Magnetofluidic-based controlled droplet breakup: effect of non-uniform force field

Abstract

We report the breakup dynamics of a magnetically active (ferrofluid) droplet in a T-shaped Lab on a Chip (LOC) device under the modulation of a non-uniform magnetic field. We adhere to high-speed imaging modalities for the experimental quantification of the droplet splitting phenomenon, while the underlying phenomenon is supported by the numerical results in a qualitative manner as well. On reaching the T-junction divergence, the droplet engulfs the intersection fully and eventually deforms into the dumbbell-shaped form, making its bulges move towards the branches of the junction. We observe that the asymmetric distribution of the magnetic force lines, acting over the T-junction divergence, induces an accelerating motion to the left of the moving bulge (since the magnet is placed adjacent to the left branch). We show that the non-uniform force field gradient allows the formation of a hump-like structure inside the left moving bulge, which triggers the onset of augmented convection in its flow field. We reveal that this augmented internal convection developed in the left moving volume/bulge, on becoming coupled to the various involved time scales of the flow field, leads to the asymmetric splitting of the droplet into two sister droplets. Our analysis establishes that, at the critical strength of the applied forcing, as realized by the critical magnetic Bond number, the flow time scale becomes minimum at the left branch of the channel, leading to the formation of larger sized sister droplets therein. Inferences of the present analysis, which demonstrates a plausible means of independently controlling the size of the sister droplet by manoeuvring the applied force field gradient, will provide a potential solution for rapid droplet splitting, which typically finds significant importance in point-of-care diagnostics.

A Novel Step-T-Junction Microchannel for the Cell Encapsulation in Monodisperse Alginate-Gelatin Microspheres of Varying Mechanical Properties at High Throughput

“…Different approaches have been reported over past years to solve such an issue. For instance, by applying a non-uniform magnetic field onto the ferrofluid inside a T-shaped microchannel, one can accurately tune the applied force filed gradient and control the rapid microdroplet breakup [ 68 ]. Here, with the use of the novel step-T-junction microchannel with embedded microcapillary that concentrates the shearing force at the special narrowing zone, monodisperse alginate–gelatin whose size overcomes the dimensional limitation of the microchannel itself could be generated at a high throughput jetting regime while maintaining a CV below 5%, i.e., limit of monodispersity, as shown in Figure 5 A [ 60 , 69 , 70 , 71 ].…”

Coalescence of immiscible sessile droplets on a partial wetting surface

“…We expect that the results and insights derived here could be helpful to applications involving microdroplet manipulation, droplet-based biochemical reactions and liquid removal. To realize better control of droplets in practical applications, external forces can also be adopted, such as magnetic fields (Li et al 2020;Shyam, Dhapola & Mondal 2022) and electric fields (Anand et al 2019), which require further study in this area.…”

“…To realize better control of droplets in practical applications, external forces can also be adopted, such as magnetic fields (Li et al. 2020; Shyam, Dhapola & Mondal 2022) and electric fields (Anand et al. 2019), which require further study in this area.…”

Magnetic regulation on evaporation behavior of ferrofluid sessile droplets

“…Ferrofluid is the most commonly used magnetic fluid, which presents a general fluid state in normal conditions but has superparamagnetic characteristics under a magnetic field. Based on the physical properties, various operations, such as droplet generation [26], deformation [27], mixing [28], separation [29], actuation [30], and heat transfer augmentation [31], are tunable by an external magnetic field with numerous applications, including optics [32], biomedicine [33], magnetic brake [34], and biosensor [35]. The existing work is devoted to the evaporation of sessile droplets with ferrofluid synthesized by the coprecipitation method and the addition of surfactants [36][37][38][39].…”