Nanoscale Structure in Short‐Chain Ionic Liquids. Issue 17 (14th August 2020)

• Record Type: Journal Article
• Authors: Pontoni, Diego; DiMichiel, Marco; Deutsch, Moshe
• Is Part Of: Chemphyschem. Volume 21:Issue 17(2020)
• Page Start: 1887
• Page End: 1897
• Publication Date: 2020-08-14
• Subjects: ionic liquids -- layering -- supra-molecular structure -- temperature dependence -- x-ray scattering; Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.202000548
• Languages: English
• ISSNs: 1439-4235

Abstract

Abstract: The temperature ( T ) and cationic chain length ( n ) evolution of the nanoscale structure of the sub‐layering‐threshold members of a model family of room temperature ionic liquids (RTILs) is investigated by x‐ray scattering. The measured curves are computer‐resolved into individual Teubner‐Strey‐like lineshapes. The polar‐apolar layering is found to start at n = 3 . Opposite n ‐trends are found at n ≤ 3 for the spacings and correlation lengths associated with the diffraction patterns' two main peaks, and assigned to a shift of balance between the two main interactions, Coulomb and van der Waals, and to increasing packing constraints due to the addition of methylenes. The spacings' thermal expansion coefficients are found to deviate from the macroscopically‐measured values, and to anomalously decrease with increasing temperature. Finally, the reduced temperature scale, t = ( T - T m ) / T m, ( T m = melting temperature), is demonstrated to render the observed trends significantly more systematic than those on a conventional T scale. Abstract : Short‐chain ionic liquids (ILs) are vigorously investigated for many chemical and electrochemical applications. Yet, their nano‐structure's temperature dependence was rarely studied. Our study establishes the threshold for layering in a model IL family, and determines their below‐threshold structure and its temperature evolution, uncovering and discussing, intriguing anomalies.