I have been through many research articles and didn't find deep eutectic solvent using choline chloride with higher quantity than glycerol... Why this is done. Can anyone explain...??
Deep eutectic solvents are used because they can give unique results. The reason is that it is not the mixture of constituents, a network like structure is formed. Choline chloride glycerol is probably the most studied DES. People show that at 1:2 ratio of choline chloride: glycerol, the depression of freezing point is highest. So, it is believed that at that fraction, network like solvent structure which is responsible for unique des properties is most probable. So, people generally study with that fraction.
Regarding if it can be prepared at higher choline chloride content, is a matter of investigation. And who knows it might show some interesting properties :-)
Whether a DES is liquid at a certain temperature is visualised in a T-x phase diagram describing the equilibrium between the solid (choline chloride) and the liquid (choline chloride + glycerol). The phase diagram has been studied by several groups and can be found here (fig 1C):
Article Eutectic Mixtures Based on Polyalcohols as Sustainable Solve...
A ratio of 2:1 corresponds to a mole fraction of 0.667 for choline chloride. This is a very high molar concentration for a solid salt in a liquid solvent, so ChCl is simply not soluble at ambient temperatures at this composition.
For a clear fundamental interpretation of the solid–liquid phase diagram, see the following two publications:
Article Quantification of the liquid window of deep eutectic solvents
Article Insights into the Nature of Eutectic and Deep Eutectic Mixtures
This question relates to a question I answered earlier:
https://www.researchgate.net/post/Why_my_natural_deep_eutectic_solvent_NaDES_does_not_form_homogeneous_liquid_with_low_water_content
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