Considerable developments have been made in the synthesis and fabrication of capsules at scales that span from the micrometer to the nanometer domains. Capsule-based technologies find applications in controlled release of drugs, dyes and enzymes that assist the biomedical, personal care and detergent sectors in effectively designing next- generation products. Microfluidics has emerged as a popular route in preparing polymer based microcapsules with the flexibility of controlling microstructures in regimes of low Reynolds-number flow and sterically confined growth domains.1,2

A polymer cation-mediated nanoparticle assembly route to produce submicron size hollow and solid spheres has been recently described. The formation mechanism is a two- step process that features electrostatic condensation reactions between linear cationic polymers and anionic salts to form polymer/salt aggregates, that are subsequently stabilized by nanoparticles to form polymer filled droplets.3-5 This research extends the previous studies to the domains of microfluidics with a view to address fundamental issues pertaining to the mechanism and kinetics of the nanoparticle assembly process and the role of mixing on resulting microstructures. Preliminary studies carried out in microfluidics provide real-time evidence of the formation of unstable polymer/salt aggregates and accentuates the previously hypothesized stabilizing role of nanoparticles in forming the spheres. We discuss strategies to control the shapes of polymer capsules by inducing hydrodynamic instabilities via novel microfluidic architecture and approaches to selectively functionalize microcapsules in microfluidics.

References:

1. Abraham, S., Jeong, E.H., Arakawa, T., Shoji, S., Kim K.C., Kim, I., Go, J.S., Lab Chip, 2006, 6, 752-756.

2. Xu, S., Nie, Z., Seo, M., Lewis, P., Kumacheva, E., Stone, H.A., Garstecki, P., Weibel, D.B., Gitlin, I., Whitesides, G.M., Angew. Chem., 2005, 117, 734-738.

3. Rana, R.K., Murthy, V.S., Yu, J., Wong, M.S., Adv. Mater., 2005, 17, 1145-1150

4. Murthy, V.S., Rana, R.K., Wong, M.S., J. Phys. Chem. B., 2006, 110(51), 25619-25627.

5. Yu, J., Murthy, V.S., Rana, R.K., Wong, M.S., Chem. Commun., 2006, 10, 1097-1099