Conformation in Ultrathin Polymer Brush Coatings Resolved by Infrared Nanoscopy

Abstract

Polymer brush coatings are effective in preventing blood coagulation or bacterial attachment, but their chain conformation, while vital for this effect, was never characterized in high spatial resolution. Here, we report mid-infrared spectroscopic nanoscopy studies of few-nanometer-thin poly­(ethylene oxide) (PEO) films which reveal marked spectral variations along the surface at a length scale smaller than 100 nm and originating only from the physical conformation of the chains. The conformation and average orientation of the polymer chains in the layer is extracted from the spectra with the aid of theoretic modeling, confirming the spontaneous formation of a crystalline phase. This result suggests spectroscopic nanoscopy as a powerful new tool to characterize polymer brush coatings.

Infrared-spectroscopic, dynamic near-field microscopy of living cells and nanoparticles in water

“…1 a 7 – 10 . Commercially available s-SNOMs complemented by nano-FTIR capability routinely resolving 30 nm have given new insights in many fields, from extaterrestrial minerals 11 to ultrathin polymers 12 and, as an example from biophysics, when mapping dried insulin samples' secondary-structure changes along single protofibrils 13 . A pertaining infrared-vibrational nanospectroscopic study of prion proteins undergoing conformational transitions 14 would be highly interesting but requires, as all living matter, the presence of water.…”

Macromolecular Orientation in Biological Tissues Using a Four-Polarization Method in FT-IR Imaging

“… 1 , 2 However, structural aspects are still waiting to be incorporated into this modality. 3 , 4 Taking advantage of the anisotropic orientation of molecules in solid samples, it is possible to obtain different material responses when changing linear polarization of incoming IR light. Using this fact, the determination of molecular orientation with Fourier transform IR (FT-IR) was extensively explored, but mostly for polymer samples.…”

“…Infrared (IR) spectroscopic imaging offers a wealth of information about the chemical composition of the sample in a spatially resolved manner, which is particularly attractive in biomedical applications. , However, structural aspects are still waiting to be incorporated into this modality. , Taking advantage of the anisotropic orientation of molecules in solid samples, it is possible to obtain different material responses when changing linear polarization of incoming IR light. Using this fact, the determination of molecular orientation with Fourier transform IR (FT-IR) was extensively explored, but mostly for polymer samples. , For example, polarized IR spectroscopy turned out to be an effective tool to examine the orientation and relaxation of drawn poly­(ethylene terephthalate). − A more quantitative approach in the form of Herman’s function with a two-polarization approach was used to determine the level of molecular ordering. ,,, Later, a four-polarization method was proposed, − which gave a great tool for further polymer analysis, , especially when combined with imaging modalities. ,, A variety of other techniques may be used to determine molecular orientation: nuclear magnetic resonance, X-ray diffraction, polarized visible microscopy, fluorescence microscopy, second-harmonic generation (SHG), or Raman spectroscopy (RS) .…”

Analytical Methods for Characterization of Nanomaterial Surfaces

“…Depth-resolved information has also been obtained from s-SNOM to provide 3D sample reconstruction. Nano-FTIR has been used to differentiate surface and subsurface layers, to characterize conformation and orientation of polymer coatings with a lateral resolution in the order of tens of nanometers, and to study surface domain structures …”