Integration of ultrafast scanning calorimetry with micro-Raman spectroscopy for investigation of metastable materials.

Abstract

A stage-type ultrafast scanning calorimetry (ST-UFSC) with controlled heating and cooling rates up to 10(5) K s(-1) was designed to integrate with microstructural characterization. This enables us to precisely control the evolution of fast transitional states of metastable samples provided by the UFSC platform, and to follow subtle structural changes between intermediate stages. As an example, we collected the Raman spectra of poly(ethylene terephthalate) quenched at different crystallization states obtained by programed rapid cooling and heating processes. Because of the very small sample mass for UFSC measurements, from minimum few nanograms to sub-micrograms, the sample's temperature is very sensitive to the perturbation from the laser illumination of the Raman spectrometer. Real time temperature monitoring and compensation was accompanied during the whole process of in situ spectroscopy. The results showed a good agreement of crystallization kinetics obtained from the Raman spectroscopy and from the calorimetric melting enthalpy, given that the sample temperature is well controlled during spectroscopic measurements and that the heating rate for calorimetry is fast enough to suppress structural reorganization during heating scans. We expect that the ST-UFSC is suitable to be integrated with other micro-analysis techniques to investigate the structure and dynamics of metastable states obtained by fast thermal treatments.