Archive for August, 2008
Study of Monomer Droplets in Miniemulsions
The droplet size distribution (DSD) of miniemulsions can be successfully characterized using, with adaptation, particle sizing techniques such as capillary hydrodynamic fractionation (CHDF), acoustic attenuation spectroscopy (AAS), surfactant titration, and microscopy. Because these techniques vary in size range suitability, a combination should be utilized to fully observe the DSD, which can range from tens of nanometers to several microns. The DSDs of a styrene miniemulsion were measured via different techniques. Although the measurement ranges of the techniques differ, there is good agreement between the distributions. The DSD obtained from AAS shows the presence of micron-scale droplets, observable via optical microscopy.
Seeded Dispersion Polymerization
The effect of reaction parameters on the seeded dispersion polymerization of methyl methacrylate (MMA) using submicron PMMA latex particles as seed was studied in detail. Monodisperse particles were only obtained when the methanol content was between 60% and 80%; the final particle number (N(final)) decreased with increasing methanol content. Maximum values of N(final) were found at 0.3 wt% AIBN (on MMA), 11.7 wt% MMA (on total), and 25 wt% PVP K30 (on MMA) when those parameters were varied using a constant initial seed number (N(initial) = 201012 L-1). N(final) increased linearly with N(initial) when N(initial) was greater than N(ab initio), which is the particle number obtained from the ab initio dispersion polymerization. When N(initial) was less than N(ab initio), N(final) was equal to N(ab initio). Poorer monomer swellability of the seed particles resulted in lower values of N(final) (<N(initial)) in seeded dispersion polymerizations of MMA.