Tracking high molecular weight polymer interdiffusion on a SERS-based platform

Abstract

We describe the implementation of an experimental setup based on Surface Enhanced Raman Spectroscopy (SERS) to investigate polymer interdiffusion. Ultra-thin bilayer films of deuterated polystyrene (dPS) and polystyrene (PS) are placed in contact onto SERS-active gold substrates with inverted square-base pyramidal geometry and subsequently annealed. Initially, the Raman spectrum shows only spectral features of the polymer adjacent to the substrate. Upon annealing, Raman bands of the polymer located far from the substrate start to emerge, an indication of chain diffusion into the substrate hotspot and mixing between polymer layers. The kinetics of the process is consistent with transport of polymer chains in nanometer scale, with diffusion coefficients in the range 10-13 ? 10-15cm2/s. The temperature response of the process is characterized by an activation energy of 48.93+-1.5 kcal/mol, in excellent agreement with earlier experiments. SERS experiments provide a powerful and reliable experimental platform to characterize polymer interdiffusion without the need of chemical labeling, with several prospective applications to the study of chain dynamics in advanced polymer-based nanocomposite materials.