Specific Ion Effects of Azobenzene Salts on Photoresponse of PNIPAm in Aqueous Solutions
Abstract
Ionic species are important to dominate phase separation behaviors of poly(N-isopropylacrylamide) (PNIPAm) in aqueous solutions. Herein, photoresponsive azobenzene-based salts with various ions are prepared and their photoresponsive ion effects on clouding temperatures (TcpS) of PNIPAm in aqueous solutions are explored. It is found that, despite of various structures of anions and cations, trans-TcpS under vis light irradiation are always higher than cis-TcpS under UV irradiation. Particularly, Hofmeister effect of anions on TcpS is roughly observed. For example, azobenzene with kosmotropic CO32− gives the lowest cis-Tcp while in use of typical chaotropic anions, such as ClO4−, azobenzene isomerization less affects values of Tcps. In another hand, azobenzene-based metallic salts containing lithium, sodium, and potassium cations also demonstrate photoresponsive Hofmeister effect. Trans-metallic azobenzene demonstrates a chaotropic effect on Tcps while UV induces kosmotropic behaviors on TcpS. Additionally, ionic conduction of the solution along with photoresponsive phase separations is also investigated and PNIPAm aggregations induce a sharp reduction of ion conduction during UV light illumination.
Conflict of Interest
The authors declare no conflict of interest.
Open Research
Data Availability Statement
The data that supports the findings of this study are available in the supplementary material of this article.
