A new method was developed to prepare monodisperse nano to microparticles of polystyrene ranging from 0.5 to 2.5 microns in relatively large-quantity batches (2 L, 10% by weight in water). Current commercial sources are very expensive and can typically only be acquired on a relatively small scale. Monodisperse polystyrene in this size range is an important component of laser velocimetry measurements in wind tunnels, but has many other potential uses. Polystyrene microparticles have uses in paints/coatings, adhesives, bio/immunoassays, reaction catalysts, and chromatography materials. The main benefits of this technology are low cost, scalability, and selectable size.

Various laser velocimetry techniques require micron-sized particles to be injected in the flow to provide scattering centers for the input laser light. These particles must satisfy two criteria: be small enough to follow the fluid flow with excellent fidelity, yet be large enough to provide adequate scattered light to be detected by the laser velocimeter with sufficient signal strength to yield accurate velocity measurements. Liquid aerosols and dry powders have been utilized with limited success. Their inherent polydispersity increases the overall signal-to-noise ratios and lack of reproducibility results in questionable velocity measurement accuracy.

A procedure to produce particles with diameters between 0.5 and 2.0 microns was demonstrated using a 3-L reaction kettle with temperature controlled by a heating mantle and a cold finger condenser. The control is operated by a mercury thermoregulator that alternately calls for heating or cooling, depending on the set temperature versus the sensed temperature. A condenser returns any vaporized reactants to the reaction vessel. A stirring paddle ensures sufficient agitation of the reactants.

This work was done by Pacita I. Tiemsin, Donald Oglesby, and Jackie Schryer of Langley Research Center. LAR-17777-1