Steady Shear Viscosity Measurements Research Articles

Microviscoelasticity of adhesive hard sphere dispersions: Tracer particle microrheology of aqueous Pluronic L64 solutions

DWS-based tracer particle microrheology is demonstrated to be a useful way to study the dynamics of aqueous Pluronic L64 solutions, which is viewed as a model adhesive hard sphere (AHS) system. The short-time dynamics of aqueous Pluronic L64 solutions indicate a purely hydrodynamic high frequency microviscosity as predicted by Batchelor for colloidal dispersions. The evolution of the micellar dynamics reveals a zero shear microviscosity in good agreement with steady shear viscosity measurements. As the temperature is increased, the dynamics become dominated by an apparent attractive intermicellar potential observed in microscopic creep measurements. While Pluronic L64 solutions have been reported to form a percolated micellar network, DWS-based microviscoelasticity measurements do not detect the previously observed G(') approximately G(") approximately omega(Delta) scaling expected for a static percolated network at low frequencies. This most likely owes to the fact that tracer particle microrheology is dominated by local Pluronic L64 micelle dynamics in the near sphere region and not the bulk mechanical properties as measured by traditional rheometry. The sensitivity of tracer particle microrheological measurements to the true dynamic nature of the percolated network in weak physical gels highlights the distinct differences between these micro- and macrorheology measurement techniques. Such discrepancies should be most evident in systems that are dominated by association processes such as those occurring in AHS solutions or polymer solutions approaching a phase boundary. Despite this, the AHS potential is qualitatively consistent with the results found here.

Effects of Perfluorosulfonic Acid Adsorption on the Stability of Carbon Black Suspensions

Carbon black particles were stabilized by the adsorption of perfluorosulfonic acid (PFSA) onto their surfaces in a mixture of water and isopropyl alcohol. The resulting carbon black suspensions were characterized by measurements of the adsorbed amounts of PFSA, the hydrodynamic diameter of carbon black particles with adsorbed PFSA, and by steady state shear viscosity measurements as functions of the PFSA and carbon black particle concentrations. An equilibrium adsorption of PFSA on carbon black particles was established within 1 day, and the resulting adsorption isotherm was dependent on the carbon black particle concentration; the amounts of adsorbed PFSA decreased with increased carbon black particle concentration. The hydrodynamic diameter of the carbon black particles in suspension increased with the amount of adsorbed PFSA, resulting in stabilization of the carbon black suspensions. Thus, the apparent steady-state shear viscosities of the carbon black suspensions at the first and second shear thinning regions decreased with an increase in the amount of adsorbed PFSA.

Study of the effect of PEG length in Uni‐HEUR thickener behavior

AbstractFour new models of Uni‐HEUR associative thickener were designed and synthesized using various molecular weights of poly(ethylene glycol) (PEG) as hydrophilic segments. The PEG chain ends were capped with octadecyl isocyanate as hydrophobic segments. The structure of the prepared Uni‐HEUR thickeners was confirmed by infrared spectroscopy. The steady shear viscosity measurements of aqueous solution of HEUR models showed that the relative size of hydrophilic segments to hydrophobic segments is very important. Oscillatory measurements confirmed the steady shear viscosity results. It is found, there is an optimum relative size of hydrophilic segments to hydrophobic segments to achieve the thickener with a good performance. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Novel transition behavior in aqueous solutions of a charged thermoresponsive triblock copolymer

Turbidity, dynamic light scattering, and steady shear viscosity measurements have been performed under the influence of a temperature gradient (0.2 °C/min) on aqueous solutions of a newly prepared monodisperse low-molar-mass ( M w = 1.34 × 10 4) methoxy-poly(ethylene glycol)- block-poly( N-isopropylacrylamide)- block-poly(4-styrenesulfonic acid sodium) triblock copolymer (MPEG 53- b-P(NIPAAM) 54- b-P(SSS) 4). The results on this charged triblock copolymer revealed a novel temperature-induced transition from micelles to intermicellar complexes and the formation of collapsed and charged structures at higher temperatures. These experimental methods gave similar transition peaks. Intensity light scattering experiments conducted at several fixed temperatures on solutions of the triblock copolymer disclosed similar transition peaks in the radius of gyration. Cryogenic transmission electron microscopy (Cryo-TEM) measurements on 1 wt% samples at different temperatures, disclosed the building up of association structures at the maximum of the intermediate transition peak, and the breaking down of interchain associations at high temperatures. In the presence of salt, the transition peak at intermediate temperatures was still visible but the formation of flocs at high temperatures was strengthened because of screening of the repulsive electrostatic interactions, and it is also possible that deteriorated solubility of the polymer plays a role. These findings show that even with a short-chain polymer the formed association structures can undergo a major temperature-induced transition from unimers–micelles–intermicellar complexes to collapsed structures. By comparing the heating and cooling cycles, hysteresis effects in the transition behavior were disclosed.

Viscosity study of interactions between sodium alginate and CTAB in dilute solutions at different pH values

Interactions between anionic polyelectrolyte sodium alginate and the cationic surfactant cetytrimethylammonium bromide (CTAB) have been investigated by viscosity measurement techniques. The polymer–surfactant interactions are observed between alginate and CTAB at different pH in dilute solution. The results show that the rheological response of alginate dilute solutions is sensitive to a change of pH in the low pH range. The steady shear and intrinsic viscosity measurements reveal that the strong association between alginate and CTAB by electrostatic attraction above pH 5.0. However, as the pH value of solution decrease from 5.0 to 3.0, the strong association between alginate and CTAB is affected by not only electrostatic attraction but also hydrophobic interaction.

Anomalous Transition in Aqueous Solutions of a Thermoresponsive Amphiphilic Diblock Copolymer

The influence of shear flow on aggregation and disaggregation in aqueous solutions of the thermoresponsive methoxy-poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (MPEG53-b-PNIPAAM113) copolymer that exhibits a lower critical solution temperature was investigated with the aid of turbidity, shear viscosity, and rheo small angle light scattering (rheo-SALS) methods. The turbidity results at quiescent conditions revealed a novel transition peak in the turbidity curve at intermediate temperatures, which reflects the delicate interplay between temperature-induced aggregation and shrinking of the species. A similar anomalous transition peak (located at the same temperature) was observed in the steady shear viscosity measurements at intermediate temperatures, and the amplitude of the peak was reduced with increasing shear rate as a consequence of breakup of interaggregate chains. At low temperatures (low sticking probability), enhanced shear rate generated interpolymer aggregates; whereas in the high-temperature domain (high sticking probability) association structures were broken up as the shear rate was increased. The rheo-SALS experiments disclosed growth of aggregates at low temperatures and destruction of association complexes at high temperatures. An increase of the cloud point temperature with rising shear rate is reported, which is interpreted as being a disruption of clusters under the influence of shear stresses.

Formation of fibrillar whey protein aggregates: Influence of heat and shear treatment, and resulting rheology

We have studied the effect of a combined heat and shear treatment on the formation and rheological properties of fibrillar whey protein aggregates. The amount and length distribution of whey protein fibrils were characterized using flow-induced birefringence and transmission electron microscopy (TEM). Fibril solutions were characterized macroscopically using crossed polarizers and the flow behaviour was measured with steady-shear viscosity measurements. Fibril growth was dependent on protein concentration. The use of shear flow influenced the amount of fibrils formed when the protein concentration was sufficiently high (above 3 wt%). A shear rate was found for which the amount of fibrils was maximal. The increase in the amount of fibrils as a function of shear rate was explained by enhanced supply of protein monomers towards the fibril tips in the flow field, while the following decrease at higher shear rates could be caused by the breakage of non-matured bonds inside the fibril. Viscosity measurements of the fibril solutions showed that above a critical fibril concentration, the viscosity became independent of the fibril concentration.

Self-Assembled Nanogels of Cholesteryl-Modified Polysaccharides: Effect of the Polysaccharide Structure on Their Association Characteristics in the Dilute and Semidilute Regimes

The assembly of cholesteryl derivatives of the highly branched polysaccharide mannan Mw = (5.2 x 104 g/mol) in dilute aqueous solution was investigated by 1H nuclear magnetic resonance (NMR) spectroscopy, size-exclusion chromatography coupled with multiangle laser scattering (SEC-MALLS), dynamic light scattering (DLS), atomic force microscopy (AFM), fluorescence quenching, and fluorescence depolarization measurements. In the dilute regime, cholesteryl-bearing mannans (CHM) containing approximately 1 cholesteryl group per 100 mannopyranose units formed nanogels with a hydrodynamic radius (RH) of approximately 20 nm containing approximately 8 macromolecules held together via hydrophobic nanodomains consisting of approximately 9 cholesteryl groups. Their density Phih ( approximately 0.02) was significantly lower than the density ( approximately 0.16) of nanogels formed by a cholesteryl derivative of the linear polysaccharide pullulan (CHP) of identical molar mass and level of cholesteryl substitution. In the semidilute regime, CHM nanogels formed a macrogel network for concentrations higher than 12.5% w/w, whereas CHP nanogels underwent macrogelation only above a threshold concentration of 8.0% w/w, as revealed by oscillatory and steady-shear viscosity measurements. The differences in the solution properties of CHM and CHP reflect differences in their assembly on the molecular level, in particular, the size and number of hydrophobic nanodomains and the hydration level. They are attributed to differences in the mobility of the cholesteryl groups which, itself, can be traced to the fact that in CHM the cholesteryl groups are predominantly linked to short oligomannopyranose branches, whereas in CHP they are linked to the polymer main chain. Our study provides a novel means to nanoengineer polysaccharide nanogels which may find unique biotechnological applications.

Rheological and dynamic-mechanical behavior of carbon nanotube/vinyl ester–polyester suspensions and their nanocomposites

Rheological properties of vinyl ester–polyester resin suspensions containing various amounts (0.05, 0.1 and 0.3 wt.%) of multi walled carbon nanotubes (MWCNT) with and without amine functional groups (–NH 2) were investigated by utilization of oscillatory rheometer with parallel plate geometry. Dispersion of corresponding carbon nanotubes within the resin blend was accomplished employing high shear mixing technique (3-roll milling). Based on the dynamic viscoelastic measurements, it was observed that at 0.3 wt.% of CNT loadings, storage modulus ( G′) values of suspensions containing MWCNTs and MWCNT–NH 2 exhibited frequency-independent pseudo solid like behavior especially at lower frequencies. Moreover, the loss modulus ( G″) values of the resin suspensions with respect to frequency were observed to increase with an increase in contents of CNTs within the resin blend. In addition, steady shear viscosity measurements implied that at each given loading rate, the resin suspensions demonstrated shear thinning behavior regardless of amine functional groups, while the neat resin blend was almost the Newtonian fluid. Furthermore, dynamic mechanical behavior of the nanocomposites achieved by polymerizing the resin blend suspensions with MWCNTs and MWCNT–NH 2 was investigated through dynamic mechanical thermal analyzer (DMTA). It was revealed that storage modulus ( E′) and the loss modulus ( E″) values of the resulting nanocomposites increased with regard to carbon nanotubes incorporated into the resin blend. In addition, at each given loading rate, nanocomposites containing MWCNT–NH 2 possessed larger loss and storage modulus values as well as higher glass transition temperatures ( T g) as compared to those with MWCNTs. These findings were attributed to evidences for contribution of amine functional groups to chemical interactions at the interface between CNTs and the resin blend matrix. Transmission electron microscopy (TEM) studies performed on the cured resin samples approved that the dispersion state of carbon nanotubes with and without amine functional groups within the matrix resin blend was adequate. This implies that 3-roll milling process described herein is very appropriate technique for blending of carbon nanotubes with a liquid thermoset resin to manufacture nanocomposites with enhanced final properties.

Shear and Longitudinal Viscosity of Non-ionic C12E8 Aqueous Solutions

We present an extensive set of measurements of steady shear viscosity (eta degrees(s)), longitudinal elastic modulus (M'), and ultrasonic absorption (alpha) in the one-phase isotropic liquid region of the non-ionic surfactant C12E8 aqueous solutions. Within a given temperature interval, this phase extends along the entire surfactant concentration range that could be fully covered in the experiments. In agreement with previous studies, the overall results support the presence of two separated intervals of concentration corresponding to different structural properties. In the surfactant-rich region the temperature dependence of eta degrees(s) follows an equation characteristic of glass-like systems. The ultrasonic absorption spectra show unambiguous evidence of viscoelastic behavior that can be described by a Cole-Cole relaxation formula. In this region, when both the absorption and the frequency are scaled by the static shear viscosity (eta degrees(s)), the scaled attenuation reduces to a single universal curve for all temperatures and concentrations. In the water-rich region the behavior of eta degrees(s), M', and alpha are more complex and reflect the presence of dispersed aggregates whose size increases with temperature and concentration. At these concentrations the ultrasonic spectra are characterized by a multiple decay rate. The high-frequency tail falls in the same frequency range seen at high surfactant content and exhibits similar behaviors. This contribution is ascribed to the mixture of hydrophilic terminations and water present at the micellar interfaces that resembles the condition of a concentrated polymer solution. An additional low-frequency contribution is also observed, which is ascribed to the exchange of water molecules and/or surfactant monomers between the aggregates and the bulk solvent region.

Temperature‐Induced Gelation of Concentrated Sialon Suspensions

A temperature‐induced gelation method has been developed for the preparation of sialon green bodies composed of Si3N4, AlN, Y2O3, and Al2O3. Using a polyester/polyamine condensation polymer as dispersant, stable suspension containing sialon, precursor powders could be prepared in methyl ethyl keton (MEK)/ethanol (E) solvent mixture with solids loading as high as 60 vol%. The solvency of the dispersant in MEK/E decreased dramatically on cooling. The sedimentation tests showed that the settling behavior changed from slow accumulation at ∼20°C to fast deposition of clusters at −15°C, because of the collapse of dispersant chains adsorbed at the surface of the particles. Steady shear viscosity and oscillatory measurements performed for 60 vol% suspensions as functions of temperature and added amounts of dispersant proved that suspensions were of low viscosity and high stability at room temperature, becoming predominantly very highly viscous and elastic as temperature decreased. The gelation mechanism was mainly based on the coiling up of dissolved dispersant molecules, inducing in situ gelation and the formation of a rigid network bridging the suspended particles. The green bodies showed negligible shrinkage during gelation, a small shrinkage during drying, homogeneous microstructures, narrow pore size distributions, and high relative density. It was possible to achieve dense α‐sialon ceramics through pressureless sintering at 1750°C for 2 h.

Temperature-induced gelation of concentrated silicon carbide suspensions.

Due to the steric barrier provided by the adsorption of the dispersant hypermer KD1 (a polyester/polyamine condensation polymer), stable and low-viscosity suspensions of SiC, Y(2)O(3), and Al(2)O(3) powder mixtures could be prepared in methyl ethyl ketone (MEK)/ethanol (E) solvent with solids loading as high as 60 vol%. The solvency of the dispersant in MEK/E decreased dramatically on cooling. Steady shear viscosity and oscillatory measurements were performed as a function of temperature for suspensions with different solids loading. The viscosity and elastic modulus of suspension increased with decreasing temperature and became more sensitive with the increase of solids loading. The suspensions with solids loading higher than 40 vol% could be solidified with decreasing temperature, but gelation temperature and gelation stiffness decreased with decreasing solids loading. The 60 vol% solid-loaded suspension was a stable and free-flowing fluid at 20 degrees C and gradually transformed to a very highly viscous and elastic system upon cooling to about 13 degrees C. Complete solidification occurred when the temperature was decreased to 5 degrees C. The gelation mechanism was mainly based on the collapse of the adsorbed layer as the temperature decreases, which induced incipient flocculation and formed a stiff network. The gelled body was further strengthened by separation of the dispersant from the suspension.

New Solvents for Cellulose. II. Ethylenediamine/Thiocyanate Salt System

The ethylenediamine/thiocyanate salt system was found to be a new solvent for cellulose. The solubility, dissolution behavior, solution properties, and cellulose recovered from the solutions were investigated. The dissolution took place at room temperature, and the maximum solubility achieved was 16 % (w/w) for cellulose of DP210 in the ethylenediamine/sodium thiocyanate 54/46 (w/w). The dependence of cellulose solubility on DP is also described. Tracing the dissolution behavior of the cellulose by CP/MAS 13C NMR measurements revealed the polymorphic conversion of cellulose I to III to amorphous structure during the dissolution process. The cellulose dissolved was stable for 30 days storage at room temperature. Microscopic observations and steady-shear viscosity measurements of the solutions indicated mesophase formation of cellulose in the ethylenediamine/sodium thiocyanate system. This anisotrpoic phase appeared from ca. 10 % (w/w) cellulose with DP210 and greatly depended on the cellulose concentrations. Coagulation studies disclosed that cellulose II and amorphous cellulose were recovered from the cellulose/ethylenediamine/thiocyanate salt solutions when water and alcohol were used as a coagulant, respectively. It was suggested that this solvent system has high potential for cellulosic fiber and film formations.

Feedstock Formulations for Direct Consolidation of Porcelains with Polysaccharides

Direct‐consolidation methods are becoming well‐established forming techniques for advanced ceramics, because of their advantages in terms of shape capability. These advantages could also be exploited to consolidate traditional ceramics, such as stoneware or porcelain pottery requiring handles, which could be potentially manufactured in a single step. The most limiting factor in the transfer of these technologies from advanced to traditional ceramics is related to the moderate solids loading usually achievable with clay‐based suspensions. In this work, new porcelain feedstocks are proposed that use either milled rejected pieces (MRP) of porcelain or a kaolinitic stoichiometric mixture of SiO2 and Al2O3, i.e., pseudokaolin (PK). The replacement of the clay component by MRP or PK makes it possible to obtain 60 vol% aqueous porcelain suspensions, which can be directly consolidated using a relatively low amount (1 wt%, based on liquid volume fraction) of a mixture of polysaccharides. Steady shear viscosity measurements show that these highly concentrated suspensions are fluid enough for pouring operations. The green and presintered bodies show similar values of shrinkage and relative density, because of the low amount of organic additives used. The total replacement of the clay component in the starting composition enables a decrease in the firing temperature. Otherwise, for a given firing schedule, the enhancement of quartz dissolution in the glass phase and the decrease of the aspect ratio of mullite needles lead to an increase of the pyroplastic deformation index.

Non-Newtonian flow behaviour of gellan gum aqueous solutions

Rheological properties of gellan gum solutions with and without salt have been monitored using oscillatory measurements and steady-shear viscosity measurements. The steady-shear viscosity measurements indicated that gellan gum solutions showed a wide Newtonian plateau when gellan gum molecules took a coil conformation, and that the shear-thinning behaviour became more conspicuous with conformational change of gellan gum molecules from coiled to helical, and the range of the Newtonian plateau became limited only to very low shear rates. When gellan gum solutions showed rheological behaviour as a dilute or concentrated polymer solution, these systems obeyed the Cox–Merz superposition of steady-state viscosity and dynamic viscosity. As gellan gum solutions formed a weak gel, the Cox–Merz rule was not valid; however, the deviation from this superposition was less significant than that of xanthan gum solutions which also show weak-gel behaviour.

Concentric cylinder end effects and fluid inertia effects in controlled stress rheometry: part I: numerical simulation

In a commercially available CSR controlled stress rheometer, the theoretical formulae for calculating the shear viscosity and complex viscosity of a fluid in a recessed concentric cylinder geometry, do not take into account end effects. The first part of this paper is concerned with a theoretical prediction of end effects on steady shear viscosity measurements of Newtonian fluids in a recessed concentric cylinder geometry. Fluid inertia effects are included in the theory and the relevant equations are solved using a perturbation analysis which is valid for low Reynolds number flows. The perturbation equations are solved numerically using a finite difference method. From this theory, correction formulae are produced to compensate for end effects and second order fluid inertia effects in steady shear flows on a CSR rheometer. End effects are also investigated for shear thinning fluids using the Polyflow package, and results show that they are less significant than those for Newtonian fluids. The second part of this paper is concerned with a theoretical prediction of the end effect of a recessed concentric cylinder geometry on complex viscosity measurements of a generalised linear viscoelastic fluid. The theory will include a first and second order fluid inertia perturbation analysis and the relevant equations are solved using a finite difference method. Using this theory, the existing oscillatory shear formulae which include second order fluid inertia effects, are modified to compensate for end effects.

Rheology of low nematic transition temperature thermotropic liquid crystalline copolyester HBA/HQ/SA

AbstractThe rheology of a liquid crystalline copolyester of hydroxybenzoic acid, hydroquinone, and sebacic acid (HBA/HQ/SA copolyester) was studied on both a rotational and a capillary rheometer. DSC studies show that the copolyester has a crystalmesophasic and a broad mesophasic‐isotropic transition at 170°C and 220°C. Optical texture observations show the mesophase is characterized by line defect textures, which are characteristic of a nematic structure. At 220°C, both isotropic and nematic phases coexist with the latter being the major. As temperature reaches 250°C, a clear dominance of isotropic phase is observed. At this temperature, the nematic phase of irregular shapes randomly disperses within the isotropic matrix. Subsequent rheological studies were thus conducted in crystal/nematic biphase, single nematic phase, nematic/isotropic biphase, and the near single isotropic phase. Dynamic strain sweep measurements show that a linear viscoelastic region exists at all temperatures tested. The maximum strain amplitude for the linear viscoelastic region is found to be highly structure dependent; it is > 100% in the nematic phase, ∼20% in the biphases, and only about 5% in the isotropic phase. The concurrence of curves obtained at different temperatures in a Cole‐Cole plot of G′ vs. G″ indicates similar structures in the nematic phase and biphases. Measurements of steady shear viscosity using a rotational rheometer and a roundhole capillary rheometer show that in the nematic phase the copolyester behaves as a shear thinning fluid for a wide shear rate range of 1 ∼ 10,000 s−1, in which the power law index is about 0.6 ∼ 0.8, and the viscosity is < 10 Pa.s at shear rates >1 s−1.

Steady viscometric properties and characterization of dilute drag‐reducing polymer solutions

Carefully prepared aqueous solutions of drag‐reducing polymers have been characterized by means of steady viscometric and molecular weight measurements. Solutions of anionic polyacrylamide (Cyanatrol‐750), 0.5–50 ppm, and nonionic poly (ethylene oxide) (Polyox WSR‐303), 100–1000 ppm, were investigated. Steady shear viscosity measurements, with a Rheometrics Stress Rheometer and a Contraves LS30 rheometer, reveal substantial shear thinning for Cyanatrol solutions above 2 ppm and Polyox solutions above 500 ppm, for the shear‐rate range investigated. Zero‐shear viscosity was accurately determined for all solutions. Intrinsic viscosity, hydrodynamic radius of gyration, and overlap concentration were also estimated. The Carreau and Carreau–Yasuda models successfully fit all shear viscosity data, and allow estimates of elasticity. Reduced variables were used for generalizing the shear viscosity data. Aging tests show that both polymers are stable. The molecular weight and polydispersity of Cyanatrol were measured using the technique of band sedimentation/low angle laser light scattering. The drag‐reducing capability of these polymers has been confirmed by pipe flow experiments.

The rheological behaviour of animal vitreus and its comparison with vitreal substitutes

Some important eye pathologies, such as diabetic proliferative retinopathy and retinal detachment, are strictly connected to different gel vitreus alterations. Therefore there is a strong need in ophthalmology for vitreal substitutes. Until now many synthetic and natural polymers have been tested as vitreal substitutes, but no one has proved to be an ideal vitreal substitute. An ideal vitreal substitute, apart from other characteristics, such as transparency, permanency, biocompatibility, etc. must have a rheological behaviour compatible with the surrounding tissues. The viscoelastic behaviour of different animals' gel vitreus, evaluated by means of steady shear viscosity and small-amplitude oscillatory measurements, is typical of solid-like rubbery gels with dynamic elastic modulus G′ higher than the dynamic viscous modulus G″ in the typical frequency range investigated (0.05–10 Hz). On the other hand the rheological behaviour of current or candidate vitreal substitutes (silicone oil, HPMC, high molecular weight hyaluronic acid and chemically-crosslinked hyaluronic acid), analysed with the same technique, is generally different from that of natural vitreus.

Steady shear viscosity of weakly aggregating polystyrene latex dispersions

In order to describe the steady shear behavior of weakly aggregating dispersions a microrheological model is developed. This model combines the concept of fractal aggregation in shear flow with the transient network modeling originally developed for polymer dynamics. The former accounts for the hydrodynamic stress in the aggregates, while the latter is employed to calculate the stress component arising from the forces transmitted by chains of particles combining the neighboring aggregates into a network. The contribution of this network is shown to be significant for steady shear behavior at low volume fractions of solid and low shear rates. The validity of the model is tested by fitting it to experimental data on a well characterized weakly aggregating polystyrene latex dispersion. In this way a number of relevant parameters, among which the fractal dimension df of the aggregates and the capture efficiency of particle chains belonging to neighboring aggregates, are determined. The best agreement of the calculations with the experiments is found at small capture efficiencies and rather high fractal dimensions, i.e., 2.0≤df≤2.3. Hence, combining the steady-shear viscosity measurements with the microrheological interpretation one obtains a tool for probing the structure of weakly aggregating dispersions.