Fusion Growth of Gold Nanoparticles Induced by the Conformational Change of a Thermoresponsive Polymer Studied by Distance Distribution Functions

The growth kinetics of gold nanoparticles induced by the conformational collapse resulting from the coil globule transition of thermoresponsive polymer was studied using small angle X-ray scattering (SAXS) method. The growth process of aggregates and nanoparticles formed during the reaction was determined on the basis of distance distribution functions calculated from the SAXS profiles without having to approximate or simplify the actual structures. The size of aggregates and nanoparticles reached a maximum not in the final stage of the reaction but in the middle stage, indicating that shrinkage of the particles occurred in the growth process. The surface roughness increased up to the middle stage of the reaction and then significantly decreased in the final stage. Furthermore, the dependence of polymer concentration was also investigated It was found that small particles were generated prior to the formation of main products, and size of the small particles was estimated to be ca. 7 nm in diameter. The results reveal that the formation process progresses mainly based on fusion of the small particles induced by the structural collapse of polymer. Finally, the growth mechanism is discussed in detail.