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) la tex dispersions are reported. In alcohol-water mixtures containing low weig ht fractions of alcohols higher than methanol, negatively and positively ch arged PNIPAAM particles exhibit both opposite swelling behaviour and flow c haracteristics at 20 degrees C. Negatively charged particles shrink due to cononsolvency. Shrinking lends to a decreased viscosity. Conversely, positi vely charged particles swell dramatically and exhibit an increased viscosit y. At 40 degrees C, the negatively charged particles collapse and show a si milar behaviour to those with positive charge. We observed with TEM that po sitively charged particles form random flocks after drying on the grid wher eas negatively charged ones fi,rm arrays of separated particles. This under lines our general concept that the positively charged particles an in gener al more hydrophobic.