The correlation between thermally induced precipitate-to-coacervate transition and glass transition in a polyelectrolyte-bolaamphiphile complex

Abstract

The precipitate and the coacervate are two aggregated states in the polyelectrolyte complexes (PECs). The precipitate-to-coacervate transition and glass transition in PECs have been widely reported in the past. In many cases, the two phenomena are studied independently, although both of them are apparently affected by water and small ions. Here, utilizing a PEC system consisting of poly(acrylic acid) (PAA) and a cationic bolaamphiphile (DBON), we explore the states of PECs as a function of salt, temperature, and the molecular weight of PAAs. By a combination of microscopic observation, time-resolved fluorescence measurements, and differential scanning calorimetry, we identify salt/temperature driven precipitate-to-coacervate transitions of the complexes. The thermally induced morphology transformation from the precipitate to coacervate occurs around the glass transition temperature, indicating a strong correlation between the two processes. As the molecular weight of the PAA increases, the thermal transition temperature becomes higher. This finding offers new insights on the mechanistic interactions that dictate the aggregated states of PECs. Based on the photothermal effect of DBON, we also develop a UV light-induced strategy to mediate the precipitate-to-coacervate transition, providing a fantastic platform to create functional PEC materials.