Intermediate Viscosity Research Articles

Intermediate viscosity in a gravity-driven flow and its application to simple viscometry

In a capillary tube flow, if the wall shear stress τw and apparent shear rate 4V/R are given, the viscosity reduces to the viscosity τw/(4V/R) at a dimensionless intermediate radius ra* (≡ra/R) of approximately 0.8, where the shear rate is ra* × 4V/R. This known result is extended to the quasi-steady gravity-driven flow in a capillary tube, where the fluid head decreases from Hmax to H over a period of T seconds. Using a Carreau and power-law model, the intermediate viscosity for a gravity-driven flow is derived for the logarithmic middle fluid head between Hmax and H. This intermediate viscosity and its shear rate can be obtained from a single measurement of T using a flow setup like an Ubbelohde viscometer. The experimental results validate the proposed method and show its potential for an easy and inexpensive viscometry oriented toward practical applications, like the viscosity measurement of a liquid diet for dysphagia.

Strain-rate dependence of mechanical characteristics of PLLA with different MW

Abstract Dynamic mechanical properties of polymers for biomedical applications are crucial parameters for development and engineering of new medical devices. Here, the time-dependent material behavior is a key factor for durability. Varying the strain rate is a convenient implementation of time-dependency for uniaxial testing. This study investigates time-dependence of Poly(L-Lactide) (PLLA) through uniaxial testing with different strain rates and PLLA with different molecular weight. The results show strain dependence for elongation at break and yield stress, Young’s modulus however is not rate dependent. An increase in elongation at break is also seen with increasing molecular weight of PLLA. Plastic strain increases significantly only for PLLA with an intermediate inherent viscosity. Results show distinct time dependencies regarding strain rate for PLLA with slightly different inherent viscosities. For stent-related mechanical material characteristics, higher molecular weight PLLA seems to be advantageous. This study only considers base materials, although appropriate thermal, mechanical as well as chemical post processing approaches for further adjustment of different properties have already been shown. A combination of the best possible base material and a suitable post-processing should be targeted.

Unraveling instabilities and mixing behavior in two-layered flows: A quest for the optimum viscosity ratio

A two-layer miscible displacement of density-matched but viscosity-contrasted fluids through a channel is numerically investigated in a nonlinear regime. The flow is governed by Navier–Stokes equations, which are coupled to a convection-diffusion equation via viscosity dependent concentration. Instabilities in the form of roll-ups or ligament waves are observed when a less viscous fluid is sheared over a more viscous fluid. Through interfacial length calculations, we demonstrate that the temporal evolution of the interface can be divided into three regimes: the initial diffusion-dominated regime, the intermediate convection-dominated regime, and the final diffusion-dominated regime. With the unstable roll-up growth only in a convection-dominated regime, the growth of instability delays at later times in diffusion dominated regime. Moreover, onset time ton vs R plots for each Reynolds number (Re), Péclet number (Pe), initial interface location (h), and thickness of initial mixing zone (q) depict that the instability originates early for intermediate viscosity ratios (R) than larger R. In contrast to earlier studies in the linear regime, we showed that if the viscosity ratio between two fluids is very large or small, the instability doesn't trigger in the nonlinear regime. The analysis of the concentration's global variance-based degree of mixing allows us to find optimum parameters for maximum mixing. We show that the optimal mixing is obtained at an intermediate value of R (optimum R). Furthermore, the degree of mixing is found to increase for increasing Re and decreasing Pe.

Revealing foam stability for cationic and zwitterionic triethylsilyl-containing surfactants

A fundamental understanding of surfactant structure–property–performance relationships will inform the design of next-generation alternatives to perfluoroalkyl substances (PFAS) in aqueous film-forming foams. This manuscript describes the synthesis, solution properties, and foam stability of novel triethylsilyl-containing surfactants, which elucidated the influence of the hydrophilic head group on critical micelle concentration (CMC), surface tension, and foam stability. Photocatalyzed hydrosilylation of triethylsilane and N,N-dimethyl allylamine yielded N,N-dimethyl-3-(triethylsilyl)propane-1-amine. Subsequent functionalization with either propane sultone or bromoethane afforded zwitterionic sulfobetaine surfactant, 3-(dimethyl(3-(triethylsilyl)propyl)ammonio)propane-1-sulfonate (TESDMAPS) and cationic quaternary ammonium surfactant, and N-ethyl-N,N-dimethyl-3-(triethylsilyl)propane-1-ammonium bromide (TESDMABr), respectively. Dynamic light scattering and cryo-transmission electron microscopy (TEM) characterized micelle size and shape in solutions above the CMC. Surface tensiometer analysis determined minimum TESDMAPS and TESDMABr solution surface tensions of 37.7 and 35.9 mN/m, respectively. Molecular dynamics simulations related this decrease in surface tension to a larger average interfacial area of 88 Å2 per TESDMABr molecule compared to 66 Å2 per TESDMAPS molecule. Steady-shear rheological measurements showed consistent exponential viscosity-scaling relationships between TESDMAPS and TESDMABr solutions ≤ 30 wt. %. Above this concentration, TESDMAPS displayed solution viscosities greater than TESDMABr, and a mixture of surfactants provided an intermediate concentration dependent viscosity scaling. Dynamic foam analysis revealed TESDMABr foams displayed longer 25% foam drainage times than TESDMAPS. The oscillatory rheology of TESDMABr solutions demonstrated solid-like solution behavior at low shear rates. Finally, polarized light-imaging rheology highlighted the formation of birefringent structures in TESDMABr solutions under shear. For the first time, this work relates solution viscoelasticity from shear-induced surfactant assembly to foam stability with implications on fluorine-free, next-generation, fire-fighting foams.

A pH-triggered reinforcement of transient network of wormlike micelles by halloysite nanotubes of different charge

Soft viscoelastic nanocomposites based on entangled linear wormlike micelles of cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride and aluminosilicate clay halloysite nanotubes with a surface charge triggered by pH were prepared and studied by rheometry, ξ-potential measurements, thermogravimetric analysis, and cryo-TEM. It was shown that the nanotubes induce an increase of viscosity, which can be attributed to their incorporation into the network of entangled wormlike surfactant micelles via the attachment of micellar endcaps to the surfactant double layer on the surface of the nanotubes. The junctions between the micelles and the nanotubes were visualized by cryo-TEM. The soft nanocomposites demonstrate peculiar flow curves with two shear thinning regions and a plateau between them. The two slopes were attributed to the orientation of the nanotubes (at lower shear rates) and then of the micellar worms (at higher shear rates) along the direction of flow. The intermediate viscosity plateau may represent a stable flow when all nanotubes are oriented, while the micellar worms are not. The nanocomposite system was shown to be pH responsive. Its viscosity increases by 30 times with increasing pH from 4 to 9, which was explained by increasing surface charge of the nanotubes favoring the interaction with oppositely charged WLMs. Such soft materials with easily triggered rheological properties are very promising for various applications.

Development of a facial biocosmetic containing levan, almond and cinnamon oils with antioxidant and moisturizing properties

The addition of natural molecules such as microbial exopolysaccharides in cosmetics is a trend in the current market, adding properties and improving the product quality. Therefore, the aim of this study was to develop a facial biocosmetic formulation containing microbial levan, almond and cinnamon oils. The centroid-simplex design was used to evaluate the spreadability, antioxidant activity, moisture retention capacity and viscosity of formulations. Since it is a facial cosmetic, the formulation was optimized using the intermediate viscosity. The optimized formulation with intermediate viscosity was 75% (0.75 g) levan and 25% (2 mL) almond oil, without the addition of cinnamon oil. This formulation was submitted to 90 days under different exposure conditions, and the results showed a spreadability of 805 mm2, pH and density ideal for the facial area, with an antioxidant activity of 72%, hydration capacity of 100.3%, viscosity with no-Newtonian behavior, and normal organoleptic properties when stored at room and low temperature. The formulation with levan associated with almond oil showed potential for application in the facial area, with high antioxidant properties, moisturizing intermediate viscosity and stability for 90 days. The utilization of centroid-simplex design allowed the development of a biocosmetic with desired characteristics just by adjusting the concentrations of the bioactive.

Mixing in density- and viscosity-stratified flows

The lock-exchange problem is used extensively to study the flow dynamics of density-driven flows, such as gravity currents, and as a canonical problem to mixing in stratified flows. Opposite halves of a domain are filled with two fluids of different densities and held in place by a lock-gate. Upon release, the density difference drives the flow causing the fluids to slosh back and forth. In many scenarios, density stratification will also impose a viscosity stratification (e.g., if there are suspended sediments or the two fluids are distinct). However, numerical models often neglect variable viscosity. This paper characterizes the effect of both density and viscosity stratification in the lock-exchange configuration. The governing Navier–Stokes equations are solved using direct numerical simulation. Three regimes are identified in terms of the viscosity ratio μ2/μ1=(1+γ) between the dense and less dense fluids: when γ≪1, the flow dynamics are similar to the equal-viscosity case; for intermediate values (γ∼1), viscosity inhibits interface-scale mixing leading to a global reduction in mixing and enhanced transfer between potential and kinetic energy. Increasing the excess viscosity ratio further (γ≫1) results in significant viscous dissipation. Although many gravity or turbidity current models assume constant viscosity, our results demonstrate that viscosity stratification can only be neglected when γ≪1. The initial turbidity current composition could enhance its ability to become self-sustaining or accelerating at intermediate excess viscosity ratios. Currents with initially high excess viscosity ratio may be unable to dilute and propagate long distances because of the decreased mixing rates and increased dissipation.

Surface Viscosity-Dependent Neurite Initiation in Cortical Neurons.

Dynamic extracellular environments profoundly affect the behavior and function of cells both biochemically and mechanically. Neurite initiation is the first step for neurons to establish intricate neuronal networks. How such a process is modulated by mechanical factors is not fully understood. Particularly, it is unknown whether the molecular clutch model, which has been used to explain cell responses to matrix rigidity, also holds for neurite initiation. To study how mechanical properties modulate neurite initiation, substrates with various well-defined surface viscosities using supported lipid bilayers (SLBs) are synthesized. The results show that ligands with intermediate viscosity greatly maximize neurite initiation in primary neurons, while neurite initiation is drastically limited on substrates with higher or lower viscosity. Importantly, biochemical characterizations reveal altered focal adhesion and calpain activity are associated with distinct neurite initiation patterns. Collectively, these results indicate that neurite initiation is surface viscosity-dependent; there is an optimal range of surface viscosities to drive neurite initiation. Upon binding to ligands of varying viscosities, calpain activity is differentially triggered and leads to distinct levels of neurite outgrowth. These findings not only enhance the understanding of how extracellular environments regulate neurons, but also demonstrate the potential utility of SLBs for neural tissue engineering applications.

Detailed study of single bubble behavior and drag correlations in Newtonian and non-Newtonian liquids for the design of bubble columns

A study of the effects of fluid type (shear-thinning, Newtonian, and shear-thickening) and periodic shape fluctuations of bubbles on the drag coefficient is presented for three bubble sizes (2 mm, 4 mm and 6 mm), three flow consistency indexes (μwater, 10μwater, 100μwater) and three flow behavior indexes (0.8, 1, 1.2). Computational Fluid Dynamics (CFD) simulations were performed in addition to previous measurements to obtain local data of the flow hydrodynamics. The results were used to evaluate 12 different drag coefficient estimation models, which are essential for the design of bubble columns. The Dijkhuizen et al. and Rodrigue correlations are suitable for the prediction of terminal velocity in both Newtonian and non-Newtonian liquids with high or intermediate viscosity. Finally, a modification of the correlations enables the prediction of small bubble terminal velocity also in low-viscosity liquids.

Thermocapillary effects on viscoelastic drops suspended in axisymmetric pressure driven flows

Dynamics and deformation of a viscoelastic drop in another immiscible viscoelastic medium in the presence of externally imposed pressure and temperature gradients are analyzed asymptotically in the present work. Both of the phases obey the linear Phan–Thien–Tanner constitutive model, capable of accounting for shear thinning behavior in polymeric fluids. The first two asymptotic corrections to the leading order Newtonian behavior are reported here, in the limit of small Deborah and Capillary numbers, which, respectively, characterize the extent of viscoelasticity and interfacial deformation. We establish that the viscoelastic properties of the inner phase strongly influence the migration velocity and the interfacial deformation of the drop. Our analysis reveals the possibility of realizing a maximum migration velocity for an intermediate viscosity of the interior phase, provided it has stronger viscoelastic characteristics than the suspending medium. We further compute the critical thermal gradient required to completely arrest the drop's motion and demonstrate that the same depends on the Deborah number as well as the viscosity of the inner phase. The viscoelastic stresses also dictate the deformation as the drop's shape changes from prolate to oblate when those stresses become significant. Our results may find potential applications in areas such as polymer processing and handling of biologically relevant media in medical diagnostics.

Numerical analysis of SiO2-SDS surfactant effect on oil recovery in sandstone reservoirs

Currently, the demand for using nanoparticles (NPs) in Enhanced Oil Recovery (EOR) is very high. The use of NPs can drastically benefit EOR by changing the rock wettability, improving the mobility of oil phase and decreasing the interfacial tension (IFT) between oil/water. Most of the previous studies were experimentally conducted and limited to specific operating conditions. This study contributes to the understanding of nanoparticle behaviour at altered operating conditions. In this investigation, a 3-D numerical model of silica nanofluid proposed for EOR is presented. A numerical model of core-scale sandstone was developed using Computer Modelling Group (CMG)-STARS simulator. The developed model was well validated against an experimental data. Then Silicon Dioxide (SiO2) and Sodium Dodecyl Sulphate (SDS) nano-surfactant mixture were injected with different concentrations. The optimum concentration of SiO2–SDS solution was obtained at 0.15 wt% with the highest recovery factor of 71.86% achieved. Moreover, SiO2–SDS solution injection rate and temperature were investigated and it was found that the optimum operating conditions of injection rate and temperature were 2 cc/min and 60 °C with the highest recovery achieved. In addition, a heavy crude oil showed a significant increment of oil recovery compared with a light crude with 3.13% and 0.6%, respectively. The intermediate viscosity of used crude oil had the highest oil recovery increment.

Sessile liquid drops damp vibrating structures

In this study, we explore the vibration damping characteristics of singular liquid drops of varying viscosity and surface tension resting on a millimetric cantilever. Cantilevers are displaced 0.6 mm at their free end, 6% their length, and allowed to vibrate freely. Such ringdown vibration causes drops to deform, or slosh, which dissipates kinetic energy via viscous dissipation within the drop and through contact line friction. Damping by drop sloshing is dependent on viscosity, surface tension, drop size, and drop location. A solid weight with the same mass as experimental drops is used to compare against the damping imposed by liquids, thereby accounting for other damping sources. Neither the most viscous nor least viscous drops studied imposed the greatest damping on cantilever motion. Instead, drops of intermediate viscosity strike the most effective balance of sloshing and internal dissipative capacity. Very thin cantilevers with sloshing drops express more than one dominant frequency and vibrate erratically, often shifting phase, presenting a challenge for quantification of damping. Finally, we introduce a new dimensionless group aimed at incorporating all salient variables of our cantilever-drop system.

A review on the mechanics of inertial microfluidics

In a number of microfluidics-based systems where the Reynolds number is in an intermediate range, both viscosity and inertia are significant, and thus, plenty of interesting effects appear including inertial motion and secondary flow. In recent years, this rapidly expanding area of science has opened a new window of possibilities for micro-particle inertial focusing in high-throughput cellular separation and physiological fluids processing. Moreover, this science is applicable in bio-particle focusing in clinical diagnostics along with widespread applications in environmental cleanup. In this review, fundamental concepts governing the mechanics and physics of inertial microfluidics are discussed. Furthermore, recent mathematical frameworks and theoretical developments that have made this science what we know today are presented in detail. Finally, a number of possible futuristic promising directions in this novel field are proposed since, despite tremendous recent progress, this mainstream technology is still a nascent area of research.

Biodegradable Film Preparation Using Arracacha Thermoplastic Starch and Polylactic Acid

This work aimed to characterize the starch from arracacha at two phenological stages (S1: twelve months and S2: fourteen months) and assess its potential use blended with poly (lactic acid) (PLA) for thermoplastic starch biodegradable film preparation using the extrusion technique. Arracacha starches showed high amylose content (25% and 24% for S1 and S2, respectively), which is related to its easy to cook properties, intermediate final viscosity, and the potential for its use as material for biodegradable films preparation. Production of Thermoplastic starch biodegradable films (SF1 and SF2) using arracacha starch blended with PLA as raw materials were successful, the biofilms exhibited low solubility and water vapor permeability (VWP), which is due to the hydrophobic nature of PLA, these results indicate its potential use for packaging of foods with intermediated or low water contents. Besides, biodegradable films showed good thermal properties, which are related to the stability of degradation. Arracacha for starch extraction and its use for biodegradable film preparation could be an alternative to add value to this crop. Likewise, the preparation of thermoplastic films using arracacha starch blended with PLA is presented as an alternative to the use of plastic packaging.

Viscosity of Aqueous Polysaccharide Solutions and Selected Homogeneous Binary Mixtures

The viscosity (η) of dextran (Dex), methyl cellulose (MC), hydroxypropylmethyl cellulose (HPMC), κ-carrageenan (KC), alginate (Alg), and carboxymethyl cellulose (CMC) was measured as a function of the shear rate (γ̇) over a broad range of concentrations both in salt-free water and in 0.1 M NaCl. The concentration (C) dependence of the Newtonian viscosity (η0) was found to be universal for neutral polysaccharides and anionic polysaccharides in 0.1 M NaCl when C was multiplied with the intrinsic viscosity. The dependence was compared with theoretical predictions assuming dominant hydrodynamic or dominant topological interactions. The effect of electrostatic interactions was observed for anionic polysaccharides in salt-free water but not at higher concentrations. Master curves of the shear thinning behavior at different concentrations were obtained when η/η0 was plotted versus τ. γ̇, with τ being a concentration-dependent time that characterizes the onset of shear thinning. Binary mixtures of two neutral polysaccharides (MC and HPMC), two anionic polysaccharides (Alg and CMC), and a neutral (Dex) and anionic polysaccharide (KC) were investigated as a function of the composition and the total polysaccharide concentration. The behavior of the first two mixtures was similar to that of a single polysaccharide with an intermediate intrinsic viscosity. Significant synergy was observed for the third type of mixtures in salt-free water demonstrating the important effect of electrostatic interactions between charged polysaccharides at low concentrations even in concentrated solutions of neutral polysaccharides.

Development and characterization of highly structured rinse-off conditioners containing vegetable oils

The appearance of the hair interferes with people's self-esteem and may indicate characteristics about their lifestyle. Due to their importance, hair treatment cosmetics correspond to a significant portion of the sector's sales. This research aimed to develop and characterize highly structured conditioners, prepared with avocado, wheat germ and grape seeds oils. The formulations were developed through a ternary phase diagram, using cationic surfactant (cetyl trimethyl ammonium chloride), oily phase (mineral or vegetable oils) and aqueous phase. The formulations obtained were classified according to their aspect and viscosity, with the most appropriate ones chosen for the intended use. They were evaluated by polarized light microscopy (PLM) to verify the structure of the system and, also, by means of rheology, small angle X-ray scattering (SAXS) and sun protection factor (SPF) determination. After the classification of the formulations, the opaque and uniform ones, with intermediate viscosity, compatible with the application on the hair were chosen, guaranteeing acceptance by possible consumers. PLM offered images indicative of highly structured systems, confirmed by the SAXS technique. Rheology indicated that the use of vegetable oils, compared to mineral oil, generated formulations with slightly lower viscosity, allowing the choice of the formulation (12, of the ternary diagram) with higher viscosity among the others. Finally, the determination of the SPF did not indicate the ability to protect against ultraviolet radiation. Thus, in this study, a highly structured formulation, prepared with cationic surfactant and vegetable oils was developed, offering another possibility of an innovative product to consumers of hair cosmetics.

Experimental study on the oil return characteristics of miscible or partially miscible oil in R290 room air conditioners

R290 is a promising new refrigerant for room air conditioners because of its environmental friendliness and excellent thermophysical properties. It is necessary to lubricate the moving parts of compressors with oil. However, if a large amount of oil migrates into the heat exchanger from the compressor during system operation, the pressure drop will increase, and the heat transfer coefficient will decrease. There has been little research on the oil return in R290 air conditioners. In this study, the oil return characteristics of mineral oil (MO) with a relatively high viscosity grade and polyalkylene glycol (PAG) with an intermediate viscosity grade in an R290 room air conditioner were investigated using cold start-up, oil retention, and cyclic tests. The oil retention outside of the compressor in the steady state and the oil level and mixture viscosity of the oil sump in the compressor were measured. The results showed that the oil supply was adequate at the minimum oil level and that both the MO and PAG could return to the compressor within 35 min in the cold start-up tests. In addition, the oil retention in the system was 3.2–3.7 g for PAG and 3.5–8.2 g for MO in the steady state. The results suggested that both the R290/MO and R290/PAG systems exhibited good oil return.

Friction properties of superhydrophobic ridges

The extreme mobility of droplets on non-wetting materials implies the necessity of controlling their motion, direction or speed. In this paper, we show how ridges allow us to tune drop friction. Depending on the liquid speed and viscosity, two regimes emerge: fast drops with low viscosity dynamically deform and undergo inertial friction, so that their velocity is eventually fixed by the deformations induced by the ridges; in contrast, viscous drops hardly interact with the texture, so that their velocity is classically limited by viscous dissipation, as on a flat substrate. The transition between these two regimes reveals spectacular morphological changes: drops with intermediate viscosity elongate and adopt worm-like shapes, which we qualitatively describe.

Dynamics of laser-induced cavitation bubbles at a solid–liquid interface in high viscosity and high capillary number regimes

No unified model is available yet to explain the dynamics of laser-induced cavitation bubbles during laser ablation of solid targets in liquids, when an extremely high capillary number is achieved (>100), i.e., when the viscous forces strongly contribute to the friction. By investigating laser-induced bubbles on gold and yttrium-iron-garnet targets as a function of the liquid viscosity, using a nanosecond laser and an ultrafast shadowgraph imaging setup, we give a deeper insight into what determines the bubble dynamics. We find that the competition between the viscous forces and the surface tension (capillary number Ca), on the one hand, and the competition between the viscous forces and inertia (Reynolds number Re), on the other hand, are both key factors. Increasing the viscous forces, and hereby Ca up to 100 has an impact on the bubble shape and results in a very pronounced rim, which separates the bubble in a spherical cap driven by inertia and an interlayer. The temporal evolution of the footprint radius of the interlayer can be addressed in the framework of the inertiocapillary regime. For an intermediate viscosity, the thickness of the interlayer is consistent with a boundary layer equation. Interestingly, our data cannot be interpreted with simplified hydrodynamic (Cox–Voinov) or molecular-kinetic theory models, highlighting the originality of the dynamics reported when extremely high capillary numbers are achieved. Upon bubble collapse, spherical persistent microbubbles are created and partly dispersed in water, whereas the high-viscous polyalphaolefines lead to long-standing oblate persistent bubbles sticking to the target’s surface, independent of the ablated target. Overall, liquid’s viscosity determines laser ablation-induced cavitation.

Lack of Standardization in Commercial Thickeners Used in the Management of Dysphagia

Introduction: Oral feeding safety is necessary to provide nutrition, hydration, and eating pleasure for patients with dysphagia. Commercial thickeners are prescribed for these patients to change food viscosity and may alter the proper preparation of modified food. Objective: Analyze composition, employed terminology, preparation instructions, recommended amount and weight of provided measuring spoons, nutritional information, and viscosity of 7 commercial thickeners. Methods: The sample comprised all thickeners from different brands available in Brazil, named A to G. Products were submitted to viscosity analysis using viscometer and the International Dysphagia Diet Standardization Initiative (IDDSI) test. Samples were prepared with mineral water (25°C) and with the amount of thickener recommended to obtain intermediate viscosity (level 2) according to the manufacturer’s instructions. Results: Products B, C, and E presented similar composition. Manufacturer’s information about the amount and preparation procedure, time, temperature, and base liquid was incomplete. Viscosity tests revealed that thickener C was basically solid while D displayed results out of the desired viscosity level. Conclusions: The study showed differences in components and viscosity, beyond the lack of label details. There was no established correlation between viscosity classifications provided by National Dysphagia Diet and IDDSI.