Analysis of collision and mixing of droplets on the textured surface by confocal microscopy and micro-PIV

This study investigates the phenomenon of head-on collisions between a moving droplet and stagnation droplet by self-assembled monolayer method. At this research, we utilized experiment analysis to observe the characteristics of flow field during the transport and mixing process by varying the property of viscosity and surface tension. The coalescence dynamic are visualized by a high-speed camera; while the internal flow patterns are resolved by micro-PIV and micro-LIF.
Surface energy transformed to kinematic energy before the coalescence between two droplets, remnant energy will cause oscillation on the contour. According to Webber number, Collision parameter, and Peclect number we found that the behavior of collision mode is permanent coalescence and convective intensity is proportional to velocity field. By scaling law, we know that convection is not the main dominate parameter but diffusion while mixing. For quantify the mixing mechanisms, we used fluorescent dye to define the mixing index that provided the mixing behavior within a droplet after collision.
The contribution of this study is the application of textured surface and provided more data of biochemical fluid. Most important of all, we established a way to visualize into the droplet.