Wilhelmy plate procedure

Interfaciai Tension Procedure. IFT measurements were made by the Wilhelmy plate method. The apparatus was the same as that described previously (2). A standard protocol was followed for all IFT determinations. The desired interface was formed at a specified temperature by partially filling a thermostatted sample holder with the desired aqueous phase. This phase, distilled water (mono triple) or a supernatant aqueous phase isolated from a complex coacervate system, completely covered the Wilhelmy plate (roughened platinum). The desired citrus oil was carefully layered onto the aqueous phase. It had been preheated (or cooled) to the same temperature as the aqueous phase. Once the citrus oil/aqueous phase interface was formed, the Wilhelmy plate was drawn completely through the interface and into the oil phase where it was zeroed. 

Apparatus and Procedure. Surface Isotherms. The technique for determining the n-A and AV-A curves of the lipid films has been described (6). Briefly, the Wilhelmy plate method was used to measure surface tension, from which the surface pressure was calculated (n = 7h2o—yfiim) The surface potential was measured by means of a radioactive (226Ra) air electrode and a saturated calomel electrode connected to a high impedance model 610 B Keithley electrometer (Keithley Instruments, Cleveland, Ohio). 

The initial concentration (0.001 wt% active) was selected from the measurement of surface and interfacial tensions. It lies in the range of CMC value for these measurements, which were performed by using the Wilhelmy plate method in a Rosano surface tensiometer. The standard procedure described in the manual was carefully followed. Surface tension was measured against the air, whereas the interfacial tension was measured against isooctane, which was used to simulate dense CO2. It is well known fact that good foamers are most effective well above the CMC range and in subsequent tests the concentrations were increased well above that range. 

The Wilhelmy plate method procedurally is identical to the du Noiiy method described earlier. Because an infinitely long plate has the same plane of symmetry as the suspended liquid, a correction factor is not necessary. The equation to measure the sinface tension is trivial and becomes... 

Finally, measuring the forces involved is another way to determine surface tensions. The procedure here consists of bringing into contact a liquid and an object with a well-defined geometry (often a plate or a fiber Figure 2.24). The objective is to measure the capillary force exerted on the object (Wilhelmy s method). As we have seen in equation (2.35), this force can be written as... 

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