Properties of differently charged poly(N‐isopropylacrylamide) Latex dispersions in alcohol‐water mixtures

Results of size control experiments, TEM and viscosity measurements on both negatively and positively charged poly(N-isopropylacrylamide) (PNIPAAM) latex dispersions are reported. In alcohol-water mixtures containing low weight fractions of alcohols higher than methanol, negatively and positively charged PNIPAAM particles exhibit both opposite swelling behaviour and flow characteristics at 20 degrees C. Negatively charged particles shrink due to cononsolvency. Shrinking lends to a decreased viscosity. Conversely, positively charged particles swell dramatically and exhibit an increased viscosity. At 40 degrees C, the negatively charged particles collapse and show a similar behaviour to those with positive charge. We observed with TEM that positively charged particles form random flocks after drying on the grid whereas negatively charged ones fi,rm arrays of separated particles. This underlines our general concept that the positively charged particles an in general more hydrophobic.