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Aggregation of an ionic-liquid type hydrotrope 1-Butyl-3-methylimidazolium p-toluenesulfonate in aqueous solution

Yin, Tianxiang, Chen, Yaling, Shen, Weiguo
Colloids and surfaces 2019 v.564 pp. 95-100
aggregation behavior, aqueous solutions, cations, colloids, light scattering, surface tension, temperature
In this work, the aggregation behavior of 1-butyl-3-methylimidazolium p-toluenesulfonate (BmimTOS), a new type of cationic hydrotrope, was investigated, where two distinct inflection points C1 and C2 were reflected by the change of conductivity, micro-polarity, surface tension. Therefore, it is speculated that small aggregate was formed in BmimTOS aqueous solution after C1 and structure change of these aggregates may be presented to form larger aggregates after C2. The formation of aggregate and the change of the aggregate size were further confirmed by dynamic light scattering (DLS) measurements. However, as suggested by micro-polarity measurements, these aggregates are not typical micelle-like ones. Furthermore, such two-step aggregation behavior was shown to be presented at a wide temperature region from 288.15 K to 318.15 K; however, the phenomenon cannot be observed when the alkyl chain length on imidazolium cation was changed into ethyl-, hexyl-, or octyl-.