Spatial Differentiation of Polymer Microdomains Using Nanoscale Infrared Spectroscopy
Marcott, Curtis A.
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Atomic Force Microscopy (AFM) and infrared (IR) spectroscopy have been combined in a single instrument capable of producing nanoscale spatial resolution IR spectra and images. This new capability enables the spectroscopic characterization of microdomain-forming polymers at levels not previously possible. Films of poly(3-hydroxybutyrate-co-3-hydroxyheanoate) were solution cast on ZnSe prisms, followed by melting and annealing to generate spherulites of different sizes. A tunable IR laser generating pulses of the order of 10 ns was used for excitation of the sample films. Short duration thermal waves, due to infrared absorption, were studied by monitoring the resulting excitation of the contact resonance modes of the AFM cantilever. Dramatic differences in the IR spectra are observed in the 1200-1300 cm-1 range as a function of position on a spatial scale of less than one micron. This spectral region is particularly sensitive to the polymer crystallinity, enabling the identification of crystalline and amorphous domains within a single spherulite of this copolymer. The talk will focus on four key points: The nanoIR instrument enables, for the first time, the spectroscopic differentiation of local regions of molecular order in microdomain-forming copolymers at nanoscale spatial resolutions. Studying biodegradable poly(hydroxyalkanoate) (PHA) copolymer, the AFM-IR technique reveals crystalline and amorphous microdomain spectra not previously seen with bulk FTIR. By collecting spectra at 200-nm increments starting from a nucleation site, it is possible to gain insights into the crystallization mechanism of polymer systems. Using heating via nanoscale thermal probes, the researchers locally modified the crystalline content and observed corresponding changes in nanoscale IR absorption spectra.
- Nano@Tech Lecture Series