Wilhelmy plate dynamic

Fig. ni-19. Trough for dynamic surface measurements A, stainless-steel dish B, aluminum mantle C, inlet thermostatting water D, lower PTFE bars E, oscillating bars F, attachment lower bars G, Wilhelmy plate. (From Ref. 140.)... 

Dynamic surface tension has also been measured by quasielastic light scattering (QELS) from interfacial capillary waves [30]. It was shown that QELS gives the same result for the surface tension as the traditional Wilhelmy plate method down to the molecular area of 70 A. QELS has recently utilized in the study of adsorption dynamics of phospholipids on water-1,2-DCE, water-nitrobenzene and water-tetrachloromethane interfaces [31]. This technique is still in its infancy in liquid-liquid systems and its true power is to be shown in the near future. 

Formation Wettability Studies that Incorporate the Dynamic Wilhelmy Plate Technique... 

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. 

The Wilhelmy hanging plate method (13) has been used for many years to measure interfacial and surface tensions, but with the advent of computer data collection and computer control of dynamic test conditions, its utility has been greatly increased. The dynamic version of the Wilhelmy plate device, in which the liquid phases are in motion relative to a solid phase, has been used in several surface chemistry studies not directly related to the oil industry (14- 16). Fleureau and Dupeyrat (17) have used this technique to study the effects of an electric field on the formation of surfactants at oil/water/rock interfaces. The work presented here is concerned with reservoir wettability. 

Figure 1. Schematic diagram of the dynamic Wilhelmy Plate Apparatus.

The computer interface system lends itself well to the determination of interfacial tension and contact angles using Equation 3 and the technique described by Pike and Thakkar for Wilhelmy plate type experiments (20). Contact angles for crude oil/brine systems using the dynamic Wilhelmy plate technique have been determined by this technique and all three of the wetting cycles described above have been observed in various crude oil/brine systems (21) (Teeters, D. Wilson, J. F. Andersen, M. A. Thomas, D. C. J. Colloid Interface Sci., 1988, 126, in press). The dynamic Wilhelmy plate device also addresses other aspects of wetting behavior pertinent to petroleum reservoirs. 

This same technique should be helpful in understanding wetting properties important in the oil industry since wetting is very dependent on mineral surface energies. The use of contact angle hysteresis information may allow a better understanding of the effects of surface heterogeneities of natural mineral samples. The dynamic Wilhelmy plate technique is ideally suited for such experiments ... 

Figure 16 shows the experimental arrangement for the measurement of the surface pressure. The trough (200 mm long, 50 mm wide and 10 mm deep) was coated with Teflon. The subphase temperature was controlled within 0.1 C by means of a jacket connected to a thermostated water circulator, and the environmental air temperature was kept at 18 °C. The surface tension was measured with a Wilhelmy plate of platinum(24.5 x 10.0 x 0.15 mm). The surface pressure monitored by an electronic balance was successively stored in a micro- computer, and then Fourier transformed to a frequency domain. The surface area was changed successively in a sinusoidal manner, between 37.5 A2/molecule and 62.5 A2/molecule. We have chosen an unsaturated phospholipid(l,2-dioleoyl-3-sn-phosphatidyI-choline DOPC) as a curious sample to measure the dynamic surface tension with this novel instrument, as the unsaturated lipids play an important role in biomembranes and, moreover, such a "fluid" lipid was expected to exhibit marked dynamic, nonlinear characteristics. The spreading solution was 0.133 mM chloroform solution of DOPC. The chloroform was purified with three consecutive distillations. 

The Wilhelmy plate method provides an extremely simple approach that, unlike the ring detachment method, permits the measurement of continuously varying or dynamic surface tensions. If a thin plate (e.g., a microscope slide, a strip of platinum foil, or even a slip of filter paper) is attached to a microbalance and suspended so that its lower edge is just immersed in a liquid, the measured apparent weight Wj, is related to the actual weight of the plate Wp and the surface tension y by the following simple equation ... 

Figure 4. Automatic dynamic surface tension balance showing Wilhelmy plate suspended in surface. Photograph supplied by Cahn Instruments, Inc.

This unit will introduce two fundamental protocols—the Wilhelmy plate method (see Basic Protocol 1 and Alternate Protocol 1) and the du Noiiy ring method (see Alternate Protocol 2)—that can be used to determine static interfacial tension (Dukhin et al., 1995). Since the two methods use the same experimental setup, they will be discussed together. Two advanced protocols that have the capability to determine dynamic interfacial tension—the drop volume technique (see Basic Protocol 2) and the drop shape method (see Alternate Protocol 3)—will also be presented. The basic principles of each of these techniques will be briefly outlined in the Background Information. Critical Parameters as well as Time Considerations for the different tests will be discussed. References and Internet Resources are listed to provide a more in-depth understanding of each of these techniques and allow the reader to contact commercial vendors to obtain information about costs and availability of surface science instrumentation. 

The Wilhelmy plate and du Noiiy ring methods provide a single value for surface tension of a given surfactant at a given concentration. Examples are provided in unitd3.5 (see Figure D3.5.5). Examples of dynamic surface tension values are also provided in unitd3.5. 

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. 

It is very well known that the nature of the monolayer partially depends on the strength of interfacial interactions with substrate molecules and that of polymer in-tersegmental interactions. And it is normal to expect that the viscoelastic properties of polymer monolayer are also dependent on these factors. The static and dynamic properties of several different polymer monolayers at the air - water interface have been examined with the surface quasi-elastic Light Scattering technique combined with the static Wilhelmy plate method [101]. 

A number of methods are available for the measurement of surface and interfacial tension of liquid systems. Surface tension of liquids is determined by static and dynamic surface tension methods. Static surface tension characterises the surface tension of the liquid in equilibrium and the commonly used measurement methods are Du Notiy ring, Wilhelmy plate, spinning drop and pendant drop. Dynamic surface tension determines the surface tension as a function of time and the bubble pressure method is the most common method used for its determination. 

For measurement of interfacial tension see also -> Wilhelmy plate (slide) method, -> drop weight method, -> ring method. There are also a number of other static and dynamic methods for the determination the interfacial tension [viii]. 

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. 

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