Thermodynamic Study of Alkylsilane and Alkylsiloxane-Based Ionic Liquids

• Type: Article in International Scientific Journal
• Date: 2024

Authors

Silva, RMA (Author) Other; Montes-Campos, H (Author) Other; Ferreira, AIMCL (Author) Other; Bakis, E (Author) Other; Luis M N B F Santos (Author) FCUP

Journal

Title: Journal of Physical Chemistry B Materials

Vol. 128

Pages: 3742-3754

ISSN: 1089-5647

Publisher: American Chemical Society

Indexing

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Other information

Authenticus ID: P-010-8B4

DOI: 10.1021/acs.jpcb.3c08333

Abstract (EN): The thermodynamic properties of ionic liquids (ILs) bearing alkylsilane and alkylsiloxane chains, as well as their carbon-based analogs, were investigated. Effects such as the replacement of carbon atoms by silicon atoms, the introduction of a siloxane linkage, and the length of the alkylsilane chain were explored. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the thermal and phase behavior (glass transition temperature, melting point, enthalpy and entropy of fusion, and thermal stability). Heat capacity was obtained by high-precision drop calorimetry and differential scanning microcalorimetry. The volatility and cohesive energy of these ILs were investigated via the Knudsen effusion method coupled with a quartz crystal microbalance (KEQCM). Gas phase energetics and structure were also studied to obtain the gas phase heat capacity as well as the energy profile associated with the rotation of the IL side chain. The computational study suggested the existence of an intramolecular interaction in the alkylsiloxane-based IL. The obtained glass transition temperatures seem to follow the trend of chain flexibility. An increase of the alkylsilane chain leads to a seemingly linear increase in molar heat capacity. A regular increment of 30 JK-1mol(-1) in the molar heat capacity was found for the replacement of carbon by silicon in the IL alkyl chain. The alkylsilane series was revealed to be slightly more volatile than its carbon-based analogs. A further increase in volatility was found for the alkylsiloxane-based IL, which is likely related to the decrease of the cohesive energy due to the existence of an intramolecular interaction between the siloxane linkage and the imidazolium headgroup. The use of Si in the IL structure is a suitable way to significantly reduce the IL's viscosity while preserving its large liquid range (low melting point and high thermal stability) and low volatilities.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 13