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The appearance of ice I in the smallest possible clusters and the nature of its phase coexistence with liquid water could not thus far be unraveled. The experimental and theoretical infrared spectroscopic and free-energy results of this work show the emergence of the characteristic hydrogen-bonding pattern of ice I in clusters containing only around 90 water molecules. The onset of crystallization is accompanied by an increase of surface oscillator intensity with decreasing surface-to-volume ratio, a spectral indicator of nanoscale crystallinity of water. In the size range from 90 to 150 water molecules, we observe mixtures of largely crystalline and purely amorphous clusters. Our analysis suggests that the liquid–ice I transition in clusters loses its sharp 1st-order character at the end of the crystalline-size regime and occurs over a range of temperatures through heterophasic oscillations in time, a process without analog in bulk water.
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Calibration-Free Second Harmonic Generation (SHG) Image Analysis for Quantification of Trace Crystallinity Within Final Dosage Forms of Amorphous Solid Dispersions
A statistical model enables auto-calibration of second harmonic generation (SHG) images for quantifying trace crystallinity within amorphous solid dispersions (ASDs) over a wide dynamic range of crystallinity. In this paper, we demonstrate particle-counting approaches for quantifying trace crystallinity, combined with analytical expressions correcting for particle overlap bias in higher crystallinity regimes to extend the continuous dynamic range of standard particle-counting algorithms through to the signal averaging regime. The reliability of the values recovered by these expressions was demonstrated with simulated data as well as experimental data obtained for an amorphous solid dispersion formulation containing evacetrapib, an Eli Lilly and Company compound. Since particle counting independently recovers the crystalline volume and the SHG intensity, the average SHG intensity per unit volume can be used as an internal calibrant for quantifying crystallinity at higher volume fractions, for which particle counting is no longer applicable.
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- Award ID(s):
- 1710475
- PAR ID:
- 10545789
- Publisher / Repository:
- SAGE Publications
- Date Published:
- Journal Name:
- Applied Spectroscopy
- Volume:
- 72
- Issue:
- 11
- ISSN:
- 0003-7028
- Format(s):
- Medium: X Size: p. 1594-1605
- Size(s):
- p. 1594-1605
- Sponsoring Org:
- National Science Foundation
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