INTERFACIAL-TENSION BETWEEN WATER AND NONPOLAR FLUIDS UP TO 473-K AND2800-BAR

The method of the Pendant Drop or Standing Bubble is applied to measur e interfacial tensions between water and nonpolar fluids to high tempe ratures and pressures. The high pressure cell with two sapphire window s and the auxiliary equipment with several feed autoclaves is describe d. The shapes and sizes (about 2 mm) of drops and bubbles are recorded with microscope and video camera. A digital image processing procedur e was developed which permits fast, objective and precise determinatio n of the contour parameters. The six gases helium, neon, argon, nitrog en, methane, and propane have been investigated to 473 K (with nitroge n to 573 K) and (in part) to 2800 bar. Gas densities came close to liq uid density values. For comparison, water plus liquid n-hexane, n-deca ne, and toluene was investigated to 473 K and 3000 bar. For these liqu id hydrocarbons, the interfacial tension gamma always increases with p ressure. At 373 K for water-n-hexane gamma is 41.8 mN/m at 100 bar and 47.3 mN/m at 2600 bar, respectively. In the water-gas systems gamma d ecreases with pressure and passes through a flat minimum around 1000 b ar. For water-nitrogen at 373 K gamma = 52.5, 46.5 and 48.3 mN/m at 20 0, 1400 and 2800 bar. Only with water-helium gamma increases continuou sly with pressure.