Photoresponsive aqueous foams with controllable stability from nonionic azobenzene surfactants in multiple-component systems

Chen, Shaoyu; Liang, Fei; Ge, Fangqing; Wang, Chaoxia

doi:10.1039/c9sm01379b

Cited by 13 publications

(10 citation statements)

References 42 publications

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“…Switchable molecular building blocks for responsive materials have gained considerable attention in the past and are part of a growing field of interest in biochemistry, catalysis, polymer science and in particular colloid and interface chemistry. [1][2][3][4] The responsiveness can be reached by different stimuli such as light, [5][6][7][8][9][10][11][12][13][14] temperature, 15,16 pH, 17,18 magnetic or electric fields, 19 or through a combination of these factors to yield multiresponsive systems. 3,[20][21][22] In particular, light as a stimulus to trigger interfacial and material responses has the advantage that it can be controlled precisely in time and space, thus offering material control in four dimensions.…”

Section: Introductionmentioning

confidence: 99%

Photo-Switchable Surfactants for Responsive Air–Water Interfaces: Azo versus Arylazopyrazole Amphiphiles

et al. 2020

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Arylazopyrazoles (AAPs) as substitutes for azo derivatives have gained considerable attention due to their superior properties offering E/Z photo-isomerization with high yield. In order to compare and quantify their performance, azobenzene tetraethylammonium (Azo-TB) and arylazopyrazole tetraethylammonium (AAP-TB) bromides were synthesized and characterized in the bulk (water) using NMR spectroscopy. At the air-water interface complementary information from vibrational sum-frequency generation (SFG) spectroscopy and neutron reflectometry (NR) has revealed the effects of E/Z isomerization in great detail. In bulk water the photostationary states of >89 % for E/Z switching in both directions were very similar for the surfactants, while their interfacial behavior was substantially different. In particular, the surface excess Γ of the surfactants changed drastically between E/Z isomers for AAP-TB (maximum change of Γ: 2.15 µmol/m²); for Azo-TB the change was only moderate (maximum change of Γ: 1.02 µmol/m²). Analysis of SFG spectra revealed that strong non-resonant contributions that heterodyned the resonant vibrational bands were proportional to Γ, enabling the aromatic C-H band to be interpreted as an indicator for changes in interfacial molecular order. Close comparison of Γ from NR with the SFG amplitude from the aromatic C-H stretch as a function of concentrations and E/Z conformation revealed substantial molecular order changes for AAP-TB. In contrast, only Γ and not the molecular order varied for Azo-TB. These differences in interfacial properties are attributed to the molecular structure of the AAP center that enables favorable lateral interactions at the air-water interface, causing closed-packed interfacial layers and substantial changes during E/Z photo-isomerization.

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Section: Introductionmentioning

confidence: 99%

Photo-Switchable Surfactants for Responsive Air–Water Interfaces: Azo versus Arylazopyrazole Amphiphiles

et al. 2020

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“…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.…”

Section: Dynamic Functions Of Photoresponsive Molecular Amphiphiles In Gibbs Monolayersmentioning

confidence: 99%

“…Aiming at industrial applications,W ang and co-workers synthesized as eries 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][137][138][139][140][141] Thef oamability and stability of the corresponding colored photoresponsive foams were reversibly tunable by light-stimuli. In this way,s table foams can be used in the textile coloring process with excellent performance,w hile the photo-controllable rupture of the stable residual foams enabled them to be readily recycled, allowing for an early zero-pollutant discharge coloring process (Figure 8).…”

Section: Dynamic Functions Of Photoresponsive Molecular Amphiphiles In Gibbs Monolayersmentioning

confidence: 99%

Self‐Assembly of Photoresponsive Molecular Amphiphiles in Aqueous Media

et al. 2021

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Amphiphilic molecules, comprising hydrophobic and hydrophilic moieties and the intrinsic propensity to self‐assemble in aqueous environment, sustain a fascinating spectrum of structures and functions ranging from biological membranes to ordinary soap. Facing the challenge to design responsive, adaptive, and out‐of‐equilibrium systems in water, the incorporation of photoresponsive motifs in amphiphilic molecular structures offers ample opportunity to design supramolecular systems that enables functional responses in water in a non‐invasive way using light. Here, we discuss the design of photoresponsive molecular amphiphiles, their self‐assembled structures in aqueous media and at air–water interfaces, and various approaches to arrive at adaptive and dynamic functions in isotropic and anisotropic systems, including motion at the air–water interface, foam formation, reversible nanoscale assembly, and artificial muscle function. Controlling the delicate interplay of structural design, self‐assembling conditions and external stimuli, these responsive amphiphiles open several avenues towards application such as soft adaptive materials, controlled delivery or soft actuators, bridging a gap between artificial and natural dynamic systems.

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“…However, a prerequisite for the latter are highly responsive materials [12][13][14][15][16][17][18][19] and building blocks [20][21][22] such as fluid interfaces 23 that react to an external stimulus by massive changes in their physicochemical properties. [23][24][25][26][27][28][29] At a fluid interface, this can be achieved by ad-and desorption of molecules 30 and by charging and discharging of the interface 1 which can largely change electrostatic interactions at the interface as well as by significant molecular structure changes.…”

Section: Introductionmentioning

confidence: 99%

“…Such materials are capable of changing their properties like optical appearance, stability, or their structure on demand to new situations if a feedback mechanism can be established. However, prerequisites for the latter are highly responsive materials − and building blocks − such as fluid interfaces that react to an external stimulus by massive changes in their physicochemical properties. − At a fluid interface, this can be achieved by ad- and desorption of molecules and by charging and discharging of the interface which can largely change electrostatic interactions at the interface as well as by significant molecular structure changes . Such electrostatics are often used to render colloidal systems like foam or nanoparticle dispersions more stable as the long-range electrostatic disjoining forces increase when the interfaces in a colloidal system become highly charged. , In this work, we are focusing on aqueous foams as these are inherently interface-controlled systems with an established hierarchy from the molecular building blocks that are adsorbed at the air–water interface to thin foam films, bubbles, and ensembles of bubbles and finally to the macroscopically visible foam. , The latter inherits the properties of the air–water interface through structure–property relations. , Thus, aqueous foams are an ideal playground to test responsive interface-active moieties that are used to tailor also responsive foam ,,,, as a model system for soft matter materials.…”

Section: Introductionmentioning

confidence: 99%

Spiropyran Sulfonates for Photo- and pH-Responsive Air–Water Interfaces and Aqueous Foam

et al. 2020

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Responsive foams and interfaces, are interesting building blocks for active materials that respond and adapt to external stimuli. We have used the photochromic reaction of a spiropyran sulfonate surfactant to render interfacial, rising bubble as well as foaming properties active to light stimuli.In order to address the air-water interface on a molecular level, we have applied sum-frequency generation (SFG) spectroscopy which has provided qualitative information on the surface excess and the interfacial charging state as a function of light irradiation and solution pH. Under blue light irradiation, the surfactant forms a closed ring spiro form (SP), whereas under dark conditions the ring opens and the merocyanine (MC) form is generated. Using SFG spectroscopy, we show that at the interface, different pH conditions of the bulk solution lead to changes in the interfacial charging state. We have exploited the fact that the MC surfactant's O-H group can be deprotonated as a function of pH, and used that to tune the molecules net charge at the interface. In fact, SFG spectroscopy shows that with increasing pH the intensity of the O-H stretching band from interfacial water molecules increases which we associate to an increase in surface net charge. At a pH of 5.3, irradiation with blue light leads to a reversible decrease of O-H intensities, whereas the C-H intensities were unchanged compared to the corresponding intensities under dark conditions. These results are indicative of changes in the surface net charge with light irradiation, which are also expected to influence the foam stability via changes in the electrostatic disjoining pressure. In fact, measurements of the foam stabilities are consistent with this hypothesis with higher foam stability under dark conditions. At pH 2.7 this behavior is reversed as far as the surface tension and surface charging as well as the foam stability are concerned. This is corroborated by rising bubble experiments, which demonstrated an unprecedented reduction of ~30 % in bubble velocity when the bubbles were irradiated with blue light compared to the velocity of bubbles with the

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Photoresponsive aqueous foams with controllable stability from nonionic azobenzene surfactants in multiple-component systems

Abstract: Photoresponsive foams can be generated from single-component solutions of a nonionic azobenzene surfactant, as well as from multiple-component industrial systems.

Cited by 13 publications

References 42 publications

Photo-Switchable Surfactants for Responsive Air–Water Interfaces: Azo versus Arylazopyrazole Amphiphiles

Photo-Switchable Surfactants for Responsive Air–Water Interfaces: Azo versus Arylazopyrazole Amphiphiles

Self‐Assembly of Photoresponsive Molecular Amphiphiles in Aqueous Media

Spiropyran Sulfonates for Photo- and pH-Responsive Air–Water Interfaces and Aqueous Foam

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