Viscous Liquid Research Articles

Exploration of diffusion-thermo and thermo-diffusion on the nonlinear radiative heat flow of a conducting fluid over a permeable surface

The featured problem explores the impact of cross-diffusion on the two-dimensional electrically conducting flow of a viscous liquid over a nonlinearly stretching sheet through a permeable medium. An inclusion of radiative heat energizes the heat transport phenomenon whereas the solutal transfer enriches by the conjunction of the chemical reaction. To justify the behavior of electromagnetic radiation, the Rosseland approximation is used by considering nonlinear thermal radiation. Further, the convective boundary conditions also affect the flow properties. The approachable transformations are employed to get a suitable non-dimensional form of the governing equations for the formulated problem. Due to the complex nature of the distorted equations, the system of equations is solved using an in-built code bvp5c predefined in MATLAB. The computation is carried out for the involvement of the suitable values of contributing parameters on the flow characteristics and along with the simulations of the rate coefficients. Further, the assigned particular parameters present an outcome that validates with a good correlation. Finally, the important outcomes are — enhanced suction due to the permeability of the surface augments the fluid velocity whereas the trend is reversed in the case of injection. The augmentation in the fluid temperature is exhibited for the radiating heat but the reacting species attenuates the fluid concentration.

Stable and impalement-resistant superamphiphobic coatings enabled by phase-separated adhesive for anti-adhesion of viscous liquids with low surface tension

Superamphiphobic coatings have great potential in various fields but surfer from weak mechanical stability, low impalement resistance and poor repellency to viscous liquids with low surface tension. Here, we report stable and impalement-resistant superamphiphobic coatings enabled by phase-separated adhesive for anti-adhesion of viscous liquids with low surface tension. By fluorination of silica (F-silica) nanoparticles and solvent induced phase separation of an adhesive, a homogeneous suspension was obtained, which could be readily used for preparing superamphiphobic coatings via spray-coating. The effects of phase separation degree and adhesive/F-silica mass ratio on superamphiphobicity, impalement resistance and mechanical stability of the coatings were studied. The coatings have a hierachical micro-/nanostructure and numerous perfluorodecyl groups on the surface. Thus, the coatings show excellent static and dynamic superamphiphobicity, e.g., high contact angles, low sliding angles, high maximum release height, short solid-liquid contact time and large bouncing height for various liquids with high viscosity and low surface tension. The coatings also show excellent mechanical stability, good chemical and temperature stability. Furthermore, the coatings are applicable onto diverse substrates and could be easily scaled-up.

Does Viscosity Decoupling Guarantee Dynamic Heterogeneity? A Clue through an Excitation and Emission Wavelength-Dependent Time-Resolved Fluorescence Anisotropy Study.

Traditionally, deviation from Stokes-Einstein-Debye (SED) relation in terms of viscosity dependence of medium dynamics, i.e., with p ≠ 1, is taken as a signature of dynamic heterogeneity. However, it does not guarantee medium heterogeneity, as the decoupling may also originate from the deviation of the basic assumption of SED. Here, we developed a method to find a stronger relation between viscosity decoupling (p ≠ 1) and dynamic heterogeneity in terms of rotational motion. Our approach exploited the fact that in heterogeneous media, a solvatochromic probe will be solvated to a different extent at different microdomains (subpopulations), and photoselection of these subpopulations can be achieved by excitation or emission wavelength-dependent measurements. We hypothesized that the dynamics of a homogeneous system might show viscosity decoupling, but the extent of decoupling at different excitations (or at different emissions) should not be different. On the other hand, in a heterogeneous medium, this extent of viscosity decoupling (p-value) should be different at different excitations (or at different emissions). As proof of concept, we investigated three versatile solvent media: squalane (viscous molecular liquid), 1-ethyle-3-methylimidazolium ethyl sulfate ionic liquid (IL), and [0.78 acetamide + 0.22 LiNO3] deep eutectic solvent (DES). We found that squalane is homogeneous, although it shows fractional viscosity dependence (p ≠ 1). Interestingly, mild heterogeneity in IL and significant heterogeneity in the DES were observed. Overall, we conclude that the difference in the p-value as a function of excitation (or emission) wavelength-dependent might be a superior way for the detection of dynamic heterogeneity.

Observation of a Large Slip Effect in the Nanoscale Flow of Highly Viscous Supercooled Liquid Metals.

Understanding and controlling the flow of materials confined in channels play important roles in science and engineering. The general no-slip boundary condition will result in it being more challenging to drive the flow as the channel size decreases to the nanoscale, especially for highly viscous liquids. Here, we report the observation of a large boundary slip in the nanoscale flow of highly viscous supercooled liquid metals (with viscosities of ≲108 Pa s), enabled by the hydrophobic treatment of smooth nanochannels. The slip length significantly depends on the pressure, which can be rationalized by the shear-dependent viscosity. Our findings provide not only new insights into the field of nanofluidics but also a practical technique for resolving the challenge in the net formation of highly viscous supercooled liquid metals at the nanoscale.

Observation of viscous liquid flow in tobacco substrate during heating using optical coherence tomography.

The present study used optical coherence tomography (OCT) to monitor the dynamics of a highly viscous liquid in a porous tobacco substrate during heating. The OCT technique was integrated with a specially designed heating chamber and an air pump for measuring. Two transitional points in the liquid behaviours at different temperatures were estimated using OCT and statistical analysis of the attenuation coefficient. The first point, 'A', shows the time approximation at which the penetration-dominant zone transitions into the evaporation-dominant zone. The second point, 'B', indicates the time approximation at which rapid evaporation of free liquid transitions into slow evaporation of trapped and bound liquid. This analytical system is an alternative for tracking liquid transport in porous biomass during heating.

13C Hyperpolarization of Viscous Liquids by Transfer of Solid-Effect 1H Dynamic Nuclear Polarization at High Magnetic Field.

Dynamic nuclear polarization (DNP) is routinely used as a method for increasing the sensitivity to nuclear magnetic resonance (NMR). Recently, high-field solid-effect DNP in viscous liquids on 1H nuclei was demonstrated using narrow-line polarizing agents. Here we expand the applicability of DNP in viscous media to 13C nuclei. To hyperpolarize 13C nuclei, we combined solid-effect 1H DNP with a subsequent transfer of the 1H polarization to 13C via insensitive nuclei enhanced by polarization transfer (INEPT). We demonstrate this approach using a triarylmethyl radical as a polarizing agent and glycerol-13C3 as an analyte. We achieved 13C enhancement factors of up to 45 at a magnetic field of 9.4 T and room temperature.

Atomization of High Viscous Liquids Using a MEMS Vibrating Mesh With Integrated Microheater

Aerosol generation is important for a wide range of applications including drug delivery, additive manufacturing, spray cooling, and numerous other applications. However, current aerosol generation devices often have poor droplet uniformity or are limited to low viscosity liquids ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 2 cp). This work presents the development of a Microelectromechanical systems vibrating mesh atomizer capable of atomizing higher viscosity fluids while maintaining high droplet size uniformity. The overall system consists of microfabricated silicon vibrating mesh atomizer, a piezoelectric film, and a flexible thin film microheater. The Si vibrating mesh atomizer was designed to increase atomization thresholds, while the microheater is designed to reduce liquid viscosity to meet the atomization threshold. Atomizers with varying nozzle dimensions were experimentally validated using liquids with varying viscosity and physiochemical properties, such as water, glycerol, propylene glycol, and vegetable glycerin. The microheater was designed to provide local rapid heating with low power consumption of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 1 W. The droplet size distribution results show that when fluid viscosity increases, the volume median diameter of droplets increases, and the spray angle decreases. The Si-vibrating mesh atomizer was able to atomize liquids up to 49.73 cP at room temperature compared to normal metallic vibrating mesh atomizers which have a threshold of approximately 2 cP. The integrated heater enabled atomization of liquids with viscosities as high as 111 cP with low heating ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C). 2023-0042

A hybrid approach based on Lagrangian particles and immersed-boundary method to characterize rotor–stator mixing systems for high viscous mixtures

In-line multi-stage rotor–stator mixing systems are the recent industrial solution for mixing highly viscous liquids in a short period of time while minimizing temperature increase throughout the mixing process. Unlike their predecessors, namely batch mixers, in-line rotor–stator mixers facilitate a continuous mode of operation. However, there is a lack of detailed insight into their flow patterns, power consumption, and mixing behavior, as these mixers, particularly the multi-stage variants, are rarely studied in the scientific community. In this work, we propose a computational framework for modeling rotor–stator mixers using Lagrangian particle tracking and the immersed-boundary method. The tracer particles present an alternative to the commonly used Eulerian approach, which is susceptible to numerical diffusion. The use of the immersed-boundary method for modeling the motion of the rotor not only significantly reduces pre-processing time but also facilitates the modeling of various rotor–stator shapes with different motion patterns, making it possible to complete the modeling in a short time. The proposed method is used to investigate an industrial in-line multi-stage rotor–stator mixer, and the accuracy of the numerical results is verified by comparing them with experimental data. The simulations unveiled that at a rotational Reynolds number of up to 4000, significant back-mixing occurs, whereas for lower Reynolds numbers, the flow maintains a smooth forward motion without any back-mixing. The study also examines the residence time of the additive in the mixer, revealing that, particularly when dealing with high-viscosity mixtures, the additive has the potential to persist in the mixer for up to 3.5 times the theoretical residence time. Additionally, the obtained results are utilized to derive empirical equations that enable predicting the mixer’s performance for different Reynolds numbers.

Wafer-Scale Epitaxial Growth of Two-dimensional Organic Semiconductor Single Crystals toward High-Performance Transistors.

The success of state-of-the-art electronics and optoelectronics relies heavily on the capability to fabricate semiconductor single-crystal wafers. However, the conventional epitaxial growth strategy for inorganic wafers is invalid for growing organic semiconductor single crystals due to the lack of lattice-matched epitaxial substrates and intricate nucleation behaviors, severely impeding the advancement of organic single-crystal electronics. Here, an anchored crystal-seed epitaxial growth method for wafer-scale growth of 2D organic semiconductor single crystals is developed for the first time. The crystal seed is firmly anchored on the viscous liquid surface, ensuring the steady epitaxial growth of organic single crystals from the crystal seed. The atomically flat liquid surface effectively eliminates the disturbance from substrate defects and greatly enhances the 2D growth of organic crystals. Using this approach, a wafer-scale few-layer bis(triethylsilythynyl)-anthradithphene (Dif-TES-ADT) single crystal is formed, yielding a breakthrough for organic field-effect transistors with a high reliable mobility up to 8.6 cm2 V-1 s-1 and an ultralow mobility variable coefficient of 8.9%. This work opens a new avenue to fabricate organic single-crystal wafers for high-performance organic electronics.

Structural characterization of exopolysaccharide produced by Streptococcus thermophilus and rheology of mixed protein-polysaccharide systems

This study determined the constituents and structural properties of extracellular polysaccharides of Streptococcus thermophilus (STEP) and investigated the rheological properties of the blended system of STEP and whey protein (STEP/WP). Two STEP, neutral polysaccharides (STEP-1) and acidic polysaccharides (STEP-2), were isolated and purified from S. thermophilus. Their molecular weights were 2197.74 and 141.99 kDa, respectively. STEP-1 were mainly composed of galactose, glucose, and rhamnose, whereas STEP-2 were mainly composed of galactose, mannose, and glucose. Methylation and NMR analyses confirmed that the STEP structural backbone included α- and β-type pyranose residues and many branching structures. The rheological results revealed that the apparent viscosity of STEP/WP was higher than that of STEP, while STEP/WP mainly acted as a viscous liquid under the influence of dairy processing parameters. These findings may be useful for STEP/WP application in the production of dairy products such as fermented milk and cheese.

Research on tool stick-slip erosion wear mechanism in cutting nickel-based alloy GH4169

Nickel-based superalloys GH4169 are typical hard-to-machine materials. It can still maintain high strength and hardness at high temperatures, so the tools for cutting nickel-based superalloys are worn seriously. In this paper, the tool wear mechanism when cutting nickel-based superalloy using YG8 (K-type cemented carbide tool) is studied. The stick-slip erosion wear mechanism of cutting tool is put forward in this paper. At high temperature, micro plastic deformation and macro sliding occurs when the chip slides against the tool surface, resulting in wear similar to that of a viscous liquid when it erodes a solid. Erosion wear has a latent period. The faster the cutting speed, the worse the wear is. When chip stick-slip erodes the tool, two adiabatic zones are generated. One is the adiabatic impact zone I generated on the front surface of the tool. The other is the adiabatic shear band II formed under chip compression. The adiabatic impact zone I causes the temperature of tool surface to rise sharply. After high-temperature erosion, the surface of the cutting tool exhibits wear patterns such as lips, pits, layers, and furrows. Among them, the lips are a typical morphology of erosion wear, but the quantity is relatively small. Pits and layers are the main morphological features after erosion wear. The main reason for the above characteristics is that GH4169 has a small deformation coefficient and weak chip deformation ability. Therefore, most lips are impacted and sheared by micro-convex bodies, ultimately leaving pits on the tool surface. In addition, when a portion of the lip has not yet formed, the fracture of the cell boundary cracks in the adiabatic shear zone leads to the occurrence of lamellar detachment, leaving a lamellar damaged surface.

Development of 2% w/w sodium fluoride oral gels for prevention of dental caries in patients with xerostomia

For prevention of dental caries in xerostomic patients, 2% w/w sodium fluoride oral gel is frequently prescribed; however, the product has not been officially approved for clinical use in Thailand. Therefore, this study aimed to develop 2% w/w sodium fluoride oral gels dispensed specifically to patients in Rajavithi Hospital. Both single and combined gel bases were prepared from different gelling agents, including gelatin, xanthan gum, hydroxypropyl methylcellulose, sodium carboxymethylcellulose, and Carbopol 940P. They were subsequently characterized according to their physicochemical properties, i.e., clarity, spreadability, pH values, and apparent viscosity. All the gel bases were clear viscous liquids of good spreadability, except the xanthan gum gel bases, which were slightly cloudy. The pH values indicate that the gelatin, xanthan gum, and Carbopol 940P gel bases were acidic, while the cellulose gel bases were neutral. The apparent viscosity ranged from 3 to 11.5 x 105 cPs, depending mainly on type and concentration of the gelling agents. After preparation, the gel bases were then incorporated with 1 M pH 7.4 phosphate buffer solution to the final concentration of 5% w/w. Macroscopic characteristics of the buffered gel bases were generally unchanged, except for the apparent viscosity, which decreased slightly. Sodium fluoride was subsequently added to the selected buffered gel bases. The resulting sodium fluoride gels were neutral and transparent viscous liquids of good spreadability and exhibited good stability against the heating-cooling cycle and accelerated testing. Thus, it is conceivable that 2% w/w sodium fluoride oral gels with acceptable physicochemical characteristics and excellent stability were successfully developed.

Gas-assisted microfluidic step-emulsification for generating micron- and submicron-sized droplets

Micron- and submicron-sized droplets have extensive applications in biomedical diagnosis and drug delivery. Moreover, accurate high-throughput analysis requires a uniform droplet size distribution and high production rates. Although the previously reported microfluidic coflow step-emulsification method can be used to generate highly monodispersed droplets, the droplet diameter (d) is constrained by the microchannel height (b), dgtrsim 3b, while the production rate is limited by the maximum capillary number of the step-emulsification regime, impeding emulsification of highly viscous liquids. In this paper, we report a novel, gas-assisted coflow step-emulsification method, where air serves as the innermost phase of a precursor hollow-core air/oil/water emulsion. Air gradually diffuses out, producing oil droplets. The size of the hollow-core droplets and the ultrathin oil layer thickness both follow the scaling laws of triphasic step-emulsification. The minimal droplet size attains dapprox 1.7b, inaccessible in standard all-liquid biphasic step-emulsification. The production rate per single channel is an order-of-magnitude higher than that in the standard all-liquid biphasic step-emulsification and is also superior to alternative emulsification methods. Due to low gas viscosity, the method can also be used to generate micron- and submicron-sized droplets of high-viscosity fluids, while the inert nature of the auxiliary gas offers high versatility.

Experimental study of the effect of viscous media on the hydrodynamic characteristics of a rotating packed bed

A simple and robust quantitative approach was proposed to determine liquid entrainment and flooding in rotating packed beds (RPBs), which complements visual observations and pressure drop measurements. The RPB was modified by installing a hydrocyclone at the gas outlet to quantify the amount of liquid ejected. The original technique previously introduced in the literature for air-water systems, was explored using a viscous mixture to determine the flooding onset. This approach eliminates bias in the criteria used to define the onset of liquid entrainment and flooding in RPBs. The method also minimizes inaccuracies introduced by unexplained pressure drops during flooding in RPBs. In the method, flooding occurred when entrainment exceeds 8% of the total liquid inlet flow rate. The study used a water-glycerine mixture with viscosities of 13 and 30 mPa.s and found that the entrainment of viscous liquids in RPBs begins with a small volume of liquid droplets, progressing to moderate volumes of liquid-film entrainment. The quantitative approach used in this study enhances the reliability of fundamental data essential for the design and scale-up of RPBs. This study is an indispensable guide for using RPBs in high-viscosity mass transfer and separation processes.

Skin‐Inspired Nanofluid‐Filled Surfaces with Tunable Icephobic, Photothermal, and Energy Absorption Properties

AbstractIce buildup can significantly and negatively impact system performance in various industrial sectors, and has remained a persistent challenge for decades. Many compliant materials exhibit excellent de‐icing performance but are easily eroded by impacts from supercooled water droplets, sand, dust, and debris. A composite panel inspired by animal skin, consisting of a facesheet protecting a nanofluid layer beneath, which exhibits durable anti‐icing and tunable photothermal properties is proposed. The viscous liquid layer beneath the facesheet increases flexural rigidity, preventing large deflections and increasing deformation resistance, which alters ice's adhesion to the surface. The non‐uniform fluid pressure exerted by the viscous nanofluid‐filled composite panels facilitates ice detachment, resulting in ice adhesion strengths as low as τice ≈ 10 kPa. Further, by altering the fluid properties, different additional functionalities can be endowed to the system. Incorporating fumed silica in a fluid‐filled composite panel results in rheopectic behavior, and this doubles their impact resistance when the shear thickening properties are properly tuned. Additionally, the combination of a transparent facesheet and a solar light absorbent nanofluid allows for tunable photothermal properties, further enhancing the anti‐icing performance of the system. This durable and tunable nanofluid‐filled composite panel shows great promise as a multifunctional de‐icing material.

Numerical analysis of nonlinear interaction between a gas bubble and free surface in a viscous compressible liquid

Liquid viscosity has a potential effect on bubble dynamics. This paper is concerned with bubble dynamics in a compressible viscous liquid near the free surface. The liquid–gas flow is modeled using the Eulerian finite element method coupled with the volume of fluid method. The numerical results have been shown to be in excellent agreement with those from the spherical bubble theory and experiment. Parametric studies are carried out regarding the Reynolds number Re and the stand-off parameter γd. It clearly demonstrated that the liquid viscosity inhibits bubble pulsation, jet flow, free surface jet, and bubble splitting. Quantitatively, as Reynolds number Re decreases, the maximum bubble volume, jet tip velocity, free surface spike, and crown height decrease, and the toroidal bubble splitting weakens. As the stand-off parameter γd increases, the maximum bubble volume, jet velocity, and bubble average pressure peak increase while the height of the free surface spike decreases. Close observation reveals that the free surface crown tends to disappear at small Re or large γd, further indicating the complex mechanism behind the crown spike evolution.

Electrolubrication in flowing liquid mixtures

We describe the “electrolubrication” occurring in liquid mixtures confined between two charged surfaces. For a mixture of two liquids, the effective viscosity decreases markedly in the presence of a field. The origin of this reduction is field-induced phase separation, leading to the formation of two low-viscosity lubrication layers at the surfaces. These layers facilitate larger strain at a given stress. The effect is strong if viscosities of the two liquids are sufficiently different, the volume fraction of the less viscous liquid is small, the gap between the surfaces is small, and the applied potential is large. The phase separation relies on the existence of dissociated ions in the solution. The effective viscosity is reduced by a factor α; its maximum value is the ratio between the viscosities of the two liquids. In most liquids, α∼1–10, and in mixtures of water and glycerol, α∼80–100 under relatively small potentials.

Mathematical and computational models in spheroid-based biofabrication.

Ubiquitous in embryonic development, tissue fusion is of interest to tissue engineers who use tissue spheroids or organoids as building blocks of three-dimensional (3D) multicellular constructs. This review presents mathematical models and computer simulations of the fusion of tissue spheroids. The motivation of this study stems from the need to predict the post-printing evolution of 3D bioprinted constructs. First, we provide a brief overview of differential adhesion, the main morphogenetic mechanism involved in post-printing structure formation. It will be shown that clusters of cohesive cells behave as an incompressible viscous fluid on the time scale of hours. The discussion turns then to mathematical models based on the continuum hydrodynamics of highly viscous liquids and on statistical mechanics. Next, we analyze the validity and practical use of computational models of multicellular self-assembly in live constructs created by tissue spheroid bioprinting. Finally, we discuss the perspectives of the field as machine learning starts to reshape experimental design, and modular robotic workstations tend to alleviate the burden of repetitive tasks in biofabrication. STATEMENT OF SIGNIFICANCE: Bioprinted constructs are living systems, which evolve via morphogenetic mechanisms known from developmental biology. This review presents mathematical and computational tools devised for modeling post-printing structure formation. They help achieving a desirable outcome without expensive optimization experiments. While previous reviews mainly focused on assumptions, technical details, strengths, and limitations of computational models of multicellular self-assembly, this article discusses their validity and practical use in biofabrication. It also presents an overview of mathematical models that proved to be useful in the evaluation of experimental data on tissue spheroid fusion, and in the calibration of computational models. Finally, the perspectives of the field are discussed in the advent of robotic biofabrication platforms and bioprinting process optimization by machine learning.

ON THE EFFECT OF VISCOSITY RELAXATION ON ELECTROMAGNETIC RADIATION INTENSITY OF AN OSCILLATING CHARGED DROPLET

Theoretical asymptotic calculations linear with respect to small dimensionless amplitude of oscillations have been employed to study the influence of the viscoelastic properties of a charged droplet of an electrically conducting viscous liquid on the intensity of its electromagnetic radiation. It has been shown that allowance for the effect of viscosity relaxation leads to a decrease in the damping decrement value, which is determined by energy losses for electromagnetic wave emission, and the intensity of high-frequency electromagnetic radiation; a substantial reduction in the viscous damping decrement of small cloud droplets; and an essential dependence of the viscous damping decrement on the characteristic relaxation time. It has been found that the viscosity relaxation of a liquid has no significant effect on damped capillary oscillations and electromagnetic radiation of rain droplets. Viscoelasticity and viscosity of the liquid do not influence the conditions critical for the realization of the electrostatic instability of a droplet with respect to its own charge.

Liquid Soap with Active Ingredients of Methanol Extract of Sambang Darah Leaves (Excoecaria cochinchinensis L.): Formulation, Characterization, and Antibacterial Activity

The methanol extract of sambang darah leaves (Excoecaria cochinchinensis L.) contains flavonoids, saponins, tannins and triterpenoids which have the potential as antibacterial compounds. The goal of this research is to produce liquid soap that preparations with four formulas by varying the methanol extract of sambang darah leaves as the active ingredient, characterizing, and understanding its antibacterial activity. Organoleptic tests, foam stability, pH, specific gravity, and viscosity were all used to characterize liquid soap. The best results were obtained with liquid soap formulation 3 (3 g extract), which had foam stability of 84.10%, a pH of 9.62, specific gravity of 1.03 g/mL, and viscosity of 492.933 cP. The organoleptic test revealed that the liquid soap was a homogeneous viscous liquid with a blackish-brown color and a characteristic extract odor. The inhibition zone for antibacterial activity against Staphylococcus aureus and Escherichia coli was 9.15 mm and 13.72 mm, respectively. In antiseptic tests, all soap formulas reduced bacteria on the thumb.