Liquid spreading on solids

Our own investigations have concerned (a) liquid spreading on solids and the laws relating the equilibrium contact angle and the critical surface tension of wetting to solid and liquid constitution (26, 27, 28, 53, 54,62), (b) liquid/liquid displacement from solid surfaces (1,5), (c) the properties of adsorbed monolayers on solids and their relation to the monolayer retraction method (28, 54, 62), (d) the surface electrostatic potentials of adsorbed organic monolayers on metals (9, 10, 11, 58, 59), (e) the effects of surface constitution on adhesion and abhesion (60),... 

Kalliadasis S, Chang H-C (1996) Dynamics of liquid spreading on solid surfaces, bid Eng Chem Res 35 2860-2874... 

Ngan C, Dussan E. (1989) On the dynamics of liquid spreading on solid-surfaces./T/KtW Mech 299-. 191-226. 

Young s equation is the basis for a quantitative description of wetting phenomena. If a drop of a liquid is placed on a solid surface there are two possibilities the liquid spreads on the surface completely (contact angle 0 = 0°) or a finite contact angle is established.1 In the second case a three-phase contact line — also called wetting line — is formed. At this line three phases are in contact the solid, the liquid, and the vapor (Fig. 7.1). Young s equation relates the contact angle to the interfacial tensions 75, 7l, and 7sl [222,223] ... 

Figure 7.15 Liquid spreading on a solid surface with a precursor film. ...

Molten mixtures of CaF2-Al203 rich in CaF2 have a viscosity of the order of a few mPa.s, comparable to that of liquid metals. Results of Sorokin et al. (1968), reported by Popel (1994), showed that the initial spreading rate of these mixtures on A1203 substrate is close to 1 m/s, as for liquid metals on solids, and decreases strongly with time, particularly when the instantaneous contact angle becomes very low. 

If the liquid makes no contact with the sohd, then 9 = 180° and the solid is referred to as being nonwettable by the liquid in question. This may be the case for a perfectly hydrophobic surface with a polar liquid such as water. However, when 180° >6> 90°, a case of poor wetting may be referred to. When 0° <6 <90°, partial (incomplete) wetting is the case, whereas when 9 = 0° complete wetting occurs and the liquid spreads on the solid substrate, forming a uniform liquid film. 

HBL Assumption. The first of these may be called the Harkins-Boyd-Livingston (HBL) assumption [16,44], These workers focused their attention primarily (but not exclusively) on cases which involved liquids spreading on the solid surfaces chosen for investigation. This situation no doubt provided the motivation for the following assumption ... 

Equation 4 tells us that if 9 = 0—that is, if liquid L 2 spreads on solid Si—the maximum reversible work of adhesion is always in excess of the work of cohesion by an amount at least - Sivj) >... 

Adhesives must effectively wet and completely contact the surfaces to assure a strong bond. The ability to wet a surface, wettability, is related to the ease with which a liquid spreads on a solid surface and is essential in maximizing coverage and minimizing voids in the bondlines. Wettability is measured by the equilibrium contact angle, 6, which is defined by balancing surface-tension forces in Young s equation ... 

Lopez, J., Miller, C.A., and Ruckenstein, E., Spreading kinetics of liquid drops on solids, J. Colloid Interface Sci., 56, 460, 1976. 

All liquids spread on glass, metals, and ionic crystals. By contrast, wetting may be total or partial on plastics and molecular crystals, depending on which specific liquid is used. The empirical criterion worked out by Zis-man allows us to classify solids. Each solid substrate has a critical surface... 

A more complex model for pool spread has been developed by Webber (1991). This model is presented as a set of two coupled diiSerential equations which models liquid spread on a flat horizontal and solid surface. The model includes gravity spread terms and flow resistance terms for both laminar and turbulent flow. Solution of this model shows that the pool diameter radius is proportional to t in the limit where gravity balances inertia, and as in the limit where gravity and laminar resistance balance. This model assumes isothermal behavior and docs not include evaporation or boiling effects. 

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