Oppositely Sensitive pH-Responsive Surfactants Derived from Polymer-Grafted Carbon Dots

This study reports the development of two pH-responsive Pickering emulsifiers utilizing carbon dots (CDs) as the core component. Both emulsifiers were fabricated via a post-synthetic method, involving the grafting of poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) onto the surface of CDs to create CD-based emulsifier. Notably, despite employing an identical synthetic route, the two CD-based emulsifiers exhibit markedly distinct pH-responsive behaviors. The findings demonstrate that both CD-based emulsifiers effectively stabilize Pickering emulsions, and their emulsification and demulsification behaviors can be precisely controlled by adjusting the pH, displaying excellent reproducibility in their pH-responsive performance. To elucidate the underlying reason for this differing pH-responsiveness, the concept of hydrophilic-lipophilic balance (HLB) was introduced. The analysis of the HLB values of the two CD-based emulsifiers revealed that their hydrophilic-lipophilic properties exhibit opposite trends under differing pH conditions, contributing to their contrasting pH-responsive behaviors. This study not only lays a fundamental basis foundation and offers guidance for further research and applications of CD-based smart-responsive emulsifiers but also presents novel insights into design and development of more intelligent and functional emulsifying agents. Moreover, owing to the enhanced fluorescence characteristics of CDs, these pH-responsive emulsifiers hold significant potential for interdisciplinary applications, such as oil and gas exploration and fluorescent labelling.