Low Viscosity Newtonian Fluids Research Articles

Xanthan and gum acacia modified olive oil based nanoemulsion as a controlled delivery vehicle for topical formulations

In this study, olive oil nanoemulsion modified with xanthan gum and gum acacia was explored as a potential controlled topical delivery vehicle. Oil-in-water nanoemulsion formulated with optimized composition of olive oil, tween 80, and water was used as the drug carrier and further modified with gum. Effect of gum on nanoemulsion different physiochemical characteristics, stability, rheology, drug release and encapsulation efficiency were investigated. Results showed that developed nanoemulsion behaved as low viscosity Newtonian fluid and released 100 % drug within 6 h. Modification with xanthan and gum acacia had significantly improved formulation viscosity, drug encapsulation efficiency (>85 %) and controlled drug release up to 40 % with release pattern following Korsmeyer–Peppas model. Additionally, xanthan gum modified formulation exhibited shear thinning rheology by forming an extended network in the continuous phase, whereas gum acacia modified formulation behaved as Newtonian fluid at high shear rate (>200 s−1). Furthermore, xanthan gum modified formulations had improved zeta potential, stability, monodispersity, and hemocompatibility and showed high antibacterial activity against S. aureus than gum acacia modified formulations. These results indicate the higher potential of xanthan gum modified formulation as a topical delivery vehicle. Moreover, skin irritation test demonstrated the safety of developed formulations for topical application.

Global characterization of hydrodynamics and gas-liquid mass transfer in a thin-gap bubble column in presence of Newtonian or non-Newtonian liquid phase

Bubble columns are commonly used as photobioreactors (PBRs) due to their good mixing and mass transfer capabilities. Modification in design and operating parameters are nevertheless needed to intensify volumetric productivity. Thin-gap bubble column can be used in this context to operate with high biomass concentration, up to conditions where the culture becomes non-Newtonian. In the present study, the global hydrodynamics and gas–liquid mass transfer inside a 4 mm thickness thin-gap bubble column are characterized in presence of low viscosity Newtonian fluid (water) and two aqueous solutions of Carboxymethyl Cellulose and Xanthan Gum. These shear-thinning solutions are used to mimic high concentration cultures of Chlorella Vulgaris at 42 g.L−1. A range of superficial gas velocities and different capillary diameters are explored to investigate the effect of sparging on hydrodynamics and gas–liquid mass transfer. Studied parameters are flow regimes, mixing, and gas–liquid mass transfer. Results are compared with literature results in classical bubble columns to put into evidence the original effects of both confinement and liquid rheology. Among others, these results show that compared to Newtonian media, non-Newtonian media result in higher gas holdup and mixing times and a lower gas–liquid mass transfer coefficient. The findings suggest that the presence of smaller bubbles would improve mass transfer due to the increased interfacial area, while the presence of larger bubbles would improve mixing performance due to increased vorticity in their wake and relatively greater species transport.

Stimuli-Responsive Systems Based on Polymer-like Wormlike Micelles of Ionic Surfactants and Their Modern Applications

Solutions based on polymer-like micelles of ionic surfactants attract the attention of scientists as stimuli-responsive systems that can transform from a low-viscosity Newtonian fluid to a viscoelastic solution having a viscosity of up to 10 kPa s and an elastic response. The shape of micelles and their length are determined by the balance of hydrophobic and electrostatic interactions; therefore, the use of various low molecular weight substances or functional nanoparticles as additives can significantly change the rheological properties of such solutions and impart new stimuli-responsive properties to them. This review presents the most commonly used methods for controlling the properties of multicomponent solutions of wormlike surfactant micelles, including nanocomposite systems. Modern areas of practical application of such systems and prospects for their development are described.

Pulsatile parallel flow of air and a viscoelastic fluid with multiple characteristic times. An application to mucus in the trachea and the frequency of cough

We study the dynamics of a binary fluid, where the two fluids are flowing parallel to each other in a cylindrical geometry, and driven by a pulsatile pressure gradient. One of the fluids is a low viscosity Newtonian fluid, the other one is viscoelastic. In order to be able to apply the model to different biofluids, we consider that the viscoelastic fluid has several characteristic times. We characterize the dynamics of the fluids as generalized Darcy’s laws, with linear response functions to pulsatile pressure gradients, whose parameters are coupled for both fluids through the fluid–fluid boundary conditions. We apply our results to the dynamics of mucus and air in the trachea and find that the frequency that allows for a larger movement of the mucus, coincides with the experimental frequency of cough. This allows us to propose a plausible explanation for the frequency of cough in healthy individuals, a mechanical process to expel noxious substances from the respiratory system.

Effect of the rheological properties of the liquid carrier on the in vitro swallowing of solid oral dosage forms

Solid oral dosage forms (SODF) are the most popular oral drug delivery forms, but they can be difficult to swallow, especially for patients suffering from swallowing disorders. This study investigated the dynamics of different combinations of liquid carriers and SODF during the oral phase of swallowing using an in vitro model. The rheological properties of the carriers were characterized using shear and extensional rheometry, and their effect on bolus velocity, bolus shape, post-swallow residues, and SODF position within the bolus was evaluated. The latter has been identified as a novel and promising variable to discriminate between alternative formulations. When swallowed with water, capsules and tablets did not impact significantly the velocity of the bolus, but they lagged behind the liquid bolus, suggesting that low viscosity Newtonian fluids are not efficient carriers for SODF. Increasing the viscosity of the carrier at high shear rates improved the ability of the liquid to transport the SODF but also increased the amount of post-swallow residues. At equivalent shear viscosity, elastic and extensional properties of carriers influenced positively the position of the SODF in the bolus. Capsules and tablets were transported toward the front of these boluses, during the oral phase of swallowing, which is considered beneficial to avoid SODF sticking to the mucosa in the following stages of swallowing. Thin elastic liquids appear as an interesting option to promote safe swallowing of capsules and tablets. Clinical studies are, however, necessary to confirm this positive effect in healthy and dysphagic patients.

Rheological property and rheokinetics of novel photogelling fluids

ABSTRACTA novel photorheological fluid composed of cationic Gemini surfactant N, N’-bis (octadecyl dimethyl)-1, 2-dichloride-propyl ammonium salt (C18-3-C18) and trans-ortho-methoxycinnamic acid (trans-OMCA) was investigated. When C18-3-C18 and trans-OMCA are mixed in equimolar quantities, the result is a low-viscosity Newtonian fluid with no thixotropy. After irradiation by UV light (365 nm), trans-OMCA is converted to cis-OMCA, and in turn, the solution undergoes more than 50 fold increase in the relative viscosity and exhibits shear thinning and thixotropy. The viscosity rise is associated with the formation of wormlike micellar network in the solution, which was confirmed by cryo-scanning electron microscopy (cryo-SEM). Furthermore, the rheokinetics process of the C18-3-C18/trans-OMCA solutions during UV irradiation was studied and rheokinetics equation was established, which can well describe the dynamic changing of the rheological properties. Critical packing parameter was introduced to explain the mechanism of photo-induced micelle transition.

The observation and evaluation of extensional filament deformation and breakup profiles for Non Newtonian fluids using a high strain rate double piston apparatus

Summary This paper reports a new design of experimental double piston filament stretching apparatus that can stretch fluids to very high extensional strain rates. Using high speed photography, filament deformation and breakup profiles of a strategically selected range of fluids including low and higher viscosity Newtonian liquids together with a viscoelastic polymer solution, biological and yield stress fluids were tested for the first time at extensional strain rates in excess of 1000 s−1. The stretching rate was sufficiently high that observation of low viscosity Newtonian fluid stretching, end pinching and break was observed during the stretching period of the deformation, whereas for a higher Newtonian viscosity, filament thinning and breakup occurred after the cessation of piston movement. Different fluid rheologies resulted in very different thinning and breakup profiles and the kinetics, in particular of yield stress fluids showed a striking contrast to Newtonians or viscoelastic fluids. Surprisingly all the tested fluids had an initial sub millisecond “wine glass” profile of deformation which could be approximately captured using a simple parabolic mass balance equation. Subsequent deformation profiles were however very sensitive to the rheology of the test fluid and where the final breakup occurred before or after piston cessation. In certain cases the thinning and break up was successfully matched with a 1D numerical simulation demonstrating the way numerical modelling can be used with the fluids correct rheological characterization to gain physical insight into how rheologically complex fluids deform and breakup at very high extensional deformation rates.

Two-Phase Acto-Cytosolic Fluid Flow in a Moving Keratocyte: A 2D Continuum Model.

The F-actin network and cytosol in the lamellipodia of crawling cells flow in a centripetal pattern and spout-like form, respectively. We have numerically studied this two-phase flow in the realistic geometry of a moving keratocyte. Cytosol has been treated as a low viscosity Newtonian fluid flowing through the high viscosity porous medium of F-actin network. Other involved phenomena including myosin activity, adhesion friction, and interphase interaction are also discussed to provide an overall view of this problem. Adopting a two-phase coupled model by myosin concentration, we have found new accurate perspectives of acto-cytosolic flow and pressure fields, myosin distribution, as well as the distribution of effective forces across the lamellipodia of a keratocyte with stationary shape. The order of magnitude method is also used to determine the contribution of forces in the internal dynamics of lamellipodia.

Displacement of yield-stress fluids in a fracture

We consider a displacement of several yield-stress fluids in a Hele-Shaw cell. The topic is relevant to the development of a model for the flow of multiple phases inside a narrow fracture with application to hydraulically fracturing a hydrocarbon-bearing underground formation. Existing models for fracturing flows include only pure power-law models without yield stress, and the present work is aimed at filling this gap. The fluids are assumed to be immiscible and incompressible. We consider fluid advection in a plane channel in the presence of density gradients. Gravity is taken into account, so that there can be slumping and gravitational convection. We use the lubrication approximation so that governing equations are reduced to a 2D width-averaged system formed by the quasi-linear elliptic equation for pressure and transport equations for volume concentrations of fluids. The numerical solution is obtained using a finite-difference method. The pressure equation is solved using an iterative algorithm and the Multigrid method, while the transport equations are solved using a second-order TVD flux-limiting scheme with the superbee limiter. This numerical model is validated against three different sets of experiments: (i) gravitational slumping of fluids in a closed Hele-Shaw cell, (ii) viscous fingering of fluids with a high viscosity contrast due to the Saffman–Taylor (S–T) instability in a Hele-Shaw cell at microgravity conditions, (iii) displacement of Bingham fluids in a Hele-Shaw cell with the development of fingers due to the S–T instability. Good agreement is observed between simulations and laboratory data. The model is then used to investigate the joint effect of fingering and slumping. Numerical simulations show that the slumping rate of yield-stress fluid is significantly less pronounced than that of a Newtonian fluid with the same density and viscosity. If a low-viscosity Newtonian fluid is injected after a yield-stress one, the S–T instability at the interface leads to the development of fingers. As a result, fingers penetrating into a fluid with a finite yield stress locally decrease the pressure gradient and unyielded zones develop as a consequence.

Weakly nonlinear waves in fluids of low viscosity: Lagrangian and Eulerian descriptions

Acoustics equations are derived in low-viscosity newtonian fluids, when nonlinear effects are of first order relative to a small dimensionless parameter ∊, which is a measure of the Mach number. Another small dimensionless parameter ζ is used to define low-viscosity precisely. In this context, using conservation of mass and of linear momentum, one derives governing equations for complex motions (simultaneous forward and backward propagation) and simple motions (forward propagation only). Propagation equations are obtained for four physical quantities (particle displacement, particle velocity, mass density, and pressure) in eulerian as well as in lagrangian form. For simple waves, the equations for particle velocity, mass density and pressure are found to be of the Burgers type; that for the displacement is not of the Burgers type. Consistent with the weak nonlinearity, proper boundary conditions for the simple-wave equations are derived in both eulerian and lagrangian forms; these new results are expressed only in terms of the source displacement and the fluid constants.

Nonstandard Inkjets

Inkjet printers eject drops from microscopic nozzles and deposit them on substrates. For a number of years after its initial development, inkjet printing remained a method for visualizing computer output and printing documents. Beginning in the late 1990s, a number of researchers realized that inkjet printers could be employed as robotic pipettes to create microarrays, manufacture three-dimensional parts and spherical particles, print electrical devices, and facilitate combinatorial chemistry. Although most inks are low-viscosity Newtonian fluids, liquids in new applications are complex fluids. At the same time that these new applications were emerging, the replacement of traditional photography by digital imaging and the quest for ever-faster printing speeds resulted in the development of novel printing methods. Whereas most previous reviews of the field have focused on evaluations of well-known printing methods, this review instead presents a critical analysis from a fluid mechanics perspective of the recent developments in nonstandard printing techniques and the increasingly widespread use of nonstandard inks of complex fluids.

The matching of a “one-dimensional” numerical simulation and experiment results for low viscosity Newtonian and non-Newtonian fluids during fast filament stretching and subsequent break-up

This paper develops a model for fast filament stretching, thinning, and break-up for Newtonian and non-Newtonian fluids, and the results are compared against experimental data where fast filament relaxation occurs. A 1D approximation was coupled with the arbitrary Lagrangian Eulerian (ALE) formulation to perform simulations that captured both filament thinning and break-up. The modeling accounts for both the initial polymer stretching processes from the precise movement of the two moving pistons and also the subsequent thinning when the pistons are at rest. The simulations were first validated for a low viscosity Newtonian fluid matched to experimental data obtained from a recently developed apparatus, the Cambridge Trimaster. A non-Newtonian polymer fluid, with high frequency linear viscoelastic behavior characterized using a piezoaxial vibrator rheometer, was modeled using both an Oldroyd-B and FENE-CR single-mode constitutive models. The simulations of the filament deformation were compared with experiment. The simulations showed a generally reasonable agreement with both the stretch and subsequent relaxation experimental responses, although the mono mode models used in this paper were unable to capture all of the details for the experimental time evolution relaxation profile of the central filament diameter.

Dilution induced thickening in hydrotrope-rich rod-like micelles

Dilution induced changes in the microstructure and rheological behavior of micelles formed by a cationic surfactant–anionic hydrotrope mixture has been investigated in the hydrotrope-rich region. The surfactant used is cetyltrimethylammonium bromide (CTAB) and the hydrotropic salt is sodium 3-hydroxy naphthalene 2-carboxylate (SHNC). The concentration of the mixture is varied from 0.5% to 10.0% w/w (ϕ=0.005–0.100) at a fixed weight ratio of hydrotrope to surfactant (85:15). Rheological studies indicate Newtonian flow behavior at low and high volume fractions (0.005 and 0.100) while a shear thinning behavior is observed at intermediate volume fractions. The zero-shear viscosity η0 also passes through a maximum upon changes in the concentration. The most striking feature in our study is that a low viscosity Newtonian fluid transforms to a viscoelastic fluid, upon dilution, and then again to a Newtonain fluid. Small angle neutron scattering studies of 10.0% micellar solution show the presence of rod-like aggregates. Upon dilution, the scattering intensity per unit concentration shows an increase in the low q-region. The nature of pair distance distribution function and subsequent model fitting indicates a transition from rod-like micelles to unilamellar vesicles upon dilution. This behavior is explained in terms of the volume fraction dependant solubilization of hydrotropes in the rod-like micelles and consequent changes in the composition of the mixed micelles.

Micro-flow metering and viscosity measurement of low viscosity Newtonian fluids using a fibreoptical spatial filter technique

The paper describes an experimental method that is capable of measuring liquid flows of the order of millilitres per hour. Volume flow of laminar flows of Newtonian liquids in pipes or channels can be determined by measurement of the centreline velocity and application of the equation of Hagen-Poiseuille. Micro-flow meters with double fibre-array sensor were developed for the measurements of liquid volume flow in capillaries and micro-channels. The main units of the micro-flow meters are a laser-diode system, a double fibre-array sensor and different transparent capillaries or micro-channels. The accuracy of the measured water volume flow was tested with a balance and a syringe pump with given volume flow. Furthermore, the influence of the size of tracer particles on the volume flow results was also determined. This method of flow metering of Newtonian liquids needs no calibration and the results are not influenced by changes in temperature, pressure or nature of Newtonian liquid. An additional measuring result is the determination of the viscosity function by the application of a stripe model of the two-dimensional micro-channel flow. Possible applications of the fibreoptical micro-flow meter lie in micro- volume flow measurements of different Newtonian liquids and in viscosity measurements of Newtonian and non-Newtonian liquids.

A Planar Two-Layer Unsteady State Model for Mucociliary Transport

In this paper, a planer two – layer unsteady state fluid model is proposed to study the transport of mucus in the respiratory tracts due to cilia beating and air motion by considering mucus as a viscoelastic fluid. The serous layer is considered to be a low viscosity Newtonian fluid. The effect of air motion due to forced expiration and other processes is considered by prescribing shear stress at the mucus-air interface. It is shown that the mucus transport increases as the pressure drop, acceleration due to gravity and shear stress due to airmotion increases. Also, it is shown that mucus transport decreases as its density and elastic modulus increases. It has been also shown that the mucus transport decreases as the viscosity of serous layer fluid or mucus increases.

Numerical modelling of reverse-density structures in soft non-Newtonian sediments

Abstract A numerical code has been used to simulate the flow patterns in geological soft sediments that are driven by buoyancy forces resulting from reverse-density stratification. The aim was to provide a clearer understanding of the different roles of initiating conditions, inertia and rheological behaviour on the morphologies and timing of formation of natural features such as load casts and flame structures. Particular attention was paid to the cuspate form of rising intrusions that is commonly seen in nature but that has proved elusive in most earlier experiments. The numerical results demonstrate that large localised initiating perturbations and inertial influence during flow both tend to cause a decrease in the wavelength of the resulting flow pattern and can, under certain circumstances, serve to promote a cuspate morphology. The use of a relatively low viscosity Newtonian fluid as an approximation of the coarse-grained upper layer coupled with, critically, power-law behaviour in the underlying clayey layer was also found to promote a cuspate form in the rising intrusion.

Gas Dispersion in Rheologically-Evolving Model Fluids by Hybrid Dual Mixing Systems

Gas dispersion experiments (0.18≤Fr≤0.71, 0.02≤Fl≤0.09) were carried out using a hybrid dual mixing system, which included a helical ribbon impeller and either a Smith or a Rushton turbine. Newtonian and non-Newtonian model fluids were used as rheologically-evolving fluids to evaluate changes in gas dispersion performance. A motionless helical ribbon agitator was used as a baffle in low-viscosity Newtonian fluids. Both Smith and Rushton turbines produced a vortex, which was eliminated by the motionless helical ribbon impeller. Gas dispersion in low-viscosity fluids was enhanced when the helical ribbon agitator and turbine of the dual hybrid mixing system was kept at a rotational speed ratio of 10 (N T /N HR =10), which allowed dispersion at a lower Fr than the turbine alone. For moderate-viscosity Newtonian fluids, gas dispersion was achieved at Fr≤0.71 and Fl≤0.05. Flow properties of non-Newtonian fluids played an important role in gas dispersion; transition from dispersing to flooding stages was observed for the fluids that were more shear-thinning (n≤0.38).

Interfacial tension in polymer blends

AbstractTheoretical models of the interfacial tension coefficient in polymer blends, v12, were evaluated. A new working relation was derived that makes it possible to compute v12 from the chemical structure of two polymers. The calculations involve determination of the dispersive, polar and hydrogen‐bonding parts of the solubility parameter from the tabulated group and bond contributions. The computed values of v12 for 46 blends were found to follow the experimental ones with a reasonable scatter of ± 36%.Next, the experimental methods of v12‐measurements were critically examined. Although many have been developed for low viscosity Newtonian fluids, most are irrelevant to industrial polymeric systems. For the present studies two were selected. Values of v12 were measured using the so‐called “capillary breakup method,” and a newly developed method based on the retraction rate of deformed drop.

A new general-purpose least-squares finite element model for steady incompressible low-viscosity laminar flow using isoparametricC1-continuous Hermite elements

This paper deals with a critical evaluation of various finite element models for low-viscosity laminar incompressible flow in geometrically complex domains. These models use Galerkin weighted residuals UVP, continuous penalty, discrete penalty and least-squares procedures. The model evaluations are based on the use of appropriate tensor product Lagrange and simplex quadratic triangular elements and a newly developed isoparametric Hermite element. All of the described models produce very accurate results for horizontal flows. In vertical flow domains, however, two different cases can be recognized. Downward flows, i.e. when the gravitational force is in the direction of the flow, usually do not present any special problem. In contrast, laminar flow of low-viscosity Newtonian fluids where the gravitational force is acting in the direction opposite to the flow presents a difficult case. We show that only by using the least-squares method in conjunction with C1-continuous Hermite elements can this type of laminar flow be modelled accurately. The problem of smooth isoparametric mapping of C1 Hermite elements, which is necessary in dealing with geometrically complicated domains, is tackled by means of an auxiliary optimization procedure. We conclude that the least-squares method in combination with isoparmetric Hermite elements offers a new general-purpose modelling technique which can accurately simulate all types of low-viscosity incompressible laminar flow in complex domains.

Non-Newtonian effects on immiscible viscous fingering in a radial Hele-Shaw cell.

The displacement of a high-viscosity non-Newtonian fluid by a low-viscosity Newtonian fluid in a Hele-Shaw cell is capable of producing ramified viscous-fingering patterns exhibiting fractal characteristics. Recently, it was established that interfacial tension has little influence on the formation of these fractal patterns. However, the precise mechanism behind their formation is not as yet fully understood. In this paper, we consider the immiscible displacement of a non-Newtonian fluid in a radial Hele-Shaw cell, and present a detailed analysis of the flow, thus exposing features which until now have not been reported. In particular, we find an effective length compression for the formation of viscous-fingering patterns and accelerated growth rates, which upon consideration of recent experimental results, are consistent with the formation of fractal viscous-fingering patterns.