Introducing Innovative Approaches to Materials Characterization

The 2023 Innovations in Materials Characterization Summit was held at Carnegie Mellon University in Pittsburgh, PA August 7-9, 2023. This event gathers scientific experts in a wide range of material characterization approaches for two days of presentations and discussions around the challenges they face and the solutions they’ve discovered. This year’s summit was sponsored by Waters Corporation (Milford, MA) and Bausch + Lomb (Bridgewater, NJ). Presentations covered a wide variety of topics including new material synthesis, chromatographic analysis, mass spectrometry (MS) advances, and integrated analytical approaches. Highlights from the presentations are included below.

Materials characterization using mass spectrometry

MS is a very powerful materials characterization method due to its combination of specificity, range of applications, and ease of use. Chrys Wesdemiotis from Akron University, Thierry Fouquet from Bausch + Lomb, Mark Morris from Covestro, Chris Shaffer from 3M Company, and Mark Bier from Carnegie Mellon University addressed different approaches of applying MS to a wide range of polymeric materials.

Highlights from their presentations included:

Improvements in polymer MS data analysis using improved Kendrick analysis
Using matrix assisted laser desorption/ionization (MALDI) MS to characterize by-products of polymerization
MS/MS to sequence polymer architecture including branching and heterogeneity
Ion mobility to explore polymer architecture
Mild pyrolysis MS through techniques like direct analysis in real time (DART) and atmospheric solids analysis probe (ASAP)
Surface layer MALDI to examine surface specific species, contaminants, and determine the root cause of defects
Using a nebulizer to evenly apply the MALDI matrix to a sample
ASAP MS approaches coupled with principal component analysis to identify where in the process the performance issues occur.
Nanoelectrode ambient ionization (NAI) using super sharp needles to ionize analytes in air
Mechanospray ionization (MoSI) using vibration to make droplets that are introduced to a MS instrument. MoSI is a softer ionization method than electrospray ionization and enables the analysis of dimers and adducts
Superconducting tunnel junction (STJ) enables the analysis of ultrahigh molecular mass species. The signal is proportional to the kinetic energy of the ion striking the detector, and can detect molecules in the GD range
Optical ion trap (OIT) combines a linear ion trap, a laser and fluorescence to monitor the motion of ultrahigh mass species.

An important takeaway from the MS discussions was Fouquet’s approach to transform MS data into powerful two-dimensional plots that provide information about the polymers by inspection. The key to this approach is to plot the fractional excess mass versus the nominal mass to charge ration (m/z). A further refinement redefines the reference mass from ¹²C equals 12.000 D to something relevant to the analysis, like defining the mass of methyl methacrylate to 100.000 D. This approach shows great promise in speeding up the analysis of polymeric materials by high resolution MS, even of unknown materials.

Integrated analytical approaches to material characterization

Most characterization work on complex materials involves a team of scientists and a variety of complementary techniques. While no single approach can fully solve the problem, learning about parts of the material through different experiments often leads to successful results. This approach requires teamwork, cooperation, and generalist skills. Drew Hoteling from Bausch + Lomb, Kathryn Beers of the National Institute of Standards and Technology (NIST), Anthony Gies from Dow, Inc, Aaron Hedegaard from 3M Company, and Rachel Behrens from the University of California Santa Barbara all used a variety of tools and approaches to solve important problems.

Highlights from their presentations included:

Determining the fate of the soft polymer produced by the polymerization of n-vinylpyrrolidone, which is important to maximize the comfort of a contact lens
Using multiple techniques to train a high performance near infrared system using artificial intelligence software to understand crystallinity and branching in polyolefins
Determining the optimal operational balance to manufacture isocyanate products using atomic analysis, viscosity, nuclear magnetic resonance (NMR), and a variety of MS techniques
Using thermomechanical modeling involving time – temperature – cure superposition to demonstrate that shrinkage could be used as a proxy for cure
Using chromatography, MS, rheology, thermal, and infrared analyses to analyze different real-world polymer films.

There were two key takeaways from this session. The first was the detail, cooperation, and power of a truly integrated analytical approach as described by Hoteling. The multi-technique approach answered key questions about the nature of the complex material. His talk emphasized the need for different techniques and expertise, and the ability to combine the data to solve complex challenges. While describing the role of 14 different methods, Hoteling showed how the different pieces of data supported the conclusions drawn by the team.

The second was the importance of improving polymer recycling as described by Beers, who emphasized the benefits of keeping atoms and molecules inside the economy, rather than committing them to waste streams. She showed multiple examples of using better data to help understand and improve material recycling challenges. One of the key advances was the use of infrared spectroscopy, high temperature SEC, differential scanning calorimetry, and density data to train a high performance near infrared system using artificial intelligence software to understand crystallinity and branching in polyolefins. NIST has created a public dataset using these data to help promote more intelligent recycling approaches for plastics.

Chromatographic analyses of complex polymers

Chromatographic separation techniques are very helpful in characterizing complex materials and formulations. Separating components enables them to be analyzed individually, simplifying the characterization process. Miroslav Janic from Dow, Inc., Catherine Smith from Arkema, Inc., and Judit Puskas of the Ohio State University discussed powerful, hyphenated systems designed to get more information from chromatographically separated samples.

Highlights from their presentations included:

Coupling size exclusion chromatography (SEC) or advanced polymer chromatography (APC) with ICP/MS provided quantitation of heteroatoms in formulated systems
Coupling APC with electrospray ionization MS to characterize complex polymers
Analyzing SEC fractions with pyrolysis gas chromatography mass spectrometry
Designing a multi-detector system that can perform SEC, liquid chromatography, and liquid chromatography at critical conditions

A key takeaway from this session was the flexibility that comes with coupling APC to ICP/MS presented by Janic. Using APC extends the solvent systems available to ICP. The very short experiment times deliver much less solvent to the torch, limiting the issues associated with many organic solvents. Janic found no significant peak broadening when hyphenating with ICP/MS.

Synthetic approaches to modern materials

Improvements in materials requires collaboration between synthetic scientists who focus on inventing new materials, develop more sustainable feedstocks, and improve processes to generate useful materials, and the analytical scientists who develop innovative characterization methods to understand what was made. Krzysztof Matyjaszewski. Kevin Noonan, and Daphne Chan from Carnegie Mellon University presented work from their research groups making new materials combining composition, topology, and functionality.

Key highlights from this session include:

Improving the oxygen sensitivity of atom transfer radical polymerization to enable these reactions to be done at the bench
The benefits of using π-conjugated materials, especially furans as sustainable feedstocks
Functionalizing the starting monomers to create interesting three-dimensional helical structures
Using proteins to replace hard segment polymers in crosslinked structures
Functionalizing proteins to reduce the moisture sensitivity of the resulting materials
Including dynamic covalent bonds to greatly aid reprocessing and recycling of materials.

The key takeaway from this session is the need for more sustainable feedstocks available to synthetic chemists to make modern materials. Both Noonan and Chan emphasized the importance of finding and improving natural and sustainable building blocks in the creation of their materials. Their work connects well with Beers presentation on improving circularity in the materials economy.

One of the key benefits of smaller conferences like this is the ease of meeting and talking with all of the participants. There is ample opportunity to ask questions, get new ideas, and propose potential solutions to all the experts in the room. The participants came from very diverse technical and organizational backgrounds and the sharing was rich and useful.