Colorimetric sensing properties of catechol-functional polymerized vesicles in aqueous solution and at solid surfaces

Polymerized vesicles containing adhesive amphiphiles with dihydroxyphenylalanine (DOPA) groups coupled to diacetylenes, allow to combine a well-controlled presentation of adhesive functions over the surface and intrinsic colorimetric sensing properties upon external stimuli. In this study, the colorimetric response of such polymerized adhesive vesicles is first evaluated after synthesis in aqueous solution as a function of vesicle compositions and polymerization times under UV light. The development of blue to red color serves as a qualitative measure for the successful formulation of the adhesive vesicles. In a second step, the colorimetric response of adhesive vesicles adsorbed onto solid surfaces was quantified. Therefore, the adhesive vesicles were confined into a spot by drop casting the aqueous solution onto lithographically patterned model substrates and subsequent drying. The colorimetric response of such an adhesive spot was studied as a function of the vesicle composition or polymerization conditions, with comparable behavior to the vesicles in dispersed state. Interestingly, the colorimetric response varies linearly within certain ranges of vesicle concentration. Finally, the color sensitivity of an adhesive spot after thermal curing and mechanical solicitation under normal load and shear load was demonstrated, indicating favorable sensitivity to heating temperature, heating time and loading levels. In this study, a potential tool has been developed for quality assessment and failure analysis of adhesive interfaces in future.