Solid Surface Tension Research Articles

Effect of physicochemical properties on critical sinking and attachment of respirable coal mine dust impacting on a water surface

Respirable coal mine dust (RCMD) inhalation is identified as the main cause of the resurgence of coal worker’s pneumoconiosis (CWP) since the mid-1990s. At present, the predominant dust control technology is the water spray system. However, in practice, the capture efficiency of RCMD by this technology is relatively low. To understand the capturing mechanism and develop improvement strategies, this research is focused on the surface chemistry study of RCMD and its impact on a water surface using a dynamic model. Proximate analysis, chemical, and mineral composition of a run-of-mine (ROM) coal sample from Appalachian region were analyzed using a proximate analyzer, Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and X-ray Diffraction (XRD), respectively. Contact angles were measured by capillary rise test using the Washburn equation. Based on the dynamic model, the effects of particle size, density, contact angle, and surface tension on the critical sinking were investigated. It was pointed out in this work that reducing surface tension, in turn, decreases contact angle, which has been neglected in the literature. Regime maps for different minerals were created and showed that organic matter has the highest critical velocity due to its low density and high contact angle. Reducing water surface tension to the critical solid surface tension of coal around 30 mN/m could maximize the attachment efficiency. Scaling laws, constructed by force balance, led to the criteria of critical sinking: Ucr∼61-cosθ2D+1γlvρlR, i.e., Wecr∼121-cosθ2D+1. A semi-empirical formula for critical velocity was obtained by fitting the simulation data, Ucr=1.0961-cosθ2D+1γlvρlR. Attachment efficiency was defined and formulated as Pa=U02Ucr2=We0Wecr, establishing relationships between attachment efficiency and the physicochemical properties of RCMD and water droplets.

A theoretical model to determine solid surface tension through droplet on film configuration and experimental verification

Determination of the surface tension of solids has been a challenging issue. This work presents an approach to the issue based on the configuration of a droplet spreading on a free standing film. Firstly, a theoretical model for the equilibrium configuration of a droplet spreading on a film is developed, which reveals that the surface elasticity has little contribution to the equilibrium configuration, and the effective strain of the film is determined by the bulge angle analytically. Based on these observations, a new procedure is presented to measure the surface tension of the film through droplet loading, which is realized by extrapolating the film tension as a function of the product of the film thickness and the effective strain. Finally, as a validation, we use this approach to extract the surface tension of soft elastomers. This work provides a viable and robust approach to determination of the surface tension of solids.

Surface Energy in the Processes of Disintegration of Solids

Objective. The purpose of the study is to experimentally measure the surface energy of solids during their grinding.Method. The study is based on the use of methods for determining the surface tension of solids. At least 20-25% of all electricity produced in the world is spent on grinding materials in industry. When the resulting particles are reduced to tens of nanometers, the contribution of surface energy (st) to the grinding work becomes so large that it is difficult not to take it into account. Measuring the surface tension of liquids has long been proven. But measuring (st) of solids causes great difficulties. Currently, more than twenty methods for determining (st) are known.Result. Based on the phenomenon of spontaneous bending of thin thread-like structures, a method for determining (st) has been developed. Examples are given in which (st) at the phase interface plays an important role in obtaining samples with a microstructure using the method of severe plastic deformation (SPD). To obtain fine metal powders, one of the variants of the SPD method has been proposed. A method has been found for the physical activation of aluminum granules, which increases the reaction rate of the metal in an aqueous environment by about a thousand times. This is necessary for the development of an anaerobic power plant capable of operating at great depths.Conclusion. The new technology makes it possible to obtain high-purity, non-oxidized metal powders without toxic waste and emissions and with energy costs lower than in all known methods.

The application of chitosan as an eco-filler of polymeric composites

The aim of the study was the synthesis of polymer biocomposites based on acrylates with the addition of various amounts of chitosan as an eco-filler. The composites (BPA.DA + NVP) were prepared using the photopolymerization technique. The obtained materials were subjected to physicochemical tests, determining, among others, their hardness and thermal properties by the DSC and TG/DTG methods. The ATR/FT-IR analysis and optical profilometer as well as the values of the solid surface tension calculated from the contact angle of model liquids and van Oss et al. approach to the solid-liquid interface tension were performed to confirm the chemical structure of the obtained biocomposites.

Thermodynamic Consideration of the Solid Saponin Extract Drop-Air System.

The aim of this research was to elucidate the surface active properties of Saponaria officinalis (soapwort) extract containing the plant surfactants saponins. To this end, the advancing contact angle (θ) of water, formamide and diiodomethane on the glass, as well as θ of the aqueous solution of S. officinalis extract fractions on PTFE, PMMA and glass, were studied. Based on the obtained results, the wetting behaviour of saponins was considered with regard to the surface tension components and parameters of the solutions and solids. The investigations also involved the description of the θ isotherms, the dependences between the cosine of contact angle and/or the adhesion of the solution to the solid surfaces and solution surface tension, as well as the critical surface tension of PTFE, PMMA and glass wetting. These dependences were studied based on the saponin adsorption at the different interfaces, which was deduced from the dependence between the adhesion and surface tension of the solution, as well as using the Gibbs and Frumkin isotherm equations. This proved that the saponins are poor wetting agents and that the contact angle isotherm can be described by the exponential function of the second order as well as the Szyszkowski equation, but only for PTFE.

Phenomenological Laws of Single Point Contact: Pre-Rolling Contact Resistance through Pendulum

The development results of a single-point contact system set up as a pendulum to study the laws of rolling resistance to contacting bodies at a distance significantly reduced compared to the elastic contact spot size. The designed device uses a physical pendulum sustained by only one ball on a flat polished surface. The problem of stability of the pendulum swing plane is solved. A phenomenological theory of rolling resistance is described. The surface tension of solids on the contact zone, parameters of the frequency-independent internal friction and the pressure of the adhesion forces are found.

Formulation and Evaluation of Polyherbal Shampoo Containing Different Herbal extract

The aim of the present study is to formulate and evaluate polyherbal shampoo containing natural ingredients with an emphasis on safety and efficacy. It clears dirt and dandruff, promotes hair growth, luster, strengthens and darkens the hair. The shampoo is prepared by taking the polyherbal extract from Hibiscus Flowers, Pomegranate Peels, Neem Leaves, Curry Leaves, Shikakai and Amla Fruit in different proportions. Several physicochemical tests were performed for visual assessment, wetting time, pH, viscosity, assurance of solid contents, surface tension, dirt dispersion, conditioning performance and foam stability. The formulated polyherbal shampoo is brown in color with demonstrable good froth stability, good cleansing ability, low surface tension, optimum pH and conditioning activity. Dirt dispersion of polyherbal shampoo is light in colour along with 25 ml foam height. All these are the ideal characteristics of good quality polyherbal shampoo to be used in daily life. However, further scientific investigation is required for validation of its overall quality.

Growth-Induced Wrinkles and Dotlike Patterns of a Swollen Fluoroalkylated Thin Film by the Reaction of Surface-Attached Polymethylhydrosiloxane.

The design of hydrophobic surfaces requires a material which has a low solid surface tension and a simple fabrication process for anchoring and controlling the surface morphology. A generic method for the spontaneous formation of robust instability patterns is proposed through the hydrosilylation of a fluoroalkene bearing dangling chains, Rf = C6F13(CH2)3-, with a soft polymethylhydrosiloxane (PMHS) spin-coated gel polymer (0.8 μm thick) using Karstedt catalyst. These patterns were easily formed by an irreversible swelling reaction due to the attachment of a layer to various substrates. The buckling instability was created by two different approaches for a gel layer bound to a rigid silicon wafer substrate (A) and to a soft nonswelling silicone elastomer foundation (B). The observations of grafted Rf-PMHS films in the swollen state by microscopy revealed two distinct permanent patterns on various substrates: dotlike of wavelength λ = 0.4-0.7 μm (A) or wrinkle of wavelength λ = 4-7 μm (B). The elastic moduli ratios of film/substrate were determined using PeakForce quantitative nanomechanical mapping. The characteristic wavelengths (λ) of the patterns for systems A and B were quantitatively estimated in relation to the thickness of the top layer. A diversity of wrinkle morphologies can be achieved by grafting different side chains on pristine PMHS films. The water contact angle (WCA) hysteresis of fluorinated chain (Rf) was enhanced upon roughening the surfaces, giving highly hydrophobic surface properties for water with static/hysteresis WCAs of 136°/74° in the resulting wrinkle (B) and 119°/41° in the dotlike of lower roughness (A). The hydrophobic properties of grafted films on A with various mixtures of hexyl/fluoroalkyl chains were characterized by static CA: WCA 104-119°, ethylene glycol CA 80-96°, and n-hexadecane CA 17-61°. A very low surface energy of 15 mN/m for Rf-PMHS was found on the smoother dotlike pattern.

Development of carbon-coated aluminosilicate nanolayers composite shape-stabilized phase change materials with enhanced photo-thermal conversion and thermal storage

Latent heat thermal energy storage (LHTES) system that centers on organic phase change materials (PCM) is regarded as an efficient strategy for the utilization of solar energy. The leakage problem and insensitivity to the sunlight of organic PCM significantly limit the large-scale application in the solar energy storage field. In the current study, a composite shape-stabilized phase change material (ss-PCM) for solar energy utilization was fabricated by incorporating stearic acid (SA) into the carbon-coated aluminosilicate nanolayers developed through intercalation of kaolinite with potassium acetate and then calcination. The resulting composite ss-PCM without leakage possesses excellent encapsulation ability (63.8%) and high latent enthalpy (132.0 J/g), which are ascribed to the higher specific surface area and pore volume of the carbon-coated aluminosilicate nanolayers, and good compatibility. The photo-thermal conversion efficiency of the final composite ss-PCM is up to 92.1%. After 500 heating-cooling cycles, the number of thermal cycles does not show an apparent effect on the enthalpy of the composite ss-PCM, implying its outstanding thermal cycle stability. The mechanism of leakage proof and photo-thermal conversion performance enhancement of composite ss-PCM were explored. The leakproof ability of composite ss-PCM is not only related to the solid capillary force and surface tension of carbon-coated aluminosilicate nanolayers but also the strong chemical bond between SA molecules and these nanolayers. The carbon layers of the supporting material provide an excellent light absorption property. Hence, this work may offer a new idea for designing and constructing the clay mineral (kaolinite) with a special nanolayer structure for preparing composite ss-PCM with superior photo-thermal conversion and solar energy storage capacity.

Formulation and Evaluation of Polyherbal Anti-Dandruff Shampoo

The Malassezia furfur fungal infection leads to dandruff formation. Dandruff cannot be fully eliminated but can only be effectively controlled. This study intends to formulate and evaluate the polyherbal anti-dandruff shampoo. The prepared formulation not only cleans the dirt and dandruff but also makes hair soft and lustrous and promotes hair growth. The formulation eliminates the use of harmful chemical ingredients that damages hair. The formulation uses various herbs like Neem, Bhringraj, Shikakai, Tulsi, Reetha, Aloe vera, Lemon juice, Orange peel, Ginger, Curry leaves, Hibiscus and other ingredients for preparing base shampoo which make an effective anti-dandruff formulation with smooth and shiny hairs, also provide conditioning and promotes hair growth. The formulated shampoo was subjected to evaluation parameters like visual inspection, pH, viscosity, dirt dispersion, surface tension, foaming ability, foam stability, antidandruff test and stability studies, etc. The major goal of the present study is to formulate and evaluate anti-dandruff shampoo for treating various hair issues. Dandruff is a common disorder affecting the scalp condition caused by yeast Pityrosporum. Dandruff cannot be completely eliminated but can only be managed and effectively controlled. Shampoo is a hair care product used for the removal of oils, dirt, skin particles, dandruff, environmental pollutants and other contaminant particles that gradually build up in hair. Herbal anti-dandruff shampoos were formulated using herbal based ingredients like Lemon Grass Oil, Neem oil, Henna, Aloe Vera gel and other ingredients for preparing base shampoo. The formulated shampoos were subjected to evaluation parameters like visual inspection, pH, viscosity, Percentage of solids contents, Dirt dispersion, Surface tension, Foaming ability and foam stability. The main objective of this study was to eliminate harmful synthetic ingredient from anti-dandruff shampoo formulation and substitute them with a safe natural ingredients.

Plateau Rayleigh instability of soft elastic solids. Effect of compressibility on pre and post bifurcation behavior

Solid surface tension can deform soft elastic materials at macroscopic length scales. At a critical surface tension, elastocapillary instabilities in soft filaments emerge that resemble the Plateau–Rayleigh (P–R) instabilities in liquids. The experimentally observed P–R instability of soft elastic filaments has been recently investigated via numerical and theoretical approaches. However, these contributions focus on the incompressible limit and preclude the nonlinear Poisson’s ratio effects in materials, for example, compressible hydrogels with Poisson’s ratios that can go as low as 0.1. Moreover, most of the research on the solid P–R instability elaborate on the onset, ignoring the post-bifurcation regime. Here we show that compressibility matters and the form of the assumed compressible strain energy density has a significant effect on the onset and the post-bifurcation behavior of elastic P–R instability. For example, the P–R instability can be entirely suppressed depending on the form of the free energy density and Poisson’s ratio. To this end, we employ a robust and variational elastocapillary formulation and its computer implementation using surface-enriched isogeometric finite elements at finite strains. We use an arclength solver to illustrate both stable-unstable amplitude growth and bifurcation points in the entire equilibrium path. Stability maps are drawn with distinct stable-unstable regions over various shear moduli, surface tensions, fiber radii, and applied stretches for cases ranging from quasi-compressible to fully compressible. The presented elastocapillary model proves to be useful in quantifying the surface and bulk energies in competition at finite strains and expected to help improve mechanical characterization of soft materials with at least one dimension that is on the orders of the elastocapillary lengthscale lsolid∼O(nm – mm).

Non-Fluorine Oil Repellency: How Low the Intrinsic Wetting Threshold Can Be for Roughness-Induced Contact Angle Amplification?

Surface chemistries for realizing oil repellency are mostly based on perfluoro compounds (PFCs) owing to their low surface energy. However, PFCs are not sustainable because of their persistent and bioaccumulative properties, and their usage, even short-chain ones, has begun to be phased out. To date, studies on non-fluorine oil repellency have been extremely rare, and the obtained oil repellency has been limited. Here, we report the non-fluorine oil repellency of a coating prepared on a tightly woven plain-weave fabric through hydrolysis and polycondensation of difunctional chlorosilane. The coated fabric exhibited a contact angle of 119.0° for castor oil and 81.4° for hexadecane, as well as a contact angle of 51.9° for decane with a surface tension as low as γLV = 23.5 mN m-1. According to the standard ISO 14419:2010, oil repellency was rated Grade 6. The solid surface tension of the coating was calculated to be γSV = 22.1 mN m-1. Through the test of the difference in contact angles between rough and smooth surfaces, the intrinsic wetting threshold (θIWT) for such a surface chemistry was determined to be ranging from 8.9 to 14.5°. A study on the effects of surface morphologies suggests that the realization of an oil-repellency rating of 6 and a θIWT as low as 8.9-14.5° strongly depends on the roughness topographies. We hope that this study will be useful for the design─and our understanding─of non-fluorine oil repellency for applications including stain-resistant textiles and grease-resistant food packaging.

Gradients in solid surface tension drive Marangoni-like motions in cell aggregates

Gradients in the solid-like surface tension of model tissues, such as cell aggregates result in fast, internal cellular motions. The image shows the velocity (arrows) and vorticity (color) of cellular motions.

The growth and the decay of a visco-elastocapillary ridge by localized forces.

A soft solid layer develops a ridge-like deformation below the contact line due to the pulling force of the liquid-air surface tension when a droplet is in contact with it. We investigate the growth and the decay of a viscoelastic wetting ridge. The global features, e.g. the ridge height, evolve with time scales corresponding to the relaxation of the viscoelastic material. In contrast, we show that locally around the tip of the ridge, the surface tensions not only determine the equilibrium shape, but also have a significant impact on the dynamics, for which the relaxation has a characteristic spreading velocity depending on the solid surface tension. The relaxation time to an equilibrium state depends on the distance from the contact line, which can be much smaller than the long-term relaxation time scale of the viscoelastic material. The different dynamics between the global features of the ridge and the tip morphology suggests an alternative focus when investigating the contact line dynamics in soft wetting, such as stick-slip motion.

Binary mixture droplet wetting on micro-structure decorated surfaces

Liquid surface tension as well as solid structure play a paramount role on the intimate wetting and non-wetting regimes and interactions between liquids droplets and solid substrates. We hypothesise that the coupling of these two variables, independently addressed in the past, eventually offer a wider range of understanding to the surface science and interfacial communities.In this work, intrinsically hydrophobic micro-pillared surfaces varying in the spacing between structures, and pure ethanol, pure water and their binary mixtures (as well as acetone–water and ethylene glycol–water mixtures) are utilised, accessing a wide range of substrate solid fractions and liquid surface tensions experimentally. Wettability measurements are carried out at different azimuthal directions to exemplify the wetting/non-wetting behaviour as well as the droplet asymmetry function of both liquid composition and structure spacing.Our findings reveal that high water concentration droplets, i.e., high surface tension fluids, sit in the Cassie-Baxter regime while partial non-wetting Wenzel or mixed-mode regimes with enhanced droplet asymmetry ensuing for medium and high ethanol concentrations, i.e., low surface tension fluids, below certain micropillar spacing. Beyond micropillar spacing s ≥ 40 µm, the impact of the surface structure on the droplet shape is negligible, and droplets adopt a similar contact angle and circular shape as on a flat smooth hydrophobic surface. Wetting and non-wetting regimes are then supported by classical wetting theories and equations. A wetting regime map for a wide range of surface tension fluids and/or their mixtures on a wide domain of solid fractions is then proposed.

Effect of ethanol on wetting and adhesion properties of rhamnolipid

The wetting and adhesion properties of the surfactants and biosurfactants play a very important role in the processes occurring in practice. These properties can be changed by the addition to the aqueous solution of the surfactants and biosurfactants different kinds of the substances influencing the structure of water and the hydration of the head and tail of the surfactants molecules. Therefore, we studied effect of the ethanol on the wetting and adhesion properties of rhamnolipid by the measurements of the contact angle of the aqueous solution of rhamnolipid in the presence of ethanol on the polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA) and quartz surface. The obtained results of the contact angle were analyzed in the light of the surface tension components of the solids, water, ethanol as well as the head and tail of the rhamnolipid surface tension. Based on these analyses the adsorption of the ethanol and rhamnolipid at the solid-solution, the dependence between adhesion and surface tension, the dependence between the adhesion work of the solution to the solid surfaces and solution surface tension as well as the critical surface tension of solid wetting were considered. The critical surface tension was compared to the surface tension of the solid. From above mentioned consideration, it appeared, among other things, that on the basis of the PTFE-aqueous solution of ethanol (ET) and PTFE-aqueous solution of rhamnolipid (RL) interface tension, it is possible to predict the contribution of ET and RL adsorption at the PTFE-solution of RL and ET mixture. It also appeared that it is possible to determine the Gibbs standard free energy of ET and RL adsorption at the solid-air and solid-solution interfaces, by using the Gibbs excess concentration of ET and RL at these interfaces determined on the basis of contact angle in Langmuir equation modified by de Boer. • Replacement of RL by ET molecules in interfaces layer can cause contact angle increase. • Above ET CAC contact angle depends practically on its adsorption at interfaces but not RL. • Parameter changes linearly as a function of logarithm from sum of and but not • Solution of ET and RL mixture spreads complete over PMMA and quartz at C of ET higher than its CAC. • For PMMA and quartz there is linear dependence between adhesion work and

Modeling of Wetting Transition of Liquid Metals on Organic Liquid Surfaces

Wettability of liquid metal gallium is of vital significance in the field of modern industries, such as direct writing printing and microfluidics. A liquid interface is a recently developed and promising approach to regulate wettability but has not been well applied in liquid metals yet. This study focuses on the wetting performance of gallium droplets on organic liquid films. The results show that the organic liquid film could change the wetting state of the gallium droplet. Based on the solid substrate roughness and surface tension of the organic liquid, we could estimate whether the gallium droplet is in a slippery Wenzel or a Cassie state. Subsequently, we apply the thermodynamic stable model on different organic liquid films by spreading parameters to predict a priori whether an arbitrary combination of solid roughness and organic liquid is suitable for designing lubricant-infused surfaces (LIS) used in gallium droplets. More interestingly, we found that the cloaking could delay surface oxide formation, which will benefit the manipulation of liquid metal droplets. This paper would provide a better understanding of wettability of liquid metal on an organic liquid surface.

Measuring Surface Tensions of Soft Solids with Huge Contact-Angle Hysteresis

The equilibrium contact angle of a droplet resting on a solid substrate can reveal essential properties of the solid's surface. However, when the motion of a droplet on a surface shows significant hysteresis, it is generally accepted that the solid's equilibrium properties cannot be determined. Here, we describe a method to measure surface tensions of soft solids with strong wetting hysteresis. With independent knowledge of the surface tension of the wetting fluid and the linear-elastic response of the solid, the solid deformations under the contact line and the contact angle of a single droplet together reveal the difference in surface tension of the solid against the liquid and vapor phases. If the solid's elastic properties are unknown, then this surface tension difference can be determined from the change in substrate deformations with contact angle. These results reveal an alternate equilibrium contact angle, equivalent to the classic form of Young-Dupr\'{e}, but with surface tensions in place of surface energies. We motivate and apply this approach with experiments on gelatin, a common hydrogel.

A ternary phase‐field model for wetting of soft elastic structures

AbstractSoft wetting, that is, the interaction of liquid–fluid interfaces with deformable elastic structures, provides a rich variety of physical phenomena (stick‐slip motion, durotaxis, Shuttleworth effect, etc.) which are not yet understood. We propose a novel phase‐field approach to study such problems. The method uses two phase‐fields to describe the three domains (solid, liquid, ambient fluid) by the ternary Navier–Stokes Cahn–Hilliard equations. We use a recent phase‐field approach for fluid‐structure interaction to equip one phase with elastic properties. The resulting method is significantly simpler than all previous approaches for soft wetting, since no grids are used to represent the geometries. Accordingly, the method avoids grid‐based computation of interface curvature, mappings between different grids, complicated mesh generation, and retriangulation, while the elastic object can move freely through the computational domain. As a special feature, the elastic structure is for the first time represented as a neo‐Hookean Kelvin–Voigt–Maxwell material which makes it very versatile. The accuracy of the method is shown in a benchmark simulation of a droplet on an elastic substrate. The geometrical flexibility is illustrated by simulating a rotating solid object within a fluidic interface. Finally, we provide the first 3D simulations of soft wetting including solid surface tensions.

Synthesis and wettability of cellulose based composites by aqueous solutions of nonionic surfactant

The synthesis and characterization of the new UV-cured polymeric composites with microcrystalline cellulose (MCC) as a bio-filler are presented. The different contents of MCC from 0% to 20% wt. were applied. The polymeric parts of the composites were: bisphenol A glycerolate diacrylate (BPA.DA) as a cross-linking monomer and N-vinylpyrrolidone (NVP) as an active diluent. Due to the application of bulk polymerization method and UV-initiator (2,2-dimethoxy-2-phenylacetophenone), regular plates with the dimensions of 60 × 50 × 3 mm were obtained. The surface properties of the obtained solids were determined by the infrared spectra (ATR-FTIR) and optical profilometer as well as the values of the solid surface tension calculated from those of the contact angle of model liquids and van Oss et al. approach to the solid-liquid interface tension. Next the contact angle measurements of aqueous solutions of the nonionic surfactant Triton X-100 (TX100) (C = 10−6–10−3 M) were performed in the time range from 0 to 12 min for each drop. It was proved that with the MCC addition the composites become more hydrophobic and the TX100 adsorption at the solid-water interface as well as the surface structure are not the same as at the water-air one. Also the wetting and the spreading processes depend on the amounts of hydroxyl groups on the composites surface and the surface roughness as well as on the conformation and hydration of hydrophilic parts of TX100 molecules.