Drop contact angle

Analytical Techniques. Sessile drop contact angles were measured with a NRL C.A. Goniometer (Rame -Hart, Inc.) using triply distilled water. The contact angles reported are averages of 2-8 identically treated samples with at least three measurements taken on each sample. ESCA spectra were obtained on a Kratos ES-300 X-ray Photoelectron Spectrometer under the control of a DS-300 Data System. Peak area measurements and band resolutions were performed with a DuPont 310 Curve Resolver. 

FIGURE 18.1 (a) Drop contact angle and (b) a sessile drop showing characteristic dimensions. 

Far from a wellbore, the velocity of reservoir fluids is about one linear foot per day. Near a wellbore, the velocity can increase one-hundred fold. A static or quasi-static test such as the sessile drop (contact angle) test may not represent the dynamic behavior of the fluids in the field. The dynamic Wilhelmy device gives results which are comparable in interface velocity to the field displacement rate. The interface in the Wilhelmy test described here moved at a steady rate of 0.127 mm/sec or 36 ft/day. The wetting cycle for a hybrid-wetting crude oil system was not affected by moving at a rate less than 1 ft/day. 

The surface area expansion process in Figure 3.5 must obey the basic thermodynamic reversibility rules so that the movement from equilibrium to both directions should be so slow that the system can be continually relaxed. For most low-viscosity liquids, their surfaces relax very rapidly, and this reversibility criterion is usually met. However, if the viscosity of the liquid is too high, the equilibrium cannot take place and the thermodynamical equilibrium equations cannot be used in these conditions. For solids, it is impossible to expand a solid surface reversibly under normal experimental conditions because it will break or crack rather than flow under pressure. However, this fact should not confuse us surface tension of solids exists but we cannot apply a reversible area expansion method to solids because it cannot happen. Thus, solid surface tension determination can only be made by indirect methods such as liquid drop contact angle determination, or by applying various assumptions to some mechanical tests (see Chapters 8 and 9). 

TABLE 10-2. SURFACE CONTACT POTENTIALS AND DROP CONTACT ANGLES FOR ADSORBED FILMS ON PLATINUM... 

Substance Contact potential, fil/, mV Drop contact angle, deg. 

At a first approach we can take the feasibility of desorption as the distinguishing difference between physically adsorbed and chemisorbed films. Even though this criterion may break down both experimentally and semantically in certain cases, it is workable as an initial guideline and it keeps us from becoming enmeshed in exceptions and modifications before we are ready for them. Chemisorbed films can be put on the adsorbing surfaces by the same techniques as physically adsorbed films retraction from the melt or from the liquid, retraction from solution, vapor deposition, etc. Chemisorbed films iHu respond to probes for the nature of the film—e.g. drop contact angle or surface potential — in the same way as physically adsorbed films. It is not until we attempt to desorb the film that we become aware of the difference between physical adsorption and chemisorption, as exemplified by the observations of Timmons and Zisman cited above [10]. 

Table 4.4 Water drop contact angle test on plasma-treated metal surfaces [4], Proc SPIE 2009, reprinted with permission...

Reflection goniometry showed that all fullerene Ceo layers were relatively highly hydrophobic. The continuous and micropattemed layers had similar water drop contact angles ranging from 95.3 + 3.1° to 100.6 + 6.8°. 

There are a number of techniques that can be used to measure the degree of hydrophobicity of a surface. Direct techniques such as water uptake measurements and sessile drop contact angles are often supplemented with spectroscopic studies using FTIR and NMR to provide evidence of structural groups present in aerogel samples and to quantitate the relative number of those groups. These methods are described below. 

Values were experimentally obtained from the sessile drop contact angle measurements. ... 

Figure 14.2. Schematic of a sessile drop contact angle system...

Fig. 4 Comparison between single-fiber Wilhelmy, static sessile drop, and dynamic sessile drop contact angles for plain Toray TGP-H paper. The substrate on which the water droplet is sitting top-left comer) is plain TGP-H paper, with a single approximately 10 pm diameter TGP-H fiber penetrating the water droplet (the fiber was extracted from the paper substrate)...

Fig. 10 Before and after comparison of static sessile-drop contact angles of SGL SIGRACET GDL 24BC aged for 1,006 h in 80°C deionized water with air sparging gas Bars on left represent the MPL surface and bars on right represent the non-MPL sirrface...

Modeling of Heterogeneous Sessile-Drop Contact Angles... 

To understand the differences between single-fiber contact angles discussed in Sect. 3.2 and sessile-drop contact angles discussed in Sects. 3.3 and 4.1, a more advanced equation is needed than the Young equation to explain the phenomena. 

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