Rheological Properties Of Complex Fluids Research Articles

Rheological characterization of human follicular fluid under shear and extensional stress conditions

The rheology of human follicular fluid has been empirically evinced to be related to the reproductive health status of individuals, which supports its use as an indicator for improving the success rates of in vitro fertilization. However, there is a dearth of studies investigating the viscoelastic properties of human follicular fluid. Moreover, a comprehensive elucidation of the rheological properties of complex fluids necessitates the assessment of data regarding both shear and extensional viscosities. Nonetheless, to the best of our knowledge, the extant literature does not include reports on the behavior of follicular fluid under extensional conditions. Consequently, this study aimed to analyze the shear and extensional viscosities of human follicular fluid. Primarily, the impact of oocytes on the rheology of follicular fluid was evaluated by measuring the shear viscosity of this fluid using a high-resolution coaxial cylinder viscometer. The shear viscosity of follicular fluid exhibited marked differences depending on the presence or absence of oocytes. Subsequently, a measurement system that enables the handling of minute quantities of body fluid was developed to determine the extensional viscosity of follicular fluid, which contains albumin. A comparison of the acquired follicular fluid data with that of the protein solution containing albumin demonstrated that the follicular fluid alone displayed extensional behavior, whereas the protein solution did not. Therefore, it can be inferred that the protein solution is not its sole determinant, as other constituents of the fluid, such as peptides and cumulus cells, may determine its rheological properties. This observation was not attained through the conventional technique consisting in shear viscosity measurements.

Editorial: theme issue on complex rheology in biological systems

Editorial: theme issue on complex rheology in biological systems

Complex fluids in animal survival strategies.

Animals have evolved distinctive survival strategies in response to constant selective pressure. In this review, we highlight how animals exploit flow phenomena by manipulating their habitat (exogenous) or by secreting (endogenous) complex fluids. Ubiquitous endogenous complex fluids such as mucus demonstrate rheological versatility and are therefore involved in many animal behavioral traits ranging from sexual reproduction to protection against predators. Exogenous complex fluids such as sand can be used either for movement or for predation. In all cases, time-dependent rheological properties of complex fluids are decisive for the fate of the biological behavior and vice versa. To exploit these rheological properties, it is essential that the animal is able to sense the rheology of their surrounding complex fluids in a timely fashion. As timing is key in nature, such rheological materials often have clearly defined action windows matching the time frame of their direct biological behavior. As many rheological properties of these biological materials remain poorly studied, we demonstrate with this review that rheology and material science might provide an interesting quantitative approach to study these biological materials in particular in context towards ethology and bio-mimicking material design.

Capillary breakup extensional electrorheometry (CaBEER)

A new electrorheological cell for the capillary breakup extensional rheometer (HaakeTM CaBER 1TM, Thermo Scientific) allowing the analysis of the rheological properties of complex fluids under the simultaneous application of an extensional flow and an electric field has been developed and tested. In this study, the add-on is described in full detail and different cornstarch suspensions in olive oil are characterized under different stretching conditions with and without an electric field. The results show that, under extensional flow and no electric field, the sample behaves as a Newtonian-like fluid, showing a linear relationship between time and filament minimum diameter. However, when the external electric field is imposed, the filament thinning process delays increasing the breakup time. If the external electric field is further increased, then the filament may even not break, depending on the imposed voltage, the Hencky strain, and the concentration of particles in the fluid sample.

Size effects on rotational particle diffusion in complex fluids as probed by Magnetic Particle Nanorheology.

Rheological approaches based on micro- or nanoscopic probe objects are of interest due to the low volume requirement, the option of spatially resolved probing, and the minimal-invasive nature often connected to such probes. For the study of microstructured systems or biological environments, such methods show potential for investigating the local, size-dependent diffusivity and particle-matrix interactions. For the latter, the relative length scale of the used probes compared to the size of the structural units of the matrix becomes relevant. In this study, a rotational-dynamic approach based on Magnetic Particle Nanorheology (MPN) is used to extract size- and frequency-dependent nanorheological properties by using an otherwise well-established polymer model system. We use magnetically blocked CoFe2O4 nanoparticles as tracers and systematically vary their hydrodynamic size by coating them with a silica shell. On the polymer side, we employ aqueous solutions of poly(ethylene glycol) (PEG) by varying molar mass M and volume fraction φ. The complex Brownian relaxation behavior of the tracer particles in solutions of systematically varied composition is investigated by means of AC susceptometry (ACS), and the results provide access to frequency dependent rheological properties. The size-dependent particle diffusivity is evaluated based on theoretical descriptions and macroscopic measurements. The results allow the classification of the investigated compositions into three regimes, taking into account the probe particle size and the length scales of the polymer solution. While a fuzzy cross-over is indicated between the well-known macroscopic behavior and structurally dominated spectra, where the hydrodynamic radius is equal to the radius of gyration of the polymer (rh ∼ Rg), the frequency-related scaling behavior is dominated by the correlation length ξ respectively by the tube diameter a in entangled solutions for rh < Rg.

Basic Fundamentals of Petroleum Rheology and Their Application for the Investigation of Crude Oils of Different Natures

A pair of basic methods for investigating the rheological properties of complex fluids were considered: steady flow and small amplitude oscillatory shear. The methods were applied to study rheological properties of eight petroleum samples belonging to different classes (light, heavy, waxy crude oils, and bitumen). It was shown how the viscosity of a crude oil depends on its nature, temperature, and applied stress. To characterize the viscous behavior of oils, one can use their glass transition temperature: the Williams–Landel–Ferry equation makes it possible to construct a universal temperature dependence of the viscosity. The latter determines the viscosity of any petroleum at temperature of interest from that at some other temperature. Linear and nonlinear viscoelastic properties of oils were demonstrated, and the manifestations of viscoelasticity by various crude oils were shown. It was revealed how the pour point of heavy oil can be calculated from its viscosity.

New insight into rheology and flow properties of complex fluids with Doppler optical coherence tomography.

Flow properties of complex fluids such as colloidal suspensions, polymer solutions, fiber suspensions and blood have a vital function in many technological applications and biological systems. Yet, the basic knowledge on their properties is inadequate for many practical purposes. One important reason for this has been the lack of effective experimental methods that would allow detailed study of the flow behavior of especially opaque multi-phase fluids. Optical Coherence Tomography (OCT) is an emerging technique capable of simultaneous measurement of the internal structure and motion of most opaque materials, with resolution in the micrometer scale and measurement frequency up to 100 kHz. This mini-review will examine the recent results on the use of Doppler-OCT in the context of flows and rheological properties of complex fluids outside biomedical field.

A new instrument for dynamic helical squeeze flow which superposes oscillatory shear and oscillatory squeeze flow

Simple shear flow has been widely used as a model flow system to investigate the rheological properties of complex fluids. Although it is useful and easy to apply, the shear flow is too simple compared with the complicated flows encountered in real processes. For this reason, it is necessary to study the rheological properties of viscoelastic fluids subjected to more complicated flow field. In this paper, we report a new instrument in which dynamic helical squeeze flow is generated. It superimposes the oscillatory squeeze flow on the oscillatory shear flow, and was designed to get more information on the microstructural change of complex fluids in the flow field which is more complex than conventional simple shear but is still well-defined. This instrument has advantages: the shear and normal stresses can be obtained simultaneously under the coupled flow field; the present design can be used to investigate the structural anisotropy in the direction of both rotational and vertical motion. This study provides a new design and methodology to investigate the rheological responses of complex fluids under dynamic helical squeeze flow.

Scaling of critical velocity for bubble raft fracture under tension

The behavior of materials under tension is a rich area of both fluid and solid mechanics. For simple fluids, the breakup of a liquid as it is pulled apart generally exhibits an instability driven, pinch-off type behavior. In contrast, solid materials typically exhibit various forms of fracture under tension. The interaction of these two distinct failure modes is of particular interest for complex fluids, such as foams, pastes, slurries, etc. The rheological properties of complex fluids are well-known to combine features of solid and fluid behaviors, and it is unclear how this translates to their failure under tension. In this paper, we present experimental results for a model complex fluid, a bubble raft. As expected, the system exhibits both pinch-off and fracture when subjected to elongation under constant velocity. We report on the critical velocity vc below which pinch-off occurs and above which fracture occurs as a function of initial system width W, length L, bubble size R, and fluid viscosity for both monodisperse and polydisperse systems. Though both exhibit a transition from pinch-off to fracture, the behavior as a function of L/W is qualitatively different for the two systems. For the polydisperse systems, the results for the critical velocity are consistent with a simple scaling law vcτ/R∼L/W, where the fluid viscosity sets the typical time for bubble rearrangements τ. We show that this scaling can be understood in terms of the dynamics of local bubble rearrangements (T1 events). For the monodisperse systems, we observe a critical value for L/W below which the system only exhibits fracture.

Enhanced rheological properties of dilute suspensions of magnetic nanoparticles in a concentrated amphiphilic surfactant solution

We present an experimental study of the magnetorheological response of dilute suspensions of magnetic nanoparticles in concentrated amphiphilic surfactant solutions. Low particle content (<0.4% v/v) induced significant increase in viscosity, enhancing the shear thinning behavior observed in the absence of the nanoparticles. A magnetic field induced yield stress of up to 10 Pa at magnetic fields of up to 0.4 T was also observed. Experiments under small amplitude oscillatory shear indicate a transition from viscous to elastic behavior at a critical magnetic field which depends on the frequency of the oscillatory shear. At low applied magnetic fields loss and storage moduli are independent of the magnetic field and increase with the frequency of the oscillatory shear. At high applied magnetic fields both the loss and storage moduli seem to asymptote to a power law dependence on the magnetic field magnitude. These results illustrate the possibility of inducing dramatic changes in the rheological properties of complex fluids by addition of minute amounts of magnetic nanoparticles and application of magnetic fields.

The Microcantilever: A Versatile Tool for Measuring the Rheological Properties of Complex Fluids

Silicon microcantilevers can be used to measure the rheological properties of complex fluids. In this paper, two different methods will be presented. In the first method, the microcantilever is used to measure the hydrodynamic force exerted by a confined fluid on a sphere that is attached to the microcantilever. In the second method, the measurement of the microcantilever's dynamic spectrum is used to extract the hydrodynamic force exerted by the surrounding fluid on the microcantilever. The originality of the proposed methods lies in the fact that not only may the viscosity of the fluid be measured, but also the fluid's viscoelasticity, that is, both viscous and elastic properties, which are key parameters in the case of complex fluids. In both methods, the use of analytical equations permits the fluid's complex shear modulus to be extracted and expressed as a function of shear stress and/or frequency.

Karhunen–Loève Galerkin method with decimated sampling technique for the simulation of complex fluids defined in the phase space

In complex fluids, solute molecules with structural length scales much larger than atomic are dispersed in solvents of simple fluids such as water. The rheological properties of complex fluids are determined by dynamics of solute molecules which can be modeled by the Fokker–Planck equation defined in a six-dimensional phase space. In the present investigation, we devise a method of efficient simulation of complex fluid flows employing the Karhunen–Loève Galerkin (KLG) method. Adopting the decimated sampling of solvent flow fields, a reduced-order model for the Fokker–Planck equation is obtained, which can be employed for the the simulation of complex fluids with a decent computer time. As a specific example, we consider a flow of dilute polymeric liquids over a cylinder, whose constitutive equation is the FENE (finitely extensible nonlinear elastic) model. It is found that the KLG method with the decimated sampling technique yields accurate results at a computational cost less than a hundredth of that for the numerical simulation using the Fokker–Planck equation. The KLG method supplemented by the decimated sampling technique is an efficient method of coarse-graining for equations of complex fluids defined in the phase space.

The influence of flow confinement on the rheological properties of complex fluids

The rheological properties of plastic and viscoplastic complex fluids have been investigated using constant velocity squeeze flow rheometry at small gaps in order to examine the influence of the resulting flow confinement. The fluids investigated were aqueous carbopol suspensions and three commercial products (Tesco English mustard, Tesco value lemon curd and Heinz tomato ketchup (HTK)). The bulk rheological properties were measured using parallel plate rheometry. Rough plates were used to eliminate wall slip in both rheometric configurations. The commercial products are Herschel–Bulkley fluids and, for gaps less than a critical value of ~200 μm, the yield stresses tended to large values. There was a corresponding trend to small values for the flow consistencies except for HTK, which has a negligibly small bulk value. A possible explanation is that the micro-structural correlation lengths of these fluids are of the order of that of the critical separation. The yield stresses of the carbopol suspensions also increased sharply at the critical gap but then decreased gradually with decreasing gap separation. The transition may correspond to the formation of a jammed state with the subsequent plastic flow at smaller gap separations arising from localised shearing.

Towards a continuous microfluidic rheometer

In a previous paper we presented a way to measure the rheological properties of complex fluids on a microfluidic chip (Guillot et al., Langmuir 22:6438, 2006). The principle of our method is to use parallel flows between two immiscible fluids as a pressure sensor. In fact, in a such flow, both fluids flow side by side and the size occupied by each fluid stream depends only on both flow rates and on both viscosities. We use this property to measure the viscosity of one fluid knowing the viscosity of the other one, both flow rates and the relative size of both streams in a cross-section. We showed that using a less viscous fluid as a reference fluid allows to define a mean shear rate with a low standard deviation in the other fluid. This method allows us to measure the flow curve of a fluid with less than 250 μL of fluid. In this paper we implement this principle in a fully automated set up which controls the flow rate, analyzes the picture and calculates the mean shear rate and the viscosity of the studied fluid. We present results obtained for Newtonian fluids and complex fluids using this set up and we compare our data with cone and plate rheometer measurements. By adding a mixing stage in the fluidic network we show how this set up can be used to characterize in a continuous way the evolution of the rheological properties as a function of the formulation composition. We illustrate this by measuring the rheological curve of four formulations of polyethylene oxide solution with only 1.3 mL of concentrated polyethylene oxide solution. This method could be very useful in screening processes where the viscosity range and the behavior of the fluid to an applied stress must be evaluated.

A versatile single-screw-extruder system designed for magnetic resonance imagingmeasurements

A versatile system has been developed for magnetic resonance imaging (MRI)measurements, in which a ceramic barrel/outer cylinder (0.04 m internal diameter)can be configured either as a single-screw extruder (polyetheretherketone (PEEK),length to diameter ratio 4.575, root diameter 0.03 m), or as a concentric-cylinderCouette device (PEEK, length 0.156 m, inner cylinder diameter 0.03 m). A secondchannel in the sample inlet allows two streams of fluid to be pumpedsimultaneously through the system for mixing. The shaft rotation speed can be setbetween 5 and 1200 revolutions per minute (rpm); the barrel and sample feedercan be separately thermostatted to ±0.2 °C in the range of−10 to +60 °Cvia coolant jacket systems; samples with viscosity up to 10 Pa scan be pumped at rates up to 36 l h−1.This enables studies to be conducted with the system configured as a Couettedevice to provide knowledge of the rheological properties of complex fluids beforemore complicated studies of their flow and mixing with the system configured as asingle-screw extruder.Bench and MRI measurements have been carried out to testthe thermostat function of the system. The bench tests showed that the internalvolume of the device reached thermal equilibrium after 1 h of running and could bemaintained at constant temperature (within ±0.2 °C) forperiods of over 6 h. The MRI tests were conducted with the device configured in a Couettegeometry for measurements of the flow velocities of pure glycerol and 1% aqueoussodium carboxymethylcellulose (CMC) in the range of 10–60 °C, and atvarious rotation speeds. Results showed that although the azimuthal velocity distributions versusthe radius (v(r))were independent of temperature for glycerol, there was strong temperaturedependence for the CMC solution. On the latter the power-law index(n) from MRIdata agreed well with the literature values for the same concentrations and temperatures,and showed nvalues increasing with increase of temperature; this demonstratedthat the temperature control was reliable. However, thenvalues increased with decrease of the average shear rate; this is incontrast to the results from conventional rheometry, for which thenvalue is constant, regardless of shear rates at each temperature. Thiswas attributed to the differences between conventional, very-narrow-gapCouette rheometers and the MRI, wide-gap device, and showed theadvantage of using MRI for wide-gap concentric-cylinder rheometry.Couette flow of an aqueous suspension of 35% (w/w)tapioca starch, made of 37% (w/w) sucrose and 1% (w/w)CMC solutions, was measured at 20 °Cand a rotation speed of 20 rpm. This showed that wall slip developed with time,especially at the inner wall of the rotating cylinder.Velocity measurements in threedirections were made for the flow of 1% CMC solution at 22 °Cthrough the single-screw extruder using the pulsed-field gradient spin-echo imagingsequence for two-dimensional transverse or coronal images. Two-dimensional MRI formixing of fluids (1% CMC) in the single-screw extruder at 22 °Cis also demonstrated.

Shape of a liquid front upon dewetting.

The profile of a liquid front of a polymer film dewetting a solid substrate is examined by atomic force microscopy. The material removed from the substrate is accumulated in a rim next to the three-phase contact line. Theory predicts the leading edge of the rim profile to be a damped harmonic oscillation for a large class of systems. This is investigated experimentally for the first time, and we show that a non-Newtonian liquid behaves qualitatively different due to viscoelastic effects. It is pointed out that analysis of the rim shapes allows one to study quantitatively the rheological properties of complex fluids on a nanometer scale.

SASFLOW '98 focuses on soft matter

In the last five years, a major challenge among the soft matter community has been to elucidate the relationship between rheological properties of complex fluids and their mesoscopic structure as revealed by small angle scattering (SAS) experiments.

Static and dynamic properties of dissipative particle dynamics

The algorithm for the dissipative particle dynamics (DPD) fluid, the dynamics of which is conceptually a combination of molecular dynamics, Brownian dynamics, and lattice gas automata, is designed for simulating rheological properties of complex fluids on hydrodynamic time scales. This paper calculates the equilibrium and transport properties (viscosity, self-diffusion) of the thermostated DPD fluid explicitly in terms of the system parameters. It is demonstrated that temperature gradients cannot exist, and that there is therefore no heat conductivity. Starting from the $N$-particle Fokker-Planck, or Kramers equation, we prove an $H$ theorem for the free energy, obtain hydrodynamic equations, and derive a nonlinear kinetic equation (the Fokker-Planck-Boltzmann equation) for the single-particle distribution function. This kinetic equation is solved by the Chapman-Enskog method. The analytic results are compared with numerical simulations.

Elongational, hysteresis, and oscillatory flows of complex fluids

AbstractThe simple model proposed earlier to describe te rheological properties of complex fluids is used to calculate (a) the extensional viscosity, (b) the hysteresis loops, and (c) the complex viscosity. It has been found that the rheological properties predicted by the model agree with experimental observations. It is shown that for some viscoelastic fluids the extensional viscosity is always finite and for some other fluids the extensional viscosity tends t infinity at finite extensional rate. In the latter case, steady flow is not attainable. The shape of the hysteresis loops depends on the maximum shear‐rate. It also depends on the material properties. In a small amplitude oscillatory flow, our model reduces t a linear viscoelastic fluid.

Unsteady Flow of Suspension through a Pipe

The unsteady flow of a binary mixture of fluids in a long rigid cylinder of circular and sectorial cross-sections, under the influence of an arbitrary time varying pressure gradient, is studied. Velocity of both the phases are explicitly determined for various particular pressure gradients of physical importance. Finally, to gain insight into the patterns of flow, numerical study of the results has been made using a digital computer. A strong motivation of the present analysis has been the hope that such a theory of fluids is useful in providing some insight in rheological properties of complex fluids as polymers, liquid crystals and, in particular, blood in the vessels of small diameter. Also the theory of mixture of fluids might provide an improved understanding of such diverse subjects as diffusion of proteins, swimming of microorganism and particle diposition in respiratory tract.