Dwivedi Prateek, Ashraf Sobiya, Kumar Pawan, Pillai Dipin, Mangal Rahul
Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur, India.
J Chem Phys. 2025 Jul 7;163(1). doi: 10.1063/5.0262693.
Active droplets serve as simple artificial model systems to elucidate the chemical and hydrodynamics-driven interactions between biological organisms. We investigate the pairwise interactions between such micellar solubilization based active droplets, capable of self-generating chemical and hydrodynamic fields. We experimentally demonstrate that the solute Péclet number (Pe), characterizing the relative strength of its convective to diffusive transport, plays a crucial role in determining how the chemical and hydrodynamic fields impact their interactions. At low Pe, strong chemo-repulsive interactions dominate, resulting in consistent scattering behavior regardless of the approach symmetry. In contrast, at high Pe, hydrodynamic interactions become dominant, enabling transient contact, synchronized motion, or reduced repulsion. Furthermore, by analyzing droplet-wake interactions across both high and low Pe regimes, we demonstrate that the scattering behavior is invariant to the relative approach orientation and is fundamentally governed by the droplet's intrinsic chemical polarity, which in turn is set by its Pe number. Our results not only offer robust experimental validation of recent theoretical predictions on the scattering behavior of active droplets but also present a clear rationale for the observed angular deflection and its invariance to the approach angle of droplets. Our findings establish a systematic framework correlating the Pe-dependent intrinsic chemical polarity of droplets to the scattering outcomes in both droplet-droplet and droplet-wake interactions. These mechanistic insights advance our understanding of active droplet interactions and can serve as a basis for modeling and engineering collective behaviors in chemically active systems within the framework of multi-agent interactions, where simple local interaction rules result in emergent collective dynamics.
活性液滴作为简单的人工模型系统，用于阐明生物有机体之间由化学和流体动力学驱动的相互作用。我们研究了这种基于胶束增溶的活性液滴之间的两两相互作用，这些液滴能够自我产生化学和流体动力学场。我们通过实验证明，溶质佩克莱数（Pe）表征了其对流传输与扩散传输的相对强度，在决定化学和流体动力学场如何影响它们的相互作用方面起着关键作用。在低Pe值时，强烈的化学排斥相互作用占主导，无论接近对称性如何，都会导致一致的散射行为。相反，在高Pe值时，流体动力学相互作用占主导，能够实现瞬时接触、同步运动或减少排斥。此外，通过分析高低Pe值区域内的液滴-尾流相互作用，我们证明散射行为对于相对接近方向是不变的，并且从根本上由液滴的固有化学极性决定，而液滴的固有化学极性又由其Pe数设定。我们的结果不仅为近期关于活性液滴散射行为的理论预测提供了有力的实验验证，还为观察到的角偏转及其对液滴接近角度的不变性提供了清晰的理论依据。我们的发现建立了一个系统框架，将液滴的Pe依赖型固有化学极性与液滴-液滴和液滴-尾流相互作用中的散射结果联系起来。这些机理见解推进了我们对活性液滴相互作用的理解，并可作为在多智能体相互作用框架内对化学活性系统中的集体行为进行建模和工程设计的基础，在该框架中，简单的局部相互作用规则会导致涌现的集体动力学。
