(643f) Microfluidic Synthesis of Non-Spherical Polymeric and Composite Particles

Colloidal particles in the nano- or micrometer size range are some of the most commonly encountered forms of materials in nature. Such monodisperse spherical and non-spherical colloidal suspensions and their assemblies have diverse applications in optic-electronics, photonics, catalysis, drug delivery, and field responsive rheological fluids. However, the synthesis of such highly monodispersed particles with tunable functionalities has been a great challenge. Several reports have documented the synthesis protocols of various morphologies of inorganic nano- and micro-sized particles. Heterophase polymerization methods including microemulsion and suspension polymerization have been developed and used to synthesize both polymeric particles and their composites. This polymerization approach does not offer control over the size and morphology and has been primarily used to synthesize spherical particles.

However, non-spherical particles have applications in a number of areas including liquid body armor applications due to potential shape-induced enhancements in shear thickening behavior. Microfluidics technology presents an alternative approach to synthesizing non-spherical particles with tunable functionalities. Using this approach, it is possible to synthesize colloidal based nano/microparticles and their composites with predetermined shapes usable in sensors, optical devices, microelectromechanical systems (MEMS) and field-responsive rheological fluids for liquid body armor applications.

The microfluidics method is dependent on the use of UV-curable prepolymer, with an appropriate photo-initiator. In this study, a photo mask patterned with pores defining the shape of the particles blocks the UV light while the pores allow the passage of light thereby cross linking the liquid prepolymer in the light path. The prepolymer solution flows through a microfluidic device fabricated by bonding poly(dimethylsiloxane), PDMS, molds to a glass slide. An Olympus BX51WI Microscope focuses the UV light to synthesize micron sized organic particles. Micron-sized organic particles in cubic, pentagonal, triangular, hexagonal, and tetragonal shapes were synthesized with this method using poly(ethylene glycol diacrylate) as the precursor. These particles were characterized, and it can be shown that the extruded depth of the particle is a function of the depth of the microfluidic channel.  Also, the cross sectional area of the particle is dependent on the mask pore size and the magnification of the microscope objective.  In addition to filled polymeric particles, composite particles and polymeric particles with vias have also been synthesized.