Doyoung Moon

Quantitative image analysis of broadband CARS hyperspectral images of polymer blends.

We demonstrate that broadband coherent anti-Stokes Raman scattering (CARS) microscopy can be very useful for fast acquisition of quantitative chemical images of multilayer polymer blends. This is challenging because the raw CARS signal results from the coherent interference of resonant Raman and nonresonant background and its intensity is not linearly proportional to the concentration of molecules of interest. Here we have developed a sequence of data-processing steps to retrieve background-free and noise-reduced Raman spectra over the whole frequency range including both the fingerprint and C-H regions. Using a classical least-squares approach, we are able to decompose a Raman hyperspectral image of a tertiary polymer blend into quantitative chemical images of individual components. We use this method to acquire 3-D sectioned quantitative chemical images of a multilayer polymer blend of polystyrene, styrene-ethylene/propylene copolymer, and polypropylene that have overlapping spectral peaks.

Multi-sample micro-slit rheometry

We have developed a multi-sample micro-slit rheometer (MMR) which is capable of measurements over a broad range of temperatures, viscosities and shear rates. The instrument is mechanically simple as the flow is generated by external gas pressure and the shear rate is measured through optical tracking of the flow front. In the current implementation, the required volume of each sample is approximately 20μL and we measure four samples simultaneously. We demonstrate the performance of the MMR by measurement of the flow curves (viscosity versus shear rate) of three representative polymers: A polydimethylsiloxane melt, a polyisobutylene solution, and a polystyrene melt. We adapt standard data correction methods to account for shear-thinning and entry/flow-front effects. We report a high level of accuracy and precision. This instrument will be particularly useful in cases of multiple samples, limited material quantity, and when optical access is useful.