Liquid surface energies

Liquid Surface energy in ml m (at 20 °C) Type of intermolecular bonding... 

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]

Figure 6.7. Experimental values of the work of adhesion for non-reactive pure metal/monocrystalline AI2O3 systems versus the liquid surface energies of metals. From (Eustathopoulos and Drevet 1998) [17].

Figure 6.10. Experimental values of the work of adhesion versus the liquid surface energies for molten Al and Si on monocrystalline Al2Ov These values exceed significantly the values of the straight line for van der Waals bonded systems shown in Fig. 6.7.

The first term results from the heat of mixing of A-B alloy (see equations (4.3) and (4.4)). The second term comes from the cohesion energies of pure A and pure B and is related to the liquid surface energies adhesion energy of pure A and B on the external phase. When the external phase is the vapour, B ex = A-ex = 0 and the molar adsorption energy is reduced to equation (4.8) ... 

Figure 6.28. a) Effect of small additions of an alloying element on the interfacial or liquid surface energies of a non-reactive binary alloy/ceramic system for very positive and very negative values of adsorption energy, b) A very negative value of the slope of 0 implies a negligible slope... 

The differences between the values of viscosity, rj, and liquid surface energy, ctlv, of metals and glasses are of importance because the ratio orv/ 1 is of major significance in determining spreading rates (see equation (2.4)) and flow rates in capillaries (see equation (10.1)). For glassy materials, the ratio is less, and... 

Table 9.1. Properties of some glassy silicates, Si02 (T urkdogan 1983) and Cu. The values of density, p, viscosity, ij and liquid surface energy,

For liquids, the quantities surface energy and surface tension, usually given the symbol y, are numerically the same and are given in units of millijoules per square meter. Liquid surface energy, or surface tension, is easily observed in that liquids appear to have a skin. Surface energies of common organic liquids vary from about 10 mj /m2 up to about 65 mj /in2 at room temperature. The room-temperature surface energy of water is approximately 72 nij/ni2. 

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... 

Surface Liquids Surface energy (mN/m) Surface tension >l (mN/m)... 

As mentioned earlier, vegetable oils, because of their amphiphilicity, can adsorb onto surfaces and change various surface properties. Properties that can be modified due to adsorption of vegetable oils onto surfaces include surface tension of liquids, surface energy of solids, interfacial tension, boundary friction, adhesion, wettability, etc. The extent to which these properties are modified depends on a variety of factors, including the properties of the surfaces and the structure of the vegetable oil. Thus,... 

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