Amphiphilic azo polymers: Molecular engineering, self-assembly and photoresponsive properties

Abstract

Amphiphilic polymers are well known for their characteristics to form various self-assembling structures under proper conditions. Amphiphilic azo polymers, which are amphiphilic polymers functionalized with aromatic azo moieties, can combine wealthy photoresponsive properties with the self-assembling feature. In recent years, a wide variety of amphiphilic azo polymers have been developed through different molecular design strategies and synthetic routes. This article reviews the background, recent development, current approaches, and outlook of this rapidly developing research area. The emphasis is placed on the synthesis, self-assembly, and photoresponsive properties of amphiphilic azo polymers. According to the molecular architecture, the amphiphilic azo polymers are classified as homopolymers, random copolymers, block copolymers, star-like and dendritic polymers. The polymers show strong tendency to form well-organized structures at surfaces or interfaces, in solutions or dispersion mediums, and through phase-separation in solid thin-films. Colloidal arrays and porous thin films of amphiphilic azo polymers can be obtained through the vertical deposition method and solvent-induced structure inversion. The amphiphilic azo polymers and their self-assembled structures exhibit a variety of photoresponsive properties triggered by the trans–cis photoisomerization of azo chromophores. Some interesting variations caused by the light irradiation, such as the surface wettability change, surface-relief-grating formation, domain orientation, colloid deformation, micelle dissociation, vesicle bursting and fusion, are described in this review in detail. Such properties are promising for applications in areas such as optical devices, sensors, and drug delivery.