Temperature-dependent Rheology Research Articles

Manifestation of surfactant–carrier interaction in ferrofluids in temperature-dependent magnetic rheology

The present study investigates surfactant–carrier interactions in non-aqueous ferrofluids with magneto-rheology at different temperatures. To the authors’ knowledge, such a study has not yet been reported. For this purpose, three ferrofluids—A, B, and C—were procured from Ferrotec, which had identical particles but different surfactant–carrier combinations. The study also encompasses structural and magnetic techniques to elucidate these samples’ physicochemical nature. The results show that the average magnetic size of particles (10 nm) is the same for all the three fluids. The nominal value of the surfactant chain length (4.5 nm) was derived from dynamic light scattering measurements, and the Rosensweig viscosity model and the Shliomis theory were the same. The magneto-rheological properties, e.g., shear stress vs shear rate in zero field and relative increase in ferrofluid viscosity in the applied field at two different temperatures (300 and 313 K), were fitted with Rosensweig and Shliomis models. They showed some variations in surfactant chain lengths. The results suggested the presence of surfactant–carrier interactions in these colloids. This new investigation may be useful in characterizing the stability of a ferrofluid and its practical aspects.

A vertically non-uniform temperature approach for the friction term computation in depth-averaged viscoplastic lava flows

Recently, depth-averaged shallow flow models have been adapted to modelling liquefied lava flows, generally characterized by a marked temperature-dependent non-Newtonian rheology. Modelling these complex flows requires to include the effects of the depth-averaged temperature gradients in the governing equations. The most significant term to correctly predict the lava mobility is the flow resistance term, which is widely estimated using the linear viscoplastic Bingham model. This non-Newtonian model allows to relate the bed shear stress to the depth-averaged lava flow features by means of a cubic equation with analytical solution when assuming a uniform temperature distribution along the vertical profile. Nevertheless, the lava temperature is non-uniform along the vertical due to the heat transfer at the bottom and the free surface, and hence the classical cubic Bingham model is not valid anymore. In this work, a depth-averaged shallow flow model is adapted for realistic lava flows considering influence of the non-uniform vertical temperature profile in the non-Newtonian resistance. This requires to modify the rheological viscoplastic models for ensuring the coupling between flow dynamics and temperature evolution. Three non-uniform temperature vertical distributions are considered: linear, piece-wise and diffusion profiles. Synthetic tests are used to show the influence of the temperature vertical profile on the numerical results. Furthermore, laboratory experimental data are used to validate this novel viscoplastic resistance formulation and to show that the calibration of its parameters is possible.

Viscoelastic phenomena in methylcellulose aqueous systems: Application of fractional calculus

Fractional calculus models can potentially describe the viscoelastic phenomena in soft solids. Nevertheless, their successful application is limited. This paper explored the potential of using fractional calculus models to describe the viscoelastic properties of soft solids, focusing on methylcellulose aqueous systems. Methylcellulose is an important food additive, and it is known for its complex rheological behaviors, including thermogelation, which still puzzle rheologists. Through dynamic mechanical analysis and fractional rheology, we demonstrated that fractional calculus described the frequency- and temperature-dependent rheology of methylcellulose. This paper also showcased how including one springpot could potentially replace numerous spring-dashpot arrangements. Our findings using fractional calculus suggested that the thermogelation of methylcellulose involves the cooperative mobility of polymer chains and can be described as a process analogous to the glass transition in polymers. This study highlighted the power of combining fractional calculus and rheology to understand complex viscoelastic phenomena in soft solids.

Progressive weakening within the overriding plate during dual inward dipping subduction

The evolution of dual inward dipping subduction (DIDS) is crucial to understand multiple slab interaction. Yet, how DIDS influences the thermo-mechanical behaviour of the overriding plate remains unclear, as previous DIDS investigations all applied a compositional or Newtonian rheology that excludes temperature dependency. Here we apply a composite rheology, including temperature dependent creep deformation mechanisms, in 2-D thermo-mechanical numerical modelling to investigate how DIDS modifies the rheological structure of the overriding plate. Three variables on plate sizes are investigated to understand what may control the maximum degree of plate weakening. We find that reducing the initial length or initial thickness of the overriding plate and increasing the initial thickness of the subducting plate can enhance the viscosity reduction within the overriding plate. The progressive weakening can result in a variety of stretching states ranging from 1) little or no lithosphere thinning and extension (<5% accumulation of strain), to 2) limited thermal lithosphere thinning (<30% accumulation of strain), and 3) localised rifting followed by spreading extension. Compared with single sided subduction, DIDS further reduces the magnitude of viscosity in the overriding plate. It does this by creating a dynamic fixed boundary condition for the overriding plate and forming a stronger upwelling mantle flow, both of which promote the progressive weakening in the overriding plate. The result implies that these generic DIDS effects are important aspects to consider to understand extension developed in natural DIDS cases. We also demonstrate that both temperature dependent creep rheologies and yielding deformation mechanism contribute significantly to the continuous viscosity reduction. The finding may also have a broader implication for more general processes that involve plate scale weakening, strain localisation and the formation of new plate boundaries.

Early asymmetric growth of planetary stagnant lids

Convection within planetary bodies is often modelled using a temperature-dependent rheology which, when cooled from the surface, naturally leads to the formation of a so-called stagnant lid at the cold outer surface. However, for sufficiently large planets the phase diagram describing the partially molten system may depend significantly on pressure in addition to temperature, leading to significant variations in solid fraction. The aggregate rheology may therefore exhibit significant dependence on both the temperature and pressure, and hence may exhibit marked dependence on depth in addition to the dependence on the thermal structure due to convection. Here, we consider the growth and stability of a planetary stagnant lid. We first characterise the effect of a pressure- and temperature-dependent rheology on the evolution of a symmetric, planetary stagnant lid. This analysis further suggests that the pressure dependence of the rheology may lead to an instability of the growing stagnant lid which, importantly, may lead to asymmetric lid growth. We find that the most unstable mode is at the longest wavelengths, and discuss the implications for stagnant-lid convection and the growth of asymmetric surfaces of planetary bodies. In particular, we discuss the possibility that this instability has implications for the formation of the crustal dichotomy found on the Moon.

A non-isothermal approach to evaluate the impact of the cooling stage on the startup flow of waxy crude oils

Waxy crude oils submitted to low temperatures at quiescent conditions turn into a gel with a corresponding yield stress. Thus, a higher pressure drop is needed to restart, leading to a flow assurance issue. Generally, this problem is tackled by considering the material at rest, with a given state and an imposed pressure drop. In the present work, we investigate how the cooling process after a shutdown impacts the problem. We emulate a stoppage of short duration so that the cooling after the shutdown stage does not lead to a condition of uniform temperature. The temperature-dependent rheology of the material is such that the crude oil shows viscoplastic behavior only below the gelation temperature. The early stages of the process, before and during the shutdown, resulting in a heterogeneous gel, which serves as an initial condition for the restart stage. We perform 2D non-isothermal simulations in a pipe considering three stages, namely (i) normal operation conditions; (ii) cooling stage at rest after stoppage; (iii) restart by an imposed pressure drop. Particular emphasis is given to the role of the plastic number ( P l ) and the duration of the cooling after the shutdown stage. A comparison with the corresponding homogeneous condition is also made. The results show that higher values of P l and higher waiting times in the cooling after the shutdown stage lead to conditions less prone to restart. Only cooling times of short duration lead to restart in the same conditions as the normal operation ones. The pressure drop necessary for a restart is an increasing function of the cooling time. • We examine the restart problem of a waxy crude oil modeled as a viscoplastic material. • The rheological properties are dependent on the temperature. • The previous stages like normal flow and cooling after shutdown are considered. • Heterogeneous initial conditions at the restart are obtained for different cooling times. • Comparisons between heterogeneous and homogeneous conditions show the importance of previous stages.

Crust first–mantle second and mantle first–crust second; lithospheric break-up scenarios along the Indian margins

Abstract Compared segments of the East and West Indian passive margins have different evolutions and crustal architecture. The East Indian margin is less magmatic. It results from a crust first–mantle second break-up scenario of a continent experiencing two rift events. The West Indian margin is more magmatic. It results from a mantle first–crust second break-up scenario of a continent experiencing four rift events. The architecture across both margins can be divided into stretching, thinning and hyperextension zones. The East Indian margin is characterized by oceanward-dipping listric normal faults that accommodate thinning in the thinning and hyperextension zones, and a zone of exhumed mantle separating continental and oceanic crusts. The West Indian margin in contrast is characterized by landward-dipping listric faults that accommodate magma-assisted thinning in the thinning and hyperextension zones, and no exhumed mantle. The final break-up affects the lithospheric mantle layer in the East Indian case and the crustal layer in the West Indian case. Although the temperature-dependent rheologies of these two last unbroken layers are somewhat different, seismic interpretation suggests that they are both broken by upward-convex normal faults, which succeeded the development of listric faults. They appear to be the first spontaneously formed faults in the break-up-delivering process, although their nucleation may be magma-assisted. The main difference between the controlling factors of the aforementioned break-up scenarios affecting similar lithospheres at similar extension rates is the cumulative length of time of the pre-break-up rift events, which is 62 and 115 myr for the East and West Indian margins, respectively.

Temperature-controlled dripping-onto-substrate (DoS) extensional rheometry of polymer micelle solutions.

Capillary-driven thinning of a liquid bridge is commonly used to measure the extensional rheology of macromolecular solutions for assessment of material sprayability, printability, and jettability. Methods like dripping-onto-substrate (DoS) rheometry are often preferred to methods like capillary breakup extensional rheometry (CaBER) due to low required sample volume and ability to measure low-viscosity fluids; however, DoS measurements to-date have been limited to ambient temperatures. Here, an environmental control chamber is developed to enable temperature-controlled DoS (TC-DoS) measurements, and the temperature-dependent extensional rheology of a model system of poloxamer 234 (P234) in NaF brine is examined. Spherical P234 micelles at ambient conditions exhibit inertiocapillary (IC) thinning; above the sphere-to-rod transition temperature, the liquid bridge evolves towards viscocapillary (VC) thinning as micelles lengthen and shear viscosity increases. Above 37 °C, wormlike micelle (WLM) formation results in pronounced elastocapillary (EC) thinning, and further WLM growth and entanglement results in three elasticity-dominated flow regimes: EC thinning, beads-on-a-string (BOAS) instability formation, and BOAS thinning. Despite having a substantially larger amphiphile molecular weight and micelle cross-sectional radius than surfactant WLMs, entangled P234 WLMs exhibit similar extensional behavior and achieve comparable maximum Trouton ratios. Comparing DoS measurements of P234 WLMs with prior studies on surfactant WLMs reveals that the maximum Trouton ratio depends on the ratio of shear and extensional relaxation times, a trend undetectable via CaBER due to pre-deformation during the initial step stretch. These findings reveal rich temperature-dependent flow behaviors in polymer micelles and highlight the importance of using a minimally-disruptive method such as TC-DoS when measuring the extensional rheology of microstructured and thermosensitive fluids.

Models of convection and segregation in heterogeneous partially molten crustal roots with a VOF method – I: flow regimes

SUMMARYWe investigate numerically some thermomechanical conditions for the development of crustal scale diapirism and convection in a heterogeneous continental crust independently from the action of regional tectonics. Here, we consider a hot crust, with unmolten and partially molten domains of specific temperature and strain-rate dependent power-law rheologies. We take advantage of the volume of fluid (VOF) method to capture the coalescence and separation of deformable inclusions in the partially molten domain. The inclusions, of several hundred metres in size, are more or less dense and viscous with respect to the ambient medium (they also behave with a power-law rheology). We restrict our study to a 20 Myr time scale, during which gravitational dynamics may dominate over lateral tectonics and lithospheric thermal re-equilibration. The motion of these inclusions during the development of gravitational instabilities displays distinct flow regimes that depend on two Rayleigh numbers denoted RaUM and RaPM, for the unmolten and partially molten rock properties, respectively. A ‘suspension’ regime occurs at high RaUM and high RaPM, in which most of the light compositional heterogeneities remain entrained in the convective cells. In contrast at low RaUM and high RaPM, a ‘layering’ regime is characterized by merging of the light inclusions as floating clusters below the rigid upper crustal lid. This regime occurs in association with a sharp viscosity gradient at upper-to-middle crust transitional depths. In these two regimes, the dense inclusions accumulate at the bottom of the partially molten zone. Finally at moderate RaPM, a ‘diapiric’ regime reflects the segregation of the heavy and the light inclusions, respectively downward and upward, without global convection. These numerical experiments lead to a first order evaluation of the physical parameters required for the segregation of deformable inclusions of variable densities and convection, in a partially molten crust, and provide insights on the conditions for the development of migmatite domes. Geological data indicate that these processes likely occur in a large number of settings from Archean to Phanerozoic times, and contribute to the differentiation of the continental crust.

Thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate)-ran-(polyethylene glycol methacrylate) graft copolymers exhibiting temperature-dependent rheology and self-assembly

Graft copolymers with brush-type architectures are explored containing poly(ethylene glycol) methacrylates copolymerized with “thermoresponsive” monomers which impart lower critical solution temperatures to the polymer. Initially, the chemical structure of the thermoresponsive polymer is explored, synthesizing materials containing N-isopropyl acrylamide, N,N-diethyl acrylamide and diethylene glycol methyl ether methacrylate. Thermoresponsive graft-copolymers containing di(ethylene glycol) methyl ether methacrylate (DEGMA) exhibited phase transition temperature close to physiological conditions (ca 30 °C). The effect of polymer composition was explored, including molecular weight, PEG-methacrylate (PEGMA) terminal functionality and PEGMA/DEGMA ratios. Molecular weight exhibited complex relationships with phase behavior, where lower molecular weight systems appeared more stable above lower critical solution temperatures (LCST), but a lower limit was identified. PEGMA/DEGMA feed was able to control transition temperature, with higher PEGMA ratios elevating thermal transition. It was found that PEGMA terminated with methoxy functionality formed stable colloidal structures above LCST, whereas those the hydroxy termini generally formed two-phase sedimented systems when heated. Two thermoresponsive DEGMA-based graft polymers, poly(PEGMA7-ran-DEGMA170) and poly(PEGMA1-ran-DEGMA38), gave interesting temperature-dependent rheology, transitioning to a viscous state upon heating. These materials may find application in forming thermothickening systems which modify rheology upon exposure to the body’s heat.

Synthesis of Silica-Based Boron-Incorporated Collagen/Human Hair Keratin Hybrid Cryogels with the Potential Bone Formation Capability.

Tissue engineering and regenerative medicine have evolved into a different concept, the so-called clinical tissue engineering. Within this context, the synthesis of next-generation inorganic-organic hybrid constructs without the use of chemical crosslinkers emerges with a great potential for treating bone defects. Here, we propose a sophisticated approach for synthesizing cost-effective boron (B)- and silicon (Si)-incorporated collagen/hair keratin (B-Si-Col-HK) cryogels with the help of sol-gel reactions. In this approach, collagen and hair keratin were engaged with a B-Si network using tetraethyl orthosilicate as a silica precursor, and the obtained cryogels were characterized in depth with attenuated total reflectance-Fourier transform infrared spectroscopy, solid-state NMR, X-ray diffraction, thermogravimetric analysis, porosity and swelling tests, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda analyses, frequency sweep and temperature-dependent rheology, contact angle analysis, micromechanical tests, and scanning electron microscopy with energy dispersive X-ray analysis. In addition, the cell survival and osteogenic features of the cryogels were evaluated by the MTS test, live/dead assay, immuno/histochemistry, and quantitative real-time polymerase chain reaction analyses. We conclude that the B-Si-networked Col-HK cryogels having good mechanical durability and osteoinductive features would have the potential bone formation capability.

Dual Functionalization of Gelatin for Orthogonal and Dynamic Hydrogel Cross-Linking.

Gelatin-based hydrogels are widely used in biomedical fields because of their abundance of bioactive motifs that support cell adhesion and matrix remodeling. Although inherently bioactive, unmodified gelatin exhibits temperature-dependent rheology and solubilizes at body temperature, making it unstable for three-dimensional (3D) cell culture. Therefore, the addition of chemically reactive motifs is required to render gelatin-based hydrogels with highly controllable cross-linking kinetics and tunable mechanical properties that are critical for 3D cell culture. This article provides a series of methods toward establishing orthogonally cross-linked gelatin-based hydrogels for dynamic 3D cell culture. In particular, we prepared dually functionalized gelatin macromers amenable for sequential, orthogonal covalent cross-linking. Central to this material platform is the synthesis of norbornene-functionalized gelatin (GelNB), which forms covalently cross-linked hydrogels via orthogonal thiol-norbornene click cross-linking. Using GelNB as the starting material, we further detail the methods for synthesizing gelatin macromers susceptible to hydroxyphenylacetic acid (HPA) dimerization (i.e., GelNB-HPA) and hydrazone bonding (i.e., GelNB-CH) for on-demand matrix stiffening. Finally, we outline the protocol for synthesizing a gelatin macromer capable of adjusting hydrogel stress relaxation via boronate ester bonding (i.e., GelNB-BA). The combination of these orthogonal chemistries affords a wide range of gelatin-based hydrogels as biomimetic matrices in tissue engineering and regenerative medicine applications.

3D printed, mechanically tunable, composite sodium alginate, gelatin and Gum Arabic (SA-GEL-GA) scaffolds

Biomimicking the mechanical properties of native tissues is one of the key requirements of engineering tissue scaffolds, rendering a need for materials and manufacturing processes with a high level of control over the mechanical properties of such scaffolds. To address this need, we present a 3D printable, composite hydrogel consisting of sodium alginate (SA), gelatin (GEL) and gum Arabic (GA), referred to herein as SA-GEL-GA hydrogel, mechanical properties of which can be controlled through tuning its cross-linking process. Here, the aqueous solution of the three constituents is used as the bioink to 3D print porous scaffolds in a temperature-controlled extrusion-based printing process. 3D-printed scaffolds are then crosslinked through a multi-step approach, realizing the gelation of GEL, ionic crosslinking of SA and GA, and covalent cross-linking of all three components. Here, we show that the inherent mechanical properties of SA-GEL-GA hydrogels can be controlled through the duration of the covalent crosslinking step. SA-GEL-GA bioinks exhibit highly temperature-dependent rheology with elastic solid-like behavior below room temperature and a viscoplastic, shear thinning nature above 28 ​°C. Using a cooled build-plate and heated printhead, high resolution scaffolds were printed with filament diameter of 250 ​μm and extruded from a 100 ​μm diameter nozzle. The compressive elastic modulus of these scaffolds can be tuned to the 50–250 ​kPa range through the combined effect of the scaffold pores size and covalent crosslinking step duration. 3D printed and crosslinked scaffolds carry over 500% of their dry weight in water and can be dried and reswollen to over 400% of their dry weight. Finally, our degradation analysis showed that increased covalent cross-linking duration led to reduced long-term structural stability due to mechanical failure of the scaffolds. These results indicate that SA-GEL-GA hydrogels offer exciting opportunities for manufacturing customizable artificial tissue scaffolds with biomimicking mechanical properties, particularly for soft tissues.

Connecting the Stimuli-Responsive Rheology of Biopolymer Hydrogels to Underlying Hydrogen-Bonding Interactions.

Many biopolymer hydrogels are environmentally responsive because they are held together by physical associations that depend on pH and temperature. Here, we investigate how the pH and temperature responses of the rheology of hyaluronan hydrogels are connected to the underlying molecular interactions. Hyaluronan is an essential structural biopolymer in the human body with many applications in biomedicine. Using two-dimensional infrared spectroscopy, we show that hyaluronan chains become connected by hydrogen bonds when the pH is changed from 7.0 to 2.5 and that the bond density at pH 2.5 is independent of temperature. Temperature-dependent rheology measurements show that because of this hydrogen bonding the stress relaxation at pH 2.5 is strongly slowed down in comparison to pH 7.0, consistent with the sticky reptation model of associative polymers. From the flow activation energy, we conclude that each polymer is cross-linked by multiple (5–15) hydrogen bonds to others, causing slow macroscopic stress relaxation, despite the short time scale of breaking and reformation of each individual hydrogen bond. Our findings can aid the design of stimuli-responsive hydrogels with tailored viscoelastic properties for biomedical applications.

Streamline Simulation of Compositional Nonisothermal Flows of Viscoplastic Oils

The aim of this study is to develop a numerical method providing the possibility of computing nonisothermal compositional flows faster than traditional finite-volume methods. A plane problem of oil, water, and gas flows is considered. The oil phase is represented by two components: the light fraction and the heavy fraction, which, similarly to water, can be gasified. The study takes into account both the nonlinearity of the oil flow law and the temperature dependence of the parameters of this law. This formulation of the problem is relevant for the simulation of the development of high-viscosity oilfields. To reduce the computational complexity of the problem, the streamline method with splitting with respect to physical processes is used. It separates the convective transport directed along the flow’s propagation from processes related to the heat conduction and gravity, which directions do not coincide with the convective flow. A distinctive feature of the proposed method is the joint solution of the pressure, energy-balance, and mass-component equations both on streamlines and on the initial grid. This feature allows us to correctly calculate oil flows with a complex temperature-dependent rheology. Numerical solutions of the system of flow equations on a two-dimensional grid and on streamlines are obtained by the IMPEC method. For the presented streamline method, we propose an algorithm accounting for the thermal conductivity and transition criteria between calculations on streamlines and on a two-dimensional grid. The developed software is verified by comparison with the analytical solutions and with the results of calculations by finite-volume methods on five-point and nine-point finite-difference stencils.

Temperature-Induced Aggregation in Portlandite Suspensions.

Temperature is well known to affect the aggregation behavior of colloidal suspensions. This paper elucidates the temperature dependence of the rheology of portlandite (calcium hydroxide: Ca(OH)2) suspensions that feature a high ionic strength and a pH close to the particle's isoelectric point. In contrast to the viscosity of the suspending medium (saturated solution of Ca(OH)2 in water), the viscosity of Ca(OH)2 suspensions is found to increase with elevating temperature. This behavior is shown to arise from the temperature-induced aggregation of polydisperse Ca(OH)2 particulates because of the diminution of electrostatic repulsive forces with increasing temperature. The temperature dependence of the suspension viscosity is further shown to diminish with increasing particle volume fraction as a result of volumetric crowding and the formation of denser fractal structures in the suspension. Significantly, the temperature-dependent rheological response of suspensions is shown to be strongly affected by the suspending medium's properties, including ionic strength and ion valence, which affect aggregation kinetics. These outcomes provide new insights into aggregation processes that affect the temperature-dependent rheology of portlandite-based and similar suspensions that feature strong charge screening behavior.

In Situ Preparation of Crosslinked Polymer Electrolytes for Lithium Ion Batteries: A Comparison of Monomer Systems.

Solid polymer electrolytes for bipolar lithium ion batteries requiring electrochemical stability of 4.5 V vs. Li/Li+ are presented. Thus, imidazolium-containing poly(ionic liquid) (PIL) networks were prepared by crosslinking UV-photopolymerization in an in situ approach (i.e., to allow preparation directly on the electrodes used). The crosslinks in the network improve the mechanical stability of the samples, as indicated by the free-standing nature of the materials and temperature-dependent rheology measurements. The averaged mesh size calculated from rheologoical measurements varied between 1.66 nm with 10 mol% crosslinker and 4.35 nm without crosslinker. The chemical structure of the ionic liquid (IL) monomers in the network was varied to achieve the highest possible ionic conductivity. The systematic variation in three series with a number of new IL monomers offers a direct comparison of samples obtained under comparable conditions. The ionic conductivity of generation II and III PIL networks was improved by three orders of magnitude, to the range of 7.1 × 10−6 S·cm−1 at 20 °C and 2.3 × 10−4 S·cm−1 at 80 °C, compared to known poly(vinylimidazolium·TFSI) materials (generation I). The transition from linear homopolymers to networks reduces the ionic conductivity by about one order of magnitude, but allows free-standing films instead of sticky materials. The PIL networks have a much higher voltage stability than PEO with the same amount and type of conducting salt, lithium bis(trifluoromethane sulfonyl)imide (LiTFSI). GII-PIL networks are electrochemically stable up to a potential of 4.7 V vs. Li/Li+, which is crucial for a potential application as a solid electrolyte. Cycling (cyclovoltammetry and lithium plating-stripping) experiments revealed that it is possible to conduct lithium ions through the GII-polymer networks at low currents. We concluded that the synthesized PIL networks represent suitable candidates for solid-state electrolytes in lithium ion batteries or solid-state batteries.

Effect of ionic liquid on sol-gel phase transition, kinetics and rheological properties of high amylose starch

The effect of 1-butyl-3-methylimidazolium chloride (BMIMCl) as a plasticizer on sol-gel phase transition, rheological, and physical properties of high amylose rice starch was studied. The inter-relationships of parameters were determined using principal component analysis. The sol-gel phase transition temperature and storage modulus of starch was varied significantly (p ≤ 0.05) in the presence of BMIMCl. The sol-gel phase transition temperature of native starch was varied between 53.99 and 39.7 °C, whereas, for starch with ionic liquid varied between 49.50 and 40.6 °C. The changes in storage modulus (G') during the sol-gel phase transition were suitable with first order kinetics. The temperature dependent rheology of starch during the sol-gel phase transition was efficiently (0.93 ≤ R2 ≤ 0.98) explained using the Arrhenius model. The thermal stability of the gel was improved in the presence of BMIMCl. The textural and electrical properties of the gel were significantly affected by the presence of BMIMCl. The inter-relationships between the parameters were developed and the initial temperature, resistance, and storage modulus showed a strong interrelation.

Conversion of resins and asphaltenes under thermo-catalytic influence of magnetite at 200°C

This paper discusses the influence of magnetite on conversion of Ashal’cha heavy oil under the temperature of 200°C. The role of catalyst in in-situ upgrading of heavy oil is directed on the content reduction of high-molecular components such as resins and asphaltenes, as well as their molecular masses. The significant increase (10%) in the content of aromatic fraction and decrease in high-molecular hydrocarbons (8%) is observed. The results of measurements indicate the positive influence of catalyst on the rheology. Magnetite participates in destruction of associated complexes in resins and thereby decreases the viscosity of crude oil. The destruction products increase the content of light hydrocarbons, particularly saturates and aromatics. Investigation of temperature-dependent rheology characteristics revealed significant viscosity reduction in the products of catalytic aquathermolysis.

Heat-transfer enhancement for corn straw slurry from biogas plants by twisted hexagonal tubes

Heat-transfer geometries that enhance heat transfer performance for slurries increase the net raw biogas production in the bio-methane process. In this study, the precise temperature-dependent rheologies of corn straw slurry with 6 and 8% total solid were determined, collected, and modeled to conduct a numerical simulation via CFD, the first instance of such research. Subsequently, the reliability of the numerical results was verified with heat-transfer experiments. The heat-transfer performances of the circular, twisted square and twisted hexagonal tubes were estimated numerically, ultimately showing that the twisted hexagonal tube performed optimally with an enhancement factor of up to 2.0 in the turbulent region, compared to the circular tube. Based on the numerical results, the mechanism of heat-transfer enhancement was revealed, showing balanced radial mixing and the near-wall shear effect that leads to a strong and continuous shear rate under a considerable radial-flow intensity. An engineering equation was obtained for the performance evaluation, and the waste-heat recovery from corn straw slurry was analyzed, showing the twisted hexagonal tube can increase the net raw biogas production by up to 17.0% compared to the circular tube.