Strong Shear Thinning Research Articles

Chain conformation and rheological behavior of exopolysaccharide from Bacillus mucilaginosus SM-01

The chain conformation and rheological behavior of an acidic hetero-exopolysaccharide from Bacillus mucilaginosus (BMPS) in aqueous solution were evaluated by using static and dynamic light scattering, viscometry and atomic force microscopy (AFM). BMPS displayed typical polyelectrolyte behavior in pure water and the intrinsic viscosity dramatically decreased with the addition of NaNO3. The Huggins constants k′ of 0.303 and the positive second virial coefficient A2 of BMPS in 0.1 M NaNO3 aqueous solution at 25 °C suggested that 0.1 M NaNO3 aqueous solution was a good solvent for BMPS. The relative stiffness parameter (B-value) was estimated to be 0.018, indicating the semi-flexibility of the BMPS backbone. The dependences among the intrinsic viscosity ([η]) and the radius of gyration (<s2>1/2) on molecular weight (Mw) in the range of Mw from 265 × 104 to 37.3 × 104 g mol−1, as well as the ratio of geometric to hydrodynamic radius revealed that BMPS exhibited an extended coil geometry in 0.1 M NaNO3 aqueous solution. The molecular size and shape of BMPS was further characterized by a wormlike cylinder model and observed directly by using AFM. The rheological results indicated that BMPS in pure water exhibited strong shear thinning property, and viscoelastic behavior was observed with solutions within 1.4–2.7% (w/v) consistent with the formation of entangled macromolecules in solution.

Modeling of rheological behavior for polymer nanocomposites via Brownian dynamic simulation

Reptation dynamics of the coarse-grained polymer molecular chain is investigated to predict rheological behavior of polymeric nanocomposites by applying Brownian dynamics simulation to the proposed full chain reptation model. Extensibility of polymer chain and constraint release from chain stretch or retraction are of main concern in describing the nanocomposite systems. Rheological results are well predicted by applying the improved simulation algorithm using stepwise Wiener processes. Strong shear thinning and elongational strain hardening are predicted and compared with the experimental results of polyamide 6/organoclay nanocomposites. The full chain reptation model enables us to predict dynamic motion of the polymer chain segments and understand mechanisms for characteristic rheological behaviors.

The W-criterion for the onset of shear banding in complex fluids

A stability analysis of planar shear flow shear of a homogeneous, complex fluid predicts that shear banding instabilities can grow in fluids with a shear thinning strength above Wc = 1 and dampen out in fluids with W < 1. The shear thinning strength, \( W\left(\dot{\gamma}\right)=-\kern0.32em \partial \kern0.5em \log \eta /\partial \kern0.5em \log \dot{\gamma} \), arises naturally as the lead material function for the stability analysis of shear thinning fluids. The onset of shear banding is modeled as shear-thinning instability, which is attributed to anomalously strong shear thinning. Not considered here are inertial or elastic instabilities. In lack of suitable viscosity data from experiments, a Carreau powerlaw fluid and a Carreau-Yasuda powerlaw fluid serve as testbeds for the W-criterion. The analysis shows that the limiting high shear viscosity, η∞, plays an important role in shear banding and that the ratio of the limiting high shear viscosity and zero shear viscosity, η∞/η0, has to be sufficiently small for shear banding to occur. The main purpose of this brief communication is to share this new stability criterion. Extensive testing is still needed and is planned for future study.

Carboxymethylated lignins with low surface tension toward low viscosity and highly stable emulsions of crude bitumen and refined oils

Kraft and organosolv lignins were subjected to carboxymethylation to produce fractions that were soluble in water, displayed a minimum surface tension as low as 34mN/m (25°C) and a critical aggregation concentration of ∼1.5wt%. The carboxymethylated lignins (CML), which were characterized in terms of their degree of substitution (31P NMR), elemental composition, and molecular weight (GPC), were found suitable in the formulation of emulsions with bitumens of ultra-high viscosity, such as those from the Canadian oil sands. Remarkably, the interfacial features of the CML enabled fuel emulsions that were synthesized in a very broad range of internal phase content (30–70%). Cryo-replica transmission electron microscopy, which was used here the first time to assess the morphology of the lignin-based emulsions, revealed the droplets of the emulsion stabilized with the modified lignin. The observed drop size (diameters<2μm) was confirmed by light scattering, which revealed a normal size distribution. Such characteristics led to stable emulsified systems that are amenable for a wide range of applications. Emulsification with CML afforded bitumen emulsions with very high colloidal stability (no change was noted for over one month) and with a strong shear thinning behavior. Both features indicate excellent prospects for storage, transport and spraying, which are relevant in operations for power generation, which also take advantage of the high heating value of the emulsion components. The ability of CML to stabilize emulsions and to contribute in their combustion was tested with light fuels (kerosene, diesel, and jet fuel) after formulation of high internal phase systems (70% oil) that enabled operation of a fuel engine. A significant finding is that under certain conditions and compared to the respective pure fuel, combustion of the O/W emulsions stabilized by CML presented lower NOx and CO emissions and maintained a relatively high combustion efficiency. The results highlight the possibilities in high volume application for lignin biomacromolecules.

Extra dissipation and flow uniformization due to elastic instabilities of shear-thinning polymer solutions in model porous media.

We study flows of hydrolized polyacrylamide solutions in two dimensional porous media made using microfluidics, for which elastic effects are dominant. We focus on semi-dilute solutions (0.1%-0.4%) which exhibit a strong shear thinning behavior. We systematically measure the pressure drop and find that the effective permeability is dramatically higher than predicted when the Weissenberg number is greater than about 10. Observations of the streamlines of the flow reveal that this effect coincides with the onset of elastic instabilities. Moreover, and importantly for applications, we show using local measurements that the mean flow is modified: it appears to be more uniform at high Weissenberg number than for Newtonian fluids. These observations are compared and discussed using pore network simulations, which account for the effect of disorder and shear thinning on the flow properties.

Emulsion Inks for 3D Printing of High Porosity Materials.

Photocurable emulsion inks for use with solid freeform fabrication (SFF) to generate constructs with hierarchical porosity are presented. A high internal phase emulsion (HIPE) templating technique was utilized to prepare water-in-oil emulsions from a hydrophobic photopolymer, surfactant, and water. These HIPEs displayed strong shear thinning behavior that permitted layer-by-layer deposition into complex shapes and adequately high viscosity at low shear for shape retention after extrusion. Each layer was actively polymerized with an ultraviolet cure-on-dispense (CoD) technique and compositions with sufficient viscosity were able to produce tall, complex scaffolds with an internal lattice structure and microscale porosity. Evaluation of the rheological and cure properties indicated that the viscosity and cure rate both played an important role in print fidelity. These 3D printed polyHIPE constructs benefit from the tunable pore structure of emulsion templated material and the designed architecture of 3D printing. As such, these emulsion inks can be used to create ultra high porosity constructs with complex geometries and internal lattice structures not possible with traditional manufacturing techniques.

A Note on Heat Transfer Enhancement in Laminar Impinging Flows With Shear Thinning Inelastic Fluids

A recent article presented axisymmetric numerical calculations showing substantial heat transfer enhancement in a laminar impinging flow with shear thinning inelastic fluids. This paper compares enhancement in planar and axisymmetric geometries and presents empirical dependencies correlating heat transfer rates to fluid rheology. The parametric correlation is expressed in the form ∼ ReGp. ReG is a generalized Reynolds number based on the reference strain rate and fluid rheology, and it is larger than the Newtonian Reynolds number for the same mean nozzle velocity and flow geometry. The value of p &gt; 0 is estimated from the numerical data for weak and strong shear thinning. Within the impinging zone spanning the nozzle cross section, the value of p is essentially similar for both geometries, but in the wall jet the planar flow shows a somewhat larger value. The total heat transfer rate in the planar wall jet may be two to ten times larger for a shear thinning fluid. This is because in shear thinning flow, the primary separation vortex is able to maintain the Nusselt number at a higher average value over a significantly longer length scale in the streamwise direction.

Physical, thermal, chemical and rheological characterization of cellulosic microfibrils and microparticles produced from soybean hulls

Soybean hulls were used to isolate cellulosic microfibrils (SMF) and brick-like microparticles (SMP) by combining chemical and mechanical pretreatments. The key physical and chemical features of SMF and SMP were compared with those of micro and nanofibrillated cellulose (MNFC) obtained from fully bleached wood fibers. SMF and SMP chemical composition includes residual polysaccharides and lignin that endow such biologically-derived materials with properties typical of nanocellulosics. Compared to MNFC, SMF and SMP exhibit enhanced crystallinity (∼>10% higher) and thermal stability (onset degradation temperature >295°C and maximum degradation at 361 and 355°C). Such observations make SMF and SMP suitable for reinforcement in thermoplastic composites. A strong shear thinning behavior was observed for aqueous dispersions of SMF and SMP, revealing that these cellulose microstructures are of interest for rheology modification, coatings and films. Overall, the availability and low cost of biomass from residual soybean hulls constitutes a viable option for their use as a feedstock for the production and development of novel materials from SMF and SMP.

Rheological properties of a polysaccharide isolated from Adansonia digitata leaves

The rheological properties of Adansonia digitata leaf polysaccharide were studied in dilute and semi-dilute solutions. The intrinsic viscosity of the polysaccharide obtained by Fedors equation and the combined Huggins and Kraemer extrapolations was ∼3.27 dL/g. The polysaccharide contained random coil macromolecules with mass average molecular mass of 4.01 × 106 g/mol. The polysaccharide in semi-dilute concentrations exhibited strong shear thinning property, and viscoelastic behaviour was observed with solutions within (3–5% (w/w)) consistent with the formation of entangled random coil macromolecules in solution. The polysaccharide solutions were sensitive to temperature and the minimum energy to initiate flow in 4.0% polysaccharide solution calculated from Arrhenius plot of zero shear viscosity as a function of temperature was 48.6 kJ/mol. The FTIR spectral studies of the polysaccharide confirmed the presence of uronic acid groups.

Rheological, Textural and Flavour Properties of Yellow Mustard Sauce as Affected by Modified Starch, Xanthan and Guar Gum

Influence of a modified starch-gum thickening system on the rheological, textural and flavour properties of yellow mustard sauce was studied. The rheological measurements indicated that the sauces exhibited a weak gel-like, strong shear thinning behaviour. Dynamic viscoelasticity measurements showed that the sauces with modified starch (MS) and xanthan gum (XG) presented superior viscoelastic properties to those with MS and guar gum (GG) samples. All tested sauces showed non-Newtonian, pseudoplastic and thixotropic fluids characteristics. Parameters such as hardness, springiness, cohesiveness, gumminess and spreadability were used to evaluate the textural properties, and the results indicated that MS/XG was more influential than MS/GG on the textural properties. Sensory analysis suggested that 0.4 % MS/0.3 % XG, 0.4 % MS/0.4 % XG and 0.4 % MS/0.4 % GG were superior thickeners for the yellow mustard sauces. The flavours of these three sample groups with the highest sensory scores and a sample with only MS were analysed by an electronic nose, which showed that the electronic nose was able to distinguish their differences.

Double emulsions for the compatibilization of hydrophilic nanocellulose with non-polar polymers and validation in the synthesis of composite fibers.

A route for the compatibilization of aqueous dispersions of cellulose nanofibrils (CNFs) with a non-polar polymer matrix is proposed to overcome a major challenge in CNF-based material synthesis. Non-ionic surfactants were used in CNF aqueous dispersions equilibrated with an organic phase (for demonstration, a polystyrene solution, PS, was used). Stable water-in-oil-in-water (W/O/W) double emulsions were produced as a result of the compromise between composition and formulation variables. Most remarkably, the proposed route for CNF integration with hydrophobic polymers removed the need for drying or solvent-exchange of the CNF aqueous dispersion prior to processing. The rheological behavior of the double emulsions showed strong shear thinning behavior and facilitated CNF-PS co-mixing in solid nanofibers upon electrospinning. The morphology and thermal properties of the resultant nanofibers revealed that CNFs were efficiently integrated in the hydrophobic matrix which was consistent with the high interfacial area of the precursor double emulsion. In addition, the morphology and quality of the composite nanofibers can be controlled by the conductivity (ionic strength) of the CNF dispersion. Overall, double emulsion systems are proposed as a novel, efficient and scalable platform for CNF co-processing with non-polar systems and they open up the possibility for the redispersion of CNFs after removal of the organic phase.

Glycerine Treated Nanofibrillated Cellulose Composites

Glycerine treated nanofibrillated cellulose (GNFC) was prepared by mixing aqueous nanofibrillated cellulose (NFC) suspensions with glycerine. Styrene maleic anhydride (SMA) copolymer composites with different loadings of GNFC were prepared by melt compounding followed by injection molding. The incorporation of GNFC increased tensile and flexural modulus of elasticity of the composites. Thermogravimetric analysis showed that as GNFC loading increased, the thermal stability of the composites decreased marginally. The incorporation of GNFC into the SMA copolymer matrix resulted in higher elastic modulus (G′) and shear viscosities than the neat SMA copolymer, especially at low frequencies. The orientation of rigid GNFC particles in the composites induced a strong shear thinning behavior with an increase in GNFC loading. The decrease in the slope of elastic modulus with increasing GNFC loading suggested that the microstructural changes of the polymer matrix can be attributed to the incorporation of GNFC. Scanning electron microscopy (SEM) images of fracture surfaces show areas of GNFC agglomerates in the SMA matrix.

Rheology of cellulose nanofibrils in the presence of surfactants.

Cellulose nanofibrils (CNFs) present unique opportunities for rheology modification in complex fluids. Here we systematically consider the effect of ionic and non-ionic surfactants on the rheology of dilute CNF suspensions. Neat suspensions are transparent yield-stress fluids which display strong shear thinning and power-law dependence of modulus on concentration, G' ∼ c(2.1). Surfactant addition below a critical mass concentration cc produces an increase in the gel modulus with retention of optical clarity. Larger than critical concentrations induce significant fibril aggregation leading to the loss of suspension stability and optical clarity, and to aggregate sedimentation. The critical concentration was the lowest for a cationic surfactant (DTAB), cc ≈ 0.08%, while suspension stability was retained for non-ionic surfactants (Pluronic F68, TX100) at concentrations up to 8%. The anionic surfactant SDS led to a loss of stability at cc ≈ 1.6% whereas suspension stability was not compromised by anionic SLES up to 8%. Dynamic light scattering data are consistent with a scenario in which gel formation is driven by micelle-nanofibril bridging mediated by associative interactions of ethoxylated surfactant headgroups with the cellulose fibrils. This may explain the strong difference between the properties of SDS and SLES-modified suspensions. These results have implications for the use of CNFs as a rheology modifier in surfactant-containing systems.

Rheological and microstructural properties of the chia seed polysaccharide

Chia seed polysaccharide (CSP) was extracted from chia (Salvia hispanica) seeds, and its rheological and microstructural properties in aqueous solutions were studied. CSP solution exhibited Newtonian and shear thinning flow patterns depending on shear rate when the concentration was ≤0.06% (w/v). CSP solutions at concentrations >0.06% (w/v) exhibited strong shear thinning behaviour within the shear rate tested (0.001–300s−1). The transition from dilute to semi-dilute regime occurred at a critical concentration (C*) of 0.03gdL−1. The intrinsic viscosity was high (∼16dLg−1) and concentration dependence of zero shear viscosity in the semi-dilute regime followed η0∝C2.7 relationship. The storage modulus (G′) was higher than the loss modulus (G″) at all experimental frequencies and their frequency dependence was negligible at all tested concentrations. Apparent shear viscosity was smaller than dynamic complex viscosity at equivalent values of deformation and G′ varied with the square of concentration indicating a gel-like behaviour in CSP solutions within 0.02–3.0% (w/v) concentrations. Controlled acid hydrolysis of purified CSP yielded various low molecular fractions with fairly uniform polydispersity giving a Mark–Houwink–Sakurada relationship of intrinsic viscosity equaling to 1.52×10−4 (molecular weight)0.803 (dLg−1).

The influence of rare earth ions on the rheological behavior of polyamide

The polyamide 66 (PA66)/lanthanum acetate blends with small amounts of salt loadings (a parts per thousand currency sign 1 wt% of PA) have been prepared in a twin-screw extruder. The rheology of PA66 and its blends has been investigated by a rotational rheometer. The results suggested that with the salt loading in excess of 0.2 wt% the typical Newtonian viscosity plateau disappeared and both the low-frequency complex viscosities eta* and storage modulus G' of blends were much higher than those of neat PA66, the storage modulus was higher than the loss modulus at low frequencies (tan delta GaEuro(3)). While the viscosity followed a strong shear thinning with increasing frequency, the eta* and G' decreased significantly even lower than those of neat PA66 at high frequencies. The combination of dynamic mechanical analysis (DMA) and X-ray photoelectron spectroscopy (XPS) analysis has revealed that coordination effect occurred between lanthanum and carbonyl oxygen atoms in amide groups of the polymer to form pseudocrosslinked network structure, which makes the glass transition temperatures (T (g)) and storage modulus (E') of blends enhanced. The network structure formation-destruction and chains entanglement-disentanglement processes at different frequencies are responsible for the above rheological behaviors of blends.

Controlling shear thinning property of lime silica based mold flux system with borate additive at 1623 K

We have studied the shear thinning property of mold flux with borate additive using a rotational type rheometer at various shear rates. Mold flux at 1623K is currently used in the steel industry as a lubricant to reduce the shear force exerted on a solidifying steel shell in an oscillating mold. In an actual casting process, the enhancement of shear thinning property might be beneficial for a casting process. Therefore, the present study is designed to control the shear thinning property of mold flux at 1623K by changing a borate concentration. For the first step of the present study, Raman spectroscopy is used to identify structural change of mold flux with increasing a borate concentration. The second step is to conduct viscosity measurement by changing shear rates with a rotational rheometer. The degree of shear thinning has been successfully estimated by the flow behavior index of Oswald–de Waele's power law. In doing so, we successfully achieved the strong shear thinning property of mold flux and discovered the rationale behind this. In order to maximize the shear thinning property of lime silica based glass forming liquid, it is essential to understand the degree of polymerization (DP) and stiffness of entire mold flux structure.

Controlling the shear thinning property of calcium silicate melts by addition of Si3N4

Calcium silicate melts at high temperature are valuable as a lubricant for continuous casting of steel. They are limited by the contradictory situation in that high viscosity is required under low shear rate whereas low viscosity is needed under high shear rate. To resolve such problem, we conducted a rheological study to generate a strong shear thinning behavior of a calcium silicate melts which is an ideal thermal property for continuous casting of steel. We found that a small amount of silicon nitride leads to a strong shear thinning property, allowing a high viscosity at low shear rate without significant changes in the viscosity at higher shear rates. Such trend is completely opposite to the one previously suggested with a borate additive. This improvement of the shear thinning property arises because each additive enables these calcium silicate melts to have a shear thinning favorable structure in thoroughly different manner.

Study the Effects of Xanthan Gum and Aluminium Stearate on the Properties of Oil-in-Water Emulsion Drilling Fluids

This research article investigates the effects of xanthan gum and aluminium stearate on the rheological and filtration properties of oil-in-water emulsion drilling fluids. In addition, the stability of emulsion drilling fluids was analysed by measuring interfacial properties such as zeta potential, interfacial tension, contact angle and microscopic properties to estimate the effects of xanthan gum and aluminium stearate on the shape and size of emulsion droplets. The rheological and filtration properties were measured using API recommended standard procedures. Xanthan gum worked as viscosity modifier, aluminium stearate worked as filtrate loss-controlling agent, and both additives also worked as perfect stabilizer for the emulsion systems. The steady-state shear stress–shear rate measurement technique was applied to examine the shear thinning (pseudoplastic) behaviour of the emulsion drilling fluids. The fluids followed strong shear thinning (pseudoplastic) behaviour with increasing concentration of diesel oil and xanthan gum which is a desirable parameter for drilling fluids. It was also found that rheological and filtration properties are stable at 80°C temperature. By optimizing the concentrations of the additives in emulsion system, favourable drilling fluids can be developed which may be used for oil and gas well drilling.

Thermal behavior, dynamic mechanical properties and rheological properties of poly(butylene succinate) composites filled with nanometer calcium carbonate

PBS/nano-CaCO3 composites with various nano-CaCO3 weight fractions were prepared by melt blending. The thermal behavior, dynamic mechanical properties and rheological properties of the composites were investigated. DSC measurements revealed that the nano-CaCO3 particles had little influence on the crystallization and melting behavior of PBS. Thermogravimetric analysis showed that the introduction of nano-CaCO3 tended to improve the thermal stability of PBS. Dynamic mechanical analysis showed that the G′ and G″ of the PBS/nano-CaCO3 composites were improved significantly when the nano-CaCO3 content was not more than 3wt%, while the G′ and G″ were mainly decided by the PBS matrix when the nano-CaCO3 content exceeded 3wt%. Rheological results showed that G′ < G″ over the frequency range, illustrating the viscous behavior of the samples. The η* of all the samples remained almost constant when the frequency was not more than 0.25 rad/s, which showed the characteristic of a Newtonian fluid. A strong shear thinning effect was observed for all the samples when the frequency exceeded 0.25 rad/s. Furthermore, the microstructure and the relaxation mechanism of the PBS/nano-CaCO3 composites mainly depended on the PBS matrix.

Cellulose nanofibrils for one-step stabilization of multiple emulsions (W/O/W) based on soybean oil

Cellulose nanofibrils (CNF) were incorporated in water-in-oil (W/O) microemulsions and emulsions, as well as water-in-oil-in-water (W/O/W) multiple emulsions using soybean oil. The addition of CNF to the aqueous phase expanded the composition range to obtain W/O/W emulsions. CNF also increased the viscosity of the continuous phase and reduced the drop size both of which increased the stability and effective viscosity of the emulsions. The effects of oil type and polarity on the properties of the W/O/W emulsions were tested with limonene and octane, which compared to soybean oil produced a smaller emulsion drop size, and thus a higher emulsion viscosity. Overall, CNF are a feasible alternative to conventional polysaccharides as stability enhancers for normal and multiple emulsions that exhibit strong shear thinning behavior.