Relaxation Dynamics of Large and Anisotropic Molecules in a Weakly Polar Matrix.
- 1August Chełkowski Institute of Physics, University of Silesia, 75 Pulku Piechoty 1, Chorzów41-500, Poland.
Abstract
The dynamics of large and anisotropic molecules embedded in glass-forming liquids present complex challenges due to the interplay between molecular shape, host-guest interactions, and macroscopic viscosity. In this work, we investigate fluorophenylene isomers (ortho-F and para-F) dissolved in the ortho-terphenyl (OTP) matrix, combining broadband dielectric spectroscopy, differential scanning calorimetry, and rheology to disentangle host and probe dynamics. While calorimetry reveals a single glass transition dominated by OTP, dielectric measurements resolve two distinct α-relaxation processes: a fast process corresponding to OTP structural relaxation and a slower process associated with probe relaxation, i.e., reorientation of large and anisotropic molecules in a weakly polar matrix. Furthermore, the α-relaxation peak of the guest molecules becomes noticeably narrower upon dilution in OTP. We attribute this behavior to the dynamic homogenization of the local environment arising from the large size mismatch between the guest and the host molecules. Mechanical relaxation times derived from viscosity match the fast dielectric α-process, indicating that OTP exclusively governs the viscous response. Interestingly, the para-F/OTP mixture shows ideal Debye-Stokes-Einstein (DSE) coupling, whereas ortho-F/OTP exhibits systematic decoupling, reflecting the importance of probe dipole orientation and anisotropy.
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BibTeX
@article{blazytko2026relaxation,
title = {{Relaxation Dynamics of Large and Anisotropic Molecules in a Weakly Polar Matrix.}},
author = {Alfred Błażytko and Marzena Rams-Baron and Żaneta Wojnarowska and Marian Paluch},
journal = {The journal of physical chemistry. B},
year = {2026},
month = oct,
doi = {10.1021/acs.jpcb.6c03410},
url = {https://europepmc.org/article/MED/42910871},
note = {CC BY},
}
RIS
TY - JOUR
TI - Relaxation Dynamics of Large and Anisotropic Molecules in a Weakly Polar Matrix.
AU - Alfred Błażytko
AU - Marzena Rams-Baron
AU - Żaneta Wojnarowska
AU - Marian Paluch
PY - 2026
DA - 2026/10/01
JO - The journal of physical chemistry. B
DO - 10.1021/acs.jpcb.6c03410
UR - https://europepmc.org/article/MED/42910871
AB - The dynamics of large and anisotropic molecules embedded in glass-forming liquids present complex challenges due to the interplay between molecular shape, host-guest interactions, and macroscopic viscosity. In this work, we investigate fluorophenylene isomers (ortho-F and para-F) dissolved in the ortho-terphenyl (OTP) matrix, combining broadband dielectric spectroscopy, differential scanning calorimetry, and rheology to disentangle host and probe dynamics. While calorimetry reveals a single glass transition dominated by OTP, dielectric measurements resolve two distinct α-relaxation processes: a fast process corresponding to OTP structural relaxation and a slower process associated with probe relaxation, i.e., reorientation of large and anisotropic molecules in a weakly polar matrix. Furthermore, the α-relaxation peak of the guest molecules becomes noticeably narrower upon dilution in OTP. We attribute this behavior to the dynamic homogenization of the local environment arising from the large size mismatch between the guest and the host molecules. Mechanical relaxation times derived from viscosity match the fast dielectric α-process, indicating that OTP exclusively governs the viscous response. Interestingly, the para-F/OTP mixture shows ideal Debye-Stokes-Einstein (DSE) coupling, whereas ortho-F/OTP exhibits systematic decoupling, reflecting the importance of probe dipole orientation and anisotropy.
SN - 1520-6106
SN - 1520-5207
ER -