GROUND-breaking work on the characterisation of sub-micron polymer domains using AFM-IR has been published in the October 2011 issue of Applied Spectroscopy, a monthly journal published by the Society for Applied Spectroscopy.
Written by Isao Noda of Procter and Gamble, and Curtis Marcott of Light Light Solutions, the paper discusses the combination of atomic force microscopy (AFM) and infrared (IR) spectroscopy in a single AFM-IR instrument capable of producing sub-micrometre IR spectra and absorption images. The technique enables the spectroscopic characterisation of microdomain-forming polymers at previously-inaccessible levels.
One of the authors, Kevin Kjoller, uses the Anasys AFM-IR system
The system uses a tunable IR laser to generate 10ns pulses, which excite polymer films cast onto zinc selenide prisms. Short-duration thermomechanical waves created by the absorption of IR and resulting thermal expansion were studied by monitoring the contact resonance modes of the AFM cantilever, which in turn enables the resolution of crystalline microdomains of different sizes.
The technique generated clear and sharp spectra which reveal important sub-micron information about the samples, particularly in the differences between amorphous and crystalline regions. As a result, it is now possible to monitor the development of polymer crystalline structures at varying distances from a nucleation site, where the site was generated by bringing a heated AFM tip close to a specific location to locally anneal the sample.
The paper says the technique makes a wealth of new information available to the researcher. For example, an AFM image collected with the laser tuned at 1276cm-1 shows the distribution of the different microdomain structures. By collecting spectra at 200nm increments starting from a nucleation site, it then becomes possible to gain insights into the crystallisation mechanism of polymer systems.
Potential application areas include multilayer films and laminates, polymer blends, organic defect analysis, tissue morphology and histology, organic photovoltaics, and subcellular spectroscopy.
Ref: Spatial Differentiation of Sub-Micrometer Domains in a Poly(hydroxyalkanoate) Copolymer Using Instrumentation that Combines Atomic Force Microscopy (AFM) and Infrared (IR) Spectroscopy, Curtis Marcott, Michael Lo, Kevin Kjoller, Craig Prater, and Isao Noda. Applied Spectroscopy, Volume 65, Number 10, 2011.