Related Experiment Video
Updated: Mar 21, 2026
06:24
High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
7.0K
Solid-solid phase transitions across orientationally disordered phases: The case of tetrachloro-m-xylene
Jonathan F Gebbia1,2, Ares Sanuy1,2, Michela Romanini1,2
1Universitat Politècnica de Catalunya, Grup de Caracterizació de Materials, Departament de Física, EEBE, Eduard Maristany, 10-14, 08019 Barcelona, Catalonia, Spain.
Physical Review. E
|March 20, 2026
Summary
Researchers discovered a new solid-solid phase transition in tetrachloro-m-xylene (TCMX). This transition reorganizes molecular structure but preserves molecular dynamics, offering insights into disordered crystals and phase transitions.
Area of Science:
- Condensed matter physics
- Crystallography
- Materials science
Background:
- Tetrachloro-m-xylene (TCMX) is a hexasubstituted benzene derivative known for its orientational disorder.
- Understanding phase transitions in disordered systems is crucial for materials science.
Purpose of the Study:
- To investigate a previously unreported solid-solid phase transition in TCMX.
- To elucidate the relationship between structural changes and molecular dynamics during the transition.
Main Methods:
- Differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) were used to identify and characterize the phase transition.
- Quasielastic neutron scattering (QENS) was employed to study molecular dynamics.
- Molecular dynamics (MD) simulations were performed to understand the microscopic origins of the transition.
Main Results:
- A weak, second-order phase transition was observed near 437K, changing symmetry from monoclinic P2_{1}/n (phase II) to orthorhombic Pnnm (phase I).
- Despite the structural reorganization, molecular dynamics remained governed by 60° in-plane reorientational jumps, with minimal changes in activation energy and relaxation times.
- MD simulations confirmed the transition and revealed the vanishing of orientational correlations between molecular columns in phase I.
Conclusions:
- TCMX exhibits a rare disorder-disorder transition where molecular dynamics are preserved across the phase change.
- Subtle symmetry changes in disordered crystals can lead to significant emergent behavior, impacting plastic phases and phase transitions.
- This study advances the understanding of phase transitions in complex condensed matter systems.
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