SERS study on surface chain geometry of atactic poly (methyl methacrylate) film and nanosphere

The surface chain geometry of atactic poly (methyl methacrylate) (a-PMMA) film and nanosphere (NS) was revealed by surface-enhanced Raman scattering (SERS) spectra. The Ag nanoparticles and nanoplates were prepared by electrochemical deposition and chemical synthesis for SERS substrates. The experimental results suggested that the molecular chain axis of a-PMMA film adopted a trans-conformation on bonding to Ag surface ascribed to the short-range chemical (CHEM) effect according to the SERS selection rules. However, for the well-coated monolayer of a-PMMA NSs, the -CH3 in polymer chains stood vertically to the Ag surface due to the giant local electromagnetic effect, then the chain conformation presented in the interface between a-PMMA NSs and Ag metal was adopted the opposite orientation compared with a-PMMA film. The Raman enhancement of the Ag nanoparticles was more prominent than that of the Ag nanoplates due to the free energies of face-centered cubic crystal faces in nanoparticles, but the single crystals with (111) plane of Ag nanoplates could improve the stability of SERS signals when the annealed temperature was above T-g of a-PMMA NSs. The present work can provide some useful information of surface chain geometry and conformation of NSs for designing various materials with well-defined structure via a-PMMA NSs template. Copyright (c) 2013 John Wiley & Sons, Ltd.