Temperature-dependent Rheological Properties Research Articles

Computational Investigation of the Influencing Parameters on the Solidification of Thermoplastic Beryllium Oxide Slurry in a Cylindrical Shell

This article presents a computational study of the influencing parameters on the solidification of the thermoplastic beryllium oxide slurry in an annular forming cavity. The main purpose of this paper is to study the effect of cooling and casting conditions on the solidification of the BeO suspension by considering the temperature-dependent rheological and physical properties. The results of calculations of the Bingham–Papanastasiou rheological model with experimental data in the intervals of phase transitions with different casting rates of beryllium ceramics have been validated. The use of the regularization parameter made it possible to approximate the flow of the slurry at all levels of its shear rates as highly viscous, followed by a continuous transition to a solid state. The speed of heat removal from the molding during the solidification period is determined by the speed of movement of the slurry and the temperature field on which the width of the transition region depends. The process of solidification of the slurry mass has been evaluated by changing its heat flow distribution and density along the length of the concentric channel. The obtained model calculation results make it possible to control the casting process and eventually realize a uniform structure of castings.

Contact rheological DEM model for visco-elastic powders during laser sintering

Laser sintering is a widely used process for producing complex shapes from particulate materials. However, understanding the complex interaction between the laser and particles is a challenge. This investigation provides new insights into the sintering process by simulating the laser source and the neck growth of particle pairs. First, a multi-physics discrete element method (DEM) framework is developed to incorporate temperature-dependent contact rheological and thermal properties, incorporating heat transfer and neck formation between the particles. Next, energy transport by ray tracing is added to allow for computing the amount of laser energy absorbed during sintering. The DEM model is calibrated and validated using experimental data on neck growth and temperature evolution of particle pairs made of polystyrene and Polyamide 12. The findings show that the proposed DEM model is capable of accurately simulate the neck growth during the laser sintering paving the way for better controlling and optimizing the process.Graphical

Investigating the influence of temperature-dependent rheological properties on nanofluid behavior in heat transfer

Nanofluids are advanced heat transfer fluids whose performance is influenced by various thermo-physical properties, including nanoparticle volume fraction, base fluid, and temperature. Rheological mathematical models have been established by using empirical data in order to characterize these features as dependent on parameters such as volume fraction, base fluid composition, and temperature. These models have been integrated into transport equations. Nanofluids composed of metallic oxides (Al2O3, SiO2) and carbon nanostructures (PEG-GnP, PEG-TGr) dispersed in deionized H2O, with nanoparticle concentrations ranging from 0.025% to 0.1%, and temperatures between 30 °C and 50 °C, were utilized to investigate flow over thin needle. The rheological models contained transport equations include the partial differential equations. The transport equations were simplified through various transformations and then solved numerically. The results in form of velocity and temperature distributions were obtained, along with boundary layer parameters, Nusselt number and coefficient of skin friction. The present study contributes to the existing knowledge by elucidating the intricate relationship between nanoparticle volume fraction, base fluid properties, and temperature in nanofluid behavior.

3D printing concrete containing thermal responsive gelatin: Towards cold environment applications

Construction with cementitious materials via 3D printing requires a highly thixotropic behavior, which is a challenge for construction industry. In this work a facile and low-cost gelatin-modified thermal responsive smart cement paste formulation was developed for extrusion-based 3D printing in cold environments The paste's temperature-dependent rheological properties were characterised, and the underlying mechanism was explored. At room temperature, the modified paste presents similar rheological properties as the reference cement paste. After resting for 10 min at 5 °C, the modified cement paste has a yield stress of 1900 Pa which is 10 times that of the reference paste. Moreover, the mechanical properties of the modified paste are comparable to or higher than that of the reference paste at later age. Our approach may inspire a facile manipulation of paste rheology through temperature, which facilitates smartly controlled 3D concrete printings.

Thermosensitive Polymer Blend Composed of Poloxamer 407, Poloxamer 188 and Polycarbophil for the Use as Mucoadhesive In Situ Gel.

Herein, thermosensitive blends of poloxamer 407 (P407)/poloxamer 188 (P188)/polycarbophil (PCB) were developed in terms of maximized content of PCB (a mucoadhesive polymer) and desired temperature-dependent rheological properties of the blends as in situ gelling matrices. Maximizing PCB content while achieving the preferable rheological characteristics was accomplished through the Box–Behnken design. The quantitative effect of the polymer composition in the blends on the thermosensitive characteristics was evaluated using the fitted design model and the corresponding surface plots. The optimized P407/P188/PCB blend (OPT) was the mixture of 20.000, 7.349 and 0.595% (w/w) of P407, P188, and PCB, respectively. The thermosensitive micellization of OPT was investigated using differential scanning calorimetry which revealed an overlapping double endothermic peak caused by the temperature-induced micellization of pure micelles in co-existence with the micelles with attached PCB. Mixing PCB with the P407/P188 matrix promoted a more intense mucoadhesion of the blend. After incorporating metronidazole, a model hydrophilic drug, into OPT, the temperature-dependent characteristics of the hydrogel did not change. Metronidazole release from OPT was sustained by an anomalous mechanism. This optimal ternary hydrogel benefiting from thermosensitive gelling and mucoadhesive matrix might be used as a viable platform for mucoadhesive in situ gelling drug delivery.

Temperature Dependent on Mechanical and Rheological Properties of EPDM-Based Magnetorheological Elastomers Using Silica Nanoparticles.

Temperature is one of the most influential factors affecting the performance of elastomer matrix in magnetorheological elastomer (MRE). Previous studies have utilized silica as a reinforcing filler in polymer composite and as a coating material in MRE to improve the thermal stability of the base material. However, the usage of silica as an additive in the thermal stability of MRE has not been explored. Thus, in this study, the effect of silica as an additive on the temperature-dependent mechanical and rheological properties of ethylene propylene diene monomer (EPDM)-based MREs was investigated by using 30 wt.% carbonyl iron particles (CIPs) as the main filler, with different contents of silica nanoparticles (0 to 11 wt.%). The microstructure analysis was examined by using field-emission scanning electron microscopy (FESEM), while the thermal characterizations were studied by using a thermogravimetric analyzer and differential scanning calorimetry. The tensile properties were conducted by using Instron Universal Testing Machine in the absence of magnetic field at various temperatures. Meanwhile, the rheological properties were analyzed under oscillatory loadings in the influence of magnetic field, using a rotational rheometer at 25 to 65 °C. The results revealed that the temperature has diminished the interfacial interactions between filler and matrix, thus affecting the properties of MRE, where the tensile properties and MR effect decrease with increasing temperature. However, the presence of silica capable improved the thermal stability of EPDM-based MRE by enhancing the interactions between filler and matrix, thus reducing the interfacial defects when under the influence of temperature. Consequently, the incorporation of silica nanoparticles as an additive in EPDM-based MRE requires more exploration, since it has the potential to sustain the properties of MRE devices in a variety of temperature conditions. Thus, the study on the temperature-dependent mechanical and rheological properties of MRE is necessary, particularly regarding its practical applications.

Temperature-dependent soft wetting on amorphous, uncrosslinked polymer surfaces.

The wetting of polymer melts at high temperatures is studied by placing a glycerol drop on a poly(n-butyl methacrylate) film and measuring the wetting ridge. The height of the wetting ridge grows continuously over time. These wetting ridge growth rates can be explained by polymer chain dynamics occurring at the molecular level, determined using oscillatory shear rheology of the polymer melt. The shape of wetting ridge profile can be modeled using an equation previously used for elastomers, with a simple modification that incorporates the time-dependent storage modulus of the uncrosslinked melts.

Norbornene-functionalized methylcellulose as a thermo- and photo-responsive bioink

Three-dimensional (3D) bioprinting has emerged as an important tool to fabricate scaffolds with complex structures for tissue engineering and regenerative medicine applications. For extrusion-based 3D bioprinting, the success of printing complex structures relies largely on the properties of bioink. Methylcellulose (MC) has been exploited as a potential bioink for 3D bioprinting due to its temperature-dependent rheological properties. However, MC is highly soluble and has low structural stability at room temperature, making it suboptimal for 3D bioprinting applications. In this study, we report a one-step synthesis protocol for modifying MC with norbornene (MCNB), which serves as a new bioink for 3D bioprinting. MCNB preserves the temperature-dependent reversible sol-gel transition and readily reacts with thiol-bearing linkers through light-mediated step-growth thiol-norbornene photopolymerization. Furthermore, we rendered the otherwise inert MC network bioactive through facile conjugation of integrin-binding ligands (e.g. CRGDS) or via incorporating cell-adhesive and protease-sensitive gelatin-based macromer (e.g. GelNB). The adaptability of the new MCNB-based bioink offers an attractive option for diverse 3D bioprinting applications.

Effect of temperature on the SU‐8 photoresist filling behavior during thermal nanoimprinting

AbstractSU‐8 photoresist is an ideal thermal‐imprinting polymer, which has been widely used in micro‐nano devices in recent years. However, the research on the filling behavior of SU‐8 photoresist during thermal nanoimprinting is not complete. In this paper, the stress relaxation curves and shear stress/rate flow curves were measured to analyze the temperature dependent rheological properties of SU‐8 photoresist. The filling behavior of SU‐8 photoresist was discussed based on thermal imprinting results at various temperatures. High‐precision nanochannels were fabricated with replication error of 2.8% at optimized thermal imprinting temperature of 85°C and duration of 10 min, which paves the way for high‐precision fabrication of SU‐8‐based micro‐nanofluidic chips.

Analytical study of two-dimensional thermo-mechanical responses of viscoelastic skin tissue with temperature-dependent thermal conductivity and rheological properties

The generalized thermo-viscoelastic theory without energy dissipation is used in this work to investigate the transfer of bioheat and the mechanical heat-induced response in a human skin plane tissue with variable thermal and rheological properties. Integral transformations are used for Laplace and Fourier. In the scheme of two-dimensional equations, the exponential matrix procedure, which forms the basis of the state-space approach of modern control theory, is applied. The resulting formulation is applied to a thermal shock half-space problem. The inversion process for Fourier and Laplace transforms is carried out using a numerical method based on Fourier series expansions. Comparisons between computational measurements and Penne’s experimental verification indicate that the Green–Naghdi (II) bioheat mathematical model is an effective method for estimating the transition of bioheat to viscoelastic skin tissue. The influences of variable thermal conductivity and volume materials properties on all fields are examined.

Temperature-dependent rheological properties of viscoelastic polymer based flexible abrasive media for finishing process

The objective of the present investigation is to develop and study the thermal and rheological properties of the in-house developed flexible abrasive media. It is a mixer of viscoelastic polymer and plasticizer mixed with micro-abrasive particles, used for removing debris and irregularities present on internal and external complex surfaces used in the aerospace, automotive and medical industries. This paper presents, morphology of the developed abrasive media is captured using the Scanning Electron Microscope (SEM), thermal properties of the abrasive media are studied using Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) analysis along with tensile properties of the abrasive media ascertained using the universal testing machine. The rheological properties of the media play a major role in media flow over the intricate shapes and removing the material from the surface. To understand the media behavior, further rheological properties such as viscosity, shear stress, storage modulus, loss modulus, loss tangent, and complex viscosity are ascertained with varying shear rate and frequency at different temperature using rheometer. The TGA and DSC results shows abrasive media has good thermal stability and possibility of using the media for finishing process under lower temperature <100 °C. Rheological studies shows the shear thinning behaviour of the media and elastic solid behavior (G′ > G′′) at different temperatures which is suitable for finishing the complex internal and the external features efficiently and effectively. The developed abrasive media is used to finish the hydraulic components which are difficult to access with conventional tools and the results of finishing process are presented.

Temperature-dependent rheological, mechanical and hydration properties of cement paste blended with iron tailings

With this research, the authors intend to investigate the effects of particle size and curing temperature on the properties of cement paste blended with iron tailings (IT). The research work found that the partial replacement of ordinary Portland cement (OPC) by iron tailings (IT) accelerated the hydration of cement in the initial stage, but low cumulative heat release was noticed after long curing. Both the yield stress and plastic viscosity of fresh cement paste blended with IT were decreased due to the IT replacement. The initial setting was found to be delayed by the addition of IT. Besides, the introduction of IT led to enhanced pore volume resulting in reduced UCS and the UCS decreased with the increase of IT particle size. On the other hand, the properties of cement in the presence of IT were found to be more temperature dependent. Increasing temperature accelerated the early-stage hydration of paste with IT more strongly than that of the control paste. Temperature rising was more favorable to the UCS development of samples with IT replacement. The grow rates of both yield stress and plastic viscosity increased due to the replacement of OPC by IT when the temperature rising.

Preparation of Electron/Ion-Mixed Conducting Gel Using Liquid Metal and Ionic Liquid

Introduction Eutectic gallium-indium (Ga-In) has excellent properties, such as low melting point of 15.3 °C, high thermal and electronic conductivity, and metallic luster. Ga-In has promise as a liquid electron-conducting material owing to its low viscosity, negligible vapor pressure and low toxicity.1, 2) On the other hand, ionic liquids are ambient temperature molten salts that have attracted considerable attention because of unique properties such as high ionic conductivity, non-volatility and thermal stability. We proposed that ion gels, composed of macromolecular networks swollen with ionic liquids, exhibit self-standing film-forming ability in addition to the unique properties of ionic liquids. In this study, we prepared composite gel materials containing ionic liquid and Ga-In. This composite gel (metal gel) might have high electronic conductivity based on Ga-In and high ionic conductivity originated from the ionic liquid, as well as good mechanical properties based on the polymer, such as flexibility and strechability. These new materials are applicable to flexible or stretchable devices in wearable and flexible electronics applications. Experimental We chose hydrogen bonding copolymers of N,N-dimethylacrylamide (DMAAm) and acrylic acid (AAc) (P(DMAAm-r-AAc)) as the matrix polymers. This copolymer was combined with a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([C2mim][NTf2]) to form an ion gel.3) In order to improve dispersibility of Ga-In in the composite gel, bulk Ga-In was ultra-sonicated in ethanol and the suspension of Ga-In microdroplets was mixed with P(DMAAm-r-AAc) and [C2mim][NTf2]. The composite gels were prepared by solution casting method either in the air where thin oxide layer is formed on the Ga-In particles4) or under inert atmosphere to examine the effects of preparation conditions on their properties. Results and Discussion In tensile tests, Young’s modulus increased with increasing volume fraction of Ga-In in the composite gels. In rheological measurements, storage modulus was higher than loss modulus, confirming soft solid-like behavior of the composite gels. In both measurements, modulus of composite gels was higher than that of ion gels. We found difference in the temperature dependent rheological properties between the composite gels prepared in air and under inert atmosphere. The presence/absence of the surface oxide layer on the Ga-In particles was likely responsible for the difference in the rheological responses. Electronic conductivity was improved by a factor of 106 for the composite gels prepared under inert atmosphere compared to that of the composite gels prepared in the air. It was found that the oxide layers on the Ga-In particles had a significant impact on the rheological and electronic properties. However, electronic conductivity of the composite gels prepared under inert atmosphere was still low compared to that of bulk Ga-In. To achieve high electronic conductivity comparable to the bulk value, volume fraction of Ga-In microdroplets needs to be increased in the composite gels. In order to improve dispersibility of high-loading Ga-In in the composite gel, Ga-In microdroplets were prepared with dispersants. The results suggested that there is a trade-off between dispersibility of the Ga-In microdroplets and the electronic conductivity: better dispersibility of Ga-In microdroplets resulted in lower electronic conductivity. Acknowledgement This study was supported in part by Core Research for Evolutionary Science and Technology (CREST) of the Japan Science and Technology Agency (JST). References 1) Kazem, N. et al, Adv. Mater., 2017, 29, 1-14.2) Anderson, T. J. et al, Phase Equilibria, 1991, 12, 64-72.3) Tamate, R. et al, Adv. Mater, 2018, 30, 18027924) Ren, L. et al, Adv. Funct. Mater., 2016, 26, 8111-8118. Figure 1

Correlations between temperature-dependent rheology and electrostatic interactions in reverse wormlike micelles induced by inorganic salts.

Previous studies have shown that the plateau modulus Gp of the wormlike micelles formed in water driven by hydrophobic interactions is a constant upon heating, similar to polymer solutions, and Gp of the reverse worms formed in oils driven by hydrogen bonding decreases with increasing temperature. In this work, we investigated the reverse worms induced by three chloride salts that bind lecithin through different strengths of electrostatic interactions, in the order of LaCl3 > CaCl2 > LiCl. We correlated the interaction strengths with the temperature-dependent rheological properties and found that upon heating, Gp for all the reverse worms driven by electrostatic interactions decays slower than that driven by the weak temperature-sensitive hydrogen bonding. Furthermore, the decay rates of Gp follow an order in the inverse relation to the interaction strength, LaCl3≤ CaCl2 < LiCl, indicating that the dependence of Gp on temperature can reflect the strength of the driving forces for micellization. We utilized Fourier transform infrared spectroscopy (FTIR) to confirm the weakening of the interaction and the small angle X-ray scattering (SAXS) technique to reveal the decrease in the lengths of the reverse worms as temperature increases, both of which echo the changes in the rheological properties.

Intratumoral Injection of Norcantharidin-Loaded Poly(D,L-lactide)-b-Poly(ethylene glycol)-b-Poly(D,L-lactide) Thermosensitive Hydrogel for the Treatment of Primary Hepatocellular Carcinoma.

In this study we employed self-designed PDLLA-PEG-PDLLA (PLEL) thermosensitive hydrogel to blend with norcantharidin (NCTD), a hydrophilic chemotherapeutic drug possessing curative effect on primary hepatocellular carcinoma (HCC) and adverse effects, then utilized the composite in HCC interstitial chemotherapy. PLEL copolymer was synthesized by ring-opening polymerization, NCTD-loaded PLEL hydrogel was prepared in a simple and reasonable way. The addition of NCTD had no significant effect on the temperature-dependent rheological properties of PLEL hydrogel. The pH values of NCTD-loaded gel solutions (13 wt%) and free NCTD solutions with three drug concentrations of 0.4 mg/mL, 0.8 mg/mL and 1.2 mg/mL under different storage conditions met the pH requirement of small-volume injection. There was no significant difference among the drug release behaviors of NCTD-loaded gels with drug concentrations of 0.4 mg/mL, 0.8 mg/mL and 1.2 mg/mL, they fitted first-order dynamics, exhibited significantly slower drug release than free drug solutions and the release was mainly based on drug diffusion. Drug-loaded gel solution (13 wt%) could evenly distribute throughout tumor tissue before converting into gel after being intratumorally injected and was able to significantly prolong retention time of the drug in tumor compared to free drug solution. The sustained-release performance of NCTD-loaded gel (13 wt%) was confirmed from the perspective of pharmacodynamics in vitro. The in vivo evaluation demonstrated that intratumoral injection of NCTD-loaded PLEL gel (13 wt%) was capable of improving curative effect of the drug and reducing its toxicity.

Time- and temperature-dependent rheological properties of cemented paste backfill that contains superplasticizer

The use of suitable superplasticizers in the production of cemented paste backfill (CPB), a mix of water, binder and tailings particles, is becoming prevalent due to their ability to improve flowability without undermining other important engineering properties. Their performance under different ambient temperatures found in various regions is not well understood. No research has been conducted to understand the effects of temperature on the rheological properties of CPB with superplasticizers. Therefore, the aim of this study is to investigate the effects of a superplasticizer on the rheological properties, specifically yield stress and viscosity, of CPB prepared and cured under different temperatures. CPB mixes containing 0%, 0.05%, 0.125%, and 0.25% Master Glenium superplasticizer were prepared, and cured for 4 h at three different temperatures of 2 °C, 20 °C and, 35 °C. Yield stress and viscosity were determined at different time intervals over the period. Additional tests, such as pH, thermal analysis and zeta potential analysis were also conducted. It was found that an increase in the ambient temperature leads to higher yield stress and viscosity of CPB treated with superplasticizer. However, less amount of superplasticizer is required to maintain a sufficiently fluid CPB within few hours of production. Additionally, the results from the study showed that different dosages of the superplasticizer are required for different tailings types to achieve the same level of flowability. The findings of this study will be beneficial in the design and production of CPB material.

Thermal Stability and Rheological Properties of Epoxidized Natural Rubber-Based Magnetorheological Elastomer.

Determination of the thermal characteristics and temperature-dependent rheological properties of the magnetorheological elastomers (MREs) is of paramount importance particularly with regards to MRE applications. Hitherto, a paucity of temperature dependent analysis has been conducted by MRE researchers. In this study, an investigation on the thermal and rheological properties of epoxidized natural rubber (ENR)-based MREs was performed. Various percentages of carbonyl iron particles (CIPs) were blended with the ENR compound using a two roll-mill for the preparation of the ENR-based MRE samples. The morphological, elemental, and thermal analyses were performed before the rheological test. Several characterizations, as well as the effects of the strain amplitude, temperature, and magnetic field on the rheological properties of ENR-based MRE samples, were evaluated. The micrographs and elemental results were well-correlated regarding the CIP and Fe contents, and a uniform distribution of CIPs was achieved. The results of the thermal test indicated that the incorporation of CIPs enhanced the thermal stability of the ENR-based MREs. Based on the rheological analysis, the storage modulus and loss factor were dependent on the CIP content and strain amplitude. The effect of temperature on the rheological properties revealed that the stiffness of the ENR-based MREs was considered stable, and they were appropriate to be employed in the MRE devices exposed to high temperatures above 45 °C.

Frequency-tunable toughening in a polymer-metal-ceramic stack using an interfacial molecular nanolayer

Interfacial toughening in composite materials is reasonably well understood for static loading, but little is known for cyclic loading. Here, we demonstrate that introducing an interfacial molecular nanolayer at the metal-ceramic interface of a layered polymer-metal-ceramic stack triples the fracture energy for ~75–300 Hz loading, yielding 40% higher values than the static-loading fracture energy. We show that this unexpected frequency-dependent toughening is underpinned by nanolayer-induced interface strengthening, which facilitates load transfer to, and plasticity in, the polymer layer. Above a threshold interfacial bond strength, the toughening magnitude and frequency range are primarily controlled by the frequency- and temperature-dependent rheological properties of the polymer. These results indicate the tunability of the toughening behavior through suitable choice of interfacial molecular layers and polymers. Our findings open up possibilities for realizing novel composites with inorganic-organic interfaces, e.g., arresting crack growth or stimulating controlled fracture triggered by loads with specific frequency characteristics.

The effect of temperature on rheological properties of endodontic sealers.

Aim:The purpose of this study was to investigate temperature-dependent rheological properties of three endodontic sealers MTA Fillapex (Angelus, Brazil), AH Plus (Dentsply, Germany), and EndoREZ (Ultradent, USA).Materials and Methods:Five samples of each group of endodontic sealers (n = 30) were freshly mixed and placed on the plate of a rheometer (MCR 301, AntonPaar, Physica) and examined at 25°C and 37°C temperature, respectively. Rheological properties of the sealers were calculated according to the loss modulus (G″), storage modulus (G′), loss factor (Tan δ), and complex viscosity (η*) using dynamic oscillatory shear tests.Results:Statistical analysis (Wilcoxon signed-rank test) demonstrated that MTA Fillapex exhibited higher loss modulus (G″ > G′) and a crossover region. AH Plus and EndoREZ had a higher storage modulus (G′ > G″) at both temperatures. Loss factor (Tan δ) of MTA Fillapex was the highest compared to AH Plus, followed by EndoREZ. With a temperature change from 25°C to 37°C, MTA Fillapex exhibited a decrease while AH Plus exhibited an increase and, EndoREZ exhibited the least change, in complex viscosity (η*).Conclusions:EndoREZ exhibited better rheological properties compared to the other two test sealers.

Rayleigh–Benard convection in Herschel–Bulkley fluid

The intent of the present work is to investigate Rayleigh–Benard convection in a viscoplastic fluid prepared from Carbopol (Ultrez 20) gel. Thermorheological characterization of the test fluid has been presented and rheological properties are represented by Herschel–Bulkley model. Further, temperature dependency of rheological parameters is described by Arrhenius model. Rayleigh–Benard convection phenomenon in a square enclosure filled with viscoplastic fluid has been investigated numerically as well as experimentally. The proposed computational model uses the temperature-dependent rheological properties. Results of the proposed model show a fair agreement with our own experimental data. Use of temperature-dependent rheological properties has improved the predictions significantly. With the increase in yield stress, there is a phenomenal change in diminishing convective flow patterns. Critical Rayleigh number representing the onset of convection has been determined for different concentrations of the gel. Nusselt number correlations as a function of Rayleigh number and yield number have been developed for two different values of Prandtl number.