(400d) Geometry, Surfactant and Droplet Crystal Content Control Partial Coalescence

Destabilization due to coalescence of partially crystalline emulsion droplets during phase transition dramatically impacts the emulsion thermal and flow properties. In our recent work [Abedi, et al., Journal of Colloid and Interface Science 533, 2019, 59-70], we visualized the destabilization of disordered monodisperse 2D emulsions and found that small- and large-scale structures form through spontaneous coalescence events and coalescence propagation, respectively. Formation of these structures was controlled by contact and orientation of droplets. However, understanding the factors that initiate the coalescence of quiescent drops relies on two hypothetical mechanisms: 1- penetration of interfacial crystals which bridge the droplets and start the coalescence, and 2- local depletion of surfactant. In this work, we test these mechanisms by visualizing coalescence of a combination of liquid and partially crystalline droplets, coalescence of droplets with varied crystal content and droplets stabilized with different surfactants. We also investigate the geometric aspects of coalescence by arranging droplets in disordered and ordered 2D, and 1D configurations. Our experimental results not only demonstrate the collective behaviors of droplets during partial coalescence but also provide insights into understanding the mechanism of coalescence initiation.