Solubility and characterisation of alkyl polyglucosides (APGs) in choline chloride-urea deep eutectic solvent

• Alkyl poly glucosides (APGs) in choline chloride based deep eutectic solvent reline. • CMC determined with pyrene-probe fluorescence method. • Transfer energy of a CH 2 unit from solvent to micelle only half as large in reline than in water. • Micellisation of APG surfactants in reline is exothermic and very different than in water. The motivation for this work arises from the fact that only a few surfactants have been reported to dissolve well in reline, a deep eutectic mixture of choline chloride and urea, thus limiting the future application of this novel solvent. The solubility of different types of alky surfactants in the deep eutectic solvent (DES) reline has been investigated, and it has been observed that, in general, surfactants with glucoside head groups are well soluble, in considerable contrast to ones with ethylene oxide head groups. This finding is very interesting, as so far, only a few surfactants have been found to form aggregates in reline. This work extends this small group by the whole class of sugar surfactants. The determination of the critical micelle concentration (CMC) by the pyrene method showed that the CMC values are much higher than in water but decrease systematically with the increasing length of the alkyl chain. The thermodynamic analysis yields that the solvophobic effect, quantified by the transfer energy per CH 2 group from solvent to micelle in reline, is ∼ –0.6 kT, only about half as large as for water. Further analysis of the temperature dependence of the CMC shows that micellisation in reline is always exothermic for the studied alkyl polyglucosides (APGs), while entropy favours micellisation only at lower temperatures. Accordingly, micellisation in reline has a very different driving force than in water. APGs dissolve and self-assemble easily in the DES reline, opening the field of functionalising and applying DES in an interesting direction for formulating fully biocompatible systems.