Photo-responsive foam control base on nonionic azobenzene surfactant as stabilizer

Abstract A nonionic photo-responsive surfactant (NPS) was synthesized for obtaining photo control of foamability, exposed in ultraviolet (UV) light or visible (Vis) light irradiation. The foamability depended on the surface activity of NPS, which possessed low critical micelle concentration (CMC) and high adsorption capacity compared with the similar type of nonionic surfactants. The azobenzene component in NPS as the light-responsive group, showed high sensitive and reversibility, i.e., the trans → cis isomerization occurred only for 1 s and the time to reach reversible isomerization was 85 s. And the fatigue resistance of isomerization was also outstanding, which remained stable for 14 cycles of alternate irradiation. Due to the lack of free volume and increase of barrier for isomerization, the irradiation time and first-order kinetics of isomerization decreased with the increase of NPS concentration. The foaming ratio and foam stability promoted with the NPS concentration increase, however, the stereospecific blockade amongst cis isomers was stronger than that of trans isomers, resulting in the steep decrease of foam half-life. The sustainable foam stability control of NPS applied into foam dyeing to solve the problem of residual foam.