Contact Angle Of Liquid Droplet Research Articles

The impact of salinity on the cohesion process of quartz substracts: A molecular dynamics study.

The moisture with salt ions adsorbed on the mineral soil surface is crucial to the cohesion process when the media is exposed to marine or coastal environments. However, the impact of salinity on the cohesion of soils is not well studied at the nanoscale. In this study, the salinity effect was investigated by studying the wettability and capillary force of NaCl solutions on quartz substrates via a molecular dynamics-based approach. Besides, a new visualization method was proposed to measure the contact angle of liquid droplets from the aspect of nanoscale. The results indicated that salt ions can weaken the wettability of the liquid on the quartz surface and inhibit the capillary force. Compared with water, the liquid with a 10% NaCl solution can achieve a capillary force reduction of around 70%, resulting in a detrimental effect on the cohesion of soils. Overall, this study enhanced the understanding of the nanoscale salinity effect on the cohesion process and provided insights into the modification of the mechanical properties of soils from the aspect of nanoscale.

Equilibrium contact angle at the wetted substrate

We construct a novel model for the steady-state contact angles of liquid droplets at the wetted substrate. The non-removable, thin liquid film covering the substrate is governed by the intermolecular forces between molecules of liquid and solid, which we describe using the standard disjoining pressure approximation. Balancing the disjoining pressure against the surface tension, we find the smooth shape of the surface of the liquid. We show that we can extract an effective contact angle from the region where the film and the droplet meet. Crucially, we find that for large droplets the contact angle is independent of the droplet size. Instead, the contact angle is determined by the surface tension and the disjoining pressure parameters through a simple formula that works for both small and large contact angles. We suggest that comparing predictions of our model to experimentally measure contact angles will enable constraining the parameters of the disjoining pressure models.

Chemical Alteration of Wettability of Sandstones with Polysorbate 80. Experimental and Molecular Dynamics Study

In this work experimental and theoretical evaluations of the wettability alteration of sandstones, using the commercial surfactant polysorbate 80 (P80), are presented. The experimental evaluation started from a virgin sandstone core (water-wet); damage was then induced to modify the wettability of the rock from water-wet to oil-wet, with the purpose of evaluating the surfactant’s ability to restore the wettability of the core to the water phase. The contact angles of water and n-decane droplets were used to evaluate the wettability alteration of the surface. The theoretical evaluation was made using molecular dynamics to determine the configuration of the surfactant adsorbed on the surface and to calculate the surfactant–liquid interaction energy. Experimental results showed that a concentration of 100 ppm P80 in the impregnation solution generated the greatest contact angle for n-decane droplets and a small contact angle for water droplets using the least amount of surfactant, restoring the water-wet state of the solid and generating a lipophobic surface. The molecular dynamics results showed that adsorption of the surfactant on the surface is associated mainly with interactions between the chains of the surfactant that contain the ester group and the surface, whereas the chains containing ethylene oxides are exposed toward the liquid phase. By evaluating the interaction energy between the P80 coating and the liquid phases, it was established that the chains containing the ethylene oxides were key to restoring the water-wet state of the surface since they exerted an attractive interaction over water and a slightly repulsive interaction over n-decane, generating the lipophobic surface. The molecular model developed in this work allows the performance of predictive calculations of the contact angle of liquid droplets, with deviations, in most cases, of less than 5% compared to the experimental value.

Experimental Investigation on Contact Angle of Sintered Copper Powder Wick

Heat pipes are widely used in electronic cooling and other applications that require efficient transport or spreading of heat from local sources of high heat flux. One factor that most affect the performance of this device is the wetting properties of the wick material, whereby a hydrophilic wick material is required to transport the liquid from the evaporator to the condenser. The performance of heat pipe will decrease when the wick surface becomes hydrophobic as indicated by changes in its contact angle (CA). This study aims to determine the effect of ambient air exposure on the wettability of wick material. Wettability for a surface by a certain liquid can be shown by measuring the contact angle of liquid droplets on the surface. In this experiment, the contact angle was captured using a high speed video camera followed by image processing and then measured using Image J software. The surface of the sample/wick is a sintered copper powder which in this study through a process of forming or compaction by various parameters such as powder particle size, compacting pressure and sintering temperature. From the results of this study was found that the longer wicks were exposed in the ambient air, the contact angle of the liquid on the wick surface will be getting increased. After 7 days were contaminated on the ambient air, then all samples have been turned into hydrophobic, CA>90°.

Advances in the theory of superhydrophobic surfaces

The underlying theories interpreting wetting phenomena are still mainly focused on the Young's equation, the Wenzel equation, and the Cassie–Baxter equation, despite the fact that wetting phenomena have been studied over the past decades. Based on these theories, people have understood that both surface chemical composition and its morphology can influence the contact angle of liquid droplets on solid surfaces. However, such equations are not sufficient to thoroughly explain the mechanisms of wetting phenomena, although they are still necessary. In this feature article, we review the theory, from the classical wetting models to the most recent theoretical advances, of superhydrophobic surfaces with regard to the wetting process, and some promising breakthroughs in the advance of the theory are proposed in the final section.

Equilibrium Contact Angles of Liquid Droplets on Ideal Rough Solids

This work proposes a theoretical model for predicting the apparent equilibrium contact angle of a liquid on an ideal rough surface that is homogeneous and has a negligible body force, line tension, or contact angle hysteresis between solid and liquid. The model is derived from the conservation equations and the free-energy minimization theory for the changes of state of liquid droplets. The work of adhesion is expressed as the contact angles in the wetting process of the liquid droplets. Equilibrium contact angles of liquid droplets for rough surfaces are expressed as functions of the area ratios for the solid, liquid, and surrounding gas and the roughness ratio and wetting ratio of the liquid on the solid for the partially and fully wet states. It is found that the ideal critical angle for accentuating the contact angles by the surface roughness is 48°. The present model is compared with existing experimental data and the classical Wenzel and Cassie-Baxter models and agrees with most of the experimental data for various surfaces and liquids better than does the Wenzel model and accounts for trends that the Wenzel model cannot explain.

Hydrophobic mechanism and criterion of lotus-leaf-like micro-convex-concave surface

According to the principle that the contact angle of liquid droplet always increases on a limited liquid-solid interface, it is suggested that the integration of many small-size limited liquid-solid interfaces results in the increase of the hydrophobicity of lotus-leaf-like micro-convex-concave surfaces. Mathematical equations of the stability of liquid-droplets on the surface of lotus-leaf-like structure were established. The relationship between the theoretical critical-radius of the void of micro-convex-concave surface and the nature of the solid and the liquid was drawn. The three conditions of realizing hydrophobicity were described. The result of computation has shown that when the radius of the void of micro-concave-convex surface is less than the theoretical critical-radius rc, the droplets may always be in a stable state on the solid surface with the contact angle greater than 90°. The minimum area of the liquid-solid interface and low surface energy of solids are important factors in realizing hydrophobicity. The effective work of adhesion Wa′ was proposed as a criterion for measuring the hydrophobic ability of the solid surface.

Evaluation of the surface properties of PTFE foam coating filter media using XPS and contact angle measurements

A newly developed PTFE foam coating filter was developed which can be used for hot gas cleaning at temperatures up to 250°C. The emulsion-type PTFE was coated onto a woven glass fiber using a foam coating method. The filter surface was closely examined using X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The XPS results were used to determine the binding force between the carbon and fluorine of PTFE, which imparts coating stability to the filter medium. More than 95% of the bonds of the PTFE foam coating filter were between carbon and fluorine, and this filter demonstrated excellent hydrophobic and good oleophobic properties at the same time. The contact angles of liquid droplets on the filter surface were used to predict the potential wetability of the filter against water or oil. In addition, the very low surface free energy of the filter medium, which was evaluated using the Owens–Wendt method, demonstrates a very stable surface and a high de-dusting quality.

Specific surface free energy and the morphology of synthesized ruby single crystals

Ruby single crystals were synthesized from Mo- or Pb-based fluxes. The specific surface free energy of crystal was experimentally obtained using contact angle of liquid droplets on the crystal surface, and compared with the equilibrium grown length of each face. The proportion of the specific surface free energy and the equilibrium grown length was constant for the different faces of each individual ruby crystal, which looks to satisfy Wulff’s relationship. The relationship between specific surface free energy of the faces of the individual crystal with the same index and the equilibrium grown length of the face was linier. The difference in the specific surface free energy for the face of the same index can be explained by the difference in step length.

Determination of the specific surface free energy of natural quartz crystals using measurement of contact angle of liquid droplets

AbstractContact angle of water and formamide droplets on natural quartz crystals were observed. The specific surface free energy (SSFE) of m, r, and z faces, calculated using the Fowkes approximation, were approximately 54‐69 mN/m. The length of the normal line from the center of the crystal to each face (hi) was observed and compared with the SSFE. Though, Wulff's relationship was well satisfied for synthesized crystals, hi was not proportional to SSFE for natural crystal. We propose an idea of “γ center”, which correspond to Wulff's point for ideal equilibrium shape crystal. We concluded that, crystal face with the larger SSFE has larger growth rate even for natural crystal. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Model for the Contact Angle of Liquid Droplets on Rough Surfaces

Up to now, measured results of the contact angle on rough surfaces have been explained usually based on the Wenzel equation (1936) and the Cassie–Baxter equation (1944). However, these equations do not take into account considerations of liquid wetting behaviors on rough surfaces, and this leads to poor understanding of the mechanisms of contact between liquid droplets and rough surfaces (e.g. contact angle hysteresis). We propose a new model for the contact angle of liquid droplets. By means of the present model, we can well understand the experimental data which could not be well explained by the Wenzel equation and the Cassie–Baxter equation.

P-11 EWOD法を用いたシリコンオイル中における液滴の制御(ポスター要旨講演)

This paper describes manipulation of liquid droplet by EWOD(Electro Wetting on dielectric) method. Contact angle of liquid droplet can be controlled electrically. This study focuses on effectiveness of silicone oil for EWOD method. The contact angle response improved by silicone oil, and the response can be repeated, we tried EWOD experiment in silicone oil, because silicone effect be good for EWOD.

Specific surface free energy of ruby single crystals from Mo- and Pb-based flux

Ruby single crystals were synthesized from MoO 3, PbF 2, and PbF 2–B 2O 3 fluxes. Mo-based flux gave hexagonal bipyramidal crystals. On the other hand, plate-like crystals were given from Pb-based fluxes. The specific surface free energy of the ruby single crystal was experimentally obtained using contact angle of liquid droplets on the crystal surfaces, and compared with the length of normal line to the face from the center of the crystal, h i . The proportions of the specific surface free energies to h i ’s were constant for different faces of each individual ruby crystal synthesized from Mo-based flux. This result looks to satisfy the Wulff's relationship. However, the proportions were not equal for respective crystals from Mo-based flux, which is considered to result from the difference in the driving force. Specific surface free energies of (0 0 0 1) faces were measured for crystals from Pb-based flux and a crystal from Mo-based flux. The specific surface free energy has linier relationship with the length of normal line to the (0 0 0 1) face from the center of the crystal. Step free energy of the steps on (0 0 0 1) face gives influence to the observed specific surface free energy of the face.

Roughness effects on contact angle measurements

We have developed a simple and economical procedure to demonstrate the effects of roughness and wetting fraction on the equilibrium contact angles of liquid droplets on solid surfaces. Contact angles for droplets placed on a rough surface, which wet only a portion of the surface, are larger than the contact angles of droplets formed by condensation of steam, which wet the surface more completely. These contact angle data facilitate assessments of changes in true surface area, due to surface roughening, as well as changes in the fractional contact areas of the water droplets, due to the formation of air pockets between the rough surface and the droplet.

Surface Free Energy of Various Fullerene Derivative Films Determined by Contact Angles of Liquid Droplets

not Available.

Experimental study for the Wulff's relationship of ruby single crystals using contact angles of liquid droplets

Abstract The specific surface free energy of a ruby single crystal was experimentally obtained using the contact angle of liquid droplets on the crystal surfaces, and then compared with the morphology of each crystal. The obtained specific surface free energy satisfied the Wulff's relationship, even though the synthesized crystals should be in growth form. We propose an idea of steric energy density, which gives another interpretation for the Wulff's relationship.

Relationship between contact angle of liquid droplet and light beam position in optoelectrowetting

The contact angle of a liquid droplet on a dielectric-coated electrode can be controlled by changing the voltage between them. In addition, the insertion of a photoconductor between the dielectric layer and the electrode enables the optical control of the contact angle. In particular, by using a convergent light beam such as a laser beam, the voltage applied between the liquid droplet and the electrode can be changed locally; the contact angle can be controlled by changing the position of the convergent light beam. In this paper, we theoretically analyze the relationship between the contact angle and the position of a Gaussian light beam.

Wulff’s relationship of ruby single crystals grown from molybdenum trioxide flux studied by contact angles of liquid droplets

The contact angles of water and formamide droplets on two different ruby crystals grown from MoO 3 flux were measured. The specific surface free energies of the ( 1 1 2 ¯ 3 ) , ( 1 0 1 ¯ 3 ) , and (0 0 0 1) faces were calculated using the Fowkes approximation and compared with the length of the normal lines from the center to the crystal faces. The relationship between the specific surface free energy and the morphology of each crystal is found to satisfy Wulff’s relationship.

Morphology and Specific Surface Free Energies of Ruby Single Crystal Grown from Molybdenum Trioxide Flux Studied by Contact Angle of Liquid Droplets

Abstract Contact angles of water and formamide droplets on a ruby crystal grown from MoO3 flux were determined. The specific surface free energies of the () and (0001) faces, calculated using the Fowkes approximation, were 48 ± 1 and 65 ± 1 mN m−1, respectively. The length of the normal lines from the center of the crystal to () and (0001) faces were 1.06 and 1.45 mm, respectively. The relationship between the specific surface free energy and the morphology of the crystal satisfies Wulff’s relationship.

Specific Surface Free Energy of Ruby Thin Film Grown on Sapphire Single Crystals Studied by Contact Angle of Liquid Droplet

ABSTRACTRuby thin film was grown on sapphire substrate by evaporation method of MoO3 flux. Small amount of Na2CO3 was added in order to decrease the evaporation rate of flux. The contact angles of liquids and crystal surfaces were measured for water and formamide droplets, and the specific surface free energy of each face of the crystal was calculated using Fowkes approximation and Wu's mean equations. The growth hillocks on the synthesized thin film were observed. The addition of Na2CO3 incrased the density of hillocks and the specific surface free energy was larger for the ruby thin film, which has larger number of hillocks.