Study of the mechanical, viscoelastic, and chemical properties of polymer blend-based thin films by dynamic atomic force microscopy

P. Nickmilder1, J. Mathurin2, A. Dazzi2 and P. Leclère1

1University of Mons (UMONS), Laboratory for Physics of Nanomaterials and Energy (LPNE), Research Institute for Materials Science and Engineering, B 7000 Mons, Belgium.
2Institut de Chimie Physique, UMR8000, Université Paris-Saclay, CNRS, F-91405 Orsay, France

During the last decades, knowledge about nanoscale properties has known a leap forward thanks to the development of Atomic Force Microscopy, particularly with regard to the study of mechanical and viscoelastic properties. This knowledge is of the utmost importance since the nanoscale has a direct influence on the macroscale behavior. Among the different dynamic modes available today, Peak Force Tapping (PFT), Intermodulation AFM (ImAFM), and nano-Dynamic Mechanical Analysis (n-DMA) [1] are able to estimate these properties from the force curves using the approach-retract movement of the AFM tip and provide the quantitative mapping.

In this study, we compared these different AFM modes by analyzing thin films (few hundred nanometres) of polymer blends, taken as model systems. We focus on thin films composed of poly(styrene) (PS) and poly(-caprolactone (PCL), and PS and poly(methyl methacrylate) (PMMA) (Figure).

In fine, the analysis of their local chemical properties by AFM-IR [2] was used to confirm that the variations in physical properties correspond actually to a variation in chemical nature. This involves a combination of AFM imaging in contact mode or Tapping mode with a modulated infrared laser in order to perform infrared spectroscopy at the sub-micrometer scale (i.e. below the diffraction limit of conventional infrared microscopy). This allows us to obtain a map correlating the topography of the sample and its chemical identification with a resolution of the order of ten nanometers, as well as local IR spectra of the different regions of the sample studied, allowing us to estimate the composition of the different phases.

[1]        Pittenger, B., Osechinskiy, S., Yablon, D, Mueller, T. Nanoscale DMA with the Atomic Force Microscope : A New Method for Measuring Viscoelastic Properties of Nanostructured Polymer Materials 2019 Journal of Microscopy 71, 3390–3398.
[2]        Dazzi, A., Prater, C. B. AFM-IR: Technology and Applications in Nanoscale Infrared Spectroscopy and Chemical Imaging. 2017 Chem. Rev. 117, 5146–5173.