Near-Field Infrared Imaging and Spectroscopy of a Thin Film Polystyrene/Poly(Ethyl Acrylate) Blend

Abstract

The application of broadband, near-field infrared microscopy to the characterization of the mesoscale structure of a thin film polymer blend is described. Key features of this instrument, which couples the nanoscale spatial resolution of scanning probe microscopy with the chemical specificity of vibrational spectroscopy, include broad tunability and bandwidth, parallel spectral detection for high image acquisition rates, and infrared-transparent aperture probes. Near-field spectral transmission images of a thin film of polystyrene/poly(ethyl acrylate) acquired in the C–H stretching region are reported. An assessment of the relative importance of transmission image contrast mechanisms is a significant aim of this work. Analysis of the near-field infrared spectra indicates that the image contrast in the C–H stretching region is largely due to near-field coupling and/or scattering effects. Identification and differentiation of the operative contrast mechanisms on the basis of their relative dependence on wavelength is discussed. Analysis of the contrast attributed to absorption is consistent with the chemical morphology of this sample derived from previous chemical modification/atomic force microscopy studies.