The Local Structure of Triphenyl Phosphite Studied Using Spallation Neutron and High-Energy X-ray Diffraction

Abstract

Spallation neutron and high-energy X-ray diffraction experiments have been performed to investigate the local structural changes in triphenyl phosphite (TPP) in the crystalline, glacial, glassy, and supercooled liquid phases. The hydrogen/deuterium first-order difference method shows a large increase in intensity due to additional hydrogen correlations in the crystalline spectra compared to the glass and supercooled liquid at ∼3.0 and 3.4 Å. These features are shown to be largely due to inter-phenyl ring H-C/H interactions, which are probably associated in part with the formation of weak intermolecular hydrogen bonds. The high-energy X-ray diffraction data show a decrease in correlations at 3.12 Å which is attributed to changes in C-O/P intramolecular interactions between the glacial and crystalline forms. The structural evolution of the glacial state was also measured over time using total neutron diffraction. The largest structural differences between the early glacial and crystalline states are observed at 3.0 and 4.5 Å. Moreover, as the transformation progresses, the glacial spectra cannot be adequately described as a simple mixture of supercooled liquid and crystalline components. These results suggest that changes in molecular conformation and nearest-neighbor interactions are responsible for the existence of the glacial state.

Polyamorphism Mirrors Polymorphism in the Liquid–Liquid Transition of a Molecular Liquid

“…1(b)). 33 This result is consistent with previous x-ray and neutron scattering, 27 NMR, 28 and dielectric relaxation experiments. 34 The low contrast Maltese cross pattern observed in the droplets generated below 226 K (low crystallinity) is inconsistent with spherulitic growth.…”

“…There is considerable discussion on whether the LLT is a real transition 10,19,[27][28][29][30] or instead the arrested growth of nanocrystals. 13,22,31,32 In this nanocrystal hypothesis, as the temperature is lowered, the probability for nucleation of crystal 2 increases, however, the viscosity also increases on approaching the glass transition temperature, resulting in "a heavily nucleated state composed of nanocrystals of the stable crystalline phase embedded in the matrix of non-transformed supercooled liquid".…”

The reversibility and first-order nature of liquid–liquid transition in a molecular liquid

“…X-ray diffraction data of the glacial phase formed at a very low temperature show only broad amorphous peaks and no sharp Bragg peaks, indicating the absence of distinct translational order in the glacial phase2426353637. This feature cannot be explained by the plastic-crystal scenario.…”

Communication: Crystallite nucleation in supercooled glycerol near the glass transition

“…However, neutron and x-ray experiments suggest the glacial phase to be a liquid and nanocrystalline mixed phase. 18,[24][25][26] Although theories of supercooled liquids such as the mode coupling theory, 27 the random first-order transition theory (RFOT), 28 and the frustration-based theory 23 have been proposed, none of them includes the competition between the supercooled liquid state and the crystalline state. Recently, Stevenson and Wolynes extended the RFOT theory of glasses to account for the existence of a crystalline state.…”