Microfluidic Tensiometry Technique for the Characterization of the Interfacial Tension between Immiscible Liquids

Abstract

The interfacial tension between two immiscible fluids is of critical importance for understanding many natural phenomena as well as in industrial production processes; however, it can be challenging to measure this parameter with high accuracy. Most commonly used techniques have significant shortcomings because of their reliance on other data such as density or viscosity. To overcome these issues, we devise a technique that works with very small sample quantities and does not require any data about either fluid, based on micropipette aspiration techniques. The method facilitates the generation of a droplet of one fluid inside of the other, followed by immediate in situ aspiration of the droplet into a constricted channel. A modified Young–Laplace equation is then used to relate the pressure needed to produce a given deformation of the droplet’s radius to the interfacial tension. We demonstrate this technique on different systems with interfacial tensions ranging from sub-millinewton per meter to several hundred millinewton per meter, thus over 4 orders of magnitude, obtaining precise results in agreement with the literature solely from experimental observations of the droplet deformation.

Comparison of surfactant mass transfer with drop formation times from dynamic interfacial tension measurements in microchannels

“…The effects of surfactant concentrations and flowrates of the two phases on drop size and drop formation time were investigated, using high speed imaging. These results were used to determine the DIT at short time scales (3 ms) that cannot be reached with commercial instruments or found in previous literature [6,18,19,21,24].…”

“…DIT has been investigated mainly in T-junction microchannels [18,23] and co-flow microfluidic devices [24,25]. Flow focusing microfluidic devices are commonly used to produce droplets and exist in two configurations: hydrodynamic flow-focusing, where two liquid streams of the continuous phase surround the dispersed phase stream and break it to drops at the inlet [22,26] and geometrical focusing where the breakup of the dispersed phase happens at an orifice of size smaller than the main microchannel width [27,28].…”

Influence of head group and chain length of surfactants used for stabilising liquid crystal shells

“…The result is that the interfacial tension between the LC and the surrounding aqueous phases should be too high, rendering shell production impossible. We plan to corroborate this conjecture in a future study, using a recently devised technique for measuring interfacial tension that lends itself very well to the case of water-LC interfaces [31].…”

Interfacial Tension Measurements in Microfluidic Quasi-Static Extensional Flows

“…More importantly, the small length scales of microfluidic flows enable fast response and enhanced throughput for IFT measurements, which offers a new venue for the development of “lab-on-a-chip-tensiometer” [ 14 , 19 ]. IFTs in microfluidic platforms can be calculated by either balancing interfacial tension and drag force acting on droplets [ 16 , 20 , 21 , 22 ], or detecting pressure drop and contact angle between two immiscible liquid streams in a tapered microchannel [ 14 , 18 , 23 ]. Of these two approaches, the force balance based droplet deformation method normally gives more accurate and reproducible results than the pressure drop method.…”