arXiv subjects

Igor V. Parshin

Publications and source records attributed to Igor V. Parshin.

4 recordsLinked to original sources

arXiv2026

How alignment controls heat transport in polymer chains with kinks?

Thermal transport in polymer chains is commonly attributed to ballistic propagation of long-wavelength acoustic phonons, which act as Goldstone modes protected by translational symmetry, whereas transport by higher-frequency phonons is suppressed by Anderson localization. Consistent with this picture, highly aligned polymers exhibit exceptionally high thermal conductivity, while poorly aligned polymers are orders of magnitude less conductive and serve as efficient thermal insulators. Here we show that this striking sensitivity to molecular alignment originates from acoustic-phonon scattering by molecular kinks. In the long-wavelength limit, longitudinal acoustic (LA) phonons are completely reflected by a single kink, whereas transverse acoustic (TA) phonons exhibit a universal transmission coefficient of one half. We show that the strong reflection results from the breaking of translational symmetry caused by the change in molecular-axis direction at the kink, while the universal TA transmission originates from virtual scattering through an evanescent transverse Bloch mode. The resulting strong suppression of long-wavelength phonon transport dramatically reduces the thermal conductivity of poorly aligned chains. These findings identify kink engineering as a promising strategy for controlling thermal transport in polymeric materials.

cond-mat.soft↗

arXiv2026

Thermal conductivity of aligned polymers with kinks

Thermal conductivity of aligned polymer molecules can be exceptionally high along the alignment direction due to energy transport through strong covalent bonds. At the same time, it is highly sensitive to molecular conformation, varying by orders of magnitude as a result of gauche kinks. Here, we theoretically investigate phonon transport in kinked polymers by numerically evaluating thermal conductivity and interpreting the results in terms of phonon scattering from randomly distributed kinks. For strongly aligned polymers with restricted deviations from a linear backbone, we find that heat transport becomes superdiffusive at long lengths, with thermal conductivity scaling as $\kappa \propto L^{1/3}$. At shorter lengths, thermal conductivity exhibits non-monotonic behavior: it increases at very short scales due to ballistic transport of almost all phonons, then decreases at intermediate lengths due to the Anderson localization of most phonon modes. These results are consistent with experiments and molecular dynamics simulations, and they elucidate the microscopic mechanisms governing heat transport in polymers.

physics.chem-ph↗

arXiv2024

Ballistic Energy Transport via Long Alkyl Chains: A New Initiation Mechanism

In an effort to increase the speed and efficiency of ballistic energy transport via oligomeric chains, we performed measurements of the transport in compounds featuring long alkyl chains of up to 37 methylene units. Compounds of the N3-(CH2)n-COOMe type (denoted as aznME) were synthesized with n = 5, 10, 15, 19, 28, 37 and studied using relaxation-assisted two-dimensional infrared spectroscopy. The speed of the ballistic transport, initiated by the N3 tag excitation, increased ca. 3-fold for the longer chains (n = 19-37) compared to the shorter chains, from 14.7 Å/ps to 48 Å/ps, in line with an earlier prediction (Nawagamuwage et al. 2021, J. Phys. Chem. B, 125, 7546). Modeling, based on solving numerically the Liouville equation, was capable of reproducing the experimental data only if three wavepackets are included, involving CH2 twisting (Tw), wagging (W), and rocking (Ro) chain bands. The approaches for designing molecular systems featuring higher speed and efficiency of energy transport are discussed.

physics.chem-ph↗

arXiv2023

Maximum propagation speed and Cherenkov effect in optical phonon transport through periodic molecular chains

Optical phonons serve as the fast and efficient carriers of energy across periodic polymers due to their delocalization, large group velocity because of covalent bonding and large energy quantum compared to that for acoustic phonons, as it was observed in a number of recent measurements in different oligomers. However, this transport is dramatically sensitive to anharmonic interactions, including the unavoidable interaction with acoustic phonons responsible for the transport decoherence, suppressing ballistic transport at long distances. Here we show that this decoherence is substantially suppressed if the group velocity of optical phonons is less than the sound velocity of acoustic phonons; otherwise ballistic transport is substantially suppressed by a Cherenkov's like emission of acoustic phonons. This conclusion is justified considering energy and momentum conservation during phonon absorption or emission and supported by the numerical evaluation of lifetimes of the optical phonons. It is also consistent with the recent experimental investigations of ballistic optical phonon transport in oligomers with minor exception of relatively short oligophenylenes.

physics.chem-ph↗