Small Amplitude Oscillatory Shear Measurements Research Articles

Atomic Force Microscopy and Thermo-Rheological Characterisation of Lubricating Greases

In this work, non-perturbed microstructures of several commercial and model lubricating greases, differing in nature and concentration of the thickener agent, were examined using the atomic force microscopy (AFM) technique. Grease microstructure mainly depends on the nature of the thickener employed and, also, on thickener concentration and viscosity of the base oil. Thermal-induced changes in the viscoelastic response of lubricating greases have been investigated by using different rheological techniques in a temperature range of 0–175 °C. Small-amplitude oscillatory shear (SAOS) measurements were carried out to determine the mechanical spectra of the different samples studied. Lubricating grease rheological thermal susceptibility was analysed by following the evolution of the plateau modulus with temperature. SAOS functions dramatically decrease, in most cases, above a characteristic temperature, which depends on nature and/or concentration of the thickener used and therefore on grease microstructure. The thermo-mechanical reversibility of grease microstructure has been studied by carrying out triple-step-shear stress tests (shear stresses inside and outside of the linear viscoelasticity range), at different temperatures. The degree of lubricating grease non-reversible structural breakdown, which increases with temperature, depends on the shear stress applied above the linear viscoelasticity limits.

Influence of water content, time, and temperature on the rheological behavior of polyethylene terephtalate

AbstractIn this work, the main factors affecting the rheological behavior of polyethylene terephtalate (PET) in the linear viscoelastic regime (water content, time delay before test, duration of experiment, and temperature) were accessed. Small amplitude oscillatory shear tests were performed after different time delays ranging from 300 to 5000 s for samples with water contents ranging from 0.02 to 0.45 wt %. Time sweep tests were carried out for different durations to explain the changes undergone by PET before and during small amplitude oscillatory shear measurements. Immediately after the time sweep tests, the PET samples were removed from the rheometer, analyzed by differential scanning calorimetry and their molar mass was obtained by viscometry analysis. It was shown that for all the samples, the delay before test and residence time within the rheometer (i.e. duration of experiment) result in structural changes of the PET samples, such as increase or decrease of molar mass, broadening of molar mass distribution, and branching phenomena. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Influence of soap/polymer concentration ratio on the rheological properties of lithium lubricating greases modified with virgin LDPE

The main goal of this work was to study the feasibility of using a low-density polyethylene (LDPE) as additive to improve the rheological properties of lithium lubricating greases. The combined effect that both soap and LDPE concentrations exerts on the rheology of lithium lubricating greases and its relationship with grease microstructure were studied according to an experimental design based on the response surface methodology (RSM). Different lubricating grease formulations were manufactured by modifying lithium 12-hydroxystereate and LDPE concentrations. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements, as well as mechanical stability tests, were performed. In addition to these, environmental scanning electronic microscopy (ESEM) was used to determine grease microstructure. LDPE was found to be a useful additive to modify grease rheology, acting as filler in the entangled soap network. The values of both apparent viscosity and linear viscoelasticity functions increase with soap and LDPE concentration. However, the addition of LDPE distorts soap microstructural network, yielding greases with lower relative elastic characteristics.

Rheological Modification of Lubricating Greases with Recycled Polymers from Different Plastics Waste

There is a growing interest on the development of new materials based on recycled polymers from plastics waste, since the use of such plastics represents a low-cost source of raw material. The purpose of the present work is to evaluate, from a comparative point of view, the effect that different waste and virgin polymers, used as viscosity modifier additives, exert on the rheological properties of standard lithium lubricating greases. Grease formulations containing diverse polymers, differing in nature and/or origin, were manufactured and rheologically characterized. Particularly, the influences of the type of polymer, the molecular weight and the presence of carbon black, used as filler in recycled polymers, have been evaluated. Small-amplitude oscillatory shear (SAOS) and viscous flow measurements were carried out, as well as calorimetric and thermogravimetric analysis. In general, recycled polymers induce a more important rheological modification than virgin polymers of the same nature. Thus, the addition of some recycled polymers such as HDPE, LDPE, PP, and EVA copolymer to lithium lubricating grease significantly increases the values of the rheological parameters analyzed. The crystallinity degree, mainly dependent on the nature of the polymer, and the carbon black content of recycled polymers have been pointed out as the most highly influencing parameters on the rheology of the lubricating greases studied. However, an apparent loss in mechanical stability for lubricating greases containing recycled polymers has been found when they were submitted to a severe mechanical treatment.

Effect of thermo-mechanical processing on the rheology of oleogels potentially applicable as biodegradable lubricating greases

This work is focused on the development of oleogels potentially suitable as biodegradable lubricating greases by studying the effect that some thermo-mechanical processing variables exert on their rheological properties and microstructure. Oleogels were prepared by dispersing sorbitan monostearate (SMS) in castor oil under different agitation conditions and thermal protocols. The effect of processing variables was evaluated by performing small-amplitude oscillatory shear (SAOS) measurements, AFM observations and some mechanical and tribological tests usually employed to check lubrication performance and stability of lubricating greases. Rheological properties of oleogels can be monitored in situ during processing using a rheo-reactor. Processing conditions such as maximum temperature applied to disperse the gelling agent, heating time, agitation speed and cooling rate significantly influence gel strength. Cooling profile is the most important processing variable affecting the rheological response of oleogels. Differences of more than one decade in the values of SAOS functions were found for oleogels processed by applying different cooling profiles. A moderate agitation during SMS dispersion in oil yields maximum values of oleogel linear viscoelasticity functions. The maximum processing temperature reached during this stage should be only slightly higher than the SMS melting point. In general, oleogel samples exhibited a poor mechanical stability after sample working in a rolling element, but, on the contrary, they recovered completely their initial consistency after a moderate resting time, also exhibiting remarkable lubricant properties. Moreover, oleogel samples tested in a ball-disc tribometer show values of the friction coefficient inferior to those obtained with model lithium lubricating greases.

Effects of magnetite nanoparticles on the thermorheological properties of carrageenan hydrogels

The influence of magnetite (Fe 3O 4) nanoparticles on the rheological properties of κ-, ι- and λ-carrageenan gels has been investigated. Small amplitude oscillatory shear measurements were performed to study the effect of the presence of Fe 3O 4 nanoparticles with particle sizes of ca. 10 nm on the gel properties, as a function of carrageenan type, carrageenan concentration and magnetite load. The formation of Fe 3O 4 nanoparticles on the presence of biopolymer was observed to promote the gelation process and lead to stronger gels as indicated by an increase in the gel viscoelastic moduli and of the gelation temperature. This effect was more marked for κ-carrageenan than for ι- and λ-carrageenan and has been proposed to depend not only on Fe 3O 4 concentration but also on the concentration of potassium ions. A mechanism based on the combined effect of Fe 3O 4 nanoparticles and potassium ions was suggested, involving the adsorption of potassium ions on the negatively charged surface of the Fe 3O 4 nanoparticles, thus leading to an increase of the potassium ion concentration within the “carrageenan cages” containing the magnetite. This would, therefore, promote more extensive biopolymer helical aggregation, thus resulting in the formation of a stronger κ-carrageenan gel in the presence of Fe 3O 4, as observed. Since ι- and λ-carrageenan gels are known to be less sensitive to potassium ions concentration, the effect of precipitating Fe 3O 4 within these biopolymers is reduced.

Effect of flaxseed gum addition on rheological properties of native maize starch

Both small amplitude oscillatory and steady shear measurements were carried out at 25 °C, 50 °C, and 75 °C in order to determine the rheological properties of the mixtures of flaxseed gum (0.1–0.5%) and native maize starch (3%). It was found that the apparent viscosities of the samples increased with the increasing of flaxseed gum concentration. The apparent viscosities of the samples were fitted well to the power law model (the values of R 2 were between 0.954 and 0.999). The consistency index ( K) of the gum–starch mixtures increased with the increasing of flaxseed gum concentration. The gum–starch mixtures showed gel-like behavior since the storage modulus ( G′) was much larger than the loss modulus ( G″) and the frequency dependence of both modulus was not significant. The G′ and G″ of the gum–starch mixtures was increased with the increasing of flaxseed gum concentration. The influence of temperature was more significant for the flaxseed gum–maize starch mixtures compared to maize starch gel.

Rheological behavior of fiber-filled polymers under large amplitude oscillatory shear flow

Small and large amplitude oscillatory shear measurements (SAOS and LAOS) were used to investigate the rheological behavior of short glass fibers suspended in polybutene and molten polypropylene. Raw torque and normal force signals obtained from a strain-controlled instrument (ARES rheometer) were digitized using an analog to digital converter (ADC) card to allow more precise data analysis. The fiber concentration did not affect the torque signal in the SAOS mode, except for its magnitude, whereas the normal force signal was too low to be measurable. With increasing strain amplitude, the magnitude of the torque became a function of time. Depending on the applied frequency and strain rate, the stress in the filled polybutene increased with time, whereas for reinforced polypropylene (viscoelastic matrix), the behavior was opposite, i.e. the stress decreased with time. These effects were more pronounced at high fiber content. In addition the primary normal stress differences were no longer negligible at large deformation amplitude and exhibited a non-sinusoidal periodic response. Fast Fourier transform (FFT) analysis was performed and the resulting spectra, along with Lissajous figures of the shear stress and the primary normal stress differences, are explained in terms of fiber orientation. The experimental results for the suspensions in polybutene are well predicted by the Folgar-Tucker-Lipscomb (FTL) model.

Synthesis and Characterization of Long Chain Branched Isotactic Polypropylene via Metallocene Catalyst and T-Reagent

Long chain branched isotactic polypropylenes (LCBPP) prepared via the combination of rac-Me2Si(2-Me-4-Ph-Ind)ZrCl2/MAO catalyst and a p-(3-butenyl)styrene (T-reagent) were characterized to investigate their synthesis, structure, solution properties, and melt properties. The T-reagent, in the presence of hydrogen, simultaneously served as a comonomer and chain transfer agent, resulting in a LCBPP with high molecular weight, desirable branch point density, and relatively well-defined molecular structure. Additionally, the metallocene catalyst remained highly reactive. To understand the structure−property relationships, a series of LCBPPs were prepared with similar weight-average molecular weights of about 250 000 g/mol and different branch densities ranging from 0 (linear iPP) to 3.3 branch points per 10 000 carbons. 1H NMR and SEC equipped with triple detectors revealed structural information. Melt properties were examined by small-amplitude dynamic oscillatory shear and extensional flow measurements. LCBP...

Rheological Properties of Extruded Milk Powders

Whey protein concentrate, whey protein isolate, and nonfat dry milk may be processed through a twin-screw extruder to produce ingredients for protein-fortified food. The products ranged from rigid to flexible to soft, and small amplitude oscillatory shear measurements showed that these properties varied with extrusion temperature and moisture content. The whey proteins showed different effects than nonfat dry milk due to the type and amount of protein present. The characteristics of extruded milk powders can be manipulated through processing parameters to obtain texturized products with the desired rheological properties.

Rheology and microstructure of lithium lubricating greases modified with a reactive diisocyanate-terminated polymer: Influence of polymer addition protocol

This work deals with the influence that the addition of poly(1,4-butanediol) tolylene 2,4-diisocyanate terminated prepolymer (PBTDI) at different stages during the manufacturing process of a traditional lithium lubricating grease exerts on its rheological and morphological characteristics. With this aim, the reaction between terminal isocyanate groups and the hydroxy group located in the hydrocarbon chain of the 12-hydroxystearate lithium soap was intended to be promoted during lubricating grease processing. Several PBTDI-based greases just differing in the process stage at which this polymer was added were prepared. The polymer used and the final lubricating greases were characterized by FTIR spectroscopy and DSC techniques. The effect of PBTDI addition at different processing stages was tested on final greases by performing small-amplitude oscillatory shear (SAOS) measurements as well as atomic force microscopy (AFM) observations. Addition of PBTDI significantly increased the values of the linear viscoelasticity functions when it was added during the final cooling stage of the manufacturing process. It was demonstrated that this increment in relation to the values found for the additive-free lubricating grease was only observed when PBTDI chemically interacted with the soap network. However, the effectiveness of PBTDI as rheology modifier was much lower when the addition took place at earlier steps of the manufacturing process. Some competitive reactions due to either the presence of water or the high temperatures applied have been proposed to explain this loss of effectiveness depending on the lubricating grease processing stage at which PBTDI was added.

Effect of salt content on the rheological properties of salad dressing-type emulsions stabilized by emulsifier blends

The effects that salt content and composition of emulsifier blends exert on the rheological properties of salad dressing-type emulsions were studied. Binary blends of egg yolk and different types of amphiphilic molecules (Tween 20, sucrose laurate and pea protein), in several proportions, were used to stabilize emulsions. Salt concentration was ranged from 0 to 2.3% w/w. Steady-state flow tests and small-amplitude oscillatory shear measurements within the linear viscoelastic region were carried out. Rheological tests were complemented with droplet size distribution measurements. Rheological properties and physical stability of the emulsions studied were significantly influenced by salt content and the nature of binary emulsifier blends. In general, the values of rheological parameters studied increased with salt content. However, salt affects in much higher extent the properties of emulsions stabilized by high proportions of egg yolk or pea protein in the emulsifier blend, rather than those mainly stabilized by non-ionic low-molecular-weight surfactants, which are less sensitive to changes in the ionic strength. In this sense, the increase observed in the values of viscosity and linear viscoelastic functions of emulsions is more important when a protein is predominant in the emulsifier blend. This effect was explained on the basis of a more apparent increasing interdroplet interactions and viscosity of the continuous medium, both of them induced by salt addition, which lead to the consecution of an extensively flocculated state and improved creaming stability. On the contrary, different blends of pea protein and egg yolk showed a quite similar evolution of the rheological parameters with salt concentration.

Development of new lubricating grease formulations using recycled LDPE as rheology modifier additive

The recovery of plastic waste but also its applicability in product development may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins as additives to improve the rheological properties of lithium 12-hydroxystearate lubricating greases. The effects that both soap and recycled low-density polyethylene (LDPE) concentration exert on the rheology of lithium lubricating greases and its relationship with grease microstructure are discussed in this work. In this way, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE, according to a RSM statistical design. These lubricating greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. Recycled LDPE was found to be an effective additive to modify grease rheology, acting as filler in the soap entangled microstructure. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increase with soap and recycled polymer concentrations. However, the addition of recycled LDPE distort the microstructural network of these greases resulting greases with less relative elastic characteristics and poorer mechanical properties as LDPE content increases.

Thermorheological behaviour of a lithium lubricating grease

Thermal-induced changes in the viscous and viscoelastic responses of lubricating greases have been investigated through different rheological techniques in a temperature range of 0–175 °C. Small-amplitude oscillatory shear and viscous flow measurements were carried out on a model conventional lithium lubricating grease prepared by inducing the in situ saponification reaction between 12-hydroxystearic acid and hydrated lithium hydroxide. The linear viscoelasticity functions dramatically decrease above 110 °C, but not below this critical temperature, which determines the maximum recommended operating temperature in relation to its durability and resistance under working conditions. Two different regions, below and above this critical temperature, in the plateau modulus versus temperature plot have been detected. From this thermal dependence, a much larger thermal susceptibility of the lubricating grease at temperatures above 110 °C is apparent. The thermo-mechanical reversibility of this material has been studied by applying different combined stress–temperature protocols. Regarding the viscous flow, a minimum in the shear stress versus shear rate plots appeared at temperatures above 60 °C, more pronounced as temperature increases, resulting from material instabilities. The experimental results obtained have been explained on the basis of the thermo-mechanical degradation of the lubricating grease microstructure.

Usingin situ rheology to characterize the microstructure in photopolymerized polyacrylamide gels for DNA electrophoresis

Photopolymerized cross-linked polyacrylamide hydrogels are attractive sieving matrix formulations for DNA electrophoresis owing to their rapid polymerization times and the potential to locally tailor the gel pore structure through spatial variation of illumination intensity. This capability is especially important in microfluidic systems, where photopolymerization allows gel matrices to be precisely positioned within complex microchannel networks. Separation performance is also directly related to the nanoscale gel pore structure, which is in turn strongly influenced by polymerization kinetics. Unfortunately, detailed studies of the interplay among polymerization kinetics, mechanical properties, and structural morphology are lacking in photopolymerized hydrogel systems. In this paper, we address this issue by performing a series of in situ dynamic small-amplitude oscillatory shear measurements during photopolymerization of cross-linked polyacrylamide electrophoresis gels to investigate the relationship between rheology and parameters associated with the gelation environment including UV intensity, monomer and cross-linker composition, and reaction temperature. In general, we find that the storage modulus G' increases with increasing initial monomer concentration, cross-linker concentration, and polymerization temperature. The steady-state value of G', however, exhibits a more complex dependence on UV intensity that varies with gel concentration. A simple model based on rubber elasticity theory is used to obtain estimates of the average gel pore size that are in surprisingly good agreement with corresponding data obtained from analysis of DNA electrophoretic mobility in gels cast under identical polymerization conditions.

Influence of Soap Concentration and Oil Viscosity on the Rheology and Microstructure of Lubricating Greases

The effects that both soap concentration and base oil viscosity exert on the rheology of lubricating greases and its relationship with grease microstructure are discussed in this work. With this aim, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and the viscosity of the base oil, according to an RSM statistical design. These lubricating greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. It has been found that the structural skeleton (size and shape of the disperse phase particles) was highly influenced by the base oil viscosity. In this sense, the values of the viscoelastic functions in the linear viscoelastic region and the mechanical stability of the lubricating greases increase as the viscosity of the base oil decreases. An opposite ten...

USE OF FOURIER TRANSFORM MECHANICAL SPECTROSCOPY TO STUDY THE MELTING BEHAVIOR OF CHEESE

ABSTRACT Fourier Transform Mechanical Spectroscopy (FTMS), which employs a complex sinusoidal waveform, was investigated for its applicability in measuring the rheological properties in the cheese system. The complex wave used in FTMS is a superposition of several sine waves whose frequencies are harmonics of a base frequency. FTMS was used to investigate the rheological properties of a 10‐month‐old Cheddar cheese while the sample was heated from 10 to 90C or cooled from 90 to 10C at the rate of 1C/min or 0.5C/min. The component frequencies of the complex waveform were 0.08, 0.4, 0.8 and 4 Hz. The widely used small amplitude oscillatory shear (SAOS) measurements, which employ only discrete frequencies, were also conducted on separate cheese samples to test the robustness of FTMS results. During heating, the values of the storage modulus (G′) and loss modulus (G″) decreased by at least four orders of magnitude. In the temperature region from 44 to 55C, there was a shoulder in the G′ and G″ profiles, which was more pronounced at high frequencies; and in the high‐temperature region from 70 to 90C, the dynamic moduli values either reached a plateau or slightly increased. The frequency dependence of the dynamic moduli increased after 40C. The temperature and values of dynamic moduli at the crossover of G′ and G″ were highly dependent on frequency. Clear maxima were observed in loss tangent (LT) profiles and the temperature of maxima and their values were highly dependent on frequency. Results were similar for both rates of heating, but the heating and cooling curves for G′, G″ and LT showed hysteresis. The results from FTMS agreed well with the SAOS measurements for all the frequencies tested and indicated that the FTMS technique is a useful method to probe the molecular behavior of cheese systems while undergoing heating or cooling.

Relationship Between Physical Properties of Casein Micelles and Rheology of Skim Milk Concentrate

The properties of casein micelles in milk concentrates are of interest for the use of ultrafiltered (UF) skim milk concentrates in dairy products, and for the general understanding of colloidal stability and behavior of the casein micelle. The rheological behavior of UF skim milk concentrate with a casein concentration of 19.5% (wt/wt) was investigated at different pH and NaCl concentrations by analyzing flow viscometry and small amplitude oscillatory shear measurements. Viscometric flow curves were fitted to the Carreau-Yasuda model with the aim of determining values for the viscosity at infinite high shear rates and thereby estimate the voluminosity of the casein micelles (νcasein) in the UF concentrate. The voluminosity of the casein micelles increased with addition of NaCl and decreased when pH was decreased from 6.5 to 5.5. At pH 5.2, νcasein increased because of acid-induced aggregation of the casein micelles. The changes in νcasein could be interpreted from transmission electron microscopy of freeze-fractured samples of the UF concentrate and partly from dynamic light scattering measurements. Altered interactions between casein micelles due to different pH and NaCl concentrations are proposed to occur due to collapse of the κ-casein layer, changed ionic strength, and altered distance between casein micelles.

Effect of blending sequence on the morphologies of poly(butylene terephthalate)/epoxy/clay nanocomposites by a rheological approach

AbstractEpoxy resin was used as a compatilizer to prepare poly(butylene terephthalate)/clay nanocomposites via melt intercalation. Three different mixing sequences were attempted in the present work: (1) to mix poly(butylene terephthalate) (PBT), epoxy, and organoclay in one step; (2) first to mix epoxy and organoclay, and then mix it with PBT; (3) to prepare PBT/organoclay hybrid first, and then mix it with epoxy to get the final nanocomposites. The results from X‐ray diffraction (XRD) reveal that all these hybrids present an intercalated structure. However, it can be observed that there are distinct differences in the amount and average size of clay tactoids dispersed in those hybrids from the transmission electron microscope (TEM) photographs, which are further confirmed successfully by the rheological measurements. On the basis of the strain overshoot intensity and the low‐frequency solid‐like response level in the small amplitude oscillatory shear (SAOS) measurements, it can be concluded that the blending sequence (2) is the best way to obtain a nice dispersion of clay in the matrix, forming a percolated tactoids network with highest density and intensity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 340–346, 2006

Shear and extensional rheology of carbon nanofiber suspensions

The morphology and rheology of carbon nanofiber (CNF) suspensions were studied. The CNFs, produced by decomposing organic vapors at elevated temperature in the presence of metal catalysts, have characteristic diameter and length of 100 nm and 20–100 μm, respectively. The CNFs, as delivered, have a strong tendency to clump into mm-sized agglomerates. The efficacy of CNF/glycerol-water suspensions was studied vs. two processing parameters: mechanical sonication and chemical treatment. Experimental measurements revealed that sonication alone reduces the size of CNF clumps from millimeter to micrometer scale, but cannot achieve uniform dispersion. The chemically untreated sonicated suspensions contain clumps of nanofibers with a characteristic size of 20×50 μm, together with smaller aggregations of partially dispersed nanofibers. In response to this unsatisfactory dispersion, the effect of acid treatment before dispersion was investigated. This acid treatment, which makes the surface of the CNFs more hydrophilic, greatly improves dispersion in the aqueous solution: treatment followed by sonication results in a uniform dispersion of individual nanofibers. At the same time, however, we observed that surface treatment and subsequent sonication greatly shorten the nanofibers. The rheology of CNF/glycerol-water suspensions is highly non-Newtonian both in shear and extensional flows, with strong dependence on the dispersion, particle length, and concentration of the CNFs. As the solvent is Newtonian, all of the elastic and strain-rate dependent behavior in the CNF/aqueous suspensions derives from the addition of nanofibers. The steady shear viscosity of the untreated-sonicated (poorly dispersed, with longer fibers) suspensions is highly shear thinning with a viscosity that increases three orders of magnitude as concentration varies from 0.5 wt% to 5 wt%. Beyond 5 wt% the suspensions are too viscous to be effectively mixed by sonication. When the CNFs are chemically treated and then sonicated (resulting in much better dispersion but shorter fibers), the viscosity exhibits little shear thinning, and only varies by a factor of two from pure solvent to 5 wt%. In small amplitude oscillatory shear measurements, we found strong indications of elastic behavior in both the treated and untreated suspensions, with elastic modulus G′ greater than loss modulus G′′. In particular, for both systems G′ exhibits a low-frequency plateau when nanofiber concentration is 3 wt% or above, a characteristic of elastic solidlike response. Again, there is a strong dependence on CNF dispersion and fiber length: At low frequencies, the elastic modulus of the 5 wt% untreated suspension (with agglomerates and longer fibers) is four orders of magnitude larger than that of the 5 wt% treated suspension (with uniformly dispersed, shorter fibers). In addition, G′ of untreated suspensions is a much stronger function of concentration than that of treated suspensions, indicative of network formation. The rheology and morphology of nanofiber suspensions were related by identifying morphology of the suspensions with the assumptions of the kinetic theory-based elastic and rigid dumbbell constitutive models; the approach is to specify the parameters in the kinetic theory models in terms of microscale morphological features measured in the SEM. Of those investigated, the elastic dumbbell model with anisotropic hydrodynamic drag is the most successful, effectively modeling the small amplitude oscillatory shear and steady shear behavior of the treated sonicated suspensions. As for the treated unsonicated and untreated sonicated suspensions, which contain mesoscale agglomerates not present in the underlying assumptions of the dumbbell models, it is discovered that the elastic dumbbell with parameters assigned from morphological measurements predicts the correct trends in the steady shear experiments, but fails to accurately predict the small amplitude oscillatory shear experiments.