Surface tension method sessile drop technique

Variations in chemical composition and molecular structure can also have important repercussions on the surface energy of the material. Several techniques have been proposed for the experimental determination of surface tension, the sessile and pendant drop methods being the most promising and commonly used... 

Two methods can be used for the assessment of y and its components contact angle measurements and inverse gas chromatography (IGC) [31]. Chibowski and Perea-Carpio [32] reviewed the problems encountered when attempting to determine the surface free energy of powered solids, like silica particles, using the contact angle technique. Wu reviewed the different techniques that can be employed to measure the surface tension of polymer melts [30]. These techniques are based on the pendant and sessile drop techniques that require density data or contact angle measurements. 

The most commonly used method for the determination of surface tension of polymers is the sessile drop technique. A droplet of a purified hquid is placed on a surface using a syringe. The angle formed by adding hquid to the... 

The purpose of this chapter is to present the LAD performance experiments carried out in room temperature liquids. Bubble point and reseal pressure tests for a 325x2300, 450 X 2750, and 510 x 3600 Dutch Twill screen are conducted in storable liquids, methanol, acetone, IPA, water, and binary methanol/water mixtures of various methanol concentrations. First screen pore diameters are estimated based on analysis from scanning electron microscopy and historical data. Experimental results are used to compare methods for determining effective pore diameter. Next, contact angles are measured for both pure and binary mixture fluids using a modified version of the Sessile Drop technique. Then, the equation of state analysis from Neumann and Good (1979) is used to determine the critical Zisman surface tension for stainless steel LAD screens, which... 

Contact angles on "Mylar" films were measured using the sessile drop technique H. Surface tensions were measured by the null-buoyancy Wilhelmy plate method using a roughened glass plate showing zero contact angle to water. The plate was supported from an electronic microbalance and the values are quoted to 0.1 mNm l. 

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. 

Important techniques to measure the surface tension of liquids are the sessile drop method, the pendant or sessile bubble method, the Du-Notiy ring tensiometer, and the Wilhelmy-plate method. 

The wetting balance technique is a variant of the maximum pull (or detachment) method used to measure liquid-vapour surface tensions (Keene 1993). It is nowadays widely employed in the electronics industry to quantify wetting of solders, but has also been used for wetting studies in metal/ceramic systems (Naidich and Chuvashov 1983b, Nakae et al. 1989, Rivollet et al. 1990). As compared to the sessile drop method which needs planar substrates, solids of various geometry can be studied by this technique. 

Table 1.2. Surface tensions of water in mN m , obtained by various investigations using different techniques. Temperatures in degrees Celsius. Abbreviations for methods CR = capillary rise, WP = Wilhelmy plate, DNR = Du Nouy ring, DM = other detachment method or object in the surface. HD = hanging (pendent) drop, SD = sessile drop, MBP = maximum bubble pressure DW = drop weight.

Perhaps the most striking property of a microemulsion in equilibrium with an excess phase is the very low interfacial tension between the macroscopic phases. In the case where the microemulsion coexists simultaneously with a water-rich and an oil-rich excess phase, the interfacial tension between the latter two phases becomes ultra-low [70,71 ]. This striking phenomenon is related to the formation and properties of the amphiphilic film within the microemulsion. Within this internal amphiphilic film the surfactant molecules optimise the area occupied until lateral interaction and screening of the direct water-oil contact is minimised [2, 42, 72]. Needless to say that low interfacial tensions play a major role in the use of micro emulsions in technical applications [73] as, e.g. in enhanced oil recovery (see Section 10.2 in Chapter 10) and washing processes (see Section 10.3 in Chapter 10). Suitable methods to measure interfacial tensions as low as 10 3 mN m 1 are the sessile or pendent drop technique [74]. Ultra-low interfacial tensions (as low as 10 r> mN m-1) can be determined with the surface light scattering [75] and the spinning drop technique [76]. 

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. 

Sessile Drop Method A method for determining surface or interfacial tension based on measuring the shape of a droplet at rest on the surface of a solid substrate (in liquid—liquid systems, the droplet may alternatively rest upside down, that is underneath a solid substrate). This technique may also be used to determine the contact angle and contact diameter of the droplet against the solid. 

Pendant or Sessile Drop Method The surface tension can be easily measured by analyzing the shape of a drop. This is often done by optical means. Assuming that the drop is axially symmetric and in equilibrium (no viscous and inertial effects), the only effective forces are gravity and surface or interfacial forces. In this case, the Young-Laplace equation relates the shape of the droplet to the pressure jump across the interface. Surface tension is, then, measured by fitting the drop shape to the Young-Laplace equation. Either a pendant or a sessile drop can be used for surface tension measurement. The pendant drop approach is often more accurate than the sessile drop approach since it is easier to satisfy the axisymmetric assumption. Similar techniques can be used for measuring surface tension in a bubble. 

There are many methods available for the measurement of surface and interfacial tensions. Details of these experimental techniques and their limitations are available in several good reviews [101-104]. Table 5 shows some of the methods that are used in petroleum recovery process research. A particular requirement of reservoir oil recovery process research is that measurements be made under actual reservoir conditions of temperature and pressure. The pendant and sessile drop methods are the most commonly nsed where high temperatur pressure conditions are required. Examples are discussed by McCaffery [i05] and DePhUippis et al. [J06]. These standard techniques can be difficult to apply to the measurement of extremely low interfacial tensions (< 1 to 10 mN/m). For ultra-low tensions two approaches are being used. For moderate temperatures and low pressures the most common method is that of the spinning drop, especially for microemulsion research [107], For elevated temperatures and pressures a captive drop method has been developed by Schramm et al. [JOS], which can measure tensions as low as 0.001 mN/m at up to 200 °C and 10,000 psi. In aU surface and interfacial tension work it should be appreciated that when solutions, rather than pure liquids, are involved appreciable changes can occur with time at the surfaces and interfaces, so that techniques capable of dynamic measurements tend to be the most useful. 

A new method for the measurement of surface and interfacial tension has been developed based on a video digitising technique to measure the drop profQe of pendant and sessile drops [19]. The method gives a standard deviation of 0.5%, so the resolution, at present, is less than the maximum bubble pressure technique. It is an extremely useful technique for studying the liquid-liquid interface, and electrocapillary curves of similar shape to those obtained on mercury have been obtained for the water-nitrobenzene interface. 

The surface tension measurement techniques can be divided into the following three categories (i) Force Methods, which include the truly static methods of the capillary rise and Wilhelmy plate methods, as well as the dynamic detachment methods of the Du Nouy ring and drop weight, (ii) Shape Methods, which include the pendant or sessile drop or bubble, as well as the spinning drop methods, and (iii) Pressure Methods, which are represented by the maximum bubble pressure method. These techniques are summarized in the following sections of this chapter. 

Determinations by Roe [154] and Wu [127, 152, 153] using the pendant drop method and by Hata and coworkers [128, 175] using the sessile bubble technique have yielded values for a number of polymer pairs as a function of temperature. Gaines [ 174] and Wu [ 10,120,176] provided extensive reviews of the early work in the area of surface and interfacial tension of polymer liquids and melts. 

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