2018/03/20 by Somnath Santra, Sayan Das, Santra, Somnath +5
Engineering · Materials Science · #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Fluid Dynamics and Thin Films #Innovative Microfluidic and Catalytic Techniques Innovation #Surface Modification and Superhydrophobicity
paper · pdf · doi:10.48550/arxiv.1803.07607
openalex publication_date 2018/03/20 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
In the present study, the role of surfactants on the cross-stream migration\nof droplets is investigated both experimentally and theoretically. For\nexperimental analysis, sunflower oil is used as the carrier phase and DI water\nas the dispersed phase which is intermixed with Triton X-100 that acts as the\nsurfactant. A T-junction is used in the microchannel for the purpose of droplet\ngeneration. Presence of an imposed pressure driven flow induces droplet\ndeformation and disturbs the equilibrium that results in subsequent\nsurfactant-redistribution along the interface. This further induces a gradient\nin the surface tension, thus generating a Marangoni stress that significantly\nalters the droplet dynamics. On subsequent experimental investigation, it is\nfound that presence of surfactants reduces the cross-stream migration velocity\nof the droplet. Further, it is shown that the effect of surfactants in reducing\nthe cross-stream migration is significantly enhanced for a larger droplet as\ncompared to a smaller one within the same time span, provided the channel\nheight is kept constant. In addition, a larger surfactant concentration is\nfound to induce a greater retardation in cross-stream migration of the droplet,\nthe effect of which is reduced when the initial transverse position of the\ndroplet is shifted closer to the channel centerline. The present analysis can\nbe applied to various droplet based microfluidic as well as medical diagnostic\ndevices where manipulation of droplet trajectory is a major issue. For the\ntheoretical counterpart, an asymptotic approach is adopted in the presence of\nbulk-insoluble surfactants and under the assumption of negligible fluid\ninertia. A good match between our theoretical prediction and the experimental\nresults is obtained.\n