Liquid surface energy measurement

The contact angle is by far the most often quoted characteristic to be derived from sessile drop experiments, but reference will be made later in this Section to other liquid parameters and particularly to the liquid surface energies, (tlv. While values for both 0 and sessile drop experiment it is often convenient to use differently sized drops. Small drops will assume the profiles of nearly spherical caps and this regularity assists the estimation of 0 values from their dimensions, while the gravitational... 

Figure 3.9. Profile of a sessile drop showing the measurements used to derive liquid surface energy values. The principal radii of curvature at point Q are R = QK and R2 = QP.

Bashforth and Adams generated tables of ft and x / z for cp = 90° as well as tables of the ratios x/b and z/b for differing values of b and (p. By measurement of x90 and Z90 at cp = 90°, b and / can be determined from these tables and the liquid surface energy can then be derived from equation (3.8) with an accuracy of about 2% for / > 2 if the droplet coordinates are measured with an accuracy better than 0.1% (Sangiorgi et al. 1982). A method is presented in Appendix D allowing calculation of the mass of a droplet for an optimised [Pg.121]

Sessile drop experiments are also used to measure the effects of temperature on liquid surface energies. Because the temperature coefficient dliquid metals and oxides is usually a very small, negative, value (—0.05 to —0.5 mJ.m-2.K-1), a temperature rise of several hundred degrees is necessary to produce decreases in the surface energy that can be reliably detected by measurements of drop profiles. Even in this case, the error on the temperature coefficient lies between 30% and 100% (see Section 4.1.1). 

Sessile drop experiments have been used extensively to derive quantities characterising spreading and penetration phenomena, such as the work of adhesion and work of immersion, given by equations (1.45) and (1.54), using a single sessile drop experiment to measure both the contact angle and the liquid surface energy. 

When the optimal conditions are satisfied, i.e., a well-controlled atmosphere, a pure, homogeneous and smooth solid surface and an accurate measurement system, the Young contact angle and the liquid surface energy can be derived with an accuracy of 3 deg and 2% respectively allowing the work of adhesion (Wa = [Pg.144]

Use of the interaction parameter to correct for non-linearities present in plots of cose vs Jlv resulted in the following equations (Eq. 6,7)(Neumann et al, 7, 8) which represent a great advance in bringing surface chemistry within experimental reach, and allow calculation of solid surface energies from easily measured contact angles and liquid surface energies. Equation 6 is cubic in and some care must be taken in selecting the... 

Owing to the method of contact-angle or surface-energy measurement, the surface of wool necessarily includes the region between cuticle cells in addition to the cuticle itself Horr has further suggested that vapor adsorption due to capillary condensation may occur at the fiber cuticle scale edges, and that the phenomenon may contribute to the above interpretation that the wool surface is not entirely methyl. Horr also found that the possible composition of the wool fiber surface may even vary depending on the liquid with which it is in contact (e.g., water or methylene iodide). 

Tyson, W.R. and Miller, W.A. (1977) Siuface free energies of solid metal estimation from liquid surface tension measurements. Su. Sci., 62 (1), 267-276. Galanalds, I., BiMmayer, G., Bellini, V., Papanikolaou, N., Zeller, R., Bltigel, S., and Dederichs, P.H. (2002) Broken-bond rule for the surface energies of noble metals. Europhys. Lett., 58, 751-757. Galanalds, I., Papanikolaou, N., and Dederichs, P.H. (2002) Applicability of... 

Eq. 12 is developed for liquid adsorption on solid, although the molecules adsorbed at infinite dilution do not form an adsorbed liquid film. Schultz et al. demonstrated the validity of this equation, and of the assumptions made, under certain conditions, by comparing the surface energy measured by contact angle method with that determined by gas-solid adsorption on solid surfaces the dispersive component of the surface energy of the liquid equals the surface tension of the alkane probe at the same temperature, i.e., Tl = 7h represents the surface... 

Liquid vs Solid Surface Energy Measurement Techniques... 

This effect assumes importance only at very small radii, but it has some applications in the treatment of nucleation theory where the excess surface energy of small clusters is involved (see Section IX-2). An intrinsic difficulty with equations such as 111-20 is that the treatment, if not modelistic and hence partly empirical, assumes a continuous medium, yet the effect does not become important until curvature comparable to molecular dimensions is reached. Fisher and Israelachvili [24] measured the force due to the Laplace pressure for a pendular ring of liquid between crossed mica cylinders and concluded that for several organic liquids the effective surface tension remained unchanged... 

Before equations such as Eqs. 6, 7 and 8 can be used, values for the surface energies have to be obtained. While surface energies of liquids may be measured relatively easily by methods such as the du Nouy ring and Wilhelmy plate, those of solids present more problems. Three approaches will be briefly described. Two involve probing the solid surface with a liquid or a gas, the third relies on very sensitive measurement of the force required to separate two surfaces of defined geometry. All involve applying judicious assumptions to the experimental results. 

Many of the most widely used methods are based on measuring the contact angles of a series of test liquids on the solid surface, and evaluating the surface energies via Young s equation, Eq. 4 above. 

The surface structures of ionic liquids have been studied by direct recoil spectrometry. In this experiment, a pulsed beam of 2-3 keV inert gas ions is scattered from a liquid surface, and the energies and intensities of the scattered and sputtered (recoiled) ions are measured as a function of the incident angle, a, of the ions. Figure 4.1-16 shows a scheme of the process for both the scattered and sputtered ions. 

Measurement of the contact angle at a solid-liquid interface is a widely used method for the determination of the surface energy of solid polymers. Fowkes [1] first proposed that the surface energy of a pure phase, y y could be represented by the sum of the contribution from different types of force components, especially the dispersion and the polar components, such that ... 

For a liquid flowing in a channel inclined at an angle 0 to the horizontal as shown in Figure 3.21, the various energies associated with unit mass of fluid at a depth h below the liquid surface (measured at right angles to the bottom of the channel) are ... 

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