Thixotropic Behavior Research Articles

New insight on rheology of self-consolidating earth concrete (SCEC)

Self-consolidating earth concrete (SCEC) is a novel alternative to facilitate the earth-based construction. A new concrete-equivalent mortar (CEM) approach with constant excess-paste (EP) thickness was proposed to evaluate the rheological and thixotropic properties of various SCEC mixtures proportioned with different clay and superplasticizer types. The use of non-esterified polycarboxylate (NE-PC) and sodium polynaphtalene superplasticizer types in combination with a finer clay type led to a thixotropic behavior. Mixtures made with sodium hexametaphosphate resulted in significantly high yield stress and plastic viscosity values. The rheological properties were mainly controlled by the admixture type, followed by the type and content of clay and water-to-powder ratio (W/P). Empirical models were proposed to predict the rheology of earth-based paste, CEM, and SCEC mixtures using the governing key mixture parameters, including the fineness of the powder constituents (i.e., clay, silt, and cement), water content, EP thickness, paste volume, and packing of the granular skeleton.

Using Fibre recovered from face mask waste to improve printability in 3D concrete printing

Surgical face mask usage has rapidly increased in the last two years due to the COVID-19 pandemic. This generates vast amounts of plastic waste, causing significant risks to the ecosystem. Thus, this study assesses the potential of using recycled fibre from face mask waste as fibre reinforcement in 3D concrete printing (3DCP) applications to improve printability while reducing landfill waste. The effect of recycled fibre from waste face masks on the rheological characteristics of printable mixes and the mechanical performance of printed elements was evaluated for different contents of shredded face masks (i.e., 1% and 2% by vol). The rheological properties like static and dynamic yield strengths, apparent viscosity, and thixotropic behaviour, along with compressive and flexural strength, were evaluated for 3D printed specimens and mechanical properties were compared to their mould-cast counterparts. Further, the variation in the interlayer bond strength and porosity due to different fibre dosages was also investigated. In addition, a comparative study on the fresh and hardened properties was performed for the printable mixes with polypropylene (PP) fibres and face masks. The addition of face masks significantly improved the rheological properties with good extrudability and buildability for all the dosages. Compared to face masks, mixes with PP fibres showed poor extrudability with higher fibre dosages. The compressive strength was increased by 41% for a 1% dosage of face masks when compared to the unreinforced concrete. Furthermore, the flexural strength when tested along the weaker interface, showed an increase of 74% and 82% for the addition of 1% and 2% face mask content. The interlayer bond strength of 1% face mask content showed 21% improvement and was observed to have the highest surface moisture content. The mechanical performance of face masks and PP fibres are observed to be comparable for 1% dosage. The mechanical properties of printed and mould-cast specimens were also observed to be similar.

Fractional modelling of salinity/temperature-dependent shear rheological behavior including stress overshoot for bentonite clay suspensions

Based on the experimental studies of thixotropic behavior of bentonite clay suspensions at different salinities and temperatures, a complex nonlinear rheological phenomenon was firstly discovered in our previous work [Yin et al., Eng. Geol, 295(2021): 106,435], which exhibits multi-stage stress responses including stress overshoot and power-law flow behaviors. Motivated from this observation, in this work, a variable-order viscoelastic element and a novel viscoplastic element are combined to simultaneously characterize the complex multi-stage stress response of suspensions, where the former is used to describe stress overshoot and the latter is applied to characterize power-law flow behavior. The model is further employed to describe salinity/temperature-dependent rheological behavior of suspensions, where the criteria for model parameters are established. The results indicate that fractional order can be regarded as an index to identify the flow behavior where the order evolution exhibits three stages corresponding to the multi-stage flow behavior of bentonite suspensions. Applications of the proposed fractional model at different salinities and temperatures further validate the predictability and efficiency.

RheologyNet: A physics-informed neural network solution to evaluate the thixotropic properties of cementitious materials

Thixotropic behaviors can be predicted by rheological partial differential equations (PDEs) of cementitious materials. The ability to solve the rheological PDEs of viscous fluids accurately and efficiently has become an emerging interest in research. However, due to the growing number of parameters in rheological constitutive equations and the non-ideal behavior of materials from experiments, solving the rheological PDEs becomes computationally costive and error-prone. We propose a physics-informed neural network (PINN)-based framework, RheologyNet, as a surrogate solution to predict the general thixotropic behavior of cementitious materials. The complex PDEs are embedded in the well-designed RheologyNet architecture to link macroscopic viscous flow behaviors and microstructural changes. Numerical experiments suggested that RheologyNet can accurately and efficiently predict the rheological properties of cementitious materials compared to the traditional Fully-connected Neural Network (FNN) and mechanistic Finite Element Analysis (FEA). Particularly, RheologyNet demonstrated great promise for simulating history-dependent thixotropic behaviors.

Rheological studies of cellulose nanocrystal/dimethyl sulfoxide organogels

Cellulose nanocrystals (CNCs)/H2O gels have received significant interest in various applications for the past decades. And yet CNCs organogels, which are important to their wider application, are less explored. In this work, CNCs/Dimethyl sulfoxide (DMSO) organogels are carefully investigated by rheological methods. It is found that metal ions also can facilitate the organogel formation as in hydrogel. Charge screening and coordination effects play vital roles in the organogel formation and their mechanical strength. CNCs/DMSO gels with different cations display similar mechanical strength, while CNCs/H2O gels show increasing mechanical strength with the increasing valence of cations. It seems that the coordination between cations and DMSO alleviate the influence of valence on gel mechanical strength. Due to weak, fast and reversible electrostatic interactions among CNCs particles, both CNCs/DMSO and CNCs/H2O gels show instant thixotropic behavior, which may find some interesting applications in the field of drug delivery. The morphological changes observed in polarized optical microscope appear to be consistent with rheological results.

Optimization of guanosine-based hydrogels with boric acid derivatives for enhanced long-term stability and cell survival.

Tissue defects can lead to serious health problems and often require grafts or transplants to repair damaged soft tissues. However, these procedures can be complex and may not always be feasible due to a lack of available tissue. Hydrogels have shown potential as a replacement for tissue grafts due to their ability to support cell survival and encapsulate biomolecules such as growth factors. In particular, guanosine-based hydrogels have been explored as a potential solution, but they often exhibit limited stability which hampers their use in the biofabrication of complex grafts. To address this issue, we explored the use of borate ester chemistry and more complex boric acid derivatives to improve the stability and properties of guanosine-based hydrogels. We hypothesized that the aromatic rings in these derivatives would enhance the stability and printability of the hydrogels through added π-π stack interactions. After optimization, 13 compositions containing either 2-naphthylboronic acid or boric acid were selected. Morphology studies shows a well-defined nanofibrilar structure with good printable properties (thixotropic behaviour, print fidelity and printability). Moreover, the pH of all tested hydrogels was within the range suitable for cell viability (7.4-8.3). Nevertheless, only the boric acid-based formulations were stable for at least 7days. Thus, our results clearly demonstrated that the presence of additional aromatic rings did actually impair the hydrogel properties. We speculate that this is due to steric hindrance caused by adjacent groups, which disrupt the correct orientation of the aromatic groups required for effective π-π stack interactions of the guanosine building block. Despite this drawback, the developed guanosine-boric acid hydrogel exhibited good thixotropic properties and was able to support cell survival, proliferation, and migration. For instance, SaOS-2 cells planted on these printed structures readily migrated into the hydrogel and showed nearly 100% cell viability after 7days. In conclusion, our findings highlight the potential of guanosine-boric acid hydrogels as tissue engineering scaffolds that can be readily enhanced with living cells and bioactive molecules. Thus, our work represents a significant advancement towards the development of functionalized guanosine-based hydrogels.

Rheological Behavior of the A356 Alloy in the Semisolid State at Low Shear Rates

To control the semisolid processing of aluminum alloys produced by the additive manufacturing technique, an exhaustive knowledge of their rheological behavior is required. In the semisolid state, metallic materials can show rheological characteristics similar to those of polymers, so semisolid state shaping is one of the currently considered routes for additive manufacturing with metallic materials. In this work, an approximation of the rheological control of the A356 aluminum alloy for its subsequent 3D manufacturing was carried out at a very low shear rate. A continuous cooling rheometer was designed and used, evaluating the influence of different process parameters on the viscosity variation of the aluminum alloy in the semisolid state. The results show an anomalous flow variation, indicating dilatant, and not thixotropic behavior, for very low shear rates.

High-performance, printable quasi-solid-state electrolytes toward all 3D direct ink writing of shape-versatile Li-ion batteries

The era of miniaturized and customized electronics requires scalable energy storage devices with versatile shapes. From the perspective of manufacturing, direct ink writing (DIW)-based 3D printing has attracted unprecedented interest, paving the way to demonstrate micro-batteries with design freedom and outstanding performance. Despite demands for all-printed Li-ion batteries with maskless processing, most of the efforts have been dedicated to developing printable active electrodes or building the 3D architecture, remaining challenges in both manufacturing and printable materials toward form-free, all 3D DIW printed Li-ion batteries. Herein, we present all 3D DIW printed, scalable shape versatile Li-ion batteries (ADP-LIBs) with high-performance, printable gel polymer electrolytes (GPEs). The rheological optimization of DIW printable inks for solid-state current collectors, electrodes, electrolytes, and packaging enables us to demonstrate well-defined shape-versatile ADP-LIBs with reliable extrusion. In particular, UV-curable polydimethylsiloxane (PDMS) and ethoxylated trimethylolpropane triacrylate (ETPTA) monomers provide thixotropic fluid behaviors and a mechanical framework in the quasi-solid-state electrolytes, respectively, which results in high-throughput and mechanically robust printed electrolyte layers. Our ADP-LIBs demonstrate a great deal of promise as a realistic solution for powering the target applications on-demand with aesthetic versatility, free-form factors, and competitive electrochemical performance.

GPU-accelerated transient thermo-hydraulic simulation of weakly compressible restart flow of a non-Newtonian fluid in a long-buried hot oil pipeline

For the complex transient thermo-hydraulic restart process of a long-buried hot oil pipeline, it takes a long time to solve the restart simulation model, which cannot meet the requirements of rapid restart prediction and assessment. The modern GPU is specialized for compute-intensive and massively parallel computation, and it has great potential to accelerate transient thermo-hydraulic restart simulation. According to the computational characteristics of restart model solutions, four types of GPU parallel strategies, from the mapping of grids to the convergence judgment of the discrete equation solution, are combined to accelerate the whole process of a transient thermo-hydraulic restart simulation. The results indicate that the total computation time of the transient thermo-hydraulic simulation is reduced from 185.4 min to 8.8 min, corresponding to an acceleration rate of 21.1, which exhibits a good acceleration effect for a single GPU and is beneficial to the rapid assessment of restart schemes. Based on the GPU-accelerated numerical results, the complex transient thermo-hydraulic restart process with the changing soil temperature field, the non-Newtonian thixotropic behavior of crude oil and flow pattern evolution, is investigated. The analysis reveals that the dominant influencing factors of the restart process vary with the restart time, and the flow pattern evolution plays an important role in the thermo-hydraulic characteristics of the restart process.

Thixotropic deformation behavior, rapid spheroidization and solid-liquid homogenization of semi-solid Al0.8Co0.5Cr1.5CuFeNi HEA with multilevel microstructure

In this paper, powder metallurgy-rapid heating and isothermal-holding (PMRHI) method was proposed to realize the rapid spheroidization and suppression of solid grain coarsening in semi-solid Al0.8Co1.5Cr0.5CuFeNi HEA. The thixotropic behavior and microstructure after PMRHI were investigated. Shear thinning effect exists during thixotropic deformation. The bimodal characteristics of flow stress degenerates with the proceeding of solid grain sliding (SS) and flow of liquid incorporating solid grains (FLS), indicating solid-liquid homogeneity and stable thixotropic deformation. The solid-liquid distribution homogeneity can suppress voids and hot tearing caused by liquid film channels. In multilevel semi-solid microstructure, the orientation relationship between solidified liquid phase and solid grain is approximately Kurdjumov-Sachs relationship, fine Al-Ni and Fe-Cr rich spinodal plates and nano Cu precipitates are formed in solid grain. The rapid spheroidization is realized due to initial dispersed powder metallurgy microstructure. After the steady thixotropic deformation of 1225 °C /0.05 s−1, mechanical properties were significantly improved.

Antimicrobial Formulation of a Bacterial Nanocellulose/Propolis-Containing Photosensitizer for Biomedical Applications

With the aim of contributing to the development of more efficient materials for wound care, new topical formulations based on bacterial nanocellulose (BNC) hydrogels containing propolis were produced. Characterizations confirmed the incorporation of propolis into the BNC matrix, maintaining its structure and properties. Rheological analysis confirmed that the hydrogels showed thixotropic behavior appropriate for topical application. Chromatographic profiles showed sustained release of propolis biomarkers for at least 20 h. The formulations did not present mutagenicity. For application in photodynamic inactivation (PDI), BNC/propolis hydrogels were prepared with the photosensitizers methylene blue (MB). Spectroscopy and confocal fluorescence microscopy confirmed the interaction of MB and propolis in BNC hydrogels, as well as the formation of a new composite material. In the antibacterial assays, formulations containing MB and propolis significantly reduced Staphylococcus aureus growth. In the presence of light, BNC/MB hydrogels completely inhibited the microorganism. Therefore, the results suggest potential materials for the prevention or treatment of Staphylococcus aureus infections in wounds.

Rheological properties of binary mixtures of Lepidium perfoliatum seed gum and xanthan gum

BackgroundIn this work, viscoelasticity, flow behaviour, thixotropy and thermo-rheological properties of binary mixtures of Lepidium perfoliatum seed gum (LPSG), as an emerging food gum, and xanthan gum (XG) at various blending ratios of 100:0, 75:25, 50:50, 25:75 and 0:100 were studied for a depth insight into their interaction. FTIR analyses were also done to investigate the interaction between the XG and LPSG.ResultsFTIR results indicated the hydrogen bond formation between the hydrocolloids. At the linear viscoelastic region (LVE), XG-rich blends exhibited higher tan δLVE and τy, but lower τf. The values of apparent viscosity (ηa) and complex viscosity (η*) diminished with increasing shear rate/frequency, and XG and LPSG individual dispersions showed the greatest and the lowest values, respectively. Based on the extended Cox-Merz rule, a greater shift factor (α) is observed as the ratio of LPSG in the mixed gel increases. At higher fraction of LPSG, except for the fraction of 75%, the thixotropic behaviour appears to be less pronounced. The recovery parameter (R, %) obtained from in-shear structural recovery test decreased with increase in LPSG fraction. The results of non-isothermal kinetic analysis revealed higher thermodynamic incompatibility and immiscibility of LPSG-XG system in the presence of 75% XG. Moreover, according to the results of Cole–Cole plot, the greatest compatibility of LPSG and XG blends was for LPSG75-XG25 sample (β = 0.87), whereas the worst miscibility was found to be for LPSG25-XG75 one (β = 1.02).ConclusionsDifferent rheological properties could be obtained by blending various ratios of LPSG and XG, which in some ratios synergistic behaviour was observed. The wide variety of rheological properties obtained may be appropriate for the use of LPSG-XG mixtures in food industries and pharmaceutical and biomedical applications.Graphical

Thixotropic evaluation of a highly-workable and a flowable concrete made with Rice Husk Ash

Thixotropic behaviour of a Highly-Workable Concrete (HWC) and a Flowable Concrete (FC) containing varying volumetric dosages (10%, 15%, and 20%) of Rice Husk Ash (RHA) has been investigated using a coaxial cylinder concrete rheometer. The parameters to evaluate the thixotropic behaviour were RHA dosage and grade of concrete. The experiments showed that concrete exhibits a high degree of thixotropy when proportioned with a binary binder containing RHA. The influence of RHA on thixotropy was more pronounced in the HWC than in the FC. The measured thixotropic indices for the HWC, i.e., initial peak stress, thixotropic index, structuration rate, structure parameter, and reduction in apparent viscosity, increased with the increase in RHA dosage, compared to the control concrete. However, the influence of RHA in the case of the FC on all the thixotropic parameters was not significant. As the concrete grade increased from M − 30 to M − 50 in the HWC, thixotropic parameters in the RHA blended concrete increased significantly compared to the control concrete.

Design and Characterization of Lipid-Surfactant-Based Systems for Enhancing Topical Anti-Inflammatory Activity of Ursolic Acid.

Skin inflammation is a symptom of many skin diseases, such as eczema, psoriasis, and dermatitis, which cause rashes, redness, heat, or blistering. The use of natural products with anti-inflammatory properties has gained importance in treating these symptoms. Ursolic acid (UA), a promising natural compound that is used to treat skin diseases, exhibits low aqueous solubility, resulting in poor absorption and low bioavailability. Designing topical formulations focuses on providing adequate delivery via application to the skin surface. The aim of this study was to formulate and characterize lipid-surfactant-based systems for the delivery of UA. Microemulsions and liquid crystalline systems (LCs) were characterized by polarized light microscopy (PLM), rheology techniques, and textural and bioadhesive assays. PLM supported the self-assembly of these systems and elucidated their formation. Rheologic examination revealed pseudoplastic and thixotropic behavior appropriate, and assays confirmed the ability of these formulations to adhere to the skin. In vivo studies were performed, and inflammation induced by croton oil was assessed for response to microemulsions and LCs. UA anti-inflammatory activities of ~60% and 50% were demonstrated by two microemulsions and 40% and 35% by two LCs, respectively. These data support the continued development of colloidal systems to deliver UA to ameliorate skin inflammation.

Enhanced Thermal Insulation and Mechanical Strength of Fiberglass Porous Ceramics via Adjustment of the Structure of Pores

Fiberglass porous ceramics were prepared via a foam-gelcasting method. The relationship between the rheology of the slurries and the structure of the specimens was investigated. The results show that when the content of the dispersant was 0.25 wt %, the slurries exhibit excellent fluidity. The thixotropic behavior of the slurries was strongly influenced by the content of the foam stabilizer agent and solid content. Furthermore, as the fluidity of the foaming slurries increased, the size of the pores increased. At the same time, the thickness of the pore walls decreased gradually. In addition, promoting the uniform distribution of the pore size by improving the thixotropic behavior of the foaming slurries was beneficial. The optimal foaming slurry was composed of 65 wt % fiberglass, 0.25 wt % dispersant, and 0.1 wt % foam stabilizer agent. After calcination at 750 °C, fiberglass porous ceramics with 78.3% porosity, 2.2 MPa compressive strength, and 0.11 W m–1 K–1 thermal conductivity were obtained.

Thermophysical properties and stabilization mechanism of nano- and microfluids with [Ni5(μ5-pppmda)4Cl2] metal string complex particles

The results of thermophysical properties studies and stabilization of nano- and microfluids prepared on the basis of glycerol aqueous solutions are presented. The results of determination of thermal conductivity, rheology, interfacial tension and stability of the studied solutions are presented. Cu, Ni and Al nanoparticles were used for the preparation of nanofluids, and microparticles of the metal-string complex [Ni5(μ5-pppmda)4Cl2] synthesized in laboratory conditions were used for the preparation of microfluids. It was shown that the Ni5 microfluid has a higher stability than the studied nanofluids due to the formation of hydrogen bonds, lower density of microparticles and the formation of ensembles of particles whose sizes are determined by the buoyancy conditions. The rheology of Ni5 microfluids exhibiting thixotropic behavior is also significantly different. The investigated Ni5 microfluids exhibited almost the same increase in thermal conductivity compared to the base fluid as the nanofluids. It is shown that the increase in thermal conductivity of the microfluids is related to the single-crystal structure of the used microparticles. An equation predicting a 10-fold increase in thermal conductivity for Ni5 nanofluid solutions as compared to microfluids is proposed. Keywords: nanofluid; microfluid; thermal conductivity; viscosity; stability.

Evaluation of thixotropic behaviors of tailings pastes as a function of solids concentration

Evaluation of thixotropic behaviors of tailings pastes as a function of solids concentration

Hydrothermal and mass aspects of MHD non-Darcian convective flows of radiating thixotropic nanofluids nearby a horizontal stretchable surface: Passive control strategy

Numerous rheological examinations attested that many products employed frequently in our daily life exhibit a thixotropic rheological behavior with a shear-thinning tendency (e.g., toothpaste, hair gels, ketchup, gypsum, and paints). Motivated by the importance of nanofluids in the thermal and mass transfer processes and their rheological trends, this article aimed to analyze convective boundary layer flows of radiating thixotropic nanofluids over a horizontal stretching surface by considering the retardational influences of Darcy-Forchheimer and Lorentz forces and invoking the effective contribution of Brownian and thermophoresis diffusions in the energy and concentration equations. By adopting the boundary layer approximations along with the zero mass flux and convective conditions, the conservation equations of the present non-homogeneous nanofluid flow model are derived mathematically in the form of partial differential equations (PDEs) based on Buongiorno's approach. After converting the leading PDEs into a set of nonlinear coupled ordinary differential equations (ODEs) via feasible local similarity alterations, the resulting highly nonlinear system of governing ODEs is then solved numerically using an efficient differential quadrature algorithm. As findings, it is found that the thixotropy feature reinforces the nanofluid motion. Besides, the significant impact of the radiative term is noticed in the heat flux rate. In contrast, the induced Darcy-Forchhemier and Lorentz forces impact unfavorably on the nanofluid flow and consequently alter the intensity of drag forces. Further results are provided also graphically and tabularly.

Effect of metakaolin utilization ratio and loop method-pre-shearing process variation on rheological properties of cementitious systems having different C3A content

Thixotropic behavior, which directly affects the fresh state properties of cementitious systems such as pumpability, compressibility and hydrostatic mold pressure, is determined by applying the loop method, step change and constant shear rate. This behavior is seriously affected by parameters such as the type, amount and fineness of the binder and the process applied in rheological measurements. In this study, the effect of cement C3A content, metakaolin utilization ratio, resting time of the mixture, pre-shear rate and applying pre-shear rate on the thixotropic behavior of the mixtures at the beginning and 20th-minutes were investigated. For this purpose, 4 types of cement having different C3A contents (2.13%, 3.60%, 6.82% and 9.05%) were used. By testing each of the 4 cements (2.13%, 3.60%, 6.82% and 9.05%) for 5 conditions (no metakaolin, 3%, 6%, 9% and 12% metakaolin), a total of 20 mixtures were prepared. For each cement type, 0, 3, 6, 9 and 12% of the total binder volume was replaced with metakaolin. The loop method was used to determine the rheological parameters. According to the results, irrespective of all parameters examined, the structural build-up area values were higher than the structural breakdown ones in the mixtures and the structure formation that occurred after 20 min was mostly reversible. It was determined that rheological parameters, structural build-up area value and rate of reversible structure formation increased with the increase in cement C3A content and metakaolin utilization rate. The increase in the initial dynamic yield stress values of the mixtures with the increase of the cement C3A ratio was more pronounced in the case where the measurement is made without waiting immediately after the pre-shear application. The effect of C3A content on dynamic yield stress and viscosity values was more pronounced with an increasing pre-shear rate. The opposite was observed for the structural build-up area values.

Physical, structural, and rheological properties of γ-cyclodextrin metal-organic framework emulgels

AbstractThis study aimed to develop and characterise emulgels based on aqueous γ-cyclodextrin metal-organic framework (γ-CD-MOF) solutions with sunflower oil in the presence of Tween 20, 40, and 60 emulsifiers. The main physical, structural, and rheological properties of γ-CD-MOF emulgels were investigated. The emulgels prepared with 5% and 10% γ-CD-MOF were durable. The X-ray diffraction patterns proved the existence of β polymorph type lipid crystals. The rheological analyses showed that the gel strength increased with increased γ-CD-MOF concentration, and thixotropic behaviour was observed depending on the gel strength at 10 °C. In addition, the samples were heat resistant proved by rheological temperature ramp tests. Finally, addition of the emulsifiers did not cause any change in the centrifuge stability and colour properties of the emulgels. These samples could be used to prepare different emulsion type food products.