Advancing/receding contact angles

Experimentally, a small droplet of water was dispensed to the center of the textured area. The diameter of the contact area D was recorded and the advancing/receding contact angles Oa Or were determined. Small amount of water was added next. The diameter of the expanded drop and Oa/Or of the drop were determined. This procedure is repeated for other samples, and the data are summarized in Table 4.1. 

Advancing/receding contact angle. Advancing and receding contact angle should be determined with the drop expansion/contraction method. Typically, the measurement starts with a small sessile droplet ( 2 pL), and small amount of test liquid is added at a very slow rate, e.g., 0.2 pL/s. The drop profile is captured as the drop is... 

The Wilhelmy slide has been operated in dynamic immersion studies to measure advancing and receding contact angles [59] (see Chapter X). It can also... 

Fig. X-7. Advancing and receding contact angles of octane on mica coated with a fluo-ropolymer FC 722 (3M) versus the duration of the solid-liquid contact. The solid lines represent the initial advancing and infinite time advancing and receding contact lines and the dashed lines are 95% confidence limits. (From Ref. 75.)...

Fig. X-12. Advancing and receding contact angles of various liquids [water (circles), Gly = glycerol (squares), Form = formamide (diamonds), EG = ethylene glycol (circles), BN = abromonapthalene (squares), BCH = bicyclohexyl (diamond), HD = hexadecane (circles)] on monolayers of HS(CH2)i60R having a range of R groups adsorbed on gold and silver (open and filled symbols respectively). (From Ref. 171.)...

In a similar procedure, the atomizer test, which depends on the behavior of an advancing rather than a receding contact angle, a fine mist of water is apphed to the metal surface and the spreading of water is observed. On a clean surface, water spreads to a uniform film. With oleic acid as the test soil, the atomizer test can detect the presence of 10 mg of soil per cm, less than a monomolecular layer (115). For steel that is to be electroplated, the copper dip test is often employed. Steel is dipped into a cupric salt solution and the eveimess of the resulting metallic copper deposit is noted. 

Figure 2.6 Advancing and receding contact angle for a droplet slowly moving from left to right on a solid surface.

Angle to the main flow direction Surface coverage Advancing contact angle Dynamic contact angle Receding contact angle Density Eluid density Residual... 

Material Advancing contact angle (deg) Receding contact angle (deg)... 

Measure advancing and receding contact angles on methylated glass plates using the liquids in the order given in Table 2.3. 

CONTACT ANGLES SOME COMPLICATIONS 6.7a Advancing and Receding Contact Angles... 

FIG. 6.9 A drop on a tilted plane, showing advancing and receding contact angles. (Adapted from Johnson and Dettree 1969.)... 

FIG. 6.10 Contact angle hysteresis (a) weighing a meniscus in a Wilhelmy plate experiment versus the depth of immersion of the plate (b) both the advancing and receding contact angles are equal (c) 6a > dr. 

Since advancing and receding contact angles are likely to be different in these experiments, mercury permeation curves are expected to be different, depending on whether the mercury is being pushed in or out of the plugs. This type of hysteresis is indeed observed. We encounter another type of hysteresis associated with pore filling in Chapter 9 (Section 9.7a). 

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