Contact angle interfacial tension

FOWKES, F.M., Dispersion force contributions to surface and interfacial tensions, contact angles and heats of immersion , A.C.S. Advances in Chemistry Series, 43, 99-111 (1964)... 

Method Static Values Dynamic Values Surface Tension Interfacial Tension Contact Angle High r, P Capability... 

F. M. Fowkes, Determination of interfacial tensions, contact angles.and dispersion forces in surfaces assuming additivity of intermolecular interactions in surfaces. J. Phys. Chem. 66,382 (1962). 

F. M. Fowkes, Dispersion Force Contributions to Surface and Interfacial Tensions, Contact Angles, and Heats of Immersion. Contact Angle, Wettability, and Adhesion. Vol. 43. Los Angeles, CA American Chemical Society. 99 [1964]. 

The component theories, which are presented in Chapter 3, are useful for estimating the interfacial tensions of solid-interfaces (solid-liquid, solid-solid) and for characterizing solid surfaces using the experimental data for the few properties that can be measiued (liquid-gas surface tension, liquid-liquid interfacial tension, contact angle). Important equations in this context arc the Young equation... 

However, the most important difference between the two approaches lies on the way the surface tension components are estimated. In the van Oss-Good approach, the surface tension components for liquids and for solids are estimated from a wide range of experimental data (liquid-liquid interfacial tensions, contact angles, etc.) often regressed simultaneously for various solids and liquids. As we discussed, there are no predictive or estimation methods proposed by van Oss-Good for calculating these surface tension components. 

The physicochemical aspects of micro- and macroemulsions have been discussed in relation to enhanced oil recovery processes. The interfacial parameters (e.g. interfacial tension, interfacial viscosity, interfacial charge, contact angle, etc.) responsible for enhanced oil recovery by chemical flooding are described. In oil/brine/surfactant/alcohol systems, a middle phase microemulsion in equilibrium with excess oil and brine forms in a narrow salinity range. The salinity at which equal volumes of brine and oil are solubilized in the middel phase microemulsion is termed as the optimal salinity. The optimal salinity of the system can be shifted to a desired value hy varying the concentration and structure of alcohol. 

The contact angle 0 depends on the balance between the sohd/Vapour (ygy) and solid/liquid (yg ) interfacial tensions. The angle which a drop assumes on a solid surface is the result of the balance between the adhesion force between solid and liquid and the cohesive force in the liquid,... 

Figure 3.7 a. Schematic representation of the conditions of equilibrium where three phases (a, (S and S) intersect at a triple point, where Aa/J is the contact area between phases (a and fi) ApS is the contact area between phases (ff and S) and ASa is the contact area between phases (5and a. b. Similar schematic representation giving the interfacial tensions and angles between the three phases. 

Equation 15.6 can be also used to estimate the dispersion part of polar liquids from solid-liquid interfacial data (contact angles). This is important in many cases as polar liquids are often miscible with water and thus no liquid-liquid interfacial tension data are available. To do this, we need to know the dispersion part of... 

For example, although many reports revealed that the rare earth additions change the shape, size and composition of non-metallic inclusions formed in the steels and that they play a very important role in improving the various properties of steels, research is still not adequate. Thermodynamic data are still too scattered to accurately predict these characteristics of non-metallic inclusions and the conditions under which the shape, size and composition of inclusions are controlled. Data for the effects of rare earths on the surface and interfacial properties surface tension, contact angle, etc., of steels, are also unsatisfactory. Precise solubilities of rare earths in molten and solid iron and steels are still not available. Studies are also required on the nucleation process of the non-metallic inclusions themselves in the steels. Knowledge of all of these is essential to understand the metallurgical process and the various properties of steels. 

A zero or near-zero contact angle is necessary otherwise results will be low. This was found to be the case with surfactant solutions where adsorption on the ring changed its wetting characteristics, and where liquid-liquid interfacial tensions were measured. In such cases a Teflon or polyethylene ring may be used [47]. When used to study monolayers, it may be necessary to know the increase in area at detachment, and some calculations of this are available [48]. Finally, an alternative method obtains y from the slope of the plot of W versus z, the elevation of the ring above the liquid surface [49]. 

A. W. Neumann et al.. Applied Surface Thermodyrmmics. Interfacial Tension and Contact Angles, Marcel Dekker, New York, 1996. 

Usually one varies the head of mercury or applied gas pressure so as to bring the meniscus to a fixed reference point [118], Grahame and co-workers [119], Hansen and co-workers [120] (see also Ref. 121), and Hills and Payne [122] have given more or less elaborate descriptions of the capillary electrometer apparatus. Nowadays, the capillary electrometer is customarily used in conjunction with capacitance measurements (see below). Vos and Vos [111] describe the use of sessile drop profiles (Section II-7B) for interfacial tension measurements, thus avoiding an assumption as to the solution-Hg-glass contact angle. 

Yaminsky and Yaminskaya [114] have used a Wilhelmy plate to directly measure the interfacial tension (and hence infer the contact angle) for a surfactant solution on... 

The extensive use of the Young equation (Eq. X-18) reflects its general acceptance. Curiously, however, the equation has never been verified experimentally since surface tensions of solids are rather difficult to measure. While Fowkes and Sawyer [140] claimed verification for liquids on a fluorocarbon polymer, it is not clear that their assumptions are valid. Nucleation studies indicate that the interfacial tension between a solid and its liquid is appreciable (see Section K-3) and may not be ignored. Indirect experimental tests involve comparing the variation of the contact angle with solute concentration with separate adsorption studies [173]. 

Li and Neumann sought an equation of state of interfacial tensions of the form 7 l = /(Tlv. TSv). Based on a series of measurements of contact angles on polymeric surfaces, they revised an older empirical law (see Refs. 216, 217) to produce a numerically robust expression [129, 218]... 

Detergents may be produced by the chemical reaction of fats and fatty acids with polar materials such as sulfuric or phosphoric acid or ethylene oxide. Detergents emulsify oil and grease because of their abiUty to reduce the surface tension and contact angle of water as well as the interfacial tension between water and oil. Recent trends in detergents have been to lower phosphate content to prevent eutrification of lakes when detergents are disposed of in municipal waste. 

A reduction of the o/w interfacial tension has a disadvantage because it makes the contact angle 9 more sensitive to small differences between and y. After a certain concentration of surfactant in the oil phase has brought the contact angle to 90°, the process is repeated but with the surfactant added to the oil before the phases are brought into contact. If the water droplet does not spread and its contact angle is in excess of 90°, the surfactant is added to the aqueous phase. 

The use of the harmonic mean often leads to better predictions of interfacial tensions between polymers and better contact angles between liquids and polymer solids, but the criterion for maximization of the work of adhesion is the same as... 

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