Light‐Controlled Localized Delamination and Blistering of Azobenzene‐Containing Polymer Thin Films in an Aqueous Environment

ABSTRACT Blister formation in thin polymer films represents a localized delamination instability whereby interfacial failure leads to out‐of‐plane deformation of the supported film. It is relevant to coating failure, adhesion control, and directed surface patterning. Photoresponsive azopolymer films provide a unique model system, since mechanical stresses can be generated and tuned remotely by light. Here, we investigate blister formation in substrate‐supported azopolymer films immersed in aqueous environments under spontaneous and optically excited conditions. We show that spontaneous blistering occurs via a complex interplay between diffusion‐limited solvent transport, swelling, capillarity, poroelastic solvent uptake, and osmotic effects, and remains fully reversible upon drying. In contrast, light‐induced structuring is stable after solvent removal, indicating irreversible interfacial reconfiguration. We further demonstrate that linearly polarized light induces pronounced anisotropic deformation in both pre‐existing and newly formed blisters. This anisotropy can be understood within the orientation‐based theory of azobenzene polymer deformation, where chromophore reorientation generates anisotropic active stresses in the delaminated blister and surrounding adhered film. Together with adhesion and geometric constraints, this produces stress redistribution in a curved shell, leading to symmetry breaking and elliptical deformation governed by nonlinear shell mechanics. Overall, we provide a unified framework for swelling‐ and light‐driven interfacial instabilities in azopolymer films.