Strong Microbasicity in PVA/ChCl Eutectogels Induced by a Large Population of Bound Water

Eutectogels have emerged as versatile materials for wearable electronics, optical sensors, and biomedical applications. This study introduced the first investigation of microenvironmental basicity in poly(vinyl alcohol)/choline chloride (PVA/ChCl) eutectogels using lumichrome as a fluorescent probe. The incorporation of ChCl was demonstrated to enhance the microbasicity of PVA films, as evidenced by the significant promotion of lumichrome deprotonation. In contrast, no deprotonation occurred in deep eutectic solvents ethaline [<i>n</i>(ChCl):n(ethylene glycol) = 1:2], glyceline [<i>n</i>(ChCl):<i>n</i>(glycerol) = 1:2], and ChCl-water mixtures [<i>n</i>(ChCl):<i>n</i>(H₂O) = 1:3 and 1:4]. Therefore, the proton acceptor in PVA/ChCl eutectogels was bound water, the same as in PVA films. Differential scanning calorimetry (DSC) experiments determined a decrease of water content in PVA films after ChCl incorporation, supporting the increased proportion of bound water in PVA/ChCl eutectogels. Our findings not only certified the enhanced microbasicity of bound water but also established a simple yet effective strategy to tune PVA films' acid-base properties through ChCl loading.