Kinetics of gold nanoparticle formation facilitated by triblock copolymers

Concerns for the environmental and economic impact of organic solvents and detergents in gold nanoparticle (AuNP) solution synthesis have motivated the search for more environmentally benign alternatives. One approach is to synthesize AuNPs from tetrachloroauric(III) acid (HAuCl ₄) using triblock copolymers (TBPs). However, a major challenge of using TBPs is the heterogeneous nature of the formed nanocrystals. Establishing control over AuNP size and shape requires a detailed mechanistic understanding of precursor reduction and nanoparticle growth. By using mixtures of TBPs (L31 and F68), we demonstrate a more flexible method for adjusting the hydrophobic/hydrophilic environment to tune the size and shape. We show that AuNP morphology and size can be changed by adjusting the TBP/Au(III) ratio. Kinetic models are used to rationalize why the addition of L31 slows the rate of AuNP formation and growth. Experimental evidence of sigmoidal growth kinetics, early time bimodal gold nanoparticle size distributions, and polycrystallinity suggest that aggregative AuNP growth is an important mechanism.