  Nowadays, droplet microfluidics has become widely utilized for
high-throughput assays. Efficient mixing is crucial for initiating biochemical
reactions in many applications. Rapid mixing during droplet formation
eliminates the need for incorporating micromixers, which can complicate the
chip design. Furthermore, immediate mixing of substances upon contact can
significantly improve the consistency of chemical reactions and resulting
products. This study introduces three innovative designs for droplet generators
that achieve efficient mixing and produce small droplets. The T-cross and
cross-T geometries combine cross and T junction mixing mechanisms, resulting in
improved mixing efficiency. Numerical simulations were conducted to compare
these novel geometries with traditional T and cross junctions in terms of
mixing index, droplet diameter, and eccentricity. The cross-T geometry
exhibited the highest mixing index and produced the smallest droplets,
increasing the mixing index by 10% compared to the T junction. While the T
junction has the best mixing efficiency among traditional droplet generators,
it produces larger droplets, which can increase the risk of contamination due
to contact with the microchannel walls. Therefore, the cross-T geometry is
highly desirable in most applications due to its production of considerably
smaller droplets. Other new geometries also demonstrated comparable mixing
efficiency to the T junction. The cross junction exhibited the lowest mixing
efficiency and produced larger droplets compared to the cross-T geometry. Thus,
the novel geometries, particularly the cross-T geometry, are a favorable choice
for applications where both high mixing efficiency and small droplet sizes are
important.
