Super-resolved 3D mapping of molecular orientation with vibrational techniques

Abstract

When a sample has an anisotropic structure, it is possible to obtain different information, when changing polarization of incident light. Using polarized light of a single vibrational band to determine the in-plane orientation and internal ordering of a sample is a typical practice in materials science. Acquiring mapping data at four different polarizations with a stationary sample than just at two polarizations offers much more insight into the sample structure with proper mathematical treatment. A concurrent analysis of two vibrational bands with perpendicular transition moment orientations allows the understanding of the orientational ordering in three dimensions. We show here, to the best of our knowledge, the first application of concurrent analysis to IR spectromicroscopy data and obtain orientation angles of a model spherulite polycaprolactone sample. Moreover, we show that this method can be easily applied to high resolution, diffraction limited FT-IR and Raman imaging and even to sub-diffraction limit O-PTIR imaging. Due to the non-tomographic experimental approach, no image distortion is visible and nanometer scale orientation domains can be observed. 3D bond orientation maps will enable in-depth characterization of sample structure in a quantitative manner enabling more precise control of their physicochemical properties and function.

Insight into Poly(l-lactic acid) Coexisting Amorphous and Semicrystalline Phases Using FT-IR Imaging and Four Polarization-Three Dimensional Macromolecular Orientation Calculation

“…A detailed description of the macromolecular orientation calculation in three-dimensional space can be found elsewhere. 23,24,31 Briefly, the infrared spectrum of macromolecules sample like polymer varies with the direction of linearly polarized incident light. The orientation distribution of the transition dipole moments about the molecular chain axis determines the absorption at each spectra band.…”