Tandem variable-volume tensiometer

Recently, surfactant adsorption and y have been measured at C02-water and C02-organic interfaces with a tandem variable-volume tensiometer (Harrison, 1996). A pendant drop of an aqueous or organic phase, saturated with C02, may be suspended in C02 or a C02-surfactant mixture and equilibrated. From the digitized droplet shape and density difference between the phases, y may be calculated from the Laplace equation. In Figure 8.1, y of the binary C02-water (da Rocha et al., 1999), -polyethylene... 

The interfacial tension between CO2 and various condensed phases including water [63], styrene oligomers[64] and polyethylene glycol[8] has been measured with a tandem variable-volume tensiometer and modeled with gradient theory. Also surfactants were added to these systems to lower the interfacial tension and to determine the surfactant adsorption. A critical micelle concentration was observed for... 

The adsorption of a surfactant at an interface between CO2 and a second fluid, such as water, may be determined directly from measurement of the interfacial tension (change in Gibbs free energy with surface area), y, versus surfactant concentration. A novel tandem variable-volume pendant drop tensiometer has been developed to measure equilibrium and dynamic values of y as a function ofT.p and time (Figure 2.4-1) [21]. An organic [21] or aqueous phase [18] is preequilibrated with CO2 in the first variable-volume cell (drop-phase cell). A droplet of this liquid is injected into the second variable-volume cell, with two windows at 180° mounted on a diameter, containing either pure CO2 or CO2 and surfactant. 

Figure 2.4-1 Tandem variable-volume view cell tensiometer for measuring the interfacial tension by the pendant drop technique TC = temperature controller PG = pressure gauge.

Harrison and colleagues [40] measured the interfadal tension between SCCO2 and polyethylene glycol (MW 600) using a tandem variable-volume pendent drop tensiometer, as shown schematically in Fig. 10.3. At 45 °C the interfacial tension between the PEG-CO2 rich phase and the SCCO2 phase was reduced from 6.9 dyn cm at 100 bar to 3.08 dyn cm at 300 bar. Experimental observations were accurately predicted using a gradient model which utilized the lattice equation of state. In another piece of work, the effect of surfactants on poly-mer/C02 interfacial tension was addressed [42]. 

Fig. 10.3 Schematic diagram of a tandem variable-volume pendent drop tensiometer. (Reprinted with permission from Langmuir, Vol. 12, K. L. Harrison, K. P. Johnston and I.C. Sanchez, Effects of surfactants on the...

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See also in sourсe #XX -- [ ]

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