INTERACTION OF SURFACTANTS WITH POLY(N-ISOPROPYLACRYLAMIDE) MICROGEL LATEXES

The effects of surfactant type and concentration on the particle size and electrophoretic mobility of cross-linked poly(N-isopropylacrylamid e) (polyNIPAM) microgel latexes were studied. Without surfactant the p article diameter of the polyNIPAM decreased by a factor of 2 when the temperature was increased above 31-degrees-C, the cloud point temperat ure (CPT) for polyNIPAM homopolymer in water. Anionic sodium dodecyl s ulfate (SDS) in the concentration range 0.001-0.008 M caused the parti cle diameter to increase and the CPT to shift to higher temperatures. Higher SDS concentrations caused further swelling of the latex and the diameters became nearly independent of temperature in the range 10-60 -degrees-C. Nonionic Triton X-100 had no effect on the particle diamet er/temperature behavior indicating no surfactant binding. Below the CP T cationic dodecyltrimethylammonium bromide had no effect on swelling, whereas the cationic surfactant induced latex coagulation at the CPT. Surfactant binding was also reflected in the electrophoretic mobiliti es. Low levels of SDS binding gave higher negative mobilities which we re temperature sensitive. High SDS concentrations removed the temperat ure swelling transition so mobility was temperature insensitive. Catio nic surfactant binding increased the mobility of positively charged po lyNIPAM latex; however, in contrast to SDS, the mobility was temperatu re sensitive at high surfactant concentrations.