Browsing by Author "Wagner, Norman J."
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Item A polydisperse model for thixotropic elasto-viscoplastic suspensions of aggregating particles using population balances(AIChE Journal, 2023-09-18) Jariwala, Soham; Song, Rong; Hipp, Julie B.; Diemer, R. Bertrum; Wagner, Norman J.; Beris, Antony N.An improved population balance-based rheological constitutive framework for polydisperse aggregating suspensions is derived by incorporating detailed models for orthokinetic and perikinetic aggregation and shear breakage processes. The framework accounts for critical properties such as dynamic arrest, viscoelasticity, kinematic hardening, thixotropy, and yield stress to generate a full range of thixotropic elasto-viscoplastic (TEVP) response. Additionally, the model is thermodynamically consistent because the dynamics and timescales are completely determined by internal structural and kinetic variables. The model connects the rheological response to the structural descriptors such as the size distribution of agglomerates, mean sizes, fractal dimension, and agglomerate volume fraction. Predictions are compared against a wide range of shear rheology measurements data for model thixotropic suspensions of fumed silica and carbon black, including large amplitude oscillatory shear (LAOS), as well as ultra-small angle neutron scattering under steady shear (Rheo-uSANS).Item Anomalous rheological aging of a model thermoreversible colloidal gel following a thermal quench(The Journal of Chemical Physics, 2022-06-15) Suman, Khushboo; Wagner, Norman J.We investigate the aging behavior in a well-studied model system comprised of a colloidal suspension of thermoreversible adhesive hard spheres (AHS) but thermally quenched below the gel transition to much larger depths than previously studied. The aging behavior in the model AHS system is monitored by small amplitude oscillatory shear rheology measurements conducted while rapidly quenching from liquid state at 40{degree sign}C to a temperature below the gel temperature and new, anomalous aging behaviors are observed. Shallow quenches lead to monotonic development of the elastic modulus with time consistent with prior reports for the development of a homogeneous gel (Gordon et al., Journal of Rheology 2017). However, for deeper quenches, a unique and new phenomenon is reported - namely after an initial rise in the modulus, a reproducible drop in modulus is observed, followed by a plateau in modulus value. This drop can be gradual or sudden, and the extent of the drop, both depends on quench depth. After this drop in modulus, AHS gel evolves toward a quench-path independent state over the experimental timescale. These effects of the extent of quenching on aging behavior is hypothesized to be a consequence of quenching into different underlying thermodynamic states of colloidal gels and the possible influence of the adhesive glass dynamical arrest for the deepest quenches. The research connects homogeneous gelation with heterogeneous gel formation due to phase separation and shows that the extent of quench can be used as an independent parameter to govern the rheological response of the arrested gel.Item Combined Effects of Pressure and Ionic Strength on Protein–Protein Interactions: An Empirical Approach(Biomacromolecules, 2024-01-08) Paul, Brian; Furst, Eric M.; Lenhoff, Abraham M.; Wagner, Norman J.; Teixeira, Susana C. M.Proteins are exposed to hydrostatic pressure (HP) in a variety of ecosystems as well as in processing steps such as freeze–thaw, cell disruption, sterilization, and homogenization, yet pressure effects on protein–protein interactions (PPIs) remain underexplored. With the goal of contributing toward the expanded use of HP as a fundamental control parameter in protein research, processing, and engineering, small-angle X-ray scattering was used to examine the effects of HP and ionic strength on ovalbumin, a model protein. Based on an extensive data set, we develop an empirical method for scaling PPIs to a master curve by combining HP and osmotic effects. We define an effective pressure parameter that has been shown to successfully apply to other model protein data available in the literature, with deviations evident for proteins that do not follow the apparent Hofmeister series. The limitations of the empirical scaling are discussed in the context of the hypothesized underlying mechanisms. Graphical abstract available at: https://doi.org/10.1021/acs.biomac.3c01001Item Comparison of lunar and Martian regolith simulant-based geopolymer cements formed by alkali-activation for in-situ resource utilization(Advances in Space Research, 2021-12-20) Mills, Jennifer N.; Katzarova, Maria; Wagner, Norman J.Future human space exploration and habitation on the lunar and Martian surfaces necessitates in-situ resource utilization (ISRU) for the development of construction materials tailored for infrastructure and environmental protection. Here we explore the use of lunar and Martian regoliths to create construction materials with properties suitable for such structures as landing pads. Alkali activation of a spectrum of lunar and Martian regolith simulants generates geopolymer binders under ambient and vacuum curing conditions as well as exposure to extreme high and low temperatures (600 and −80 °C). Compressive strength is reduced for binders prepared from each simulant after curing under vacuum and exposure to sub-zero temperatures. In lunar simulant binders, the compressive strength is increased after heating to 600 °C, but the opposite effect is observed in the Martian simulant binder. Amorphous aluminosilicate content and percentage of small particles in the simulants are hypothesized to have a positive impact on compressive strength under ambient curing. Iron and magnesium content may be responsible for decreased compressive strength of the Martian binder after heating. This study offers a robust framework for comparing performance of different simulants under the same curing protocols and environmental exposures, as well as offering insight as to the effects of vacuum curing, and exposure to high and low temperature environments on cured binder samples. Developing a landing pad by transporting activator to the lunar surface is shown to be conceptually feasible within current payload constraints.Item A critical examination of the decoupling approximation for small-angle scattering from hard ellipsoids of revolution(International Union of Crystallography, 2016-09-29) Greene, Daniel G.; Ferraro, Daniel V.; Lenhoff, Abraham M.; Wagner, Norman J.; Daniel G. Greene, Daniel V. Ferraro, Abraham M. Lenhoff and Norman J. Wagner; Greene, Daniel G.; Ferraro, Daniel V.; Lenhoff, Abraham M.; Wagner, Norman J.The decoupling approximation, proposed by Kotlarchyk & Chen [J. Chem. Phys. (1983), 79, 2461–2469], is a first-order correction to the experimentally determined apparent structure factor that is necessary because of concentration effects in polydisperse and/or nonspherical systems. While the approximation is considered accurate for spheres with low polydispersity (<10%), the corresponding limitations for nonspherical particles are unknown. The validity of this approximation is studied for monodisperse dispersions of hard ellipsoids of revolution with aspect ratios ranging from 0.333 to 3 and a guide for its accuracy is provided.Item Dynamic shear rheology of a thixotropic suspension: Comparison of an improved structure-based model with large amplitude oscillatory shear experiments(The Society of Rheology, 2016-03-29) Armstrong, Matthew J.; Beris, Antony N.; Rogers, Simon A.; Wagner, Norman J.; Matthew J. Armstrong, Antony N. Beris, Simon A. Rogers, and Norman J. Wagner; Armstrong, Matthew J.; Beris, Antony N.; Rogers, Simon A.; Wagner, Norman J.Rheological measurements on a model thixotropic suspension by Dullaert and Mewis [J. Non-Newtonian Fluid Mech. 139(1–2), 21–30 (2006); Rheol. Acta 45, 23–32 (2005)] are extended to include large amplitude oscillatory shear (LAOS) flow, shear flow reversal, and a novel unidirectional LAOS flow to provide an extended rheological data set for testing constitutive models. We use this extended data set to test a new structure-based model developed by improving the Delaware thixotropic model [A. Mujumdar et al., J. Non-Newtonian Fluid Mech. 102, 157–178 (2002); A. J. Apostolidis et al., J. Rheol. 59, 275–298 (2015)]. Model parameters are determined from steady, small amplitude oscillatory, and step shear rate tests. Holding those parameters fixed, model predictions are compared to LAOS experiments. Similar comparisons are made for three contemporary models from the literature. Two of these models use a scalar internal structural parameter and include the modified Jeffreys model proposed by de Souza Mendes and Thompson [Rheol. Acta 52, 673–694 (2013)]. The third model is based on fluidity additivity [F. Bautista et al., J. Non-Newtonian Fluid Mech. 80, 93–113 (1999)]. A common weakness in all models is shown to be the use of scalar order parameters that cannot account for the reversal of flow directionality inherent in LAOS flow. This is further illustrated by comparison with flow reversal and unidirectional LAOS experiments.Item Dynamic shear rheology of a thixotropic suspension: Comparison of an improved structure-based model with large amplitude oscillatory shear experiments(The Society of Rheology, 2016-03-29) Armstrong, Matthew J.; Beris, Antony N.; Rogers, Simon A.; Wagner, Norman J.; Matthew J. Armstrong, Antony N. Beris, Simon A. Rogers, and Norman J. Wagner; Armstrong, Matthew J.; Beris, Antony N; Rogers, Simon A.; Wagner, Norman J.Rheological measurements on a model thixotropic suspension by Dullaert and Mewis [J. Non-Newtonian Fluid Mech. 139(1–2), 21–30 (2006); Rheol. Acta 45, 23–32 (2005)] are extended to include large amplitude oscillatory shear (LAOS) flow, shear flow reversal, and a novel unidirectional LAOS flow to provide an extended rheological data set for testing constitutive models. We use this extended data set to test a new structure-based model developed by improving the Delaware thixotropic model [A. Mujumdar et al., J. Non-Newtonian Fluid Mech. 102, 157–178 (2002); A. J. Apostolidis et al., J. Rheol. 59, 275–298 (2015)]. Model parameters are determined from steady, small amplitude oscillatory, and step shear rate tests. Holding those parameters fixed, model predictions are compared to LAOS experiments. Similar comparisons are made for three contemporary models from the literature. Two of these models use a scalar internal structural parameter and include the modified Jeffreys model proposed by de Souza Mendes and Thompson [Rheol. Acta 52, 673–694 (2013)]. The third model is based on fluidity additivity [F. Bautista et al., J. Non-Newtonian Fluid Mech. 80, 93–113 (1999)]. A common weakness in all models is shown to be the use of scalar order parameters that cannot account for the reversal of flow directionality inherent in LAOS flow. This is further illustrated by comparison with flow reversal and unidirectional LAOS experiments.Item Modeling the effects of polydispersity on the viscosity of noncolloidal hard sphere suspensions(The Society of Rheology, 2016-01-14) Mwasame, Paul M.; Wagner, Norman J.; Beris, Antony N.; Paul M. Mwasame, Norman J. Wagner, and Antony N. Beris; Mwasame, Paul M.; Wagner, Norman J.; Beris, Antony N.The 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.Item An optimized protocol for the analysis of time-resolved elastic scattering experiments(Royal Society of Chemistry, 2016-01-12) Calabrese, Michelle A.; Wagner, Norman J.; Rogers, Simon A.; Michelle A. Calabrese, Norman J. Wagner and Simon A. Rogers; Calabrese, Michelle A.; Wagner, Norman J.; Rogers, Simon A.A deconvolution protocol is developed for obtaining material responses from time-resolved small-angle scattering data from light (SALS), X-rays (SAXS), or neutrons (SANS). Previously used methods convolve material responses with information from the procedure used to group data into discrete time intervals, known as binning. We demonstrate that enhanced signal resolution can be obtained by using methods of signal processing to analyze time-resolved scattering data. The method is illustrated for a timeresolved rheo-SANS measurement of a complex, structured surfactant solution under oscillatory shear flow. We show how the underlying material response can be clearly decoupled from the binning procedure. This method greatly reduces the experimental acquisition time, by approximately one-third for the aforementioned rheo-SANS experiment.Item An optimized protocol for the analysis of time-resolved elastic scattering experiments(Royal Society of Chemistry, 2016-01-12) Calabrese, Michelle A.; Wagner, Norman J.; Rogers, Simon A.; Michelle A. Calabrese, Norman J. Wagner and Simon A. Rogers; Calabrese, Michelle A.; Wagner, Norman J.; Rogers, Simon A.A deconvolution protocol is developed for obtaining material responses from time-resolved small-angle scattering data from light (SALS), X-rays (SAXS), or neutrons (SANS). Previously used methods convolve material responses with information from the procedure used to group data into discrete time intervals, known as binning. We demonstrate that enhanced signal resolution can be obtained by using methods of signal processing to analyze time-resolved scattering data. The method is illustrated for a time-resolved rheo-SANS measurement of a complex, structured surfactant solution under oscillatory shear flow. We show how the underlying material response can be clearly decoupled from the binning procedure. This method greatly reduces the experimental acquisition time, by approximately one-third for the aforementioned rheo-SANS experiment.Item Rheology of Cubic Particles in a Concentrated Colloidal Dispersion Suspending Medium(American Institute of Chemical Engineers, 2016-08-02) Cwalina, Colin D.; Harrison, Kelsey J.; Wagner, Norman J.; Colin D. Cwalina Kelsey J. Harrison Norman J. Wagner; Cwalina, Colin D.; Harrison, Kelsey J.; Wagner, Norman J.The flow behavior of mixtures of micron‐sized cubic particles suspended in a concentrated colloidal dispersion is investigated across a broad range of cubic particle concentrations. In the semi‐dilute regime, the qualitative shape of the dynamic moduli and flow curves reflect those of the underlying colloidal dispersion medium. These curves are superimposed with the underlying colloidal dispersion using shift factors that are found to be larger than those obtained in a recent study of suspensions of non‐colloidal spherical particles in the same colloidal dispersion medium. At higher concentrations of cubic particles, deviations from this shifting procedure are apparent. Scaling calculations suggest depletion interactions are responsible for the increase in the low shear viscosity and confinement of the underlying colloidal dispersion can be expected to enhance the shear thickening behavior at high shear stresses. The results of this study provide guidance for formulating suspensions through control of particle shape and mixture concentration.Item Rheology of non-Brownian particles suspended in concentrated colloidal dispersions at low particle Reynolds number(The Society of Rheology, 2015-12-08) Cwalina, Colin D.; Wagner, Norman J.; Colin D. Cwalina and Norman J. Wagner; Cwalina. Colin D.; Wagner, Norman J.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.Item Short-Time Glassy Dynamics in Viscous Protein Solutions with Competing Interactions(American Physical Society, 2015-11-24) Godfrin, P. Douglas; Hudson, Steven D.; Hong, Kunlun; Porcar, Lionel; Falus, Peter; Wagner, Norman J.; Liu, Yun; P. Douglas Godfrin, Steven D. Hudson, Kunlun Hong, Lionel Porcar, Peter Falus, Norman J. Wagner, and Yun Liu; Godfrin, P. Douglas; Wagner, Norman J.; Liu, YunThe glass transition of colloidal dispersions interacting with both a short-ranged attraction and long-ranged repulsion is studied using highly purified lysozyme solutions. Newtonian liquid behavior is observed at all conditions while measurements of the dynamics in the short-time limit show features typical of glassy colloidal systems at high protein concentrations. This interesting behavior is due to the competition of the attraction and repulsion that produces a heterogeneous microstructure only at intermediate range length scales. The results demonstrate that theories for the macroscopic properties of systems with competing interactions need to include intermediate range order.Item Suppression of Segmental Chain Dynamics on a Particle’s Surface in Well-Dispersed Polymer Nanocomposites(ACS Macro Letters, 2024-06-18) Kim, Jihyuk; Thompson, Benjamin R.; Tominaga, Taiki; Osawa, Takahito; Egami, Takeshi; Förster, Stephan; Ohl, Michael; Senses, Erkan; Faraone, Antonio; Wagner, Norman J.The Rouse dynamics of polymer chains in model nanocomposite polyethylene oxide/silica nanoparticles (NPs) was investigated using quasielastic neutron scattering. The apparent Rouse rate of the polymer chains decreases as the particle loading increases. However, there is no evidence of an immobile segment population on the probed time scale of tens of ps. The slowing down of the dynamics is interpreted in terms of modified Rouse models for the chains in the NP interphase region. Thus, two chain populations, one bulk-like and the other characterized by a suppression of Rouse modes, are identified. The spatial extent of the interphase region is estimated to be about twice the adsorbed layer thickness, or ≈2 nm. These findings provide a detailed description of the suppression of the chain dynamics on the surface of NPs. These results are relevant insights on surface effects and confinement and provide a foundation for the understanding of the rheological properties of polymer nanocomposites with well-dispersed NPs.Item Surface-mediated spontaneous emulsification of the acylated peptide semaglutide(Proceedings of the National Academy of Sciences, 2024-01-16) Li, Qi; Tangry, Vasudev; Allen, David P.; Seibert, Kevin D.; Qian, Ken K.; Wagner, Norman J.Significance We identify the fundamental mechanisms of an undesired instability known as “ouzo” formation in a class of therapeutics used for treating type 2 diabetes and obesity. Spontaneous emulsification in solutions of acylated peptides in the presence of hydrophobic surfaces is elucidated as a function of physico-chemical conditions and surface hydrophobicity as characterized by Hansen solubility parameters. Quantitative prediction of the colloidal size is demonstrated using the classical Rayleigh theory, while formation rates reduce to a master curve dependent on the surface hydrophobicity and stirring rate. We demonstrate that colloidal physics and molecular thermodynamics provide quantitative predictions of the colloidal droplet size and qualitatively rank formation rates, thereby improving our understanding of this important class of therapeutic molecules. Abstract Acylated peptides composed of glucagon-like peptide-1 receptor agonists modified with a fatty acid side chain are an important class of therapeutics for type 2 diabetes and obesity but are susceptible to an unusual physical instability in the presence of hydrophobic surfaces, i.e., spontaneous emulsification, also known as ouzo formation in practice. In this work, light scattering, small-angle X-ray scattering, and circular dichroism measurements are used to characterize the physical properties of the semaglutide colloidal phase, including size distribution, shape, secondary structure, internal structure, and internal composition, as a function of solution physico-chemical conditions. The existence and size of the colloids formed are successfully predicted by a classical Rayleigh model, which identifies the parameters controlling their size and formation. Colloid formation is found to be catalyzed by hydrophobic surfaces, and formation rates are modeled as an autocatalytic reaction, enabling the formation of a master curve for various surfaces that elucidates the mechanism. Surfaces differ due to differences in surface wettability, which can be correlated with Hansen solubility parameters. This work provides insights into this unusual colloidal phenomenon and guides the peptide synthesis process and drug product formulation in the pharmaceutical industry.