Journal Article

FZJ-2026-01839

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Hydrophilicity controls thermodiffusion in alkylammonium chlorides

Rudani, B. A.FZJ* ; Kriegs, H.FZJ* ; Wiegand, S. (Corresponding author)FZJ*

2026
Springer Heidelberg

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Please use a persistent id in citations: doi:10.1140/epje/s10189-026-00561-3

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

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Contributing Institute(s):

1. Biomakromolekulare Systeme und Prozesse (IBI-4)

Research Program(s):

1. 5241 - Molecular Information Processing in Cellular Systems (POF4-524) (POF4-524)

Appears in the scientific report 2026

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Database coverage:
; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; DEAL Springer ; DEAL Springer ; Ebsco Academic Search ; Essential Science Indicators ; IF < 5 ; JCR ; SCOPUS ; Science Citation Index Expanded ; Web of Science Core Collection

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