The elegance of digital microfluidics is in incorporating high quantities of manipulated micro and nanodroplets on-chip, each of which can be considered a small-volume carrier of various chemical and biological reagents. Therefore, the analysis of on-demand manipulation of these micro and nanocarriers is extremely important in developing an optimized lab on a chip. In this work, passive coalescence and mixing between two trapped, squeezed nanodroplets inside a closed microfluidic device was investigated. The droplets are composed of glycerol dyed in blue and red, dispersed inside oleic acid as the carrier oil. A microwell with a circular cross section was fabricated on the top wall of the microchannels to trap the first droplet for increasing the mixing precision and minimizing the viscous shear stress imposed on the droplets from the channel walls. The energy minimization theory was used to develop a parametric study for this trapping technique and to choose the optimum design parameters for droplet trapping in terms of efficiency. Image processing was performed on the snapshots of the trapped glycerol nanodroplets during mixing. Growth in passive mixing percentage was demonstrated to be asymptotical and was formulated with an empirical equation of exponential form as a function of the passive mixing relaxation time. The required time for the passive mixing of a glycerol droplet pair was measured considering various thresholds for the final standard deviation of the gray intensity indices. This finding was of the order of magnitude of the diffusive mixing time scale and physically consistent with the Stokes flow regime.

The objective of the NSF RET (Research Experiences for Teachers) site program hosted by the University of Central Florida is to provide K-12 teachers with a hands-on engineering design experience covering all aspects of the Internet of Things, from the manufacturing of a sensor, to the hardware and software that allows it to connect to the Internet. This program gives teachers learning opportunities to explore the practical use of science for engineering applications, and provide a context in which students in their classroom can test their own scientific knowledge as they recognize the interplay among science, engineering and technology. The uniqueness of this site program lies in the engagement of teachers in various facets of scientific, engineering, and educational methods based on Train-the-Trainer model with rotation in multiple research labs. In order to support the STEM educational services for teachers and students in middle and high schools, our site program aims at creating competent teacher trainers who ensure quality pre-service and in-service teacher education, by providing multidisciplinary experiences that are relevant to the current technical development. Teachers in the adjacent public school districts are primary participants in this site program. Significant efforts have been made to recruit teachers serving underrepresented student populations, and female and minority teachers who can reach out to them. In our RET site program, the participants rotated to four different laboratories with a 1.5–3 week residency in each, where they learned about the practice of engineering in various disciplines at the research laboratories on the university campus under the guidance of faculty and graduate mentors. The teachers presented their learning outcomes in the final week and were invited back to share their educational implementation experiences in their classes. This site program provided teachers with interdisciplinary engineering design experiences relevant to innovative technical development, and helped them develop teacher-driven teaching modules that can be deployed in the classroom.