Generation of an O/W emulsion in a flow-focusing microchip: Importance of wetting conditions and of dynamic interfacial tension

Abstract

To date, there is no information on the microfluidic emulsification of dibutyl adipate and n-butyl acetate in water. Since these solvents are very suitable for microencapsulation by interfacial polymerization, it is highly necessary to study the emulsification behavior of these solvents in microchannel. This work shows that the microfluidic emulsification of these solvents in water may fail to obtain stabilized flow regimes. This is due to droplet coalescence and wall wetting, even if a hydrophilic microchip is used. Hydrodynamic results show that squeezing and dripping regimes are especially affected because of the wall wetting by the dispersed phase. This difficulty can be circumvented by adding a surfactant (here Tween 80) into the aqueous phase. However, high surfactant concentrations (ten times the critical micelle concentration) should be used for the water-dibutyl adipate system. Indeed, comparison of flow maps for several surfactant concentrations seems to indicate that the dynamic interfacial tension is higher than the one expected (equilibrium), for surfactant concentrations lower than one hundred times the critical micelle concentration. The estimated diffusion time of Tween 80 is compared to the droplet formation time at different conditions. The choice of more appropriate dimensionless numbers to represent flow maps is also discussed.

Effect of surfactants on drop formation flow patterns in a flow-focusing microchannel

“…The surfactant concentration at the interface may not reach equilibrium values during the drop formation, because the formation times are faster than the time required for the surfactant to transfer and absorb to the interface (Du et al, 2020). Dynamic interfacial tension values should then be used instead of the equilibrium ones in the dimensionless numbers that are used to describe the flow patterns.…”

“…Anna and Mayer (2006) observed in a geometrically flow-focusing microchannel that the addition of C12E8 surfactant in the aqueous phase could affect the formation of fine threads only at concentrations above the CMC. A recent work discussed the importance of using appropriate dimensionless numbers when plotting flow pattern maps in systems with surfactants and specifically the dynamic interfacial tension; the use of (𝐶𝑎 + 𝑊𝑒) of the dispersed phase and 𝐶𝑎 of the continuous phase were recommended as map coordinates for concentrations above CMC (Du et al, 2020). Dinh et al (2021) used the pendant drop method to measure the dynamic interfacial tension of slow adsorbing surfactants including Tween 20 and Span 80, which take about 2 mins to equilibrate.…”

Interfacial Polymerization Kinetics of Polyurea Microcapsules Formed Using Hexamethylene Diisocyanate Biuret Low Viscosity Isocyanate

“…Interfacial polymerization (IP) is a technique for encapsulation of active compounds with a large scope of applications [1,2], notably for containment or controlled release in the cosmetic [3] and soil management industries [4,5], but also for thin-film composite membranes [6]. Polyurea microcapsules are amongst the most studied today because of their high molecular weight [7] and controlable size for a wide range of release properties [8][9][10].…”

Numerical study on active droplet generation governed by pulsatile continuous‐phase flow

“…The passive method does not involve any external devices, and the droplets are generated through the squeezing, dripping, or jetting mechanisms 9–11 . However, the droplet formation is influenced by various parameters including the channel geometry, flow rate, fluid viscosity, interfacial tension, etc 8,12–17 . The droplet size and generation frequency also correlate to each other and cannot be controlled independently.…”

“…[9][10][11] However, the droplet formation is influenced by various parameters including the channel geometry, flow rate, fluid viscosity, interfacial tension, etc. 8,[12][13][14][15][16][17] The droplet size and generation frequency also correlate to each other and cannot be controlled independently. This limits the application of droplet microfluidics, especially in the cases where multiple droplets of different sizes and properties need to be simultaneously handled.…”