A colorimetric study of the interaction of cationic and anionic surfactants with anionic gold nanoparticles

The interactions of citrate-capped 10-nm gold nanoparticles with a cationic model surfactant, CTACl, and an anionic one, SDS, are explored. Results show that for CTACl, values of the c.m.c. close to those reported in the absence of nanoparticles can be obtained by simple colorimetric measurements. For SDS, its interaction with the same-charge nanoparticles is explored through the use of an indirect colorimetric method involving NaCl addition, and a surfactant-nanoparticle interaction model is postulated in this basis. C.m.c. measurements for SDS in the presence of AuNPs show that, despite both substrates being anionic, SDS micelle formation is actually promoted in the presence of gold nanoparticles.