Raman spectroscopy becomes increasingly important in both industry and fundamental research. Due to fast development of lasers, holographic optics and charge-coupled device (CCD) detectors, Raman spectrometers are getting more sensitive/precise and relatively inexpensive. Concerning this matter, in this decade, several elegant and pedagogically useful experiments were designed for teaching Raman spectroscopy in undergraduate laboratory classes. In this presentation, a more complex experiment that is appropriate for an advanced physical chemistry laboratory will be described in detail. Recent advances in understanding of the Raman spectrum of water in both the regular and supercooled states (by Markland, Ben-Amotz and coworkers) as well as the previous work on high and low density ice (by Skinner) are the theoretical foundation for the presented experiments. Our experiments are performed on bulk water and water dispersed in a liquid polymer matrix such that the water droplets consist of several thousands of molecules. The DSC experiment performed on the sample consisting of 40 wt% water dispersed in poly(propylene glycol) matrix in the temperature range from 20 to -150 0C shows a pronounced second order transition at -80 0C, but it is not clear what the aggregate state of water is. The comparison between the Raman spectra of low density ice and that of the water droplets shows that water remains unfrozen even at -150 0C provided that the cooling rate is 10 K/min or faster. These Raman spectroscopy experiments confirm the hypothesis that the thermodynamic properties of water are sample size dependent. In addition, the experiments also enable the students to better understand hydrogen bonding in water.

Identifying aggregate state and determining temperature of water below 0 0C using Raman spectroscopy: Experiments for undergraduate teaching and research in advanced physical chemistry laboratory

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.