Droplet generation in microfluidics has attracted a great deal of attention due to the potential applications in many areas
of science and technology. The understanding of the generation mechanism is still unsatisfactory and proposed models
lack generality for different microchips with flow conditions and channel geometries. In this paper, we present new
results of droplet generation in a PMMA microchip using flow-focusing technique. The current data are compared with
existing published data obtained with similar generation microchip method. The dependence of the droplet size/slug
length on the capillary number and ratio of the continuous phase and dispersed phase flow rates is investigated. A model
has been proposed which explains well the data from several similar studies.
The combined use of film transparency masks and dry film resist has allowed a rapid prototyping of designs and
structures in chips for droplet generation. Patterning of the film resist has produced channels with smooth vertical
sidewalls. The minimum feature dimension, δ, was reduced by increasing the resolution and spacing of the pattern
geometries in the film mask. For a single layer of resist (~35 μm thick), a minimum feature width of ~60 μm was
obtained using 2040 dpi transparency masks, 40 µm for 5800 dpi transparency masks and 25 μm using a Cr mask of
equal size/ spacing of features. A doubling of the spacing between features in a 2400 dpi masks resulted in an attainable
feature size of ~40 μm. The minimum feature dimension increased exponentially with thickness of 5038 resist.
Microfluidic chips which were fabricated in PMMA by this method have demonstrated controlled characteristics in the
generation of oil droplets in water.
Droplet-based in vitro compartmentalization (IVC) platform is a powerful tool in protein analysis. Reliable formation of microdroplets is important for the development of the microfluidic chip. In this study, we will examine the effect of surfactants on the formation of microdroplets in the flow focusing microfluidic device which is needed for enzyme evolution. Surfactants of Span 80 and Tween 20 are used in the continuous and dispersed phases, respectively. The droplet formation was affected distinguishably with the presence of Span 80 and Tween 20. The size of droplets decreased as the concentration of Span 80 increased. And the decrease was more pronounced with the combination of Span 80 and Tween 20.