Shear Thinning Phenomenon Research Articles

Associating behavior of one polyimide with high molecular weight in solution through a relatively weak interaction

An associating polymer generally contains a small fraction of strongly interacting groups that can form stable aggregates. In this study, a novel soluble polyimide (PI) (6FDA-TFDB) sample with high molecular weight is synthesized; it contains a large fraction of relatively weak interacting groups. Investigation on the solution property and scaling law relationship between η0-ηs and volume fraction shows that this sample exhibits the behavior of associating polymer; this behavior fits the theory of unrenormalized sticky Rouse model and sticky reptation model in a broad volume fraction region, and the scaling exponents in different volume fraction ranges and the critical volume fractions are determined. Moreover, when the volume fraction is above ϕ* (overlap volume fraction), abnormal shear thinning phenomenon occurs. Oscillation frequency experiment for concentrated polyimide solutions demonstrates that the polyimide solution tends to become a gel above the critical volume fraction due to numerous weak dipole-dipole and π-π interactions. In the UV–Vis spectra, absorption peak shows a red shift with volume fraction, demonstrating that aggregates form in concentrated polyimide solution. Synchrotron radiation small-angle X-ray scattering (SAXS) experiment reveals the appearance of domain, which comes from the aggregates of PI segments. Finally, combined with the quantum chemical calculation, one model based on relatively weak interaction (i.e., dipole-dipole and π-π interactions) from chemical units of polyimides is proposed to explain the associating behavior of high molecular weight polyimide in solution and the shear thinning phenomenon. This study broadens the range of associating polymers.

Rheological and structural characteristics of whey protein-pectin complex coacervates

Complex coacervation of protein/polysaccharide has found much interest for the encapsulation of bioactive materials. The rheological properties of the coacervates of whey protein/high methoxyl pectin (WPI/HMP) at different pH including 3.0, 3.5 and 4.0 were investigated. The complex viscosity (η*) of the coacervate was decreased linearly with frequency, showing the shear-thinning phenomenon of the coacervates. Furthermore, the highest complex modulus (G*) and more compact coacervate were obtained at pH 3.5, revealing less deformability and flow behaviour. All the coacervates showed higher storage modulus (G′) than loss modulus (G″) indicating the formation of highly interconnected gel-like structure. The maximum fracture stress was obtained at pH 3.5 revealing the highest intermolecular interactions between WPI and HMP. It seems the high fracture stress and gel strength of the complex coacervate would be suitable for encapsulation of bioactives. The high aggregation was also achieved at pH 3.5, as the lower charge density of HMP should make it more readily neutralized by whey protein binding. FTIR results showed the spectrum of the coacervate was different from each individual biopolymer, related to their compatibility and intermolecular interactions between the functional groups of HMP and WPI. Although, to get more insight toward dynamic rheological measurements in surveying the interaction of any biopolymer blends, further work should be carried out for other biopolymers.

Relaxation oscillation of borosilicate glasses in supercooled liquid region

Most supercooled non-polymeric glass-forming melts exhibit a shear thinning phenomenon, i.e., viscosity decreases with increasing the strain rate. On compressing borosilicate glasses at high temperature, however, we discovered an interesting oscillatory viscous flow and identified it as a typical relaxation oscillation caused by the peculiar structure of borosilicate glass. Specifically, the micro-structure of borosilicate glass can be divided into borate network and silicate network. Under loading, deformation is mainly localized in the borate network via a transformation from the three coordinated planar boron to trigonal boron that could serve as a precursor for the subsequent formation of a BO4 tetrahedron, while the surrounding silicate network is acting as a stabilization/relaxation agent. The formation of stress oscillation was further described and explained by a new physics-based constitutive model.

The rheological behavior of polysaccharides sequential extracted from Polygonatum cyrtonema Hua

The present study investigated the rheological properties of polysaccharides (HBSS, CHSS, DASS, CASS) sequentially extracted from Polygonatum cyrtonema Hua. The monosaccharide, uronic acid, total carbohydrate, protein content of four polysaccharides were analyzed. The total carbohydrate content of PCHPs (HBSS, CHSS, DASS, and CASS) were 78.39, 71.86, 69.99 and 73.73% respectively, containing Rha, Ara, Man, Gal besides uronic acid and protein. The non-Newtonian fluidic nature of PCHPs was affected by the types of polysaccharides, concentration, temperature, pH, types and concentration of salt ions. Specifically, the apparent viscosity of four PCHPs solutions at 1%(w/w) concentration were shown as CHSS>HBSS>CHSS>CASS with increased concentration and shear thinning phenomenon and decreased system temperature. Subsequently, the apparent viscosity of four PCHPs at pH 10 or pH 4 were lower than that at pH 7. The Na+ increased the apparent viscosity of HBSS at increasing concentrations, while, decreased for remaining fractions with increasing Na+ concentration. Moreover, higher Ca2+ concentration was inversely proportional to apparent viscosity of four PCHPs. The oscillatory rheological properties showed that linear viscoelastic region of PCHPs was 1–4% which resulted into viscoelastic material. HBSS, DASS and CASS at 0.1%(w/w) showed more viscous behavior at low frequency and enhanced elastic property with the increasing oscillation frequency.

Rheological properties of microalgae slurry for application in hydrothermal pretreatment systems

Herein, the rheological properties of microalgae slurries (Chlorella pyrenoidosa) under different mass fractions and temperatures (293–373 K) were reported, which can significantly affect the energy requirement of hydrothermal pretreatment process and hence the performance of fermentation processes. The experiment results showed that the microalgae slurry had a shear-thinning phenomenon, suggesting that microalgae slurry is a non-Newtonian fluid. For the first time, the phenomenon of variable flow behavior index under varying shear rates was discovered. In addition, the viscosity and yield stress of the microalgae slurries decreased from 293 to 343 K; above 343 K, they increased with the temperature. Scanning electron microscopy analyses showed that the surface of the microalgae cells became rougher when the temperature increased from 343 to 373 K. Finally, the equations of the viscosity of the microalgae slurry, based on the temperatures and shear rates, were obtained.

Formulation, characterization and antimicrobial properties of black cumin essential oil nanoemulsions stabilized by OSA starch.

Preparation of oil-in-water nanoemulsions has emerged as a subject of interest for the encapsulation of lipophilic functional ingredients to increase their stability and activity. In this study, black cumin essential oil nanoemulsions (BCO-NE) using different ratios of essential oil with canola and flax seed oils (ripening inhibitors) were formulated and stabilized with octenyl succinic anhydride (OSA) modified waxy maize starch. The nanoemulsions exhibited monomodal size distributions with mean droplet diameter below 200nm and zeta potential above -30, indicating a strong electrostatic repulsion between the dispersed oil droplets. Further, during storage (4weeks at 25°C±2) emulsions showed shear thinning phenomena and stability towards coalescence. Antimicrobial properties of nanoemulsions were determined by minimum inhibitory concentration and time-kill method against two Gram-positive bacterial (GPB) strains (Bacillus cereus and Listeria monocytogenes). Negatively charged BCO-NE showed prolonged bactericidal activities as compared to pure BCO due to better stability, controlled release and self-assembly with GPB cell membrane followed by destruction of cellular constituents. Our results suggest the application of BCO-NE may be exploited in aqueous food systems for extending the shelf life and other functional properties.

Lubricant shear thinning behavior correlated with variation of radius of gyration via molecular dynamics simulations.

The shear thinning of a lubricant significantly affects lubrication film generation at high shear rates. The critical shear rate, defined at the onset of shear thinning, marks the transition of lubricant behaviors. It is challenging to capture the entire shear-thinning curve by means of molecular dynamics (MD) simulations owing to the low signal-to-noise ratio or long calculation time at comparatively low shear rates (104-106 s-1), which is likely coincident with the shear rates of interest for lubrication applications. This paper proposes an approach that correlates the shear-thinning phenomenon with the change in the molecular conformation characterized by the radius of gyration of the molecule. Such a correlation should be feasible to capture the major mechanism of shear thinning for small- to moderate-sized non-spherical molecules, which is shear-induced molecular alignment. The idea is demonstrated by analyzing the critical shear rate for squalane (C30H62) and 1-decene trimer (C30H62); it is then implemented to study the behaviors of different molecular weight poly-α-olefin (PAO) structures. Time-temperature-pressure superpositioning (TTPS) is demonstrated and it helps further extend the ranges of the temperature and pressure for shear-thinning behavior analyses. The research leads to a relationship between molecular weight and critical shear rate for PAO structures, and the results are compared with those from the Einstein-Debye equation.

Low temperature produced calcium-doped zinc oxide thick film via screen printing technique as thermal interface material in LED application

Pure and calcium-doped zinc oxide thick films were deposited on Aluminium substrate by screen printing technique using nanocrystalline powder synthesized from co-precipitation method. Shear thinning phenomenon with increment of shear rate was observed during the rheological analysis for all pastes. X-ray diffraction results confirmed the formation of ZnO with preferred orientation along (101) plane. Peak shifting to lower angle was observed upon increment of doping concentration of calcium. Crystallite size of doped ZnO powder decreased in the range (from 35.4 to 42.4 nm) from 116.1 nm of pure ZnO. Surface morphology analysed by FESEM had revealed the reduction of voids with increasing doping concentration up to 7 wt% of doping, followed by a slightly increase in the number of voids at 9 wt% doping. AFM analysis showed that the surface roughness of films exhibited a decreasing trend with the increase of calcium dopant until 7 wt% but became rougher at 9 wt%. Peaks shifting of ZnO to lower wavenumber revealed by FTIR study indicated that doping had affected the lattice structure of ZnO in the films. Thermal characterization showed the introduction of calcium dopant had increased the thermal resistance of the thick films. This led to a better junction temperature (Tj) of LED of 46.4 °C when compared with Tj of pure ZnO film at 47.3 °C.

Role of hydrogen bond interactions in water–polyol medium in the thickening behavior of cornstarch suspensions

Rheological properties of suspensions are influenced by changes in the particle’s or suspending medium’s traits. Due to the ability of water and cornstarch to develop strong hydrogen bonds with each other and with hydroxyl groups of other liquids, it is promising to modify the suspending media with polyols to analyze the change in the Newtonian behavior of the suspensions. Cornstarch–water suspensions were prepared by adding different polyols viz.., glycerine, ethylene glycol (EG), and polyethylene glycol (PEG) to the suspending liquid (water) at various concentrations. The presence of possible chemical interaction due to the hydroxyl groups within the water–polyol systems was confirmed by Fourier transfer infrared spectroscopy (FTIR). The rheological parameters of pure cornstarch–water suspension were compared with that of water–polyol-based shear thickening fluids (STFs). The thickening behavior enhanced by three orders of magnitude with increasing glycerine and EG content for a constant particle concentration. However, the presence of PEG in the suspension resulted in a shear thinning phenomenon with a high yield stress unlike the other polyols. Thus, the presence of O–H interactions in the suspending liquid was presumed to control the flow phenomenon of these suspensions. A possible mechanism based on interactions has been proposed for the non-Newtonian flow in each suspension. The current work is one of a kind in demonstrating the role of hydrogen interactions within suspending medium on the thickening behavior of the cornstarch–water suspensions.

Investigation of rheological, structural, surface, optical and thermal properties of low temperature produced silver doped ZnO thick film as thermal interface material in lighting application

Effects of screen-printed AgxZn1−xO thick film deposited on Al substrate with composition 3 wt% ≤ x ≤ 9 wt% on the rheological, surface, vibrational and thermal properties were investigated in this paper. AgxZn1−xO powder with different doping concentration was synthesized through co-precipitation method and further mixed with solvent to form a thixotropic paste. The paste was screen-printed on Al substrate. Rheological behavior of pastes showed shear thinning phenomenon with increment of shear rate. Structural properties of pure and doped thick films were investigated by X-ray diffraction (XRD). It showed that (101) was a strong preferred orientation among other peaks. Field emission scanning electron microscopy (FESEM) results indicated the aggregated flake-like structure that become more prominent with increase of doping from 3 to 7 wt%. Surface roughness of the films exhibited a decreasing trend with the increase of silver content whereas the step analysis facilitated to identify the contact surface point of the film for thermal conduction in application purposes. By increasing the dopant’s concentration, peak position of ZnO had shifted within the range from 503 to 506 cm−1. FTIR spectra of the films showed no vibrational peaks related to AgO or Ag2O. Thermal characterization revealed a decreasing trend of film’s resistivity when the doping was increased to 7 wt%. The lowest achieved junction temperature with tested LED was measured at 47.32 °C at 7 wt% of silver doping.

Rheological Characteristics of Tailings Paste for Stope Backfill

In this work, rheological constants measurement and flow tests on powder slurries and tailings paste were carried out in order to get information needed to recycle tailings into backfiller for an underground stope. The tailings paste was Bingham fluid which can flow from larger stress than critical shear stress(yield stress). Apparent viscosity of the tailings paste demonstrates shear thinning phenomenon which decreases with increasing shear stress. The plastic viscosity and the yield stress of the powder slurries predicted by Bingham equation increased in order of fly ash < cement < ground blast furnace slag(GBFS) < tailings. This indicates that in case of making pastes of four powder systems (cement-fly ash-GBFS-tailings) for the stope backfill, its rheology was most affected by the tailings. Fresh tailings pastes will increase their flowability by adding the fly ash and the GBFS which can enhance long compression strength of harden tailings pastes due to pozzolanic property, thus facilitating transportation to the underground stope.

Paste-like cemented backfilling technology and rheological characteristics analysis based on jigging sands

To make backfilling body meet strength requirement, physical-chemical evaluation and proportioning tests were conducted on several backfilling materials. Jigging sands, #32.5 cement and fly ash were determined as backfilling aggregate, binding material and modified material, respectively. An optimized proportion of backfilling materials with a solid mass fraction of 78% and cement: fly ash: jigging sands mass ratio of 1:2:14, was suggested to Jiangan Pyrite Mine, China. The slurry made by optimized proportion produced obvious shear thinning phenomena, and was confirmed as paste-like slurry. To analyze its rheological characteristics, L-type pipeline test and Haake VT550 rotational viscometer test were conducted. Bingham and Casson fluid models were applied to several paste-like slurry samples to simulate flow and stress states; Casson fluid model was proved to have better simulation effect on paste-like slurry with shear thinning phenomena; rheological parameters of backfilling slurry made by suggested proportion were measured. Initial yield stress, average apparent viscosity and limiting viscosity are 55.35 Pa, 1.216 Pa·s and 0.48 Pa·s, respectively. Compared with Bingham fluid model, Casson fluid model has a better simulation effect on paste-like slurry with shear thinning phenomena, through calculating the residual standard deviations.

Cemented Backfilling Technology of Paste-Like Based on Aeolian Sand and Tailings

Aeolian sand, tailings, and #32.5 Portland cement were used to produce backfilling aggregate, and physicochemical evaluations and proportioning tests were conducted. It is revealed that a mixture of aeolian sand and tailings can be used as a backfilling aggregate for the complementarities of their physicochemical properties; e.g., high Al2O3 content in the aeolian sand and CaO content in the tailings, coarse particles of aeolian sand and fine particles of tailings, etc. In addition, the optimal backfilling aggregate was shown to have a mass fraction of 72%–74%, a cement–sand ratio of 1:8, and an aeolian sand proportion of 25%. Furthermore, viscometer tests were used to analyze the rheological characteristics, and the slurry in these optimized proportions exhibited shear thinning phenomena with an initial yield stress, which belongs to paste-like—a cemented backfilling slurry with a higher mass fraction than a two-phase flow and better flowability than a paste slurry. Finally, the application of this backfilling technology shows that it can not only realize safe mining, but also bring huge economic benefits, and has some constructive guidance for environmental protection.

Shear Thinning of Noncolloidal Suspensions.

Shear thinning-a reduction in suspension viscosity with increasing shear rates-is understood to arise in colloidal systems from a decrease in the relative contribution of entropic forces. The shear-thinning phenomenon has also been often reported in experiments with noncolloidal systems at high volume fractions. However its origin is an open theoretical question and the behavior is difficult to reproduce in numerical simulations where shear thickening is typically observed instead. In this letter we propose a non-Newtonian model of interparticle lubrication forces to explain shear thinning in noncolloidal suspensions. We show that hidden shear-thinning effects of the suspending medium, which occur at shear rates orders of magnitude larger than the range investigated experimentally, lead to significant shear thinning of the overall suspension at much smaller shear rates. At high particle volume fractions the local shear rates experienced by the fluid situated in the narrow gaps between particles are much larger than the averaged shear rate of the whole suspension. This allows the suspending medium to probe its high-shear non-Newtonian regime and it means that the matrix fluid rheology must be considered over a wide range of shear rates.

Effects of hall and ion slip on MHD peristaltic flow of Jeffrey fluid in a non-uniform rectangular duct

Purpose – The purpose of this paper is to theoretically study the problem of the peristaltic flow of Jeffrey fluid in a non-uniform rectangular duct under the effects of Hall and ion slip. An incompressible and magnetohydrodynamics fluid is also taken into account. The governing equations are modelled under the constraints of low Reynolds number and long wave length. Recent development in biomedical engineering has enabled the use of the periastic flow in modern drug delivery systems with great utility. Design/methodology/approach – Numerical integration is used to analyse the novel features of volumetric flow rate, average volume flow rate, instantaneous flux and the pressure gradient. The impact of physical parameters is depicted with the help of graphs. The trapping phenomenon is presented through stream lines. Findings – The results of Newtonian fluid model can be obtained by taking out the effects of Jeffrey parameter from this model. No-slip case is a special case of the present work. The results obtained for the flow of Jeffrey fluid reveal many interesting behaviours that warrant further study on the non-Newtonian fluid phenomena, especially the shear-thinning phenomena. Shear-thinning reduces the wall shear stress. Originality/value – The results of this paper are new and original.

Mechanical, thermal and rheological properties and morphology of poly (lactic acid)/poly (propylene carbonate) blends prepared by vane extruder

In this study, the poly (lactic acid) (PLA) and poly (propylene carbonate) (PPC) blends with different compositions were prepared by a novel vane extruder based on elongation rheology. The mechanical properties, morphologies, crystallization behavior, thermal stability, and rheological properties of the blends were investigated. Mechanical test showed that PLA could be toughened by PPC to some extent, and the impact strength of the PLA was maximized when PPC content was about 30%. Differential scanning calorimetry analysis revealed that PPC had little effect on the melting process, the crystallization behavior of PLA component in the blend was improved, and the cold crystallizability of PLA decreased with the increase of PPC content when the PPC content was less than 50%. Thermogravimetry analysis showed that the thermal stability of the blends was improved by compounding with PLA. Scanning electron microscope showed that the dispersion of PLA droplets in PPC matrix was better than that of PPC droplets in PLA matrix. Rheological test showed that the melt viscosity of the pure PLA and the blend with 10% PPC was insensitive to shear rate, and the blends melt appeared shear thinning phenomenon with the increase of PPC content. It also showed that the blends microstructure changed with the addition of PPC and the blends with PPC content in a certain range had similar stress relaxation mechanism. Copyright © 2016 John Wiley & Sons, Ltd.

Preparation and Properties of Polylactic Acid (PLA)/Silica Nanocomposites

ABSTRACTSurface-modified silica was incorporated into bio-based polylactic acid (PLA) to improve its performance. The modification by aminosilane on the silica was confirmed through FTIR (Fourier transform infrared) spectra. Following the aminosilane modification, polyethylene glycol methyl ether (PEGME) was grafted, via the aminosilane, on the silica to form the desired surface-modified silica (PEGME-silica). The grafting percentage of polyethylene glycol methyl ether was about 6.9 wt%. Unmodified silica, having underwent a similar treatment to maintain the same thermal history but without adding silane and PEGME, was also prepared. The PEGME-silica system had slightly higher tensile strength than the unmodified silica system, with a rheological study showing an enhanced polymer matrix-dispersed silica interaction and better dispersion in morphology observations being proposed as the cause. The dynamic storage modulus in the terminal zone was reduced for large amounts of highly dispersed surface-modified silica in comparison with unmodified silica. Tan δ decreased significantly with increasing unmodified silica contents in the low frequency region, resulting in solid-like behaviors. On the other hand, there was only a limited decrement for modified silica-filled samples in the corresponding ranges, especially for low dosages of the modified silica. The shear thinning phenomenon appeared to be more pronounced for unmodified silica at high silica content, but not for modified silica. To the best of our knowledge, this is the first report of the effect of polyethylene glycol methyl ether (PEGME)-modified nanosilica on the properties of PLA/silica nanocomposites prepared under a melt mixing process to illustrate the significance of surface modification via Cole–Cole plots.

Modification of polysulfone hollow fiber ultrafiltration membranes using hyperbranched polyesters with different molecular weights

A series of hyperbranched polyesters (HBPEs) using trimethylolpropane (TMP) as a core were synthesized via an esterification reaction, and the molecular weights of these HBPEs were 1600, 2260, 3370, and 5170 g/mol, respectively. Then, these HBPEs were added into dope solutions to prepare PSf hollow fiber membranes via a wet-spinning method. When the HBPE molecule weight increased from 1600 to 5170 g/mol, the initial viscosities of the PSf–HBPE–PEG400–DMAc dope solutions increased, and the shear-thinning phenomenon of these dope solutions became increasingly obvious. When these dope solutions were immersed into the deionized water, the demixing rate increased with an increase in the HBPE molecule weight at first and then decreased; this results in the increase of membrane porosity and the coexistence of finger-like and sponge-like structures. With the addition of HBPE, the start pure water contact angle and the mean effective pore size of the membranes decreased, and the Jw increased. For the mechanical properties of the membranes, the breaking strength and the elongation of the membranes also increased. Copyright © 2015 John Wiley & Sons, Ltd.

Rheological behavior and constitutive equations of heterogeneous titanium-bearing molten slag

Experimental studies on the rheological properties of a CaO–SiO2–Al2O3–MgO–TiO2–(TiC) blast furnace (BF) slag system were conducted using a high-temperature rheometer to reveal the non-Newtonian behavior of heterogeneous titanium-bearing molten slag. By measuring the relationships among the viscosity, the shear stress and the shear rate of molten slags with different TiC contents at different temperatures, the rheological constitutive equations were established along with the rheological parameters; in addition, the non-Newtonian fluid types of the molten slags were determined. The results indicated that, with increasing TiC content, the viscosity of the molten slag tended to increase. If the TiC content was less than 2wt%, the molten slag exhibited the Newtonian fluid behavior when the temperature was higher than the critical viscosity temperature of the molten slag. In contrast, the molten slag exhibited the non-Newtonian pseudoplastic fluid characteristic and the shear thinning behavior when the temperature was less than the critical viscosity temperature. However, if the TiC content exceeded 4wt%, the molten slag produced the yield stress and exhibited the Bingham and plastic pseudoplastic fluid behaviors when the temperature was higher and lower than the critical viscosity temperature, respectively. When the TiC content increased further, the yield stress of the molten slag increased and the shear thinning phenomenon became more obvious.

전단유동에서 온도, 전단속도, 계면장력 변화에 따른 에멀전의 유변학적 특성

We simulate an emulsion system under simple shear rates to analyze its rheological characteristics using the lattice Boltzmann method (LBM). We calculate the relative viscosity of an emulsion under a simple shear flow along with changes in temperature, shear rate, and surfactant concentration. The relative viscosity of emulsions decreased with an increase in temperature. We observed the shear-thinning phenomena, which is responsible for the inverse proportion between the shear rate and viscosity. An increase in the interfacial tension caused a decrease in the relative viscosity of the decane-in-water emulsion because the increased deformation caused by the decreased interfacial tension significantly influenced the wall shear stress. § 이 논문은 대한기계학회 2014년도 추계학술대회(2014. 11. 11.-14., 김대중컨벤션센터) 발표논문임. † Corresponding Author, joonlee@yonsei.ac.kr C 2015 The Korean Society of Mechanical Engineers