Quartz-crystal microbalance and spectrophotometric assessments of inter-core and inter-shell reactivities in nanoparticle thin film formation and growth

Spontaneous core-shell and shell-shell reactivities of thiolate-capped nanoparticles are exploited for assembling nanoparticle network thin films via an exchange-crosslinking-precipitation route. Gold nanoparticles of two different core sizes (2 and 5 nm) capped with decanethiolates and alkylthiols of two different functionalities, 1,9-nonanedithiol (NDT) and 11-mercaptoundecanoic acids (MUA), were studied as the assembly components. The film formation and growth involve inter-core covalent Au-thiolate bonding at both ends of NDT, or inter-shell non-covalent hydrogen-bonding at carboxylic acid terminals of MUA shells. The present work focuses on a kinetic assessment of the controlling factors based on UV-Visible spectrophotometric and quartz-crystal microbalance measurements. These measurements probe the evolution of the surface plasmon resonance band of nanoparticles and monitor the mass loading of the assembled films, respectively. Both qualitative and quantitative insights have been obtained for understanding the dependences of exchange, nucleation and crystallization processes on core size and shell structure. The implication of the results for designing nanostructured assemblies using core-shell nanoparticles as building blocks is discussed in terms of binding site, core size and shell structure.