Cosine Of Contact Angle Research Articles

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.

Effect of Adjuvants on the Wetting Behaviors of Bifenthrin Droplets on Tea Leaves

The hydrophobic epicuticle wax on fresh leaves of tea tree (Camellia sinensis (L.) 0. Kuntze) leads to the loss of pesticide droplets, reducing efficacy. In this study, four adjuvants were selected to improve the diffusion and adhesion of bifenthrin droplets on the surface of tea leaves at different growth stages. The coupling effect of bifenthrin and adjuvants on the time-dependent and concentration-dependent wettability of droplets was investigated, and the difference in the wettability between bud and leaf was explained by observing the surface morphology. It was found that adjuvants effectively reduced the contact angle of droplets and accelerated the diffusion speed, and the above phenomenon became obvious with the increase in the adjuvant concentration. The wetting promotion of young leaves was more significant due to the reduced epicuticle wax and the greater roughness compared with fresh buds. The surface tension of the pesticide mixture was negatively correlated with the cosine of contact angle after adding the four adjuvants regardless of the growth stage of tea leaves. The contact angle of 0.2% Silwet L-77 decreased to 0° within 10 s, but the extreme wettability led to the decrease in adhesion with the increase in concentration. However, the wettability and adhesion on the surface of tea leaves were simultaneously suitable with more than 0.1% nonionic surfactant. The minimum concentration of the optimal adjuvant proposed in this study can provide an experimental basis and guide more efficient plant protection in tea gardens.

Wetting properties of aqueous short-chain alcohols’ solutions

The article presents results of research on the wetting ability of aqueous solutions of short-chain alcohols in relation to selected hydrophobic materials. Polyethylene and Teflon were used as standard hydrophobic smooth materials. Dried peat with granulation d < 0.5 mm was used as the porous hydrophobic material. Physical properties of alcohols and their solutions having a direct influence on the rate of saturation of capillary layers have been discussed. The wettability of smooth surfaces was characterized by the advancing and receding contact angles and wetting tension, defined as the product of the liquid surface tension and cosine of contact angle. The contact angles were determined by Wilhelmy’s method using the Krüss K-100 tensiometer. Wettability of peat was determined by measuring the mass rate of liquid imbibition by capillary forces. For comparison, analogous tests of wettability and capillary imbibition rates were carried out using sodium dodecyl sulfate solutions and solutions of typical wetting agent used in firefighting activities. The solutions of surfactants, in the range of concentrations used in extinguishing operations, showed much better wetting properties in relation to a smooth hydrophobic surface (polyethylene) than solutions of alcohols in the entire range of concentrations (up to 100%). The imbibition capacity of the hydrophobic peat layers of alcohol solutions with concentrations above 10% was higher than the solutions of surfactants.

Emollients for cosmetic formulations: Towards relationships between physico-chemical properties and sensory perceptions

Thirteen current commercial emollients from different chemical families (hydrocarbon, ester, ether, and silicone) were firstly characterized by eight physicochemical properties which were a-priori thought to be strongly related to sensory perception. Those include usual properties as well as more original ones such as volatility, estimated by the evaporated mass fraction during a fixed duration, as well as the polar and dispersive components of the surface tension. Principal Component Analysis and Hierarchical Agglomerative Clustering led to a partition of the emollients into groups that matched fairly well with the different chemical families. It also helped to highlight the main characteristics of each group. As expected, silicone had the lowest surface properties. Hydrocarbons showed the highest volatilities and the lowest viscosities. Esters mainly displayed the highest surface properties, and within this group, diesters showed higher polar components than monoesters. Sensory evaluation was performed at the same time by a professional panel. The sensory attribute “Spontaneous spreading” was found to be larger for silicone and hydrocarbons than for esters and ether. From our set of data, a suitable correlation was obtained between the sensory attribute “Spontaneous spreading” and the calculated spreading coefficient on Teflon® which combines surface tension with the cosine of contact angle.

Wettability of Supercritical CO2–Brine–Mineral: The Effects of Ion Type and Salinity

Deep saline aquifers are considered as perfect storage sites to sequestrate CO2. Interfacial tensions (IFTs) and contact angles (CAs) are key parameters in the heat and mass transfer processes for CO2/brine/mineral systems in porous media. In the present study, a molecular dynamics simulation method was used to investigate the effects of brine salinity and ion type on wettability of CO2/brine/mineral systems at 20 MPa and 318.15 K. Four common brines were selected as NaCl, KCl, CaCl2, and MgCl2. Interfacial tensions, water contact angles, and hydrogen bond structure and dynamics have been analyzed. The effects of brine salinity and ion type on water contact angles were found to be very complicated. For MgCl2 and NaCl solutions, the contact angle increases with salinity. For CaCl2 and KCl solutions, contact angle first increases and then remains constant with salinity. The product of IFT(CO2–brine) and the cosine of CA was found to be constant for all brine solutions studied. In the context of large uncert...

Wettability of polytetrafluoroethylene and polymethyl methacrylate by aqueous solutions of TX-100 and TX-165 mixture with propanol

The measurements of the contact angle of the aqueous solutions of TX-100 and TX-165 mixture with propanol on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) were carried out. On the basis of the obtained results, the dependence between the cosine of contact angle and surface tension as well as between the adhesion and surface tension of the solutions in the light of the work of adhesion of the solutions to the PTFE and PMMA surface was discussed. The dependence between the adhesion and surface tension for PMMA was correlated to the surface concentration of propanol as well as TX-100 and TX-165 mixture concentration determined from the Frumkin equation at the PMMA-air, PMMA-solution and solution–air interfaces. For this purpose, the surface tension of PMMA covered by a surface active agent film was determined using the Neumann et al. equation and next the PMMA–solution interface tension was evaluated from the Young equation. The values of the surface tension of PMMA covered by propanol and surfactants mixture layer were applied to describe the changes of the adhesion work of solutions to PMMA surface as a function of propanol and surfactants mixture concentration. The adhesion work of the aqueous solutions of TX-100 and TX-165 mixture with propanol to the PTFE and PMMA surfaces was discussed in the light of the adhesion work of particular components of the solutions. On the basis of the results obtained from the contact angle measurements, the standard Gibbs free energy of adsorption of particular components of solution was also considered.

Accurate determination of the vapor-liquid-solid contact line tension and the viability of Young equation

In this work, we present a theoretical method to determine the line tension of nanodroplets on homogeneous substrates via decomposing the grand free energy into volume, interface and line contributions. With the obtained line tension, we check the viability of Young equation and find that the chemical potential dependence (or equivalently, droplet curvature dependence) of the interface tensions is crucial for the viability of modified Young equation at the nanometer scale. In particular, the linear relationship between the cosine of contact angle and the curvature of the contact line, which is often used to determine the line tension, is found to be incorrect at the nanometer scale.

Surface Tension of Polytetrafluoroethylene and Polymethyl Methacrylate under the Influence of the Fluorocarbon Surfactant Film

Measurements of the contact angle for water, formamide, and diiodomethane on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA) covered by Zonyl FSN-100 (FSN100) and Zonyl FSO-100 (FSO100) films were made. On the basis of the obtained values, the Lifshitz–van der Waals component and electron-acceptor and electron-donor parameters of the acid–base component of PTFE and PMMA covered by the surfactant film surface tension were determined by the use of van Oss et al. approach to the interfacial tension and Young’s equation. The components and parameters of surface tension were discussed in the light of the sorption of fluorocarbon surfactants at the polymer/solution interface and proper orientation of the surfactant molecules to this interface. Taking into account the changes of determined values of the components and parameters of PTFE and PMMA surface tension under influence of the surfactant films, the relationship between the adhesion tension and the surface tension, as well as between the cosine of contact angle and the surface tension of aqueous solution of fluorocarbon surfactants, was explained.

Wetting of polymer surfaces by aqueous surfactant solutions

An important application of surfactants is to improve the wettability of aqueous solutions on hydrophobic surfaces, as indicated by a decrease in the contact angle of the liquid on the solid. The surfactant adsorbs at the liquid/vapor interface, reducing the surface tension and adsorbs at the solid/liquid interface, reducing the interfacial tension. In this work, the reduction of the surface tension and interfacial tension was measured as well as the advancing contact angle and surfactant adsorption as a function of surfactant concentration for three anionic and three cationic surfactants on eight different polymers with varying hydrophobicity. The Zisman equation (cosine of contact angle is a linear function of surface tension) adequately describes all systems studied as the critical micelle concentration is approached. The dependence of contact angle solely on surface tension does not mean that interfacial tension reduction due to surfactant adsorption is not important; rather, interfacial tension reduction mirrors surface tension reduction with increasing surfactant concentration; the ratio of solid/liquid interfacial tension to the liquid/vapor surface tension was shown to be independent of surfactant concentration for all 48 systems studied here. In general, interfacial tension reduction and surfactant adsorption at the solid/liquid interface are less significant as polymer hydrophobicity decreases. The critical surface tension (surface tension at which contact angle is zero as extrapolated from Zisman plots) differs for the different surfactants on a given polymer, emphasizing the limited generic applicability of the Zisman hypothesis for surfactant solutions. A mathematical analysis was developed to calculate the solid/vapor and the solid/pure water interfacial tensions which depend only on the polymer characteristics. The solid/vapor interfacial tension was found to be 33.3mN/m and does not depend on polymer structure.

Wettability, adhesion, adsorption and interface tension in the polymer/surfactant aqueous solution system. I. Critical surface tension of polymer wetting and its surface tension

The contact angle of aqueous solutions of Triton X-100, Triton X-114, Triton X-165, sodium dodecylsulfate, sodium hexadecylsulfonate, cetyltrimethylammonium bromide, cetylpyridinium bromide, sodium N-lauryl sarcosinate, dodecyldimethyethylammonium bromide, tetradecyltrimethylammonium bromide and benzyldimethyldodecylammonium bromide on polytetrafluoroethylene, polymethyl methacrylate and nylon 6 was studied. The contact angle values were used in the Young equation for the polymer–solution interface tension calculation and for the determination of the critical surface tension of polymer wetting. The critical surface tension of polymer wetting was obtained on the basis of the relationship between the cosine of contact angle and/or the adhesion tension as a function of the surface tension of aqueous solution of studied surfactants and then was discussed in relation to the Lifshitz–van der Waals components and electron-acceptor and electron-donor parameters of polytetrafluoroethylene, polymethyl methacrylate and nylon 6 surface tension. The role of the parameter of interfacial interactions in the relationship between the critical surface tension of polymer wetting and the surface tension was also considered. This parameter was calculated by using the polymer–solution interface tension as well as the polymer and aqueous solutions of surfactant surface tension.

Physicochemical properties of granulating liquids and their influence on microcrystalline cellulose pellets obtained by extrusion-spheronisation technology

The use of ethanol or ethanol/water mixtures as granulation liquids in the extrusion-spheronisation process results in the formation of pellets with significantly different mechanical and structural properties from those prepared using water alone. The product of surface tension ( γ L), relative permittivity ( ɛ R) of the granulation liquid and the cosine of contact angle ( Θ) of granulation liquid on pellets solid has been introduced in order to explain the mechanism of this phenomenon. A correlation is shown between the factor γ L × cos( Θ) × ɛ R and the properties of the pellets produced. We have introduced the γ L × cos( Θ) × ɛ R which can be considered to represent the driving and counteracting forces of pellet contraction during drying. The contact angles and surface tensions were evaluated using the Wilhelmy plate method. Pellets were produced by extrusion-spheronisation technique using water, ethanol and ethanol/water mixtures as granulation liquids. Subsequent characterization of the pellets showed that their tensile strength and disintegration times increase with increase in the proposed factor γ L × cos( Θ) × ɛ R, while friability, average pore diameter and porosity decreases. The observed correlations show, that the granulation liquid influences the mechanical and structural properties of the pellets through the contraction driving and contraction counteracting forces during drying.

Transition from Incomplete to Complete Wetting of Solid Surface in Polymer–Solvent System: 2. The Regime of Strong Adsorption

The transition from incomplete to complete wetting of the solid surface by a semidilute polymer solution coexisting at equilibrium with the very-dilute polymer solution was studied using the Canh–de Gennes theory under the conditions corresponding to the tricritical state of semidilute solution and strong adsorption of the chain units on a substrate. It was established that the wetting transition can occur as the first- or second-order phase transition or as the transition of tricritical wetting depending on the repulsion energy of segments that are on the substrate surface. Near the temperatures of these transitions, the character of the variations in the differences of surface concentrations that are established at the boundaries of the substrate with semidilute and dilute polymer solutions, as well as in the differences of interfacial tensions and the cosine of contact angle were determined. It was shown that the temperature of each of these phase transitions varies in proportion to the surface potential of the substrate and does not depend on the polymer molecular mass. The observed behavior differs essentially from that established near the critical point of a polymer–solvent system.

HYDRODYNAMIC DETERMINATION OF CRITICAL SURFACE TENSION OF FIBERS

The critical surface tension (CST) pointed out by Zisman is a practical parameter related to complete wetting of fibers. In the form of fiber, in general, the value of CST is estimated with some difficulties because of complex contact of fiber with liquid or unevenness of fibersIt was found that the value of CST could also be estimated, using the previously reported hydrodynamic apparatus on estimation of wettability of fiber assemblies. This study is mainely concerned with the principles and methods of determination of CST in the fiber assembly.The measurement of CST was based on the calculations of penetrating velosity (dh/dt) of dipsolution through capillaries in fiber assembly under forced flowing of dip-solution. Continious record of water pressure during the wetting process permitted the calculations of average water level in sample chamber and two curves of pressure and water level on the same time-scale permitted the comparision of amounts of pressure occured naturally in capillaries and of pressure loss due to forced flowing. The recorded pressure, when the two kinds of pressure just compensated, gave the value of dh/dt. By determination of the relation between dh/dt and water level in chamber, the product of radius of capillary by cosine of contact angle was obtained as an average value on numerous capillaries. Further, the plotting of these products vs surface tension of dip-solutions gave the value of CST of sample fibers in accordance with Zisman's method.Using above described method, value of CST of merino '64 wool fiber was determined at about 30 dyne/cm. This value was much smaller than the values reported in literatures, but it might be considered that this represented the more real value on undamaged clean wool fiber.Consequently, the merits of this hydrodynamic estimation were summarized as follows; 1) CST was determined as an average value of numerous fibers, 2) not only the CST, but the average radius of capillaries in fiber assembly could be estimated, 3) convenient determination of CST was also possible, by comparision of the shapes of pressure-time curves obtained on a series of solutions having various surface tensions.

Contact Angles of Mercury on Low-energy Solids

THE recent theory of Fowkes1–5 concerning the attractive forces at interfaces leads to the following relationship between cosine of contact angle (θ) and liquid surface tension (γL): where γSd, γLd are the dispersion force contributions to the solid surface tension and liquid surface tension respectively.