Shaping Interfaces with Light: Evolution and Application of Azobenzene containing Photoresponsive Surfactants

Abstract

Surfactants are ubiquitous, having critical roles in biological processes, such as with lung surfactants, as well as in many consumer and industrial applications. This versatility is significantly expanded and demonstrated by stimuli-responsive surfactants, among which photoresponsive systems have garnered considerable research interest, especially in recent years. A thorough analysis of the subject is required because there aren't many review papers on photoresponsive surfactants, which limits our knowledge of this area. This review describes the historical emergence and evolution of photoresponsive surfactants. It provides a detailed analysis of the various photoresponsive moieties (e.g., azobenzene, spiropyran) that are covalently integrated into surfactant architectures, focusing on their distinct types, operational limitations, and applications. A comparative analysis of conventional versus gemini photoresponsive surfactants is presented, highlighting key differences in their physicochemical properties. This review elucidates the mechanisms of photoisomerization in azobenzene and its direct impact on molecular-level properties (e.g., polarity, geometry) and their macroscopic physical outcomes (e.g., surface tension, viscosity) in both azo-based and non-azo surfactants. The review comprehensively surveys the diverse applications for these materials, including enhanced oil recovery, environmental remediation, motion manipulation, catalysis, smart materials, and controlled drug delivery.