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@ARTICLE{Rudani:1055047,
author = {Rudani, Binny A. and Kriegs, Hartmut and Wiegand, Simone},
title = {{H}ydrophilicity controls thermodiffusion in alkylammonium
chlorides},
journal = {The European physical journal / E},
volume = {49},
number = {3},
issn = {1292-8941},
address = {Heidelberg},
publisher = {Springer},
reportid = {FZJ-2026-01839},
pages = {17},
year = {2026},
abstract = {In this study, we examine the Soret effect of ammonium
chloride (NH4Cl) and its alkyl-substitutedderivatives:
dimethylammonium chloride (DMACl), ethylammonium chloride
(EACl), and trimethylammoniumchloride (TMACl) in aqueous
solution using infrared thermal diffusion forced Rayleigh
scattering.The Soret coefficient, ST, increases
systematically with alkyl substitution, following the trend
NH4Cl <<DMACl < EACl << TMACl, while hydrophilicity
decreases correspondingly. Across the investigated
temperaturerange (15−45◦C) and concentrations (1–4
mol/kg), ST increases with both temperature andthe degree of
alkyl substitution. However, the concentration dependence
varies among the salts. DMACl,EACl, and TMACl exhibit
decreasing ST with increasing concentration and are
predominantly thermophobic;TMACl remains thermophobic under
all conditions. In contrast, NH4Cl shows a
non-monotonicconcentration dependence above 35◦C and is
largely thermophilic. We discuss the origin of this
minimumat elevated temperatures in relation to other aqueous
salt systems that exhibit non-monotonic behaviorof ST with
respect to concentration. Overall, each additional alkyl
substitution decreases the temperaturesensitivity of the
Soret coefficient, ΔST(ΔT), consistent with reduced solute
hydrophilicity. Furthermore,we observe a clear correlation
between the thermal diffusion coefficient and the thermal
expansion coefficientin these aqueous electrolyte solutions.
This is consistent with the trends reported for nonpolar
organicmixtures and aqueous solutions of non-ionic solutes.
These findings highlight thermodiffusion as a sensitiveprobe
for understanding},
cin = {IBI-4},
ddc = {530},
cid = {I:(DE-Juel1)IBI-4-20200312},
pnm = {5241 - Molecular Information Processing in Cellular Systems
(POF4-524)},
pid = {G:(DE-HGF)POF4-5241},
typ = {PUB:(DE-HGF)16},
doi = {10.1140/epje/s10189-026-00561-3},
url = {https://juser.fz-juelich.de/record/1055047},
}