Oil-drop method

To appreciate this time-lag, it is useful to recall that the electron was not recognized as an elementary particle until the twentieth century. Electron beams had been known as cathode rays since 1876, but their corpuscular nature was recognized only in 1897 [12]. The term electron was introduced in 1891 to designate the fundamental unit of electricity, namely the electric charge of a hydrogen ion [13]. Only later was it applied to Thompson s corpuscules, and it achieved general acceptance with Millikan s quite accurate determination of the electronic charge by the oil drop method [14,15]. 

Crystals that are oifly moderately unstable can be handled using the oil drop method,which became popular in the last decade. This method is extremely convenient and easy, obviating the need for glove boxes and other comphcated mounting devices. The crystals are prepared in a Schlenk vessel which is connected to an inert gas (N2 or Ar) fine, creating an excess pressure inside. Then it is possible to... 

FIG. 4-9. A diagram of the apparatus used by R. A. Millikan in determining the charge of the electron by the oil-drop method. 

More recently, Pena and Miller investigated solubilzation rates of mixtures of n-decane and squalane into 2.5 wt% solutions of pure C,2Eg at 23°C using the oil drop method described above. They first measured the rate of solubilization of pure decane, confirming that the rate was controlled by interfacial phenomena as in Carroll s work, and demonstrated that pure squalane was not solubilized to any significant extent under these conditions. Next they measured solubilization rates of decane from various mixtures of the two hydrocarbons. Figure 9.7 shows results from one of these experiments together with predictions of a model based on assuming that the rate of decane... 

Selective solubilization can also occur in mixtures of polar and nonpolar oils. Using their oil drop method described previously, Chen et al. measured solubilization rates of mixtures of triolein and oleic acid in solutions of pure nonionic surfactants. As Figure 9.9 shows for a drop initially containing 85/15 triolein/oleic acid by weight injected into 2 wt% Tergitol 15-S-7 at 35°C, they observed that the solubilization process consisted of two stages. In the first stage, the drop radius... 

The second support was shaped in the laboratory through the oil-drop method. The gel was prepared under excess of water (6.65 mol) as described above keeping the same proportions of alumina and silica precursors (0.18 mol of A1(0- C4H9)3 and 0.012 mol of Si(OC2H5)4). After the step at 80 °C, the temperature was kept at 75 °C the soluble starch (0.2 wt-% of total mass. 

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. 

Lewis, as already mentioned, used a solution of sodium glycocholate and determined the adsorption of the salt by a surface of paraffin oil. The interfacial tension solution—paraffin oil this was measured for a number of concentrations by the drop method just discussed, and the [Pg.42]

Figure 4. Variation of y of the systems. A, aqueous phase surfactant + H O oil phase toluene with pendant drop method (24 °C). Concentration of detergent = 20 g/L. NaDOC (4) NaDOC + 8% n-butanol(A) NaDDS ( ) NaDDS + 8% n-butanol (O). B, aqueous phase surfactant + H2O oil phase n-heptane by pendant drop method 25 °c). Key same as for 4A.

These studies, carried out by measuring interfacial tensions, Yq , between aqueous and oil phases, by using the pendant drop method, show that this method is very useful for ternary and quaternary systems. In one system (A), NaDDS + H2O + n-butanol + Toluene... 

Millikan s experiments wich single oil drops, beginning in 1906, provided a method for measuring extremely small charges with precision. He was able to show that the charge on his drops was always ne. with e = 1,60 x 10 19 coulomb (modem value) and n a positive or negative integer. 

For emulsions, the interfacial tension is usually of most interest. Here, the du Noiiy ring, Wilhelmy plate, drop volume, pendant, or sessile drop methods are the most commonly used. The spinning drop or captive drop techniques are applicable to the very low interfacial tensions encountered in the enhanced oil recovery and microemulsion fields. The maximum droplet pressure technique can be used when there is little or no density contrast between the phases, such as in bitumen-water systems at elevated temperature. 

Very finely divided emulsions can be prepared by increasing the temperature of the system, forcing an O/W emulsion to invert to a fine W/O emulsion, then cooling the system, causing re-inversion with the formation of very small dispersed oil drops [214]. This method is termed the PIT method. 

The electrodynamic balance (EDB) is a modern version of the Millikan oil drop apparatus in which a charged particle is levitated in an electric field [20]. By using quadrupole focusing, it is possible to suspend a single particle in a controlled environment virtually indefinitely. The size of a levitated particle can be measured by a variety of methods, the most precise of which uses the information contained in the resonant structure of light... 

When the objective is to prepare an extremely intimate mixture of two or more different oxides, each of them constituted of very small grains or particles, techniques such as spray calcination, oil drop, or freeze drying, the complcxation methods (and generally all methods described in Sections B and C above) and the sol-gel method seem to have the same potential in principle. The... 

---