Insight into a Fast-Phototuning Azobenzene Switch for Sustainably Tailoring the Foam Stability

Abstract

A photoresponsive surfactant of 4-octoxy-4'-[(trimethylamino)ethoxy]azobenzene (OTAEAzo) has been synthesized for developing a fast-phototuning foam switch based on its high sensitivity, reversibility, and fatigue resistance of the photoisomerization capability. Ultraviolet (UV)-light irradiation for 1 s enabled conversion from the trans isomer to the cis configuration, while exposure to visible (Vis)-light for 3 min induced a cis-to-trans transformation, which maintains an excellent cycling stability for 20 cycles of photoisomerization. The photoisomerization speed depended on the concentration of OTAEAzo, and a lower concentration facilitated a faster photoisomerization process. Because of the low critical micelle concentration (CMC), OTAEAzo with a small dosage of 0.2 g·L showed foamability, which accelerated the photoisomerization speed, enabling it to become a highly efficient switch. The surface activities of trans-OTAEAzo presented distinct differences from those of cis-OTAEAzo, resulting in the foam stabilization effects of trans-OTAEAzo (t = 2.58 min) and the destabilization effects of cis-OTAEAzo (t = 0.38 min). Moreover, the foam properties varied slightly in the phototuning cycles. OTAEAzo with low CMC presents high sensitivity and reversible photoisomerization capability, providing an environmental and sustainable approach for tailoring the foam stability.

Unexpected monolayer-to-bilayer transition of arylazopyrazole surfactants facilitates superior photo-control of fluid interfaces and colloids

“…Furthermore, the observed foam lifetime for green irradiation (E conformation) is much higher than that observed previously for other photo-surfactants, where the process has been shown to take several minutes. 9,10 Aqueous foams are inherently interface controlled, where the macroscopic properties can be tailored at the molecular level through structure-property relations. 2,28 Since the surface excess of an ionic surfactant such as butyl-AAP-C 4 S determines the interfacial charging state, the latter is reduced when the samples are irradiated with UV light.…”

“…2,6 Here, so interfaces are of great interest because they allow fast and reversible recongurations, e.g., by de-or adsorption of molecules triggered by an external stimulus. [7][8][9][10][11] For example, tuning the properties of uid interfaces helps to develop smart foams with self-healing and adaptive functions. 3,12 In addition, Marangoni ows can be used to pattern or aggregate particles precisely and independently of their size in the tailoring of 2D colloidal crystals.…”

Hydroxypropyl cellulose as a green polymer for thermo-responsive aqueous foams

“…A major advantage of responsive interfaces is the ability to drive materials properties such as foam stability or foamability on demand and in a non-invasive way. Photo-responsive foams are mostly based on azobenzene surfactants 5,16–18. Here, UV or blue light irradiation can trigger E to Z photo-isomerization reactions and the resulting surfactants’ conformational change can result into a different surface activity, surface tension and on larger length scales also differences in foam stability.…”

Self‐Assembly of Photoresponsive Molecular Amphiphiles in Aqueous Media

“…Aiming at industrial applications, Wang and co‐workers synthesized a series of nonionic and cationic azobenzene amphiphiles by modifying the hydrophobic chain and the hydrophilic parts for the purpose of preparing photoresponsive foams for textile foam coloring systems to reduce pollutant discharges and energy consumptions of the traditional textile coloring process [136–141] . The foamability and stability of the corresponding colored photoresponsive foams were reversibly tunable by light‐stimuli.…”