Shaping interfaces with light: evolution and application of azobenzene-containing photoresponsive surfactants

Abstract

Surfactants are ubiquitous, playing critical roles in biological processes, including those occurring in the lungs, as well as in many consumer and industrial applications. This versatility is further enhanced by stimuli-responsive surfactants, among which photoresponsive systems have garnered considerable research interest, especially in recent years. A thorough analysis of this subject is required because there are not many review papers on photoresponsive surfactants, which has limited 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 and 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 and geometry) and their macroscopic physical outcomes (e.g., surface tension and viscosity) in both azo-based and non-azo surfactants. This review comprehensively surveys the diverse applications of these materials, including enhanced oil recovery, environmental remediation, motion manipulation, catalysis, smart materials, and controlled drug delivery.