Anion-Responsive Thiourea-Based Gel Actuator

Anion-coordination chemistry is important in biological and industrial processes and to alleviate environmental issues. Although thiourea has been studied for customized anion receptor applications via hydrogen-bonding interactions, it is seldom applied to anion-responsive actuators. In this study, we prepared thiourea-based soft gels using a facile one-step synthesis and tested them for anion-specific or anion-selective responses in actuation (i.e., volume transition). The thiourea-based soft gels exhibited visually observable color changes depending on the basicity of the anions (e.g., highly basic F- and CN-); however, remarkably different size changes were observed for F- (contraction) and CN- (expansion). We investigated the anion-specific effect on volume transitions and found that similar to Hofmeister effect in water, the volume changes were due to the interaction of the basicity, solvation energy, and accompanying osmosis of the anions. These properties were utilized as anion-responsive soft actuators.