SynopsisThe effects of water-soluble and monomer-soluble impurities on the kinetics of emulsion polymerization of monomers following Case I1 kinetics (e.g., styrene) are investigated. Experimental studies reveal that impurities can have an appreciable effect on both polymer particle nucleation and growth. These effects are shown to be well predicted by a mathematical model.

SynopsisThe effect of water-and monomer-soluble impurities on the kinetics of emulsion polymerization for Case I systems (e.g., vinyl acetate and vinyl choride) was investigated. Model predictions on the effect of these impurities on polymer particle nucleation and growth rate are shown to be in satisfactory agreement with experimental results. The effect of monomer-soluble impurities is shown to be quite different from that observed in Case I1 emulsion polymerization systems.

Heterogenous ice nucleation (HIN) induced by organic materials is a long-lasting issue in wide-ranging fields from cryobiology to atmospheric physics, but efforts for controlling HIN are still restricted by incomplete understanding of its mechanism. In this work, distinct anti-icing capabilities were achieved by experimentally investigating the HIN behavior on the surfaces modified with the primary face (PF) and secondary face (SF) of cyclodextrins (CDs) (i.e., α-1,4-linked D-(+)-glucopyranose with two relatively flat and hydroxylated faces). To achieve this, CDs were first immobilized to the surfaces through selectively binding the PF and SF of CDs onto the solid surfaces; as such, either PF or SF is exposed to liquid water. Interestingly, HIN temperature and delay time assays indicate that HIN is depressed when the PF of CDs (which matches with the ice lattice) is exposed to liquid water whereas the HIN is facilitated when the SF of CDs (which mismatches with the ice lattice) is exposed to liquid water. This deviates from the common thought that surfaces with a template of ice lattice match facilitate the HIN. Instead, 1 H NMR studies show that the resonances of hydroxyl (OH) in the SF of CDs are most deshielded due to the formation of intramolecular hydrogen bonds, in comparison to that of OH in the PF of CDs, which weakens the interaction between the OH groups on the SF and water molecules. Thus, the distinct anti-icing capabilities of the PF and SF of CDs can be achieved and established by the distinct interactions between OH groups on the two faces and water, which is of great potential for practical applications. The molecular-level interactions between surfaces and water molecules may be a more appropriate criterion for forecasting materials' HIN ability.

Oscillator strengths for C 1s inner-shell excitation of the isomeric xylenes (ortho-, meta-and para-) have been derived from electron energy loss spectra recorded under scattering conditions dominated by electric dipole transitions. The lineshape of the C 1s → p* transition is found to be dependent on the substitution pattern, with para-xylene exhibiting two components, orthoxylene a single asymmetric peak, and meta-xylene a single symmetric peak at an instrumental resolution of 0.35 eV. Improved virtual orbital ab initio calculations were carried out on all three species, providing spectral shapes in reasonable agreement with experiment. The calculations indicate that the transition responsible for the splitting which is observed only in the C 1s spectrum of para-xylene is associated with the methyl-substituted ring carbons, for which there is a somewhat larger chemical shift in the para relative to the ortho-or meta-isomers. These results are compared to other recent studies of C 1s spectroscopy of di-substituted benzenes (dimethylphthalates and nitroanilines) in order to investigate trends in the sensitivity of C 1s spectroscopy to isomeric substitution patterns. ᭧

SynopsisAn investigation of the emulsion polymerization of 2-ethylhexylacrylate (EHA)-vinyl acetate (VAc)-acrylic acid (AA) has been done. It was found that the polymerization rate depends on the AA level and that particle nucleation occurs throughout the entire conversion range. At the 5% AA level, there is significant coagulation. The number of particles depends on the balance between nucleation and coagulation. Addition of a small amount of water-soluble comonomer has no significant effect on the course of polymerization, but the viscosity of the latex can increase significantly. The dependence of latex viscosity on pH on neutralization has been studied. The maximum viscosity reached on neutralization depends on the acrylic acid level and the semibatch policy used in the latex synthesis. Addition of salt is a simple and effective way to control viscosity buildup during neutralization.