The first products made in space - Monodisperse latex particles

Abstract

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 2018-05-11T20:27:33+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...

Effect of Microgravity on the Growth of Silica Nanostructures

“…Notably, our results are strikingly different than those of Vanderhoff et al, who achieved improved monodispersity in latex particles . The difference arises because their experiments involved emulsion polymerizations, which are stabilized in microgravity.…”

“…There is previous evidence that the formation of this “soft” matter is altered in microgravity. The first commercially available products from space (still available from NIST) were the monodisperse latex sphere standards of Vanderhoff et al, who demonstrated that emulsion polymerization of latexes in space resulted in better monodispersity, increased uniformity, and reduced coagulation . In addition it has been hypothesized that in unit gravity, buoyancy-driven fluid flows and sedimentation deleteriously perturb sol−gel substructures prior to gelation, and these perturbations are “frozen” into the resulting microstructure. , Hence, sol−gel pores may be expected to be smaller, more uniform, and less rough when formed in microgravity.…”