Proposal Number: 0730727 Principal Investigators: Anna, Shelley Affiliation: Carnegie Mellon University Proposal Title: Controlling Tipstreaming for Sustained Formation of Nanoscale Droplet Reactors
The goal of the proposed work is to incorporate a well-known fluid mechanical phenomenon into a flow-focusing microfluidic device. The phenomenon, tipstreaming, will allow submicron droplets to be formed in microfluidic devices which have much larger internal dimensions (tens and hundreds of microns). As part of this work, we will demonstrate that small reactors (droplets) are ideal for controlling and studying nanoparticle synthesis reactions. Successful completion of the project will require meeting three objectives: (1) quantifying the physicochemical mechanics underlying tipstreaming, (2) exploiting geometry and fluid additives to achieve controllable and sustained tipstreaming, and (3) synthesis of metal nanoparticles within tipstreaming-generated nanoreactors. Current research being performed in the PIs laboratories provides the experimental and analytical expertise needed to complete the proposed work.
Intellectual Merit: Two important problems will be tackled in the proposed work: control of an interface-dominated fluid mechanics phenomenon, and control of nanoparticle growth. We will develop fundamental principles and analytical models to control tipstreaming in a microfluidic device. This model will provide the basis for a method to form monodisperse submicron droplets in microfluidic devices that are fabricated via cost effective techniques like soft lithography. The ability to harness and control the process for submicron droplet formation will open new avenues for microreactor development and for the design of custom emulsions. The knowledge gained will be pertinent not only to the flow-focusing geometry utilized here, but is to form submicron droplets for use as microreactors in the formation of nanoparticles; we argue that these small dimensions will provide a well-controlled environment for growing metal nanoparticles. This work will enable us to verify the impact of reactor volume homogeneity on nanoparticle quality. This project will result in a device capable of properly investigating the nature of nanoparticle growth and development.
Broader Impact: The proposed work will contribute an important tool to the development of microfluidic systems, namely the ability to generate structures orders of magnitude smaller than the device. By combining robust flow control in microfluidic devices with the precision of low Reynolds number droplet dynamics, submicron droplets can be formed in devices with easily fabricated dimensions. This will add a new regime to the growing field of microfluidic and 'lab-on-a-chip' technology. The proposed research will have broad educational impact through the strong records of both PIs of involvement in educational and outreach activities on campus. The PI and co-I are committed to interdisciplinary research; between the two Investigators, we have appointments in five departments and two different colleges at CMU (Mechanical Eng., Chemical Eng., Materials Science & Eng., Chemistry and Physics). The proposed project will be truly synergistic, with significant contributions coming from both PIs? expertise and a clear necessity for close collaboration. Graduate and undergraduate students involved in the project will need to work closely with both research groups; the benefit of this interaction has already been demonstrated with two current co-advised students. The two PIs have been holding joint group meetings for the last two years to enhance the education and exposure of students to complimentary ideas and techniques; this project will grow from this existing synergy. The highly visual nature of the microfluidics component of this work will allow for easy extrapolation to outreach activities at all levels. We will also develop modules for existing outreach programs to dispel some of the common misconceptions associated with the term 'nanotechnology'. These module(s), which will be made audience-appropriate, will address the issue that even educated scientists and engineers outside of academia have little concept of the scales (length and time) involved in nanoscale processes.
