax was highly correlated (0.80<r<0.99, P<0.0001) with the rheological and visual parameters studied. Enzyme concentration and temperature had a significant effect (P<0.05) on optically-, rheologically-, and visually-derived parameters. Milk mixture proportion was not significant for optical parameters related to clotting time but was significant for the aggregation rate and rheological parameters related to curd firming and syneresis. Models for predicting cutting time were developed successfully with R2=0.93. Results strongly suggest that milk mixture proportion exerts an effect on gel assembly (i.e., on both aggregation and curd firming) and syneresis. This finding has important implications for inline process control when goat and sheep milk are used.

Influence of fat replacement by inulin on rheological properties, kinetics of rennet milk coagulation, and syneresis of milk gels

The objective of this study was to evaluate the effect of inulin as a fat replacer on the rheological properties, coagulation kinetics, and syneresis of milk gels. A randomized factorial design, replicated 3 times, with 3 inulin concentrations (0, 3, and 6%), 2 levels of fat (<0.2 and 1.5%), and 3 coagulation temperatures (27, 32, and 37°C) was used. The coagulation process was monitored using near-infrared spectrometry, small amplitude oscillatory rheometry, and visual coagulation indexes. The syneresis was evaluated by volumetric methods. Inulin addition increased the rates of aggregation and curd firming reactions in the casein gels. The observed effect, which was more evident on the aggregation reaction, depended on the concentration of inulin and the coagulation temperature. Addition of 6% inulin reduced the clotting time by approximately 26% and the time at which the gel reached a storage modulus equal to 30Pa by approximately 36%. The optical parameter R′max, defined as the maximum value of change in light backscatter profile/change in time (where R′ = dR/dt), was used to calculate an approximation of the temperature coefficients (Q10) for milk coagulation. Increasing fat concentration induced a consistent increase in all the optical, rheological, and visual parameters studied, although the observed trend was not statistically significant. The addition of inulin at a level of 6% produced a reduction in syneresis and increased the curd yield by approximately 30%. It was concluded that the addition of inulin affects the kinetics of milk coagulation and the cutting time and, therefore, the use of inline sensors such as near-infrared spectrometry may be necessary for optimal process control.

Insoluble calcium content and rheological properties of Colby cheese during ripening

Colby cheese was made using different manufacturing conditions (i.e., varying the lactose content of milk and pH values at critical steps in the cheesemaking process) to alter the extent of acid development and the insoluble and total Ca contents of cheese. Milk was concentrated by reverse osmosis (RO) to increase the lactose content. Extent of acid development was modified by using high (HPM) and low (LPM) pH values at coagulant addition, whey drainage, and curd milling. Total Ca content was determined by atomic absorption spectroscopy, and the insoluble (INSOL) Ca content of cheese was measured by the cheese juice method. The rheological and melting properties of cheese were measured by small amplitude oscillatory rheometry and UW-Melt Profiler, respectively. There was very little change in pH during ripening even in cheese made from milk with high lactose content. The initial (d 1) cheese pH was in the range of 4.9 to 5.1. The INSOL Ca content of cheese decreased during the first 4 wk of ripening. Cheeses made with the LPM had lower INSOL Ca content during ripening compared with cheese made with HPM. There was an increase in melt and maximum loss tangent values during ripening except for LPM cheeses made with RO-concentrated milk, as this cheese had pH <4.9 and exhibited limited melt. Curd washing reduced the levels of lactic acid produced during ripening and resulted in significantly higher INSOL Ca content. The use of curd washing for cheeses made from high lactose milk prevented a large pH decrease during ripening; high rennet and draining pH values also retained more buffering constituents (i.e., INSOL Ca phosphate), which helped prevent a large pH decrease.

Effect of homogenization, microfiltration and pH on curd firmness and syneresis of curd grains

Abstract The impact of the independent variables, homogenization pressure ( p 1 ), concentration factor of microfiltration ( i ) and pH on curd firmness (CF) and syneresis of curd grains was studied. Texture analysis was used to characterize CF of the rennet-induced gels. The analysis of a two-level factorial design revealed that i , p 1 , pH and the interaction of i and pH had the most important influence on CF. Cutting time was therefore individually determined for each milk system using small amplitude oscillatory rheometry for generating comparable conditions for the syneresis experiments. Syneresis of curd grains with a diameter of 11 mm was followed at 35 °C close to semi-hard cheesemaking conditions. The permeate release during microfiltration was taken into consideration, allowing an evaluation of syneresis of grains made from concentrated and unconcentrated milk. It was shown that with increasing milk concentration less curd treatment time was needed to reach a certain syneresis value. Hence, total processing time in cheesemaking is decreased. Analysis of variance revealed that syneresis was affected by the individual variables. Kinetic parameters were satisfactorily estimated through regression ( R 2 >0.98) and it was shown that milk composition and concentration due to microfiltration markedly influenced the endpoint of syneresis, RWR max . The experiments demonstrate that microfiltration and homogenization can be combined to reach CF and syneresis comparable to untreated milk used in conventional cheesemaking. This meets one claim of the cheese industry when implementing both technologies in the manufacture process, since consistency and quality of the ripened cheese are expected to be unchanged.