Highly accurate liquid–liquid interfacial tension measurement by a convenient capillary apparatus

• Homemade capillary apparatus is presented for accurate liquid–liquid interfacial measurement.
• The method features integration of two coexisting capillary actions.
• Oil–water interfacial tension is measured accurately in the range of 298–333 K.
• Each liquid–liquid system can have a characteristic capillary constant with supporting theory.
• Direct measurement provides capillary constant free from mutual solubility of liquids.

A very useful capillary apparatus is pioneered for the experimental measurement of liquid–liquid interfacial tension of two immiscible liquids, with highly accurate results. The method features integration of two coexisting capillary actions. The results of measurement for alkanes–water, heptanol–water and hexanoic acid–water systems (in the range of 298–333 K) demonstrate that this method of liquid–liquid interfacial tension measurement is highly accurate, as known to be the case for liquid–vapor system. The coexisting capillarity actions involving liquid–liquid system is studied by the capillary constant, and importantly is practiced to be the augmentation of the two neat liquid capillary constants less a length scale proportional to the extent of effective dispersion interaction at the liquid–liquid interface.

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