You have probably formed a gel or a solidified eutectic mixture. When you mixed the components of the DES, you obtained a colorless and transparent liquid with no precipitate, indicating the formation of a homogeneous mixture. However, when you shook the bottle, you likely introduced air (and some other external factors) that triggered the gelation of the DES. Gelation is a common phenomenon in some eutectic mixtures, where certain components can undergo a reversible phase transition from liquid to gel. This process can be influenced by factors such as temperature, concentration, and specific molecular interactions between the components. This state could also be influenced by the combination of hydrogen bond donor and hydrogen bond acceptor molecules used in the DES. Have you tried heating the mixture? Probably, by heating it and allowing it to cool slowly, you might see the gel return to its liquid form, although in some cases, this does not happen reversibly.

Hi, I have also encountered this issue with a couple of DES I'm working with. There was one where I left it stirring over a day and it had seemingly solidified into something resembling a white glue consistency. Heating does not return it back to a colorless, less viscous state. Attempting to dissolve it in excess water does not work and it will settle at the bottom of the bottle. I assume prolong agitation or stirring induced the formation of small air bubbles which somehow intensified the hydrogen bond networks within the mixture. The semi-solid DES is very stable and it has been sitting upside down on my desk for over a month now. Does not flow.