Search

Recently, reversible cluster formation was identified as an underlying cause of anomalously large solution viscosities observed in some concentrated monoclonal antibody (mAb) formulations, which poses a major challenge to the use of subcutaneous injection for some mAbs. A fundamental understanding of the structural and dynamic origins of high viscosities in concentrated mAb solutions is thus of significant relevance to mAb applications in human health care, as well as being of scientific interest. Herein, we present a detailed investigation of an IgG1-based mAb to relate the short-time dynamics and microstructure to significant viscosity changes over a range of pharmaceutically relevant physiochemical conditions. The combination of light scattering, small-angle neutron scattering, and neutron spin echo measurement techniques conclusively demonstrates that, upon addition of Na2SO4, these antibodies form strongly bound reversible dimers at dilute concentrations that interact with each other to form large, loosely bound, transient clusters when concentrated. This hierarchical structure formation in solution causes a significant increase in the solution viscosity.

Dense colloidal suspensions are processed in a wide variety of industries. Challenges for pumping suspensions and slurries at high concentrations include shear thickening and dilation, which can have deleterious consequences. These systems are shear sensitive close to the jamming point, meaning that a significant increase in high shear viscosity can be observed with just a few percent change in volume fractions. Therefore, accurate and rapid determination of the jamming point can greatly aid formulation. Typically, conventional rheometry identifies the jamming point by a time-consuming process, whereby multiple flow curves of suspensions of different volume fraction are measured and extrapolated to the volume fraction where the viscosity diverges. We present an alternative approach for rapid, one-step, experimental determination of the jamming point for aqueous suspensions. The procedure monitors the shear stress under constant shear stress or shear rate as the sample is dewatered using immobilization cell rheometry, until the viscosity diverges. The method is validated by comparing the results of this work with conventional rheometry for a model suspension. Then it is applied to examine the effect of grafting a short-chain polymer to particles, comprising an industrial suspension of silica-coated titania. Polymeric coating of the particles increases the jamming concentration and mitigates shear thickening, qualitatively consistent with predictions from simulations. [ABSTRACT FROM AUTHOR]

A population balance model appropriate for the shear flow of thixotropic colloidal suspensions with yield stress is derived and tested against experimental data on a model system available in the literature. Modifications are made to account for dynamic arrest at the onset of the yield stress, in addition to enforcing a minimum particle size below which breakage is not feasible. The resulting constitutive model also incorporates a structural based relaxation time, unlike existing phenomenological models that use the inverse of the material shear rate as the relaxation time. The model provides a reasonable representation of experimental data for a model thixotropic suspension in the literature, capturing the important thixotropic timescales. When compared to prevalent structure kinetics models, the coarse-grained population balance equation is shown to be distinct, emphasizing the novelty of utilizing population balances as a basis for thixotropic suspension modeling. © 2016 American Institute of Chemical Engineers AIChE J, 63: 517-531, 2017 [ABSTRACT FROM AUTHOR]

Densities and viscosities of binary mixtures containing 1-butyl-3-methylimidazolium tetrafluoroborate with water over the salt-rich region concentrations are reported for a temperature range of (283.15 to 373.15) K and compared with literature. The temperature dependence of the mixture densities and dynamic viscosities are accurately described by an empirical, linear relationship and by the Vogel-Fulcher-Tammann (VFT) equation, respectively. We identify a correlation between the excess mixture viscosity and the excess molar volume in the ionic liquid rich regime that is motivated by free volume theory. The broader validity of this correlation is tested against literature data for aqueous mixtures of similar ionic liquids. [ABSTRACT FROM AUTHOR]

The present study develops a fully consistent extension of the approach pioneered by Farris ["Prediction of the viscosity of multimodal suspensions from unimodal viscosity data," Trans. Soc. Rheol. 12, 281-301 (1968)] to describe the viscosity of polydisperse suspensions significantly improving upon our previous model [P. M. Mwasame, N. J. Wagner, and A. N. Beris, "Modeling the effects of polydispersity on the viscosity of noncolloidal hard sphere suspensions," J. Rheol. 60, 225-240 (2016)]. The new model captures the Farris limit of large size differences between consecutive particle size classes in a suspension. Moreover, the new model includes a further generalization that enables its application to real, complex suspensions that deviate from ideal non-colloidal suspension behavior. The capability of the new model to predict the viscosity of complex suspensions is illustrated by comparison against experimental data. [ABSTRACT FROM AUTHOR]

he present study develops an extension of the approach pioneered by Farris [Trans. Soc. Rheol. 12, 281-301 (1968)] to model the viscosity in polydisperse suspensions. Each smaller particle size class is assumed to contribute to the suspension viscosity through a weighting function in two ways: first, indirectly, by altering the background viscosity, and second, directly, by increasing the contribution of the larger particles to the suspension viscosity. The weighting functions are developed in a consistent fashion as a power law with the exponent, h, a function of the relative volume fraction ratio and the base, g, a function of the solid particle size ratio. The model is fit to available theoretical and experimental results for the viscosity of several binary suspensions and shows good to excellent agreement depending on the functions g and h chosen. Once parameterized using binary suspension viscosity data, the predictive capability to model the viscosity of arbitrary continuous size distributions is realized by representing such distributions with equivalent ternary approximations selected to match the first six moments of the actual size distribution. Model predictions of the viscosity of polydisperse suspensions are presented and compared against experimental data. [ABSTRACT FROM AUTHOR]

The shear flow of non-Brownian glass spheres suspended in a concentrated colloidal dispersion that exhibits non-Newtonian rheology is investigated. At low volume fractions, the addition of non-Brownian spherical particles to the colloidal dispersion leads to an increase in the steady shear viscosity as well as the dynamic moduli. The flow curves of these suspensions are qualitatively similar to the suspending colloidal dispersion medium, and as such, in this semidilute regime, the suspension data can be shifted on to that of the colloidal dispersion medium at constant shear stress with shift factors comparable to those predicted for spherical particles in a Newtonian fluid. At higher volume fractions of non-Brownian spheres, the shear thickening power law exponent increases with the addition of non-Brownian particles. This increase in the shear thickening power law exponent is shown to be consistent with the effects of confinement on the shear thickening colloidal dispersion by the larger non-Brownian particles. [ABSTRACT FROM AUTHOR]

Models, theories, and simulations for the low shear viscosity of Brownian, hard-sphere dispersions are examined and evaluated against literature data. Hydrodynamic and thermodynamic contributions are explicitly treated and the volume fraction dependence of the experimental data is validated against the high frequency or high shear viscosity. A good description of the data is realized by a new, semiempirical model based on mode coupling theory, where [lowercase_phi_synonym]m=[lowercase_phi_synonym]g=0.57, supporting dynamical arrest at the ideal glass transition. [ABSTRACT FROM AUTHOR]

The article discusses the role of shear thickening in colloidal dispersions. It states that a change in viscosity will likely to happen when colloidal fluids experience shear stress resulting to the stiffening of the products such as paints, cements and shampoos. It adds that scientists and physics community have studied the highly nonlinear materials to deal the problems occurring in the shear-thickening colloidal dispersions.

Abstract: A micromechanical model for the zero shear viscosity of polyampholyte-stabilized colloidal dispersions based on the osmotic overlap potential is proposed and tested against model system measurements. This model relates the shear viscosity of polyampholyte-stabilized colloidal dispersions to the oncotic pressure of polyampholyte solutions through an interparticle potential and an effective hard-sphere scaling. The results of viscosity calculations based on independently measured parameters compare favorably to experimental measurements on model, silica dispersions stabilized with adsorbed photographic grade gelatin. The results support a direct link between the capacity of polyampholytes and polyelectrolytes to stabilize dispersions and control dispersion viscosity and their solution oncotic pressure. The model is also demonstrated to provide a master curve for literature data for the zero shear viscosity of polyampholyte stabilized colloidal dispersions. [Copyright &y& Elsevier]

We present direct measurements of the evolution of the segmental-level microstructure of a stable shear-banding polymerlike micelle solution during flow startup and cessation in the plane of flow. These measurements provide a definitive, quantitative microstructural understanding of the stages observed during flow startup: an initial elastic response with limited alignment that yields with a large stress overshoot to a homogeneous flow with associated micellar alignment that persists for approximately three relaxation times. This transient is followed by a shear (kink) band formation with a flow-aligned low-viscosity band that exhibits shear-induced concentration fluctuations and coexists with a nearly isotropic band of homogenous, highly viscoelastic micellar solution. Stable, steady banding flow is achieved only after approximately two reptation times. Flow cessation from this shear-banded state is also found to be nontrivial, exhibiting an initial fast relaxation with only minor structural relaxation, followed by a slower relaxation of the aligned micellar fluid with the equilibrium fluid's characteristic relaxation time. These measurements resolve a controversy in the literature surrounding the mechanism of shear banding in entangled wormlike micelles and, by means of comparison to existing literature, provide further insights into the mechanisms driving shear-banding instabilities in related systems. The methods and instrumentation described should find broad use in exploring complex fluid rheology and testing microstructure-based constitutive equations. [ABSTRACT FROM AUTHOR]