Natural deep eutectic solvents from choline chloride and betaine - physicochemical properties

The preparation of natural deep eutectic solvents (NADESs) from cheap and readily available raw materials is reported. In this work, we have considered mixtures of choline chloride (CC) or betaine (Bet) with 3 sugar molecules (glucose (Glu), xylose (Xyl) and sucrose (Suc)) and 2 carboxylic acids (citric (CA) and tartaric (Tart) acids). The formation of NADESs was investigated by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The CC mixtures give origin to NADESs for 1:1 M ratio with the sugar molecules and for 2:1, 1:1 and 1:2 with the carboxylic acids, while Bet mixtures only formed NADES with the carboxylic acids. The effect of water content (up to 5% (wt.%)) and temperature in conductivity and rheology were characterized. The NADESs were found to be non-thixotropic, Newtonian liquids with high viscosity, decreasing with increasing temperature and water content. The conductivity is limited by charge carrier mobility, thus increasing with water content and temperature.Ivo Aroso acknowledges the financial support from FCT through grant SFRH/BD/42273/2007. Funding was also granted from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement no. REGPOT-CT2012-316331-POLARIS and from Project “Novel smart and biomimetic materials for innovative regenerative Medicine approaches (ref.: RL1 - ABMR - NORTE-01-0124-FEDER- 000016)” co-financed by North Portugal Regional Operational Programme (ON.2 – O Novo Norte), under the National Strategic Reference Framework (NSRF), through the European Regional Development Fund (ERDF).