Recently, Associate Professor Jinggang Zhang from the School of Building Services Science and Engineering has made a landmark breakthrough in the field of fluid mechanics. His research findings, titled “Modelling surfactant effects on the onset of spontaneous droplet breakup in both regular and irregular T-junction microchannels”, have been published in the Journal of Fluid Mechanics. Hailed as a top-tier journal in fluid mechanics, published by Cambridge University Press, with a 2024 Journal Citation Reports (JCR) impact factor of 3.9. The paper’s first and corresponding author is Jinggang Zhang. The co-corresponding author is Professor Haihu Liu from Xi'an Jiaotong University, and co-authors include Dr. Dong Wang from the City University of Hong Kong, as well as Associate Professors Haihang Cui and Li Chen from our university. Xi’an University of Architecture and Technology (XAUAT) is the first affiliated institution for this paper. This marks another publication in this top-tier journal with XAUAT as the first affiliated institution. Previously, Associate Professor Jinggang Zhang published a related paper in the same journal as the corresponding author in 2024. This latest achievement further demonstrates his long-standing academic dedication and growing influence in this field. These studies were supported by the National Natural Science Foundation of China. 

Microdroplets are typically generated through passive breakup when larger droplets flow through T-junction microchannels. Existing studies have shown that the neck contraction of clean droplets undergoes a transition from inertia-dominated to interfacial tension-dominated regimes, yet the triggering mechanism of this transition remains controversial. Furthermore, the influence of surfactants on this transition is not yet fully understood. Therefore, a systematic investigation of the breakup behavior of clean and surfactant-laden droplets in T-junction microchannels is critical for optimizing the droplet breakup process and advancing the development of droplet microfluidic devices.

At present, there are two main criteria for determining the critical neck thickness for spontaneous droplet breakup: (i) the neck curvature exceeding that of all other interfacial regions, and (ii) the capillary pressure at the neck center equilibrating with the internal pressure of the neck. However, the underlying correlation between these two criteria requires further systematic investigation. While surfactants are known to affect droplet generation and breakup, the mechanism by which they influence the critical neck thickness remains poorly understand. To fill the aforementioned research gaps, this paper conducted a numerical simulation study on the flow of clean and surfactant-laden droplets in both regular (Figure2) and irregular T-junctions (Figure 1). For regular T-junctions, the critical droplet morphologies under different confinement ratios were first determined through stop-flow simulations (Figure 2). On this basis, a new criterion for determining the critical neck thickness is proposed: spontaneous neck breakup occurs when the local capillary pressure in the triggering zone exceeds the Laplace pressure difference. A direct comparison and validation against existing criteria were also performed.

Paper Link:

//www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/abs/modelling-surfactant-effects-on-the-onset-of-spontaneous-droplet-breakup-in-both-regular-and-irregular-tjunction-microchannels/7DF85945024029BB3DE94886177AF068