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The monodisperse polystyrene latexes widely used for calibration and other scientific uses are made by seeded emulsion polymerization, i.e., by polymerizing styrene in a previously prepared monodisperse latex, to grow the particles to larger size while maintaining their uniformity. The emulsifier concentration is critical: too little results in coagulation of the latex; too much, in the nucleation of a new crop of particles. Monodisperse latexes of 0.1-2.0 pm particle size have been available for some years. Larger sizes are difficult to prepare: the extent of coagulation increases with increasing particle size above 2 pm to complete coagulation at 10 pm. Brownian motion ceases for particles larger than 2 pm, and the large sticky monomer-swollen particles cream and the polymerized particles settle; this creaming or settling is offset by stirring the emulsion polymerization, but the monomer-swollen particles are sensitive to coagulation by mechanical shear, so that the amount of coagulum increases with increasing particle size. Polymerization in space eliminates the settling or creaming, so that the latex need be stirred only enough to give good heat transfer and mixing, thus alleviating or eliminating the coagulation by mechanical shear. Thus twenty monodisperse polystrene latexes were prepared in the MLR flight hardware on the STS-3, STS-4, STS-6, STS-7, and STS-11 flights of the Shuttle. Two polymerizations were small-particle-size controls. Of eighteen large-particle-size latex polymerizations, four on STS-4 failed owing to malfunction of the flight hardware, one on STS-6 owing to a broken heating wire, and one on STS-11 owing to a broken stirrer shearpin. The remaining twelve monodisperse latexes of 4-30 pm size had narrower particle size distributions (coefficients of variation 0.9-1.4%) than the ground-based control latexes (coefficients of variation 2-5%) and contained fewer offsize larger particles. The flight polymerizations produced only negligible amounts of coagulum; the ground-based control polymerizations produced increasing amounts with increasing particle size, and so were discontinued for latexes larger than 18. The polymerization rates in space were the same as on earth wit tm in experimental error. The 10 pm STS-6 (coefficient of variation 0.9%) and the two 30 pm STS-11 (coefficients of variation 1.3%) latexes were accepted by the National Bureau of Standards as Standard Reference Materials, the first products made in space for sale on earth. Moreover, these particles were more https://ntrs.nasa.gov/search.jsp?R=19890010947 2019-04-29T22:01:00+00:00Z perfect spheres than the ground-based control particles. Thus the original rationale of the experiments was confirmed unequivolcally by: 1. the negligible amounts of coagulum formed in the flight polymerizations: 2. the smaller number of offsize larger particles in the flight latexes; 3. the broadening of the particle size distribution and the formation of more larger offsize particles during the completion on earth of the polymerization o...

Monodisperse latex microspheres ranging in size from submicrometer to several micrometers in diameter can be prepared in the laboratory. The uniformity of diameter is important for instrument calibration and other applications. However it has proved very difficult to manufacture commercial quantities of mondisperse latex microspheres with diameters larger than about 3 micrometers owing to buoyancy and sedimentation effects. In an attempt to eliminate these effects NASA sponsored a Space Shuttle experiment called the Monodisperse Latex Reactor (MLR) to produce these monodisperse microspheres in larger sizes in microgravity. Results have been highly successful.Using technology gained from this space experiment, a ground-based rotating latex reactor has been fabricated in an attempt to minimize sedimentation without using microgravity. The entire reactor cylinder is rotated about a horizontal axis to keep the particles in suspension.In this paper we determine the motion of small spherical particles under gravity, in a viscous fluid rotating uniformly about a horizontal axis. The particle orbits are approximately circles, with centres displaced horizontally from the axis of rotation. Owing to net centrifugal buoyancy, the radius of the circles increases (for heavy particles) or decreases (for light particles) with time, so that the particles gradually spiral inward or outward.For a large rotation rate, the particles spiral outwards or inwards too fast, while for a small rotation rate, the displacement of the orbit centre from the rotation axis is excessive in relation to the reactor radius. We determine the rotation rate that maximizes the fraction of the reactor cross-section area that contains particles that will not spiral out to the wall in the experimental time (for heavy particles), or that have spiralled in without hitting the wall (for light particles). Typically, the rate is close to 1 r.p.m., and design rotation rate ranges should span this value.

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