Static sessile drop

Fig. 2 Contact angle goniometry images of static sessile drop on glass slides, left column 5 A glass, right column ACP-coated glass (still photos extracted from a...

A typical static sessile drop is created by a microsyringe with an automated plunger to place a tiny drop of water on the polymer surface. Ideally, the polymer sample should be in a humidity chamber to minimize the water evaporation that would change the shape, and thus the C A of the droplet. The shape of the droplet is captured by a camera and CA is measured by an image analysis software [30]. 

Static sessile-drop 6 for P/a/n TGP-H surface is 121.8 0.3°, which is -41 higher than Wilhelmy 9 for single fiber. 

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...

Fig. 12 Cassie model of equilibrium static sessile drop water contact angles as a function of TGP-H fiber surface coverage for FEP (gray) and PTFE (black) (Wood 2007)...

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. 

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. 

Provides measuring techniques of contact angle, surface tension, interfacial tension, and bubble pressure. Suitable methods for both static and dynamic inteifacial tension of liquids include du Nous ring, Wilhelmy plate, spinning drop, pendant drop, bubble pressure, and drop volume techniques. Methods for solids include sessile drop, dynamic Wilhelmy, single fiber, and powder contact angle techniques. 

There are static and dynamic methods. The static methods measure the tension of practically stationary surfaces which have been formed for an appreciable time, and depend on one of two principles. The most accurate depend on the pressure difference set up on the two sides of a curved surface possessing surface tension (Chap. I, 10), and are often only devices for the determination of hydrostatic pressure at a prescribed curvature of the liquid these include the capillary height method, with its numerous variants, the maximum bubble pressure method, the drop-weight method, and the method of sessile drops. The second principle, less accurate, but very often convenient because of its rapidity, is the formation of a film of the liquid and its extension by means of a support caused to adhere to the liquid temporarily methods in this class include the detachment of a ring or plate from the surface of any liquid, and the measurement of the tension of soap solutions by extending a film. 

Static contact angle measurement of the sessile drop. The contact angle, 6C, is the angle formed by a liquid drop at the three-phase boundary where a liquid, a gas, and a solid intersect. It depends on the interfacial surface tensions between gas and liquid nGL, liquid and solid nLS, and gas and solid IIGS, as given by Young s6 equation of 1805 ... 

ADSA-P has been employed in various surface tension and contact angle studies, including static (advancing) contact angles [69.70], dynamic (advancing) contact angles at slow motion of the three-phase contact line [4, 71—74], and contact angle kinetics of surfactant solutions [75]. A schematic of the experimental setup for ADSA-P sessile drops is shown in Fig. 6. More details are available elsewhere [66[. 

The static methods are based on studies of stable equilibrium spontaneously reached by the system. These techniques yield truly equilibrium values of the surface tension, essential for the investigation of properties of solutions. Examples of the static methods include the capillary rise method, the pendant and sessile drop (or bubble) methods, the spinning (rotating) drop method, and the Wilhelmy plate method. 

Measurements of interfacial tensions of polymer melts were reviewed by Wu (55), Koberstein (65), and Demarquette (66). The measurements usually need long equilibrium time because of the high viscosities of polymer melts. The measurements can be divided into two groups static methods in which interfacial tension is calculated based on the equilibrium profile of the drops and dynamic methods that study the evolution of fiber or drop profiles with time. Static methods include pendant drop method, sessile drop method, and rotating drop method. Dynamic methods include breaking thread method, imbedded fiber method, and deformed drop retraction method. 

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