Photo-responsive Pickering emulsions triggered by in-situ pH modulation using a photoacid generator

Zichun Song; Jie Liu; Jing Luo; To Ngai; Man-Hin Kwok; Guanqing Sun

doi:10.1016/j.jcis.2024.10.046

Photo-responsive Pickering emulsions triggered by in-situ pH modulation using a photoacid generator

J Colloid Interface Sci. 2025 Feb;679(Pt A):1150-1158. doi: 10.1016/j.jcis.2024.10.046. Epub 2024 Oct 12.

Authors

Zichun Song¹, Jie Liu¹, Jing Luo¹, To Ngai², Man-Hin Kwok³, Guanqing Sun⁴

Affiliations

¹ Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China.
² Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China; Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong.
³ Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong. Electronic address: manhinkwok@cuhk.edu.hk.
⁴ Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China. Electronic address: guanqingsun@jiangnan.edu.cn.

PMID: 39423681
DOI: 10.1016/j.jcis.2024.10.046

Abstract

Hypothesis: Pickering emulsions that respond to changes in pH by the addition of acid or alkali have been extensively studied, but the development of photo-responsive Pickering emulsions has been more challenging. This study attempts to demonstrate a novel approach to achieve photo-responsiveness in Pickering emulsions by incorporating a photoacid generator (PAG) into the oil phase. Upon UV irradiation, the PAG is expected to release protons (H⁺), which can then regulate the pH of the emulsion system and control its stability.

Experiments: Amphiphilic colloidal particles obtained by modifying silica particles with poly (2-(dimethylamino)ethyl methacrylate) (SiO₂-PDMAEMA) are used to stabilize the Pickering emulsions. The protonation and deprotonation of the SiO₂-PDMAEMA particles at different pH values allow for the tuning of emulsion stability. By introducing the PAG into the stable Pickering emulsion system and applying UV irradiation to trigger the in-situ release of H⁺, the pH of the emulsion is systematically decreased, and the corresponding changes in emulsion stability are investigated.

Findings: The results show that UV irradiation alone cannot induce emulsion instability. However, when PAG is added to the oil phase, the Pickering emulsions exhibit a significant decrease in pH under UV irradiation, ultimately leading to emulsion destabilization and phase separation. At a UV intensity of 20 mW/cm² for 2 min, the H⁺ release from the PAG significantly lower the emulsion's pH, causing the SiO₂-PDMAEMA particles to detach from the oil-water interface and resulting in emulsion instability. Higher concentrations of SiO₂-PDMAEMA particles in the emulsion require more PAG to induce instability, as confirm by confocal laser scanning microscopy (CLSM) image. This study presents a versatile approach to develop photo-responsive Pickering emulsions which can have potential applications in areas such as drug delivery, cosmetics, and responsive materials.

Keywords: Photo-responsiveness; Photoacid generator; Pickering emulsion; Responsive emulsion.