We propose to perform a fundamental investigation of the droplet motion in digital microfluidics via the development of a fully three-dimensional Spectral Boundary Element Method for interfacial dynamics in a steady electric field. Digital microfluidics, in which an electric field is applied to manipulate droplet motion, has significant applications in biomedical research and clinical studies, including enzymatic analysis, DNA analysis and disease diagnosis. Great efforts have been made for over a decade to design reliable, affordable and convenient digital microfluidic devices. However, due to the lack of fundamental understanding of droplet motion under the influence of fluid flow and electric field, current digital microfluidic systems have to be operated with the assistance of expensive optical or electronic imaging devices. The control of fluid dynamics in experiments is achieved empirically and is extremely time consuming for new fluid systems. If a comprehensive computational tool is developed to describe the physics of droplet motion in microfluidic devices, the afore-mentioned problems can be resolved. We envision that the proposed computational work is able to provide fundamental understanding for the droplet dynamics, predict the operation of the device, and further create a solid foundation for the device design and optimization which can lead to a new generation of reliable, affordable, and operationally convenient microfluidic devices.
The intellectual merit of the proposed study lies in the following aspects. 1) The development and application of a 3D Spectral Boundary Element Method for droplet dynamics in a steady electric field in microfluidics is new and innovative. The study can provide comprehensive information for the droplet motion in microfluidics under a joint influence of fluid flow and electric force. It does not make assumptions such as axisymmetry, uniform electric field, or static droplet interface, as existing methods do. 2) It will be the first time that a Spectral method (i.e. high-order interpolation scheme) is applied for droplet dynamics in digital microfluidics under the influence of electric field. The proposed computational method will overcome the obstacles (in terms of efficiency and accuracy) of other numerical methods due to their low-order interpolation schemes. 3) It will also be the first time that a fully three-dimensional study is carried out for the dynamics of droplets in microfluidics. It was pointed out a decade ago that three-dimensional numerical simulations are in demand for microfluidics due to the difficulties in 3D hydrodynamics focusing experiments in microfluidic system.
The proposed work has a broad impact on science, outreach, and education. Although this study is focused on droplet motion in digital microfluidics, the insight gained for interfacial dynamics in general can be applied in drug delivery, fuel cells, tertiary oil recovery and water filtration technologies, etc. This research will thus contribute in health care, energy and environmental remedies. A broader participation of this research will be realized in the following ways. The PI plans to hold research workshops and give presentations on digital microfluidics at tribal colleges via the Nurturing American Tribal Undergraduate Research and Education (NATURE) program supported by North Dakota EPSCoR. The PI will provide opportunities for Native American students to participate the research activities in her laboratory by creating research assistantships for them in summers. The PI will act as a research mentor for a disabled high school student and guide him/her to conduct research in the PI's laboratory. The PI encourages undergraduate students, especially female undergraduates, to take part in research in Microfluidics. She plans to recruit female undergraduates as research assistants. The PI also plans to convince an underrepresented minority student to join her research group as a graduate research assistant. The afore-mentioned research work by underrepresented minority students, persons with disabilities and female students will be supported by the BRIGE funding. To increase the opportunities for undergraduates and graduate students to present research work in public, and to improve education in microfluidics, the PI plans to organize and hold an annual Student Symposium in Micro-scale Fluid Dynamics and Transport Phenomena at NDSU. In addition, the proposed research work will be integrated into both undergraduate and graduate courses that the PI teaches as interactive instructional software.
Digital microfluidics, in which an electric field is applied to manipulate droplet motion, has significant applications in biomedical research and clinical studies, including enzymatic analysis, DNA analysis and disease diagnosis. Great efforts have been made for over a decade to design reliable, affordable and convenient digital microfluidic devices. Due to the small volume of fluids (i.e. less than microliters) transported and the high-throughput nature of microfluidics, the optimal design and precise control of such devices requires advances in theoretical studies, especially computational studies. In this work, we developed a fully three-dimensional spectral boundary element method for interfacial dynamics in a steady electric field. This study not only contributes in fundamental investigations on droplet motion driven by electrohydrodynamic forces, but also has great potential to facilitate the emergence of a new generation of digital microfluidics. This approach takes into consideration properties of fluids (e.g. interfacial tension, viscosity, electric conductivity and resistivity), electric field properties (e.g. field strength and distribution determined by electrode locations), as well as microfluidic geometries. The study provides comprehensive information for the droplet motion in microfluidics under a joint influence of fluid flow and electric force. It does not make assumptions such as axisymmetry, uniform electric field, or static droplet interface, as existing methods do. It is the first time that a spectral method (i.e. high-order interpolation scheme) is applied for droplet dynamics in digital microfluidics under the influence of electric field. This method overcomes the obstacles (in terms of efficiency and accuracy) of other numerical methods due to their low-order interpolation schemes. A fully three-dimensional study is carried out for the dynamics of droplets in microfluidics. Three-dimensional numerical simulations are in demand for microfluidics due to the difficulties in 3D hydrodynamics focusing experiments in microfluidic system. Experiments have been created and carried out to validate our numerical results. In addition, this study has provided opportunities for females and underrepresented minorities at all levels, including K-12, undergraduate and graduate students, to participate in fundamental research in fluid dynamics, interfacial phenomena and multiphase flow.
