Intermediate Shear Rates Research Articles

Miscellaneous prospects of invasive Lantana camara biomass-a standpoint on bioenergy generation and value addition.

Investigation of Lantana camara biomass for potential bioenergy generation integrates invasive species (IS) management with the unabated demand for bio-energy. In the present investigation, L. camara was used to produce bio-oil by thermochemical conversion (pyrolysis). The resultant product evinced energy yield of 62.58% with 64.95% of elemental carbon (C) content and endorsed the suitability of L. camara bio-oil for biofuel applications and value addition. Thermogravimetric (TG-DTG) analysis revealed a short thermal degradation profile, whereas spectroscopic analyses detected a host of organic compounds such as esters, phenols, ketones, aldehydes, aliphatics, and aromatics. The economic analysis of L. camara biomass conversion technology carried out in this study proved to be commercially competitive and viable versus petroleum refining. Antimicrobial and antioxidant assays with bio-oil evinced highest zone of inhibition (ZOI) against Candida albicans (31.02mm), and displayed strong antioxidant property (DPPH IC50 value 233.72 ± 0.2μg/ml). The bio-oil exhibited rheological characteristics of shear thinning and pseudoplastic fluid, particularly at low and intermediate shear rates. The present study highlights the multifaceted advantages of utilizing L. camara biomass, which include environmental remediation via waste management, bioenergy generation, and the feasibility of generating value-added products.

Molecular Processes Leading to Shear Banding in Entangled Polymeric Solutions.

The temporal and spatial evolution of shear banding during startup and steady-state shear flow was studied for solutions of entangled, linear, monodisperse polyethylene C3000H6002 dissolved in hexadecane and benzene solvents. A high-fidelity coarse-grained dissipative particle dynamics method was developed and evaluated based on previous NEMD simulations of similar solutions. The polymeric contribution to shear stress exhibited a monotonically increasing flow curve with a broad stress plateau at intermediate shear rates. For startup shear flow, transient shear banding was observed at applied shear rates within the steady-state shear stress plateau. Shear bands were generated at strain values where the first normal stress difference exhibited a maximum, with lifetimes persisting for up to several hundred strain units. During the lifetime of the shear bands, an inhomogeneous concentration distribution was evident within the system, with higher polymer concentration in the slow bands at low effective shear rate; i.e., γ˙<τR-1, and vice versa at high shear rate. At low values of applied shear rate, a reverse flow phenomenon was observed in the hexadecane solution, which resulted from elastic recoil of the molecules within the slow band. In all cases, the shear bands dissipated at high strains and the system attained steady-state behavior, with a uniform, linear velocity profile across the simulation cell and a homogeneous concentration.

Cohesive sediment: intermediate shear produces maximum aggregate size

We interpret the Taylor–Green cellular vortex model in terms of the Kolmogorov length and velocity scales, in order to study the balance between aggregation and breakup of cohesive sediment in fine-scale turbulence. One-way coupled numerical simulations, which capture the effects of cohesive, lubrication and direct contact forces on the flocculation process, reproduce the non-monotonic relationship between the equilibrium floc size and shear rate observed in previous experiments. The one-way coupled results are confirmed by select two-way coupled simulations. Intermediate shear gives rise to the largest flocs, as it promotes preferential concentration of the primary particles without generating sufficiently strong turbulent stresses to break up the emerging aggregates. We find that the optimal intermediate shear rate increases for stronger cohesion and smaller particle-to-fluid density ratios, and we propose a simple model for the equilibrium floc size that agrees well with experimental data reported in the literature.

Phenomenological characterization of blood's intermediate shear rate: a new concept for hemorheology.

The phenomena of aggregation, breakdown, and disaggregation of the rouleaux of red blood cells (RBCs) in addition to deformability affect the human blood viscosity at different shear rates. In this study, the intermediate shear rate is introduced and defined when the effect of aggregation on the change of blood viscosity is diminished; and afterwards, the alteration in the blood viscosity is dominantly affected by the deformation of RBCs. With this respect, modeling the effective parameters on the blood shear-thinning behavior including hematocrit and plasma viscosity was performed for the two different shear regions discriminated by the proposed intermediate shear rates. The presented rheological model reflects a phenomenological approach to assess the human blood viscosity with an average error of ± 5% compared to experimental data for hematocrits between 0.299 and 0.702, subjected to various shear rates from 0.2 to 680 1/s. The temperature changes as well as biochemical effects on whole blood viscosity are characterized by the introduced plasma viscosity-dependent model. The presented comprehensive model could be used for better understanding of blood flow hemodynamics and analyzing the shear dependence of aggregation and deformability behaviors of RBCs.

Non-Newtonian Rheology in Twist–Bend Nematic Liquid Crystals

A simple qualitative model has been presented to describe shear rheological behavior of the twist–bend nematic liquid crystals (NTB). It has been found that at relatively low shear rate (dot {gamma } leqslant {{dot {gamma }}_{{c1}}}) the stress tensor σ created by this shear strain, scales as sigma propto {{dot {gamma }}^{{1/2}}}. Thus, the effective viscosity decreases with the shear rate (eta propto {{dot {gamma }}^{{ - 1/2}}}) manifesting so-called shear-thinning phenomenon. At intermediate shear rate {{dot {gamma }}_{{c1}}} leqslant dot {gamma } leqslant {{dot {gamma }}_{{c2}}}, σ is almost independent of dot {gamma } (a sort of plateau), and at large shear rate (dot {gamma } geqslant {{dot {gamma }}_{{c2}}}), sigma propto dot {gamma }, and it looks like as Newtonian rheology. Within our theory the critical values of the shear rate scales as {{dot {gamma }}_{{c1}}} propto {{(tilde {eta }_{2}^{0}{text{/}}tilde {eta }_{3}^{0})}^{2}}, and {{dot {gamma }}_{{c2}}} propto {{(tilde {eta }_{2}^{0}{text{/}}tilde {eta }_{3}^{0})}^{4}}, respectively. Here tilde {eta }_{2}^{0} and tilde {eta }_{3}^{0} are bare coarse grained shear viscosity coefficients of the effective smectics equivalent to the NTB phase at large scales. The results of our work are in the agreement with recent experimental studies.

Application of thin gap rheometry for high shear rate viscosity measurement in monoclonal antibody formulations

The key highlight of this work was to develop a thin gap methodology on a mechanical rheometer for characterizing high concentration monoclonal antibody formulations. This work was done from applied formulation perspective to provide guidance on an additional measurement protocol with the objective of further reducing sample volume requirement for biopharmaceutical formulation rheology measurements and provide viscosity data over a wide shear rate range. This is especially relevant for early stage discovery where there are sample volume limitations. This developed methodology in addition to an understanding of the diffusion interaction parameter was then in turn utilized to elucidate the effect of surfactants and excipients on the high shear rate viscosity of high concentration monoclonal antibodies. In this study, gap dependent changes in the fundamental rheological behavior were observed. At higher gaps, an initial shear thinning behavior was observed at lower shear rates and this trend was found to disappear at thin gaps. This shear thinning which is due to air water interface disappears as the gap size decreases. At high shear rates, there is a convergence of all the viscosity data for all the gaps. This also converges with the mVROC data. However, at smallest gaps studied (50 µm) shear thickening is observed at intermediate shear rates. This maybe attributable to the protein molecules undergoing flow induced aggregation due to increased confinement thereby causing shear thickening and an increase in viscosity. However, this trend eventually diminishes at higher shear rates which could be attributed to flow induced alignment of protein aggregates thereby causing a decrease in viscosity. Addition of either excipients (like Arginine- HCl, NaCl) or surfactants (like polysorbate80) seem to have a drastic impact on shear thickening caused potentially by flow induced aggregation. Addition of excipients also resulted in approximately 33–50% decrease in the viscosity of monoclonal antibody (mAb) solution and the diffusion interaction parameter kD was seen to be indicative of the high shear rate viscosity behavior of these formulations.

Unifying disparate rate-dependent rheological regimes in non-Brownian suspensions.

A typical dense non-Brownian particulate suspension exhibits shear thinning (decreasing viscosity) at low shear rate or stress followed by a Newtonian plateau (constant viscosity) at intermediate shear rate or stress values which transitions to shear thickening (increasing viscosity) beyond a critical shear rate or stress value and finally undergoes a second shear thinning transition at extremely high shear rate or stress values. In this study, we unify and quantitatively reproduce all the disparate rate-dependent regimes and the corresponding transitions for a dense non-Brownian suspension with increasing shear rate or stress. We employ discrete particle dynamics simulations based on the proposed mechanism to elucidate its accuracy. We find that a competition between interparticle interactions of hydrodynamic and nonhydrodynamic origins and the switching in the dominant stress scale with increasing the shear rate or stress lead to each of the above transitions. Inclusion of traditional hydrodynamic interactions, attractive or repulsive Derjaguin-Landau-Verwey-Overbeek (DLVO) interactions the interparticle contact interactions, and a constant friction (or other constraint mechanism) reproduces the initial thinning as well as the shear thickening transition. However, to quantitatively capture the intermediate Newtonian plateau and the second shear thinning, an additional nonhydrodynamic interaction of non-DLVO origin and a decreasing coefficient of friction, respectively, are essential, thus providing an explanation for the presence of the intermediate Newtonian plateau along with reproducing the second shear thinning in a single framework. Expressions utilized for various interactions and friction are determined from experimental measurements and hence result in excellent quantitative agreement between the simulations and previous experiments.

Thixotropic Behavior of Reconstituted Debris-Flow Mixture

Time-dependent rheological properties and thixotropy of reconstituted debris-flows samples taken from channel bank deposits are examined using a commercial rheometer equipped with a vane rotor geometric system. Sweep tests and creep tests were carried out involving mixtures having different grain concentrations ranging between 50% and 58%. Different initial conditions of the mixtures were considered in order to analyze the effects of aging and rejuvenation (thixotropy) over a short period of time and long period of time. Tested slurries show viscosity bifurcation, yield stress and time-dependent behavior. According to the experimental results, three different regimes were identified: a lower shear rate regime, corresponding to a shear rate lower than the critical value; an intermediate banding shear rate regime characterized by static and dynamic yield stress level; and a higher shear rate regime where the flowing debris behaves as a non-Newtonian fluid characterized by a constant steady state ultimate apparent viscosity. In any case, the initial state of the mixture and the sediment concentration affects the ultimate steady state rheology and the time-dependent (thixotropy) slurries’ behavior.

Soft channel formation and symmetry breaking in exotic active emulsions

We use computer simulations to study the morphology and rheological properties of a bidimensional emulsion resulting from a mixture of a passive isotropic fluid and an active contractile polar gel, in the presence of a surfactant that favours the emulsification of the two phases. By varying the intensity of the contractile activity and of an externally imposed shear flow, we find three possible morphologies. For low shear rates, a simple lamellar state is obtained. For intermediate activity and shear rate, an asymmetric state emerges, which is characterized by shear and concentration banding at the polar/isotropic interface. A further increment in the active forcing leads to the self-assembly of a soft channel where an isotropic fluid flows between two layers of active material. We characterize the stability of this state by performing a dynamical test varying the intensity of the active forcing and shear rate. Finally, we address the rheological properties of the system by measuring the effective shear viscosity, finding that this increases as active forcing is increased—so that the fluid thickens with activity.

Percolation of polydisperse nanorods in polymer nanocomposites: Insights from molecular dynamics simulation

The aspect ratio of nanorods (NR) is polydisperse in the real application which is often omitted in the electrical conductivity. In this work, by adopting a coarse-grained molecular dynamics simulation, the effect of the polydispersity index (PDI) of NRs on the conductive probability of polymer nanocomposites has been investigated in details under the quiescent state and under the shear field which aims to uncover their relationship. By analyzing the conductive network, it is found that the percolation threshold is inversely proportion to the PDI under the quiescent state. On one hand, one long NR can connect more other NRs than one short NR. In addition, more long NRs participate in building the conductive network with the PDI than short NRs, which thus enhances the conductive probability. Compared with in the quiescent state, the percolation threshold is enhanced under the shear field. By characterizing the orientation degree and the connection mode of both long NRs and short NRs, the shear field significantly changes the original conductive network which rationalizes the conductive probability. Interestingly the percolation threshold first increases and then decreases with the shear rate which reaches the maximum value at the intermediate shear rate. At the low shear rate, the initial orientation of NRs induces the breakage of the conductive network perpendicular to the shear direction which improves the percolation threshold. In addition, more short NRs participate in building the conductive network than long NRs with the further increase of the shear rate. Meanwhile more direct contact aggregation structure of NRs appears which induces the recovery of the conductive network.

Homogeneous Ice Nucleation Under Shear.

Homogeneous ice nucleation involving a water flow is subject to shear, which may greatly affect the ice nucleation rate. In this work, we investigate the homogeneous ice nucleation rate under shear through molecular dynamics simulations. It is found that the ice nucleation rate changes nonlinearly with varying shear rates and reaches a maximum at an intermediate shear rate. Such a behavior is determined by two distinct effects of shear rates. On the one hand, shear increases the free energy barrier for the nucleation, which hinders the ice nucleation. On the other hand, shear enhances the diffusion of water molecules, assists the adsorption of water molecules on the ice nucleus, and consequently promotes the growth of ice nucleus. The latter effect dominates at low shear rates, while the former effect becomes significant at high shear rates. The competition between these two effects leads to a non-monotonic dependence of the ice nucleation rate on the shear rate.

Coagulation behavior of spherical particles embedded in laminar shear flow in presence of DLVO-and non-DLVO forces

HypothesisComplex and coupled interaction between coagulation mechanisms results in a nonlinear variation of coagulation rate with shear rate. CalculationsCoagulation behavior of colloidal dispersions is investigated in a laminar shear flow by solving the Fokker-Plank equation for pair probability density function, simultaneously incorporating the effect of (i) Brownian diffusion, (ii) fluid flow, (iii) van der Waals attraction and (iv) double layer repulsion force. Furthermore, analysis foremost studies the effect of non-DLVO solvation force. FindingsTheoretical analysis with experimental validation reveals that, coagulation rate varies non-linearly with the shear rate in presence of double-layer repulsion force, due to the strong coupling of coagulation mechanisms. This is observed by an occurrence of coagulation minima at intermediate shear rate. Increase in double layer repulsion force either facilitates or hinders the occurrence of redistribution of particles, as observed by early or late fall of coagulation rate. Systems with different ionic strengths show a crossover of coagulation rates, whereas those with different solvation forces do not show similar trend. Analysis also shows that, ad hoc additivity assumption of individual Brownian and shear coagulation rates does not hold in case of laminar shear flow, against to that observed in extensional flow [Melis et al. (AIChE J., 999, 1383)].

Controlling the rheological properties of W1/O/W2 multiple emulsions using osmotic swelling: Impact of WPI-pectin gelation in the internal and external aqueous phases

The purpose of this study was to create W1/O/W2 Multiple Emulsions by controlled osmotic swelling, and gelation of whey protein isolate (WPI) and high methoxy pectin (HMP) microspheres in internal and external acidic aqueous phases. Three different kinds of W1/O/W2 multiple emulsions (ME) were prepared, with 8 wt.% Polyglycerol polyricinoleate (PGPR) in their oil phases, with WPI and HMP in internal and external aqueous phases (250 mM NaCl, pH 3.5): (i) ME1: The inner aqueous phase (W1) contained 40% buffer solution, while W2 consisted of 10% WPI and 2% HMP; (ii) ME2: W1 contained 10% WPI, with 2% HMP (250 mM NaCl) in W2; (iii) ME3: 10% WPI and 2% HMP in W1, while W2 contained 1% Tween 80. The original multiple emulsions were diluted by different factors (1:0 to 1:5 with citrate buffer solution), and subject to thermal treatment from 25 to 90 °C to compare their microstructural and rheological properties. It was observed that the ME1 emulsion had higher viscosity and shear modulus than for other emulsions. After dilution however, the shear viscosity of ME3 was higher than ME1 and ME 2 at intermediate shear rates, which showed that the emulsions were osmotically well controlled in internal aqueous phases. Optical and confocal microscopy also supported our rheological measurements with evidence of WPI-HMP gelation, and osmotic swelling, in original and in swollen multiple emulsions. The results of this work may provide useful information about the encapsulation of bioactive compounds, in internal and external aqueous phases, for the development of healthier reduced-fat products in food industry.

Alignment of worm-like micelles at intermediate and high shear rates

HypothesisRheology combined with Small-Angle Neutron Scattering (Rheo-SANS) can determine the local structural order in Worm-Like Micelle (WLM) solutions when the shear rate increases beyond the ending of the gradient shear banding. There, micelles are supposedly aligned, but viscosity reveals a transition regime as the shear rate increases. ExperimentsThe mixture of 3-[dimethyl(tetradecyl)azaniumyl]propane-1-sulfonate (TDPS), sodium dodecylsulfate (SDS) (R = [SDS]/[TDPS] = 0.55), and a water solution of NaCl (0.2 mol/L), was studied with mechanical rheology and Small-Angle Neutron Scattering (SANS) in the quiescent fluid and under flow. FindingsThe system self-assembles in WLMs and presents gradient shear banding. SANS patterns of the bands formed during the shear banding were obtained in a Couette geometry along the 1–2 plane, as well as the orientation parameter along the gap. At very high shear rates, in the paranematic phase, we found an apparent transition on the flow curves with its corresponding change in the orientation parameter. The origin of this transition is unclear, but we present possible explanations of why we observe it.

Depletion layer dynamics of polyelectrolyte solutions under Poiseuille flow

Complex liquids flow through channels faster than expected, an effect attributed to the formation of low-viscosity depletion layers at the boundaries. Characterization of depletion layer length scale, concentration, and dynamics has remained elusive due in large part to the lack of suitable real-space experimental techniques. The short length scales associated with depletion layers have traditionally prohibited direct imaging. By overcoming this limitation via adaptations of stimulated emission depletion (STED) microscopy, we directly measure the concentration profile of polymer solutions at a nonadsorbing wall under Poiseuille flow. Using this approach, we 1) confirm the theoretically predicted concentration profile governed by entropically driven depletion, 2) observe depletion layer narrowing at low to intermediate shear rates, and 3) report depletion layer composition that approaches pure solvent at unexpectedly low shear rates.

Assessing the arrest of coalescence due to Marangoni effects in flowing emulsions using population balance

The conditions for coalescence arrest due to Marangoni effect of surfactant enriched emulsions flowing through a microfluidic device are analyzed. For that aim, we develop a Population Balance Equation model that allows the quantification of coalescence occurrence for emulsion systems at different surfactant concentration making use of isotherms. Besides, our model requires three parameters with physical significance to describe the behavior of the emulsions under shear to include Marangoni flow. The results were benchmarked by comparison to microfluidic experiments reported in the literature. Hydrodynamic coupling was observed at intermediate shear rates wherein coalescence was favored compared to the kinetics without surfactant. The coalescence kinetics was found to depend on the intertwined roles of both surfactant coverage and flow properties. These results represent a step towards the use of Population Balance Equation models not only for the study and prediction of conditions leading to coalescence arrest determined by either the external shear, repulsive barriers or Marangoni based forces but also for product design and control.

Individual Molecular Dynamics of an Entangled Polyethylene Melt Undergoing Steady Shear Flow: Steady-State and Transient Dynamics.

The startup and steady shear flow properties of an entangled, monodisperse polyethylene liquid (C1000H2002) were investigated via virtual experimentation using nonequilibrium molecular dynamics. The simulations revealed a multifaceted dynamical response of the liquid to the imposed flow field in which entanglement loss leading to individual molecular rotation plays a dominant role in dictating the bulk rheological response at intermediate and high shear rates. Under steady shear conditions, four regimes of flow behavior were evident. In the linear viscoelastic regime (), orientation of the reptation tube network dictates the rheological response. Within the second regime (), the tube segments begin to stretch mildly and the molecular entanglement network begins to relax as flow strength increases; however, the dominant relaxation mechanism in this region remains the orientation of the tube segments. In the third regime (), molecular disentangling accelerates and tube stretching dominates the response. Additionally, the rotation of molecules become a significant source of the overall dynamic response. In the fourth regime (), the entanglement network deteriorates such that some molecules become almost completely unraveled, and molecular tumbling becomes the dominant relaxation mechanism. The comparison of transient shear viscosity, , with the dynamic responses of key variables of the tube model, including the tube segmental orientation, , and tube stretch, , revealed that the stress overshoot and undershoot in steady shear flow of entangled liquids are essentially originated and dynamically controlled by the component of the tube orientation tensor, rather than the tube stretch, over a wide range of flow strengths.

Dynamics of a polymer under multi-gradient fields.

Effects of multi-gradient fields on the transport of a polymer chain are investigated using Langevin dynamics simulations. We observe that the natural frequency of tumbling follows Wi 0.66 scaling, where Wi is the Weissenberg number. The distribution of angular tumbling time has exponentially decaying tails, and at high Wi, it deviates from Poisson behavior. Competition between the velocity gradient, which results in a shear flow in the system, and the solvent quality gradient arising due to the interaction among monomers reveals that there is another scaling associated with the angular tumbling time distribution. Moreover, at low temperature, we observe unusual behavior that at intermediate shear rates, the decay rate ν decreases with Wi.

Rheological study of new dispersions of carbon nanotubes in the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

Dispersions of three different types of carbon nanotubes in a 1 wt% proportion in the low viscosity 1-ethyl-3-methylimidazolium ([EMIM][DCA]) ionic liquid have been obtained. The neat ionic liquid presents Newtonian behavior, but the addition of carbon nanotubes increases the viscosity with respect to [EMIM][DCA] in the following order: Single-Walled Carbon Nanotubes (SWCNTs) > aligned Multi-Walled Carbon Nanotubes (aligned-MWCNTs) > Multi-Walled Carbon Nanotubes (MWCNTs), and the resulting fluids show non-Newtonian behavior. SWCNTs and MWCNTs dispersions present shear thinning with increasing shear rate, but a shear thickening effect for aligned-MWCNTs at intermediate shear rate values at room temperature has been observed. This effect disappears at 100 °C. The thermal response of the viscosity of [EMIM][DCA] and the CNTs-IL dispersions can be fitted to the Arrhenius model. For [EMIM][DCA] and the dispersion with MWCNTs the viscous behavior prevails at low frequencies, with a cross point at a critical frequency value which decreases with increasing temperature. However, the dispersions of SWCNTs and aligned-MWCNTs present storage modulus values higher than loss modulus in the whole range of frequency.

A quest for shear banding in ideal and non ideal colloidal rods

We assess the possibility of shear banding of semidilute rod-like colloidal suspensions under steady shear flow very close to the isotropic-nematic spinodal, using a combination of rheology, small angle neutron scattering, and laser Doppler velocimetry. Model systems are employed which allow for a length and stiffness variation of the particles. The rheological signature reveals that these systems are strongly shear thinning at moderate shear rates. It is shown that the longest and most flexible rods undergo the strongest shear thinning and have the greatest potential to form shear bands. Although we find a small but significant gradient of the orientational order parameter throughout the gap of the shear cell, no shear banding transition is tractable in the region of intermediate shear rates. At very low shear rates, gradient banding and wall slip occur simultaneously, but the shear bands are not stable over time.