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.
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