Rheopectic Behavior Research Articles

Morphological Influence on a Nonionic Bilayer Bending Rigidity and Compression Modulus.

The mechanical properties of multilamellar vesicles and their relevance to soft matter physics and material science are of significant interest. The bending rigidity, κ, and compression modulus, B, of three-dimensional (3D) finite nonspontaneous multilamellar vesicles, formed by a nonionic surfactant, are linked to nanoscale bilayer thickness, δ, estimated via small-angle X-ray scattering, and macroscopic elastic modulus measured through small-amplitude oscillatory shear experiments. κ and B significantly differ from the same system in the two-dimensional (2D) infinite nanostructured planar lamellar phase. Particularly, κ3D was found to be much smaller than κ2D, while an opposite behavior was seen for B. The 2D-to-3D morphology transition occurs under a transient mechanical field, resulting in rheopectic behavior. κ scales quadratically with δ, consistent with bilayer membrane theories, and linearly with vesicle radius in the densely packed state. These findings have implications for understanding and designing soft interfaces due to the influence of bending rigidity on transport properties.

Rheological enhancement of fresh polymer-modified cement composites via surface-modified graphene oxide

Polymer-modified cement (PMC) composites are extensively utilized in modern construction, especially in tunneling and structural applications, but their excessive flowability and reduced thixotropy continue to present fundamental rheological challenges. We present a novel approach to improving the rheological performance of PMC via surface-modified graphene oxide (GO), i.e., GOPMC composites. Specifically, the flow behavior of GOPMCs in relation to shear stress–shear strain response and apparent viscosity were investigated. The rheological parameters were analyzed by using Herschel–Bulkley's model. Additionally, zeta potential and dispersion analysis were conducted to investigate interparticle interaction forces. Flow measurement confirmed ∼20 % lower flowability of the GOPMC than the reference PMC. GOPMC composites further displayed higher yield stress of ∼82 % and ∼33 % reduced viscosity with inherent decreased shear-thickening compared to reference PMC composites. The yield stress of the GOPMC composite increased over time, disclosing distinct structural evolution linked to enhanced hydration kinetics by GO. Additionally, GO nanosheets in the GOPMC altered the rheopectic behavior of the redispersible polymer and enhanced the degree of thixotropy by ∼80 %, attributable to the promotion of bridged flocculated structures which produces a rigid system, facilitated by particle interaction forces comprising of van der Waals and steric forces. This latter observation provides a mechanistic framework for the enhanced rheological performance of GOPMC composites aiming at broader civil engineering and construction sector applications beyond tunneling.

Bioactive-Loaded Hydrogels Based on Bacterial Nanocellulose, Chitosan, and Poloxamer for Rebalancing Vaginal Microbiota.

Biocompatible drug-delivery systems for soft tissue applications are of high interest for the medical and pharmaceutical fields. The subject of this research is the development of hydrogels loaded with bioactive compounds (inulin, thyme essential oil, hydro-glycero-alcoholic extract of Vitis vinifera, Opuntia ficus-indica powder, lactic acid, citric acid) in order to support the vaginal microbiota homeostasis. The nanofibrillar phyto-hydrogel systems developed using the biocompatible polymers chitosan (CS), never-dried bacterial nanocellulose (NDBNC), and Poloxamer 407 (PX) incorporated the water-soluble bioactive components in the NDBNC hydrophilic fraction and the hydrophobic components in the hydrophobic core of the PX fraction. Two NDBNC-PX hydrogels and one NDBNC-PX-CS hydrogel were structurally and physical-chemically characterized using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and rheology. The hydrogels were also evaluated in terms of thermo-responsive properties, mucoadhesion, biocompatibility, and prebiotic and antimicrobial effects. The mucin binding efficiency of hydrogel base systems was determined by the periodic acid/Schiff base (PAS) assay. Biocompatibility of hydrogel systems was determined by the MTT test using mouse fibroblasts. The prebiotic activity was determined using the probiotic strains Limosilactobacillus reuteri and Lactiplantibacillus plantarum subsp. plantarum. Antimicrobial activity was also assessed using relevant microbial strains, respectively, E. coli and C. albicans. TEM evidenced PX micelles of around 20 nm on NDBNC nanofibrils. The FTIR and XRD analyses revealed that the binary hydrogels are dominated by PX signals, and that the ternary hydrogel is dominated by CS, with additional particular fingerprints for the biocompounds and the hydrogel interaction with mucin. Rheology evidenced the gel transition temperatures of 18-22 °C for the binary hydrogels with thixotropic behavior and, respectively, no gel transition, with rheopectic behavior for the ternary hydrogel. The adhesion energies of the binary and ternary hydrogels were evaluated to be around 1.2 J/m2 and 9.1 J/m2, respectively. The hydrogels exhibited a high degree of biocompatibility, with the potential to support cell proliferation and also to promote the growth of lactobacilli. The hydrogel systems also presented significant antimicrobial and antibiofilm activity.

Dynamics of Microbubbles Oscillating in Rheopectic Fluids Subject to Acoustic Pressure Field

In the present work, the dynamics of a single spherical gas bubble surrounded by a rheopectic fluid obeying the Quemada model is numerically investigated while the bubble undergoes oscillatory motion due to acoustic forcing. The generalized form of the Rayleigh–Plesset equation has been used for studying bubble dynamics in Quemada fluids. The integro-differential equation representing the dynamics of the bubble is solved numerically using the finite-element method (FEM) and also the Gauss–Laguerre quadrature (GLQ) method. The effect of rheopexy number (Rx) and viscosity ratio (ξ) are then investigated over a wide range of working parameters. Numerical results show that the rheopectic behavior of the fluid surrounding the bubble can dramatically affect the bubble dynamics. It is predicted that for highly anti-thixotropic fluids, harmonics are affected so much so that the bubble may exhibit chaotic behavior. For instance, at Rx = 0.001 and ξ = 1/81, a one-micron-sized bubble may attain a size almost 30 times of its initial size. The general conclusion is that, in sonography, microbubbles dispersed in rheopectic fluids may indeed be considered as a potent ultrasound contrast agent provided that the fluid is just moderately anti-thixotropic otherwise its chaotic response might damage the adjacent tissues.

Skin‐Inspired Nanofluid‐Filled Surfaces with Tunable Icephobic, Photothermal, and Energy Absorption Properties

AbstractIce buildup can significantly and negatively impact system performance in various industrial sectors, and has remained a persistent challenge for decades. Many compliant materials exhibit excellent de‐icing performance but are easily eroded by impacts from supercooled water droplets, sand, dust, and debris. A composite panel inspired by animal skin, consisting of a facesheet protecting a nanofluid layer beneath, which exhibits durable anti‐icing and tunable photothermal properties is proposed. The viscous liquid layer beneath the facesheet increases flexural rigidity, preventing large deflections and increasing deformation resistance, which alters ice's adhesion to the surface. The non‐uniform fluid pressure exerted by the viscous nanofluid‐filled composite panels facilitates ice detachment, resulting in ice adhesion strengths as low as τice ≈ 10 kPa. Further, by altering the fluid properties, different additional functionalities can be endowed to the system. Incorporating fumed silica in a fluid‐filled composite panel results in rheopectic behavior, and this doubles their impact resistance when the shear thickening properties are properly tuned. Additionally, the combination of a transparent facesheet and a solar light absorbent nanofluid allows for tunable photothermal properties, further enhancing the anti‐icing performance of the system. This durable and tunable nanofluid‐filled composite panel shows great promise as a multifunctional de‐icing material.

Biological Significance of the Respiratory Mucus Rheology in Mucociliary Clearance

Mucociliary clearance (MCC) is the first line of defense in the respiratory tract, where beating cilia and viscous mucus play a pivotal role in eliminating inhaled harmful substances. Homeostasis of mucus rheological properties is a crucial factor in maintaining the functionality of MCC. However, rheological properties of the mucus is poorly understood because of the challenges associated with collecting intact mucus samples. In this report, in vitro three-dimensionally cultured human bronchial epithelial cells were used as a source of mucus to investigate mucus rheological properties. The mucus exhibited rheopectic and shear-thinning behavior, and mucus viscosity increased over time under constant shear when the mucus concentration was high. In addition, intermittent interruption of shear forces caused further increases in mucus viscosity. The experimental conditions mimic disease-state-MCC (i.e., mucus hypersecretion and impaired ciliary function). Thus, the results match the high mucus viscosity found in respiratory disease patients. Inhibiting disulfide bonding and hydrophobic interactions between mucin molecules, which are authorized therapies for chest congestion, reduced the rheological behavior. The rheopectic behavior of respiratory mucus and its importance in MCC has been presented herein, and our experimental approach should facilitate drug discovery against respiratory diseases.

Atmospheric Pressure Cold Plasma Modification of Basil Seed Gum for Fabrication of Edible Film Incorporated with Nanophytosomes of Vitamin D3 and Tannic Acid

The purpose of this work was to first investigate the impact of cold plasma (CP) treatment, performed at various times (0-30 min), on the characteristics of basil seed gum (BSG), as well as the fabrication of functional edible films with the modified BSG. FT-IR spectra of CP-treated BSG revealed change at 1596 and 1718 cm-1, indicating the formation of carbonyl groups. Both untreated and CP-modified BSG dispersions showed shear-thinning behavior with a higher apparent viscosity for the CP-modified dispersions at studied temperatures. Untreated BSG dispersion and the one treated by CP for 10 min revealed time-independent behavior, while those treated for 20 and 30 min showed a rheopectic behavior. CP-modified BSG dispersion had higher G', G″, and complex viscosity than untreated BSG. Higher contact angle for the CP-modified BSG suggested enhanced hydrophobic nature, while the surface tension was lower compared to the untreated BSG. SEM micrographs revealed an increase in the surface roughness of treated samples. Moreover, modified BSG was successfully used for the preparation of edible film incorporating tannic acid and vitamin D3-loaded nanophytosomes with high stability during storage compared to the free form addition. The stability of encapsulated forms of vitamin D3 and tannic acid was 39.77% and 38.91%, more than that of free forms, respectively. In conclusion, CP is an appropriate technique for modifying the properties of BSG and fabrication of functional edible films.

Microstructure and time-dependent behavior of composite NaMnt-kaolin gels: Rigid - flexible platelet interactions and configurations

Composite NaMnt (SWy-2)-kaolin (KGa-2) gels at more than 10 wt% solids with the NaMnt fraction ≥ 20% formed an open cellular microstructure. The flexible, nanosized NaMnt platelets formed the continuous structure with kaolin particles dispersed within it bonding with the NaMnt platelets. The morphology adopted by the single layer NaMnt platelets is varied and complex producing a wide range of unique particle interaction configurations. Many acquired a curved shape surface with curled edges. Some of the platelets developed elongated string-like features made by the curling of edges and may have 3–5 of these strings for bonding. Kaolin particles are rigid and multilayered, and most have a platelet morphology. A common NaMnt-kaolin bonding configuration observed was the face at the curled-edge of NaMnt platelet resting on the face of the kaolin particle. A 15.5 wt% gel with a 1:2 mass ratio of NaMnt to kaolin was demonstrated to display both thixotropic and rheopectic behavior. A stepdown shear rate method was used to evaluate the structural development kinetics at 10 s−1 of this gel commencing with the structural state sheared to equilibrium at 1000 s−1. The Leong model described this kinetics well and found that the structural development characteristic time to be very fast, in seconds. The ageing behavior was also evaluated without the imposition of a constant shear. The yield stress increase continued for weeks and months for the 2:1 kaolin to NaMnt composite gels at 15.5 and 10.7 wt% solids. The characteristic time of the structural development process was much longer, in days. Upon reducing the NaMnt content from 33.3% to 20%, the 10.8% wt% gel became weakly time-dependent with a marginal yield stress. A continuous structure cannot be formed immediately upon the cessation of shear due to an inadequate NaMnt platelet concentration.

Fresh state properties of lime mortars with foam glass dust

Fine glass waste has been found to be a suitable addition to lime mortars because of the high amorphous content. The behavior of fresh air lime mortars and natural hydraulic lime mortars modified by foam glass dust is assessed with the purpose of exploring a new application of this waste dust as lime mortar admixture. The rheological parameters were correlated with relative density measurements, water retention abilities of mortars and air content in mortars. The effect of foam glass dust was found to be dosage-dependent. The fresh mortars behave generally as Hershel–Bulkley fluids with an evolution of the rheological parameters with admixture content. The replacement of lime by foam glass dust caused a reduction in mixing water reducing the yield stress simultaneously; however, the viscosity of the resulting mortars slightly increased. A change in behavior of mortars from shear-thickening to shear-thinning was observed. The natural hydraulic lime based mortars showed a gradual change from thixotropic to rheopectic behavior with increasing glass dust addition. The foam glass dust appears to be well suited to air lime plaster mixtures used in machine thin-layer rendering due to its plasticizing properties, and ability to increase water retention and reduce air content in the mortars.

Rheopectic Behavior for Aqueous Solutions of Megamolecular Polysaccharide Sacran.

The rheopectic behavior of sacran aqueous solutions, a natural giant molecular polysaccharide with a molecular weight of 1.6 × 107 g/mol, was investigated. When a low shear was applied to 1.0 wt.% sacran solution, the shear viscosity increased from 7.2 to 34 Pa·s. The increment in the viscosity was enhanced as the shear rate decreased. The shear viscosity was independent of the time at a shear rate of 0.8 s−1; simultaneously, thixotropic behavior was observed at shear rates higher than 1.0 s−1. A crossover was observed at 0.15 wt.% for the concentration dependence of both the viscosity increase and zeta potential, which was the vicinity of the helix transition concentration or gelation concentration. It was clear that the molecular mechanism for the rheopexy was different at lower and higher regions of the crossover concentration.

Flow and viscoelastic behavior of Iranian starch-based low calorie dessert (Palda)

This paper is an attempt to study the rheological properties of low-calorie Iranian starch-based dessert (Palda). Sorbitol and carrageenan (kappa, iota and kappa-iota types) were used to produce low-calorie Palda dessert. Time-independent behavior of samples was well described by the Mizrahi–Berk plastic model. All samples showed time-dependent thixotropic or rheopectic behavior, depending on the type and concentration of carrageenan. In addition, the time dependency data fitted well with Weltmann model. The oscillatory shear tests showed that all samples were typical of gel structure with G′ values (elastic behavior) higher than G″ ones (viscous), while showing little dependency upon frequency. The syneresis (%) decreased as a result of the increase in the amount of carrageenan (especially ι-carrageenan). Sensory analysis showed that the sample containing 0.5% κ-carrageenan could be considered as the best formulation.

Effect of Ethonium Adsorption on Structure Formation in Nanosilica Dispersions

Adsorption of ethonium on silica surface strongly affects the particle size distribution, stability and rheological properties of aqueous dispersions of fumed silica. The Sshape of isotherm of ethonium adsorption on nanosilica suggests the multilayer adsorption. The adsorption of ethonium leads to changes in the shape of the pHdependence of the zeta-potential and a significant increase in the particle sizes in the aqueous dispersions of silica. A marked increase in the colloidal stability is observed for the dispersions at silica concentration of 5 wt.%, while for 1 wt.% dispersions the ethonium presence almost does not affect the stability. The rheological properties of the dispersions depend on the ethonium concentration, and the maximum values of the viscosity and rheopectic behavior are observed at ethonium concentration of 0.1-0.3 wt.%

The Effect of Mechanical Activation of Lime Putty on Properties of the Autoclaved Calcium Hydrosilicate Materials

The lime putty is a non-Newtonian fluid that can be either thixotropic or rheopectic depending on burning process of the lime, the presence of the quartz sand and other parameters. One of the most important lime putty characteristics is its plasticity which affects its workability and use. It is possible to increase the lime putty plasticity by mechanical activation. This work focuses on the effect of the mechanical activation of the lime putty on its rheological behavior and on properties of lime hydrosilicate autoclaved materials. Fresh lime putty was activated in a high-speed mixer at 1000 RPM for 1, 3, 5 and 10minutes. Non-activated lime putties show rheopectic behavior. Rheopectic behavior becomes slightly more distinct after 1min. of activation and then less distinct with increasing time of activation. After 10min. of activation, the system shows no time-dependent properties, nor even slight thixotropic behavior. This trend can be related to process where smaller and smaller aggregates are fragmented in the suspension. The hydrosilicate materials were prepared in two series from quicklime and finely ground sand with the ratio C/S 0.85, under hydrothermal conditions. The amount of xonotlite in hydrosilicate material increases with activation time as the increased amount of portlandite particles retards the reaction. 11.3 Å tobermorite crystallizes more slowly and formation of xonotlite is accelerated.

The Role of Aging on Rheological Properties of Lime Putty

The role of aging on rheological properties of lime putties was investigated by rotational rheometry, scanning electron microscopy and particle size distribution analyzes. Disaggregation of large clusters during aging and resulting microstructural enrichment of micron-sized particles was found to be one of the possible reasons for the continuous increment of plasticity and yield stress of lime putties during long-term aging. The extent of thixotropic and rheopectic behavior is affected by both calcination process and microstructure development during aging.

A study on rheological characteristics of roller milled fenugreek fractions.

Fenugreek seeds were fractionated by roller milling to get various fractions. The roller milled fractions and whole fenugreek flour (WFF) were evaluated for the flow behavior and time-dependent flow properties using a rotational viscometer at the temperatures of 10-60 (0)C. The samples subjected to a programmed shear rate increase linearly from 0 to 300s(-1) in 3min and successive decrease linearly shear rate from 300s(-1) to 0 in 3min. The roller milled fractions and WFF paste exhibited non-Newtonian pseudoplastic behavior. Difference in hysteresis loop area was observed among the roller milled fractions and WFF, being more noticeable at lower temperatures. Power law and Casson models were used to predict flow properties of samples. The power law model described well the flow behavior of the roller milled fractions and WFF at temperatures tested.Except flour (FL) fraction, consistency coefficient, m, increased with thetemperature both in the forward and backward measurements. The roller milled fractions and WFF exhibited rheopectic behavior that increased viscosity with increasing the shear speed and the temperature. For all the sample tested, initial shear stress increased with increase in shear rate and temperature.

Determination of rheological behaviour of wine lees

Abstract This study deals with the rheological properties of wine lees. Samples of wine lees of the Saint Laurent variety were used in this experiment. The investigated wine lees arose in the process of production red grape wine in 2013 (Czech Republic). At first, the chemical background was determined. The chemical background includes the following chemical parameters: total acidity, pH, alcohol content, reduced sugars, free SO2, total SO2, and volatile acid. In the second phase of the study, physical properties were determined. Specifically, a sample of wine lees was subjected to rheological tests. These tests consisted in determination of dependence of dynamic viscosity on the temperature, hysteresis loop tests, dependence of dynamic viscosity on the time and step-down in the shear rate test. The experiment demonstrated that the dynamic viscosity increased with increased temperature – this phenomenon is caused by thermolabile proteins – and the wine lees has rheopectic behaviour; the degree of rheopexy was found to rise with the increasing temperature.

Comparative studies of xanthan, guar and tragacanth gums on stability and rheological properties of fresh and stored ketchup

The effect of three different hydrocolloids (Tragacanth gum, Guar gum, Xanthan gum) was compared on stability, rheological and sensory properties of fresh and 6 months stored tomato ketchup. Gums were added at five levels (0, 0.2, 0.25, 0.3, 0.35 g/100 g (w/w)) respectively to ketchup prepared with starch (0.5 g/100 g (w/w)). Statistical analysis showed gums concentration and type of gums and storage caused a significant effect on rheology and syneresis. According to results, as gums concentration was increased, a decrease occurred in syneresis values and an increase occurred in viscosity, spreadability and yield stress. Xanthan gum created the most overall texture acceptability, structure strength and links strength approximately in both fresh and stored samples in lower concentration than Guar gum and Tragacanth gum. While Xanthan gum or Guar gum created thixotropic behavior, sample containing Tragacanth gum exhibited rheopectic behavior. As concentration of Tragacanth gum was increased, a decrease occurred in rheopectic behavior. In level of 0.25 %, Xanthan gum was better than two other gums in stability, overall texture acceptability, yield stress, structure strength, spreadability, links strength in fresh and stored samples and retaining of thixotropic behavior at the end of storage, while Tragacanth gum created greater viscosity at shear rate of 500 than other two gums in fresh and stored samples that could be related to thermodynamic incompatibility between starch and this gum.

Thixotropy and rheopexy of muscle fibers probed using sinusoidal oscillations.

Length changes of muscle fibers have previously been shown to result in a temporary reduction in fiber stiffness that is referred to as thixotropy. Understanding the mechanism of this thixotropy is important to our understanding of muscle function since there are many instances in which muscle is subjected to repeated patterns of lengthening and shortening. By applying sinusoidal length changes to one end of single permeabilized muscle fibers and measuring the force response at the opposite end, we studied the history-dependent stiffness of both relaxed and activated muscle fibers. For length change oscillations greater than 1 Hz, we observed thixotropic behavior of activated fibers. Treatment of these fibers with EDTA and blebbistatin, which inhibits myosin-actin interactions, quashed this effect, suggesting that the mechanism of muscle fiber thixotropy is cross-bridge dependent. We modeled a half-sarcomere experiencing sinusoidal length changes, and our simulations suggest that thixotropy could arise from force-dependent cross-bridge kinetics. Surprisingly, we also observed that, for length change oscillations less than 1 Hz, the muscle fiber exhibited rheopexy. In other words, the stiffness of the fiber increased in response to the length changes. Blebbistatin and EDTA did not disrupt the rheopectic behavior, suggesting that a non-cross-bridge mechanism contributes to this phenomenon.

Rotational Rheology of A356 Semi-Solid Alloy at Low Solid Fractions

The main goal of investigations on semi-solid metal processing is to produce complex parts with enhanced mechanical properties. Flow behavior and die filling in semi-solid processing is an intrest area of researchers. A comprehensive understanding of the behavior of the under investigation metallic slurry is the design key of a successful manufacturing process. In this way the material’s transient response is very important for understanding of the rheological properties and also further commercial development of the process. The material used in this research is an Al-Si alloy which is widely used in automotive and aerospace applications. The experiments were conducted using a Searl rheometer which is specially designed for high temperature rheological measurements. For rheological tests of semi-solid alloy in different solid fractions, the isothermal holding and shear rate step change experiments were examined. Using practical rheological results, a single phase thixotropic model has been derived and adopted with measurements. The investigated alloy behavior was obviously thixotropic which is quantified in a theoretic model. Also instantaneous rheopectic behavior was observed for this alloy. The state of the microstructure has been applied through a structural parameter. The presented model for A356 alloy fits well with the experiments.

Physicochemical and functional characterization of the collagen-polyvinylpyrrolidone copolymer.

Collagen-polyvinylpyrrolidone (C-PVP) is a copolymer that is generated from the γ irradiation of a mixture of type I collagen and low-molecular-weight PVP. It is characterized by immunomodulatory, fibrolytic, and antifibrotic properties. Here, we used various physicochemical and biological strategies to characterize the structure, biochemical susceptibility, as well as its effects on metabolic activity in fibroblasts. C-PVP contained 16 times more PVP than collagen, but only 55.8% of PVP was bonded. Nevertheless, the remaining PVP exerted strong structural activity due to the existence of weak bonds that provided shielding in the NMR spectra. On SEM and AFM, freeze-dried C-PVP appeared as a film that uniformly covered the collagen fibers. Size analysis revealed the presence of abundant PVP molecules in the solution of the copolymer with a unique dimension related to macromolecular combinations. Calorimetric analysis showed that the copolymer in solution exhibited structural changes at 110 °C, whereas the lyophilized form showed such changes at temperatures below 50 °C. The copolymer presented a rheopectic behavior, with a predominant effect of the collagen. C-PVP had biological effects on the expression of integrin α2 and prolyl-hydroxylase but did not interact with cells through the collagen receptors because it did not inhibit or slow contraction.