Shear Thinning Phenomenon Research Articles

Influence of hybrid nano-structures on thermal performance of shear rate dependent viscosity fluid over a heated rotating cone with Hall and ion slip currents

The fluid of shear rate dependent viscosity has totally different rheology and exhibits dynamics which play a key role in heat transfer rate and friction experienced by surface over which this type of fluid is considered in this study as this type of fluids are extensively used in thermal processes. The governing laws and constitutive equations for hyperbolic tangent fluid and thermo-physical relation correlation for hybridity of nano-structures are simultaneously solved via finite element method (FEM). The predictions are recorded, and outcomes are explained. It is found from outcomes that suspension of hybrid nano-structures is the most approximate technique for the enhancement of thermal performance of coolant (hyperbolic tangent fluid). The process of diffusion of wall momentum into fluid speeds down as viscosity decreases as a function of shear rate. It is predicted from simulations that mono nanofluid is less shear thinning than hybrid nanofluid. Hence, if it is desired to reduce shear thinning phenomenon, enhance the thermal performance and suspension of hybrid nano-structures are recommended. The results are validated by comparing them with already published benchmarks. The parameters are varied, and simulations are recorded in term of numerical values and graphical data. The rotation of micro-structures has shown significant reduction in angular velocity of mono and hybrid nanofluids. Angular field has depicted an increasing trend when vortex viscosity parameter is varied through increasing values. Temperature decreases as a result of an increase in thermal relaxation time. Hence, thermal memory effects play a significant role in controlling the thermal boundary layer thickness.

Experimental study on the performance of goaf filling materials with high content of fly ash

In this paper, fly ash is studied as the main cementing material for coal mine goaf filling. The performance of the filling materials with 90% fly ash such as compressive strength, impermeability, viscosity, additive effect and diffusion rule are studied experimentally and theoretically. The results show that compressive strength and impermeability are positively correlated with cement content when water-solid ratio is 0.7:1.0 with 90% fly ash. The compressive strength increases slowly in the early stage while it increases with a faster speed in the later stage. The compressive strength of the material after 60 days of curing is 1.90 times that of 28 days. Additive could promote the activity of fly ash and improve hydration reaction. The interparticle porosity is reduced, but strength at early stage and impermeability are increased. The viscosity of the filling material has an obvious shear thinning phenomenon as shear rate increases. An inflection point appears when shear rate is 30s−1. The filling material with high content of fly ash presents the rule of horizontal diffusion and longitudinal accumulation in goaf filling treatment. The diffusion distance and accumulation height are positively correlated with grouting pressure.

Rheological and structural properties of sodium caseinate as influenced by locust bean gum and κ-carrageenan

The interactions between sodium caseinate and polysaccharide were investigated by choosing both neutral (locust bean gum) and anionic polysaccharides (κ-carrageenan). The linear and non-linear rheological properties, ζ-potential and structures of the sodium caseinate/gum mixtures were evaluated. The mixtures all displayed shear-thinning phenomenon, and the increase of either locust bean gum or κ-carrageenan content led to the increase of storage (G′) and loss (G″) moduli. The large amplitude oscillation shear (LAOS) test and Fourier-transform have been successfully used to detect the slight rheological differences caused by microstructure changes. Increasing levels of κ-carrageenan led to critical strain decreased of the mixture, but not for locust bean gum. The sodium caseinate/locust bean gum mixtures behaved as “hard gel”, while the sodium caseinate/κ-carrageenan mixtures behaved as “soft gel” in Fourier-transform rheology. Changes in viscoelasticity under large strain were illustrated using elastic and viscous Lissajous curves, which were correlated to the microstructural change within the network of the mixtures. The zeta-potential values were significantly decreased in the presence of κ-carrageenan, while the addition of locust bean gum had no significant influence. Phase separation was found more dominant to change the structure than the protein network formation in the sodium caseinate/locust bean gum mixtures. However, protein network formation was the factor to dominate the structure forming of sodium caseinate/κ-carrageenan mixtures with electrostatic forces and hydrogen bonding.

A New Viscosity Constitutive Model for Generalized Newtonian Fluids Using Theory of Micropolar Continuum

In this paper, a new viscosity constitutive relation for the analysis of generalized Newtonian fluids is presented and analyzed. The theory of micropolar continuum is considered for the derivation of constitutive relations where the kinematics at the macroscopic level leads to incorporate the micro-rotational effects in existing rheology of Carreau Yasuda model. It provides a more realistic approach to analyze the flow behavior of generalized Newtonian fluids. To the best of author’s knowledge such generalization of the existing rheology of Carreau-Yasuda is not present in literature. In order to show the effects of micro-rotations on the viscosity of generalized fluids, different computational experiments are performed using finite volume method (FVM). The method is implemented and validated for accuracy by comparison with existing literature in the limiting case through graphs and tables and a good agreement is achieved. It is observed that with the increase of micro-rotations the shear thinning phenomena slower down whereas the shear thickening is enhanced. Moreover, the effects of various model parameters on horizontal and vertical velocities as well as on boundary layer thickness are shown through graphs and contour plots It is worth mentioning that the proposed constitutive model can be utilized to analyze the generalized Newtonian fluids and has wider applications in blood rheology.

Structure and Properties of PSf Hollow Fiber Membranes with Different Molecular Weight Hyperbranched Polyester Using Pentaerythritol as Core.

A homologous series of hyperbranched polyesters (HBPEs) was successfully synthesized via an esterification reaction of 2,2-bis(methylol)propionic acid (bis-MPA) with pentaerythritol. The molecular weights of the HBPEs were 2160, 2660, 4150 and 5840 g/mol, respectively. These HBPEs were used as additives to prepare polysulfone (PSf) hollow fiber membranes via non-solvent induced phase separation. The characteristic behaviors of the casting solution were investigated, as well as the morphologies, hydrophilicity and mechanical properties of the PSf membranes. The results showed that the initial viscosities of the casting solutions were increased, and the shear-thinning phenomenon became increasingly obvious. The demixing rate first increased and then decreased when increasing the HBPE molecular weight, and the turning point was 2660 g/mol. The PSf hollow fiber membranes with different molecular weights of HBPEs had a co-existing morphology of double finger-like and sponge-like structures. The starting pure water contact angle decreased obviously, and the mechanical properties improved.

The Effects of Bituminous Binder on the Performance of Gussasphalt Concrete for Bridge Deck Pavement.

As bituminous binders greatly influence the engineering performance of gussasphalt concrete for bridge deck pavement, selecting appropriate bitumen is a critical procedure for mixture design. In this study, five different combinations of bituminous binder for potential use in the “Hong Kong–Zhuhai–Macao Bridge” project were prepared and tested. To meet the strict requirements of quality control, a new Guss-Mastic Asphalt (GMA) system was developed. Three key indices, Lueer fluidity, impact toughness, and dynamic stability, were used for GMA design and construction quality control. The test results show that the fluidity of the GMA mixtures was affected by the shear thinning phenomenon. After mixing for three hours, the Lueer value of all GMA mixtures met the requirements of pouring construction. Moreover, it was found that the influence of mixing time on GMA with styrene butadiene styrene (SBS) modified bitumen was different to other prepared mixtures. This difference is ascribed to the degradation of SBS during the blending process at an elevated temperature. Finally, the blended bitumen (30% Pen60/70 + 70% Trinidad lake asphalt (TLA)) was applied to the project of the Hong Kong–Zhuhai–Macao Bridge.

Experiment and modelling of the strain-rate-dependent response during in vitro degradation of PLA fibres

Polylactic acid (PLA) fibres present, in their pristine state, a strain-rate-dependent behaviour. Their mechanical properties evolve during in vitro biodegradation. Tensile tests of PLA fibres are performed at five different strain rates 0.0001, 0.001, 0.01, 0.05 and 0.1/s and at seven degradation stages, 0, 20, 40, 60, 90, 120 and 150 days in a phosphate buffer solution at constant temperature at 37 °C. The mechanical response is modelled using a modified three-element standard solid model proposed for polymers under finite deformations range. Observations on experimental data lead to the conclusion that the viscous parameters η1 and η2 are strain rate dependent, and they vary from 10,762/3202 (N/m s) at the lowest strain rate of 0.0001/s, and 12.2/9.1 (N/m s) at the highest strain rate of 0.1/s for η1 and η2, respectively, thus, depicting the shear-thinning phenomena with the increase in strain rate. Whereas stiffness parameters C1 and C2 are degradation dependent, they vary from 21.6/13.7 (N/m) for undegraded PLA fibres and 9.7/5.4 (N/m) for 150 days degraded PLA fibres for C1 and C2, respectively. Decay of stiffness parameters during biodegradation follows an exponential law. The model will be useful to design and develop new fibrous structures for ligament augmentation devices. It could contribute to develop better devices with improved mechanical performance helping those patients in need to repair the ligament tissue.

Study on the yielding behaviors of ferrofluids: a very shear thinning phenomenon.

The yielding behaviors of the ferrofluids are vital for many applications. However, previous studies have mainly focused on the magnetoviscous effect under relatively high shear rates and rarely involved the yielding process of ferrofluids under very low shear rates. In this study, ferrofluid samples of different particle volume concentrations were prepared and their shear thinning behaviors within a wide shear stress range were systematically studied under various magnetic field strengths and temperatures. The very shear thinning phenomenon of ferrofluids was first observed and its microscopic mechanism was analyzed. A precipitous fall-off stage as the mark of yielding appeared between the low shear and high shear plateaus in the viscosity curves of ferrofluids. The precipitous fall-off stage in the viscosity curves became steeper with the increase of the magnetic field strength or decrease in the temperature. For ferrofluids with relatively low particle volume concentrations, the high viscosity limit under the low shear region disappeared when temperature exceeded a certain value and was interpreted as the disappearance of the equilibrium columnar structures under high Brownian thermal interaction level. A composite Ellis model was proved to be suitable for the fitting of different types of yield stresses and a structural number, Sn was proposed for the dimensionless analysis of the shear thinning behaviors of ferrofluids. The findings in this study contribute to a better understanding of the microscopic mechanism of yielding behaviors of ferrofluids and also provide guidance for many practical applications.

Experimental study on the viscosity-temperature characteristics and rheological properties of offshore heavy oil

The viscosity-temperature characteristics and rheological properties of heavy oil were investigated experimentally. Experimental results indicate that viscosity is sensitive to temperature, and it is a binary function of temperature and shear rate meeting preferably Arrhenius equation. In addition, the semi-log curve of viscosity-temperature can be divided into three regions and there is no obvious turning point, which exhibits that the internal microstructure of heavy oil during the heating process changes gradually. Besides, activation energy of low temperature range is higher than that of high temperature range. Moreover, the heavy oil always behaves as Newtonian fluid when temperature is higher than crystallisation temperature. Furthermore, on condition that temperature is less than crystallisation temperature, the heavy oil behaves as pseudo-plastic fluid characterising shear thinning phenomenon when shear rate is less than critical shear rate, and it presents as Bingham fluid with yield stress when shear rate falls between 10 and 50 s−1. [Received: March 16, 2018; Accepted: October 24, 2018]

Experimental study on the viscosity-temperature characteristics and rheological properties of offshore heavy oil

The viscosity-temperature characteristics and rheological properties of heavy oil were investigated experimentally. Experimental results indicate that viscosity is sensitive to temperature, and it is a binary function of temperature and shear rate meeting preferably Arrhenius equation. In addition, the semi-log curve of viscosity-temperature can be divided into three regions and there is no obvious turning point, which exhibits that the internal microstructure of heavy oil during the heating process changes gradually. Besides, activation energy of low temperature range is higher than that of high temperature range. Moreover, the heavy oil always behaves as Newtonian fluid when temperature is higher than crystallisation temperature. Furthermore, on condition that temperature is less than crystallisation temperature, the heavy oil behaves as pseudo-plastic fluid characterising shear thinning phenomenon when shear rate is less than critical shear rate, and it presents as Bingham fluid with yield stress when shear rate falls between 10 and 50 s−1. [Received: March 16, 2018; Accepted: October 24, 2018]

Processing rheological behavior of functionalized silica/natural rubber composites

The filler networks of natural rubber (NR) silica-filled coupling agents KH560, Si69, and NXT were studied using a rubber processing analyzer (RPA). The effects of different coupling agents on the rheological behavior of silica-filled NR were investigated. The results showed that the three types of coupling agents could control the surface properties of silica, diminish the silica network, reduce the storage modulus and loss modulus, weaken the Payne effect, and improve processability. A comprehensive modification effect was observed for the coupling agent NXT. For different modified silica loading scenarios, the rheological properties of natural rubber composites filled with silica modified by the silane coupling agent NXT were assessed. The Payne effects were more obvious with the increased loading of fillers, while G′ and G″ nonlinearly rose with the increase of frequency. Finally, the platform effect appeared, demonstrating the shear thinning phenomenon. The best compatibility and minimum extent of agglomeration of silica was obtained from the composite filled with 50 phr silica.

Insight on the influence of nano zinc oxide on the thermal, dynamic mechanical, and flow characteristics of Poly(lactic acid)– zinc oxide composites

Composites of Poly(lactic acid) (PLA) and spherical zinc oxide (ZnO) nanoparticles were prepared using melt processing followed by injection molding. The effect of nanosized ZnO on the molecular structure, thermal properties, dynamic mechanical properties, and flow characteristics of PLA composites were analyzed. Scanning electron microscopy images illustrated the formation of ZnO aggregates through PLA matrix. The molecular weight of PLA‐ZnO experienced a substantial decline by 55%, suggesting the presence of ZnO provoked degradation of PLA during composite preparation. Glass transition temperature of PLA‐ZnO decreased by 18% as compared with pure PLA, confirming the deleterious role of ZnO in PLA. The ZnO nanoparticles acted as a reactant and increased the thermal degradation rate. However, the incorporation of ZnO into PLA increased the crystallinity up to 20% and the storage modulus of composites in glassy state by 10%. The higher peak value of tan δ in composites suggested the more viscous behavior, which was further supported by lower number average molecular weight. The complex viscosity of composites exhibited a large Newtonian region over low shear rate, followed by shear thinning phenomenon. A significant decrease (96%) in complex viscosity was observed with the addition of ZnO into PLA. POLYM. ENG. SCI., 59:1242–1249 2019. © 2019 Society of Plastics Engineers

Numerical simulation of debris-flow behavior based on the SPH method incorporating the Herschel-Bulkley-Papanastasiou rheology model

A rational rheology model is critical for the numerical simulation of debris-flow behavior. The Bingham model commonly used in many current studies has failed to simulate the shear thickening and thinning phenomenon in experiments. We report an alternative solution by incorporating the Herschel-Bulkley-Papanastasiou (HBP) model with the smoothed particle hydrodynamic (SPH) method. The SPH simulation is based on the open-source DualSPHysics scheme, upon which we built a development by the Bingham-based rheology model in our previous study. In this paper, a straightforward improvement is made such that the HBP model is incorporated to describe the constitutive law between particles, extending the compatibility of the simulation to dilatant and pseudoplastic fluids. To illustrate the performance of the HBP-based SPH method, first, a sensitivity analysis was performed to investigate the influence of important rheological coefficients. The proposed method was then verified by a dam-break experiment of water-clay mixtures and the case study of the 2010 Yohutagawa debris-flow event in Japan. The results indicate a good accordance between simulation and observation. A discussion regarding the potential and limitations of the current method concludes the paper.

Liquid-Behaviors-Assisted Fabrication of Multidimensional Birefringent Materials from Dynamic Hybrid Hydrogels.

Liquid-solid transition is a widely used strategy to shape polymeric materials and encode their microstructures. However, it is still challenging to fully exploit liquid behaviors of material precursors. In particular, the dynamic and static liquid behaviors naturally conflict with each other, which makes it difficult to integrate their advantages in the same materials. Here, by utilizing a shear-thinning phenomenon in the dynamic hybrid hydrogels, we achieve a hydrodynamic alignment of cellulose nanocrystals (CNC) and preserve it in the relaxed hydrogel networks due to the much faster relaxation of polymer networks (within 500 s) than CNC after the unloading of external force. During the following drying process, the surface tension of hydrogels further enhances the orientation index of CNC up to 0.872 in confined geometry, and these anisotropic microstructures demonstrate highly tunable birefringence (up to 0.004 14). Due to the presence of the boundaries of dynamic hydrogels, diverse xerogels including fibers, films, and even complex three-dimensional structures with variable anisotropic microstructures can be fabricated without any external molds.

Influence of MoS₂ Nanosheet Size on Performance of Drilling Mud.

Water-based drilling mud (WBM) is a non-Newtonian fluid that has a variety of applications such as in transporting cuttings during drilling, protecting the borehole, and cooling the drill bit. With the development of nano-technology, various nanoparticles have been synthesized and have been added to WBM to improve its performance. Shear thinning is the most important factor in drilling mud and this attribute can be improved when two-dimensional particles are added. MoS2 nanoparticles, which represent a typical two-dimensional material, are easy to synthesize in large quantities and have a high thermal conductivity and low coefficient of friction. Since the two-dimensional structure, thermal conductivity, and low coefficient of friction of MoS2 would improve the performance of WBM, we experimented with MoS2 nanosheets as an additive, under optimal conditions, using various samples each with uniform sizes and thicknesses of nanosheets. A large amount of MoS2 nanosheets was synthesized, sorted by thickness and diameter, and added to drilling mud. The diameter of MoS2 was divided into a small diameter group (about 100–400 nm) and a big diameter group (about 300–650 nm), and the thickness was divided into 1–2 nm and 5–10 nm groups. Experimental results showed that when MoS2 is added to WBM, shear thinning occurs more strongly. In addition, the addition of MoS2 with a thickness of 1–2 nm and a diameter of 300–650 nm resulted in the highest increase in viscosity and thermal conductivity of WBM. As a result, we experimentally confirmed that MoS2 can be used as an additive to increase the thermal conductivity and viscosity of WBM and to make shear thinning phenomenon more.

Rheological properties of cellulose nanocrystals engineered polylactic acid nanocomposites

Ecofriendly materials such as polylactic acid (PLA) and cellulose nanocrystals (CNCs) are widely sought as potential substitute for petrochemical-based plastics. Uniform dispersion of cellulose nanocrystals in polymer matrices has inhibited their wide-spread application. In this study the influence of masterbatch preparation techniques on molecular structure, melt strength, rheological and dynamic mechanical properties of nanocomposite were systematically analyzed. Film casting and spin-coating methods were used to prepare masterbatches. Nanocomposites were obtained by masterbatch dilution via melt compounding followed by injection molding process. The higher molecular weight and lower molecular number were observed in spin-coated samples in comparison with film cast nanocomposites. The spin-coated nanocomposites exhibited higher storage modulus than film cast samples in the glassy state. However, tan δ curves exhibited higher peak value in spin-coated nanocomposites, which were in good agreement with higher dispersity index of spin-coated samples. The complex viscosity of PLA and nanocomposites exhibited non-Newtonian behavior at a low shear rate, followed by shear thinning phenomenon. The spin-coated nanocomposites demonstrated higher complex viscosity than film cast samples, which was attributed to higher molecular weight in spin-coated samples. The shear-thinning tendency in spin-coated samples was higher than film cast nanocomposites.

Rheological characteristic of impregnating pitch from modified pitch

The refined pitch (1#) and impregnating pitch (2#) were obtained under certain conditions with the modified pitch as the raw materials. The data of viscosity and shear stress for each pitch have been tested by rotational viscometer. The flow activation energy and non-Newtonian index sample 1# and 2# have been calculated by Arrhenius equation and Saal equation. The results show that the flow activation energy of each sample was 109.13 kJ mol−1 and 133.71 kJ mol−1, and non-Newtonian index was 4.78 and 5.31, respectively. The processed data of Williams–Landel–Ferry (WLF) equation showed that the free volume of two pitches increased with increasing the temperature above the softening point. But impregnating pitch had a smaller free volume than refined pitch at the same temperature. What is more, the shear thinning phenomenon occurred under the shear rate of 40 s−1 and temperatures of 108 °C and 150 °C for sample 1# and 2#, respectively. When the shear rate was less than 10 s−1, temperatures were above 114 °C and 156 °C, and the shear thickening phenomenon has been taken place for pitch sample 1# and 2#, respectively. The impregnation temperature of samples 1# and 2# was 130 °C and 180 °C which is determined by viscosity–temperature curves. The power-law model and Robertson–Stiff model were applicable for describing the rheological characteristic of two pitches, and both pitches belonged to power-law fluid.

Recycled clay/PET nanocomposites evaluated by novel rheological analysis approach

Clay-polymer nanocomposites exhibit complex rheological behavior due to physical and also possibly chemical interactions between individual phases. Up to now, rheology of clay-polymer nanocomposites has been usually described by evaluation of complex viscosity curve (shear thinning phenomenon), storage modulus curve (G´ secondary plateau) or plotting parameters characterizing damping behavior (e.g. Van Gurp-Palmen-plot, Cole-Cole plot). On the contrary to evaluation of damping behavior, new approach – based on evaluation of rigidity behavior – was tested, where the values of cot δ were calculated and called as „storage factor“, analogically to broadly used loss factor. Afterwards, values of storage factor were integrated over measured frequency range and called as “cumulative storage factor”. In this contribution, clay-PET nanocomposites with different organoclays have been prepared and characterized by both conventional as well as novel analysis approach. Rheological results have been supported by AFM micrographs.

Rheological and structural properties of rice bran protein-flaxseed (Linum usitatissimum L.) gum complex coacervates

Complex coacervation of protein/polysaccharide mixtures has obtained considerable research in the encapsulation of bioactive materials. The rheological properties of the coacervates of rice bran protein/flaxseed gum (RBP/FG) at different pH values including 3.3, 4.0 and 5.3 and varying protein to polysaccharide ratios 3:1, 6:1 and 9:1 were investigated using small amplitude oscillatory shear (SAOS). Moreover, the interrelationship between the ζ-potential, FTIR and viscoelastic properties of the samples was studied. The coacervates showed shear-thinning phenomenon due to the linear reduction of complex viscosity (η*) by increasing frequency. Furthermore, the highest complex modulus (G*) and more compact coacervate structure were obtained at pH = 4.0, revealing less deformability and flow behavior. All the coacervates showed higher storage modulus (G′) than loss modulus (G″) indicating the formation of highly interconnected gel-like structure and were fitted by the Power law model. The maximum fracture stress was obtained at pH 4.0 revealing the highest intermolecular interactions between RBP and FG. The absolute ζ-potential of the coacervate at pH 4.0 and R = 9:1 was close to 0 and less than the other samples in which the highest fracturability and gel strength of the complex coacervate was achieved. It seems this property of the coacervate would be suitable for encapsulation of bioactive materials. The high aggregation of coacervates at pH 4.0 makes them more readily neutralized by protein binding. FTIR results showed that the spectrum of the coacervate was different from each individual biopolymer, related to their compatibility and intermolecular interactions between the functional groups of RBP and FG. Consequently, RBP/FG coacervates can be managed to some extent to achieve proper textural properties in dairy formula through manipulating pH and biopolymer mixing ratio.

Linear low‐density polyethylene/poly(ethylene terephthalate) blends compatibilization prepared by an eccentric rotor extruder: A morphology, mechanical, thermal, and rheological study

ABSTRACTIn this study, various poly(ethylene terephthalate) (PET) and linear low‐density polyethylene (LLDPE) with maleic anhydride‐grafted LLDPE (LLDPE‐g‐MAH) compatibilizer were melt blended under an elongational flow. A novel extrusion device, eccentric rotor extruder (ERE), was developed to supply such flow during the process. Including morphology, mechanical properties, melting behavior, and rheological behavior were studied. The morphological study showed that the compatibility between LLDPE and PET was greatly improved with LLDPE loading up to 80 wt %. Mechanical tests indicated that LLDPE could toughen PET to some extent. Moreover, a comparison of samples prepared between ERE and conventional extruder was made and demonstrated the sample prepared by ERE can exhibit better mechanical properties. Differential scanning calorimetry results revealed that PET can promote the crystallinity of LLDPE. Rheological behavior indicated that the complex viscosity of the blends exhibited strong shear thinning phenomenon with increasing LLDPE content, particularly in high‐frequency range blend with the LLDPE weight ratio of 80 wt % was more sensitivity to shear rate than neat LLDPE. The G′‐G″ curves of the blends also revealed that the microstructure of the blends changed significantly with the addition of LLDPE which was consistent with the scanning electron micrographs that PET particles became smaller and distributed more uniform with increasing LLDPE content. Furthermore, the blends showed similar stress relaxation mechanism with adding LLDPE content from 60 to 100 wt %. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46489.