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Advances in Nanoscale Infrared Spectroscopy to Explore Multiphase Polymeric Systems

Published: June 23rd, 2023



1Nanoscience Technology Center, Physics Department, University of Central Florida, 2Physics Department, University of Central Florida

This protocol describes the application of atomic force microscopy and nanoscale infrared spectroscopy to evaluate the performance of photothermal nanoscale infrared spectroscopy in the characterization of three-dimensional multi-polymeric samples.

Multiphase polymeric systems encompass local domains with dimensions that can vary from a few tens of nanometers to several micrometers. Their composition is commonly assessed using infrared spectroscopy, which provides an average fingerprint of the various materials contained in the volume probed. However, this approach does not offer any details on the arrangement of the phases in the material. Interfacial regions between two polymeric phases, often in the nanoscale range, are also challenging to access. Photothermal nanoscale infrared spectroscopy monitors the local response of materials excited by infrared light with the sensitive probe of an atomic force microscope (AFM). While the technique is suitable for interrogating small features, such as individual proteins on pristine gold surfaces, the characterization of three-dimensional multicomponent materials is more elusive. This is due to a relatively large volume of material undergoing photothermal expansion, defined by the laser focalization onto the sample and by the thermal properties of the polymeric constituents, compared to the nanoscale region probed by the AFM tip. Using a polystyrene (PS) bead and a polyvinyl alcohol (PVA) film, we evaluate the spatial footprint of photothermal nanoscale infrared spectroscopy for surface analysis as a function of the position of PS in the PVA film. The effect of the feature position on the nanoscale infrared images is investigated, and spectra are acquired. Some perspectives on the future advances in the field of photothermal nanoscale infrared spectroscopy are provided, considering the characterization of complex systems with embedded polymeric structures.

Atomic force microscopy (AFM) has become essential to image and characterize the morphology of a wide variety of samples with nanoscale resolution1,2,3. By measuring the deflection of an AFM cantilever resulting from the interaction of the sharp tip with the sample surface, nanoscale functional imaging protocols for local stiffness measurements and tip-sample adhesion have been developed4,5. For soft condensed matter and polymer analysis, AFM measurements exploring the nanomechanical and nanochemical properties of loc....

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1. Making polyvinyl alcohol (PVA) solution

  1. Measure water and PVA polymer pellets (see Table of Materials) to create a 10 mL solution at a 20% PVA to water ratio by weight.
  2. Heat the water in the glassware over a hot plate set to 100 °C.
  3. Place the PVA polymer pellets into the heated water. Insert a magnetic stir bar.
  4. Reduce the heat to 80 °C and stir until the PVA fully dissolves.
  5. Cover the top of the glassware to prevent contam.......

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PS ((C8H8)n) beads were deposited on a clean Si substrate (Figure 1A) and on PVA ((CH2CHOH)n) (Figure 1B,C). Due to the poor adhesion of the bead on Si, nanoIR imaging in contact mode could not be acquired for this sample. Instead, using the optical view of the sample on nanoIR, the gold-coated AFM probe was engaged on top of the PS bead in contact mode, with an estimated force of about 100 .......

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AFM combined with nanoIR spectroscopy can provide nanoscale chemical information using a cantilever in contact mode and a pulsed tunable IR light source. Model systems, such as embedding an absorber with finite dimensions in the volume of a polymeric material, are important to improve the understanding of image formation mechanisms and to determine the performance of the tool. In the case of the PS/PVA configuration presented here, optimization was carried out to obtain a stable PS bead positioned above or below the surf.......

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This work was supported by the National Science Foundation (NSF CHE-1847830).


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NameCompanyCatalog NumberComments
10|0 2200 Golden Taklon RoundZem
5357-8NM TweezersPelco
Adhesive TabsTed Pella16079
AFM metal specimen disksTed Pella16208
Cantilever for nanoIR measurementsAppNanoFORTGG
Cell culture dishesGreiner bio-one GmbH
Floating optical tableNewportRS 4000
Magnetic stir bar
Microparticles based on polystyrene size: 5 µmSIGMA-ALDRICH79633
nanoIR2 microscopeBrukerContact mode NanoIR2
Nitrogen TankAirgas
Petri dishesGreiner bio-one GmbH
Polyvinyl AlcoholSIGMA-ALDRICH363170this polymer was only 87%-89% hydrolyzed, which explains the presence of residual C=O at 1730 cm-1
Quantum Cascade LaserDaylight Solutions1550-1800 cm-1 range
Silicon waferMEMC St. Peters#901319343000
Spin coaterOscilla

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