Numerical Simulation and Experimental Validation of Liquid Metal Droplet Formation in a Co-Flowing Capillary Microfluidic Device

Abstract

A two-phase flow axisymmetric numerical model was proposed to understand liquid metal droplet formation in a co-flowing capillary microfluidics device based on a phase field model. The droplet detachment processes were observed in the experiment and are in good agreement with the simulation method. The effects of the viscosities and flowrates of the continuous phase fluid, interfacial tension as well as the wetting property of the metallic needle against the bulk liquid metal on the droplet formation and production rate were numerically investigated. It was found that the droplet diameter decreased with the increment of the viscosities and flowrates of the outer phase carrier fluid. The dispersed phase fluid with high interfacial tension tended to prolong the time for equilibrium between the viscous drag force and interfacial tension on the liquid–liquid fluid surface, delaying the droplet to be pinched off from the capillary orifice and causing large droplet diameter. Finally, the wetting performance of the metallic needle against the liquid metal was explored. The result indicate that the droplet diameter became less dependent on the contact angle while the size distribution of the liquid metal droplet was affected by their wetting performance. A more hydrophilic wetting performance were expected to prepare liquid metal droplet with more monodispersity. The numerical model and simulation results provide the feasibility of predicting the droplet formation with a high surface tension in a glass capillary microfluidic device.

A Review of Microfluidic Experimental Designs for Nanoparticle Synthesis

“…Hu et al [ 59 ] have performed a numerical investigation on a co-flowing capillary device with a micro-needle in the inlet capillary ( Figure 10 ). The microfluidic device was fabricated by assembling two tapered glass capillaries inside a square channel, concentrically aligned, with an axial spacing of 100 μm.…”

“…In this respect, numerous studies have focused on fabricating microfluidic devices, performing numerical simulations, analyzing fluid movement, and testing the developed microchips in experimental syntheses. Researchers worldwide managed to exploit the advantages of microfluidic technology for generating microdroplets [ 44 , 53 , 59 , 72 , 80 , 85 , 86 , 87 , 88 ], porous films [ 45 ], double emulsion droplets [ 55 ], nanofibers [ 69 ], microcapsules [ 82 , 83 ], and micro- [ 32 , 56 , 57 , 58 , 70 , 77 , 82 ] and nanoparticles of various compositions, sizes, shapes and morphologies [ 6 , 42 , 50 , 52 , 54 , 60 , 61 , 65 , 66 , 68 , 74 , 76 , 78 , 84 ].…”

“… Schematic representation of the micro-needle induced co-flowing microfluidic experimental setup. Reprinted from an open-access source [ 59 ]. …”

Microchannel-based Droplet Generation Using Multiphase Flow: A Review

“…Haeberle and Zengerle said that fundamental ideas in the microfluidic device come from the dominant interfacial and surface tensional force in the micro-dimension which enables the precise generation and spatial stabilization of the droplets [3]. Furthermore, microfluidic is widely applied to the following fields: drug delivery [4,5], cell sorting [6][7][8], filtering [9], fluid transport [10], material science [11], chemical engineering [12][13][14], cosmetics production [15], food technology [16], digital polymerase chain reaction (ddPCR) procedure [17], liposomes production [18], liquid metal microdroplets for advance electronics [19], and lab on a chip [3,20]. Zhuo et al have been successful in preparing magnetic thermosensitive hydrogels using microfluidic technology for drug delivery using double emulsions structure with the use of two anticancer drugs: water-soluble drug as the shell and oil-soluble drug in the core which can be released simultaneously by controlling the switch of the magnetic field [4].…”

Editorial for the Special Issue on Droplet Microfluidics

“…For instance, Jianhua Guo et al [5] harness osmotic pressure to precisely tune the thickness of the ultrathin shell of microparticles manufactured at high throughput. Employing unusual fluids, Qingming Hu et al [6] demonstrate the generation of liquid metal droplets numerically and experimentally. These two papers exemplify the ability to use droplet microfluidics to create new materials with novel properties and applications in very diverse fields.…”