Nonlinear response in oligomers across chain lengths
Year: 2025
Type: article
Abstract: We present third-order and first-order dielectric measurements on a series of N -propylene glycol ( N -PG) oligomers, focusing on the role of molecular length N in the glass transition. To avoid polymeric effects, we restricted the study to short chains ( N = 1 – 20 ). Linear dielectric susceptibility Δ χ 1 scales as 1 N , suggesting that only the terminal hydroxyl (–OH) groups contribute significantly to the dipolar response, while the flexible backbone units remain largely inactive. Third-order susceptibilities χ 3 ( 3 ) exhibit a growing hump upon cooling for all N -PG, consistent with the Bouchaud-Biroli prediction. This allows us to extract the relative evolution of the number of dynamically correlated molecules N corr , which is as expected increasing upon cooling. But surprisingly, this evolution is identical across all oligomers, regardless of chain length, even though the size of the largest molecules likely exceeds that of the dynamic heterogeneities. This robustness of the relative evolution of N corr ( τ α ) allows to deduce that it is insensitive to the backbone linking the monomers, the fragility, the OH-bond density, or the strength of the dipole-dipole interactions among oligomers, standard criteria to describe the phenomenon. These findings challenge kinetically constrained models, which fail to account for the observed behavior, while supporting the predictions of the random first-order transition theory.
Source: Physical Review Research
DOI: 10.1103/35b2-ysz4
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,625
Funder: Agence Nationale de la Recherche
OpenAlex ID: W4416931969