Dynamic sessile drop

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)...

The sessile drop method has several drawbacks. Several days elapse between each displacement, and total test times exceeding one month are not uncommon. It can be difficult to determine that the interface has actually advanced across the face of the crystal. Displacement frequency and distance are variable and dependent upon the operator. Tests are conducted on pure mineral surfaces, usually quartz, which does not adequately model the heterogeneous rock surfaces in reservoirs. There is a need for a simple technique that gives reproducible data and can be used to characterize various mineral surfaces. The dynamic Wilhelmy plate technique has such a potential. This paper discusses the dynamic Wilhelmy plate apparatus used to study wetting properties of liquid/liquid/solid systems important to the oil industry. 

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 four-to-six day duration of the dynamic Wilhelmy tests (wherein equilibrium actually occurred after one day) were much shorter than the times generally required for the sessile drop test. The conventional contact angle measurements on oil from the fields mentioned above required up to 48 days (12). 

The amphiphilic brush displayed dynamic wetting behavior towards selective solvents such as water. If the substrate was immersed in water and then air-dried, an initial contact angle (sessile drop) of 80-75° was found, because of selective swelling... 

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. 

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[. 

Abbreviations CB = captive bubble TP = tilting plate WP = Wilhelmy plate SD = sessile drop DCA = dynamic contact angle AFM = atomic force microscopy.)... 

In order to measure the surface tension of solutions containing surfactants, the maximum bubble pressure, pendant drop and Wilhelmy plate (immersed at a constant depth) methods are suitable capillary rise, ring, mobile Wilhelmy plate, sessile drop and drop weight methods are not very suitable. These methods are not recommended because surfactants preferably adsorb onto the solid surfaces of capillaries, substrates, rings, or plates used during the measurement. In a liquid-liquid system, if an interfacially active surfactant is present, the freshly created interface is not generally in equilibrium with the two immiscible liquids it separates. This interface will achieve its equilibrium state after the redistribution of solute molecules in both phases. Only then can dynamic methods be applied to measure the interfacial tension of these freshly created interfaces. 

Bubble pressure Bubble pressure Bubble pressure Bubble pressure Bubble pressure Sessile drop Dynam. dix weight Sessile drop Sessile drop Pendant drop Drop weight Pendant drop pendant drop Pendant drop... 

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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