Iodopropionic acid staining of waterborne epoxy films

The examination of polymer material by transmission electron microscopy (TEM) often relies on staining in order to improve contrast or preferentially stain a polymer phase. Stains such as osmium tetroxide for unsaturated polymers and ruthenium tetroxide for unsaturated as well as certain saturated polymers have been used quite extensively. A new stain, 3-iodopropionic acid, has been found to be very useful to stain preferentially the amine rich domains in waterborne epoxy films.An epoxy dispersion (epoxy equivalent weight, EEW=625) and a polyamine adduct curing agent (AHEW=163) at a 1.5:1 stoichiometry was prepared. The volatile organic content (VOC) was 2.6 lb./gal., and the solvent blend was 90.6% propoxy ethanol and 9.4% Aromatic 150. The particles size of the starting dispersion was obtained by TEM and disk centrifuge and found to be approximately 500 nm. Films (approximately 1.2 mil dry film thickness[DFT]) were cast on a partially fluorinated polyethylene film, 0.5, 2, 4, and 8 hours after hand mixing and cured for two or more weeks at 25° C and 50% relative humidity.