Droplet Collision, Coalescence, Mixing, and Reaction on the Textured Surface with Wettability Gradient
Date Issued
2014
Date
2014
Author(s)
Yeh, Szu-I
Abstract
Digital microfluidics attracts much attention for its prospective applications to revolutionize biological laboratory procedures by allowing efficient assays with great versatility, small sample consumption and short detection duration. Droplets collision, colalescence and mixing behavior with different viscosities and surface tensions are the basic and important research in the development process of digital microfluidics. The aim of this study is to buildup the performance of bio-chemical detection device using droplet-based microfluidics. We manipulated the droplet on the self-assambled textured surface and investigated the different droplet coalescence profile, internal flow field inside the coalesced droplet, and mixing behavior inside the coalesced droplet caused by different characteristic (viscosity and surface tension) of fluids. We also investigated the difference of fluid mixing and reaction inside the droplet, and we show a simple and maneuverable method of digital microfluidics to modulate a biochemical reaction with a ternary droplet collision using a simple chemical reaction and DNA fluorescence resonance-energy transfer (FRET) test. We utilized micro-PIV and confocal microscopy to measure the coalescence process, internal flows, and mixing patterns of droplets with different viscosities and surface tensions after a head-on collision between a moving droplet and a stationary droplet on a wettability gradient surface. The results indicate that the mixing is driven sequentially by interior convection and diffusion once the two droplets touch each other; the convection endures less than 100 ms but dominates more than 60 % of the mixing. For the collision of droplets of identical surface tension, the surface tension affects the coalescence behavior; for the collision of droplets with distinct surface tension, the coalescence behavior and mixing quality depend on the colliding arrangement of stationary and moving droplets. We also used a high-speed camera to observe the color changing reaction inside a coalesced droplet. Compare to the traditional dye-mixing test, the chemical reaction inside the coalesced droplet facilitated the mixing of two counter-reactive fluids and was more than hundred times as efficient as the unreactive fluids mixing inside the coalesced droplet. Instead of mixing, chemical reaction inside a coalesced droplet is worth attention to the applications of digital microfluidic open-system. In droplet coalescence process, the characteristic of fluids and the ratio of volumes of two droplets caused different droplet coalescence profile especially the necking-curvature which affects the shape of the material interface between the two droplets in an initial phase. Capsules are used to protect, control and deliver drugs to the specific tissue. In recent year, multilayer microcapsules and nanocapsules are under review as multifunctional delivery systems. In this study, we also show a simple and maneuverable method to modulate the bio-chemical reaction for digital microfluidics on the surface by ternary droplet collision. The coalescence behavior and mixing quality are significantly concerned with the arrangement and configuration of different droplets on a droplet-based microfluidic system. This work significantly contributes to the understanding of droplet mixing and reaction in droplet-based microfluidic systems. Instead of mass transfer and mixing, chemical reaction inside a coalesced droplet is worth attention for digital microfluidic open-system. This work illustrates a correlation between the growth and evolution of chemical reaction and the profile (necking-curvature) of a coalesced droplet, which is also a significant reference in droplet-based microfluidic systems for biochemical use. Furthermore, the moduration of initial time and initial point of reaction inside the coalesced droplet is greater development potential on bio-chimical detection and cell-drug interaction test specifically.
Subjects
Droplet collision
Droplet coalescence
Chemical reaction
Reaction control
Type
thesis
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