Contact angle advancing/receding sessile droplet

Figure 26.20 A correlation between the average of dynamic advancing and receding contact angles from the Wilhelmy method and static advancing contact angles from the sessile droplet method for untreated, TMS and TMS + O2 treated pol5rmers follows the relationship given by cos 6s = (cos 0u, .,i + cos 0D,a,i)/2.

Values of advancing 0a, receding 0r, and static 0q contact angles measured for sessile droplets on a methylated quartz plate in dependence on surfactant concentration [22] are shown in Fig. 19. To determine 0a and 0r, the drop was disposed on a polished surface of a flat cut of a thick-walled quartz capillary over its orifice. For solution concentration Cq< 0.1%, advancing angles are higher than 90° and, therefore, the capillary suction is formally impossible. However, as is shown in Fig. 18, a slow penetration of low concentrated solutions takes place. Similar results were obtained in other experiments with... 

Figure 23.8 Advancing and receding sessile droplet contact angle of water on a dry ethylene/vinyl alcohol film.

ADVANCING AND RECEDING SESSILE DROPLET CONTACT ANGLES... 

Figure 26.19 Relationship between the Wilhelmy advancing and receding contact angles, 0d, and static sessile droplet advancing contact angles 0s for all the untreated TMS treated and TMS + O2 treated conventional pol5nners the Wilhelmy contact angles are from the first cycle immersion and the static advancing contact angles are with a droplet size of 1.4 pi.

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... 

In sessile droplet contact angle measurement, the advancing contact angle could be used to describe the surface characteristics, but the receding contact angle per se is a meaningless number unless its change with respect to the contact time can be utilized to analyze the surface dynamic nature of the surface. 

Advancing and receding contact angle have been known for more than a century to be the maximum and minimum angle that can be measured reliably and reproducibly when liquid is added to or withdrawn from a liquid droplet at a very slow rate [4,5]. Most of the current goniometer is equipped with an automated dosing system, where drop volume and rate of addition/withdraw can be controlled very precisely. The needle-embedded sessile drop method is the most frequently used method and is schematically shown in Fig. 2.15. 

Fig. 2.16 Sessile drop images of water droplets on PTFE during advancing and receding contact angle measurement...

Figure 6.1 schematically depicts the three interactions between a liquid droplet and a surface. These three interactions are actually governed by the movement of the contact line. When the liquid first wets the surface, the contact line advances outward, and the first information one seeks is wettability. The adjectives to describe the surface are wettable and non-wettable. As for the liquid, it will either wet or partially wet the surface or repel from it. As discussed in Chap. 5, wettability is measured by the advancing angle Oa- Once the liquid partially wets the surface, a static sessile drop is formed. There exist two interactions between the sessile drop and the surface. In the vertical direction, it is the adhesion and it is measured by the receding angle 0r. The only motion for the contact line is receding, and an interface (liquid-solid) is eliminated when the liquid droplet is detached from the surface. 

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