SOLUBLE POLYMER DIRECTED CONTROLLED SYNTHESIS OF GOLD NANOPARTICLES: EFFECT OF CLOUD POINT, REDUCING AGENT, AND MIXING METHOD ON NANOPARTICLES PREPARATION

Abstract

Au(0) metallic nanoparticles (Au NPs) were first prepared in triblock copolymer poly (methyl vinyl ether) PMVE-water dispersions. The wax formed from cloud point appearance in PMVE (0.6 wt.%)-water on heating the solution at 40°C worked as a template to trap the reduced Au NPs of 3 nm (σ = 0.8) size. Cooling the solution to 25°C, the cloud point disappeared as a result the particles aggregated to larger oval shape crystals with major and minor diameters 99.5 nm (σ = 4.5) and 84 nm (σ = 2), respectively when solution was stirred for one week for the completion of reaction. Smaller (4.4. nm (σ = 1.2)) particles were obtained when Au salt HAuCl4⋅3H2O (hydrogen tetrachloroaurate (III) trihydrate) was reduced by 5 equivalents of NaBH4 , whereas the addition of 10 equivalents NaOH gave larger particles of 13 nm (σ = 2.4) diameter. PMVE polymer alone acted as a reducing and stabilizing agent but the time of completion of reduction was much longer (one week) compared to the reduction conducted by NaBH4 or NaOH where the reaction completed in 15 min. In neat PMVE polymer-water dispersions a number of mixing methods employed to reduce Au salt followed the order: combination of sonication and stirring > sonication > stirring. Au NPs formation was 27%, 21%, and 5%, respectively in 4 h of reaction time. The mixing experiments justified the development of microchannel mixers for NPs production on a large scale.