Insight into a Fast Photo-Tuning Azobenzene Switch for Sustainably

Research Article www.acsami.org

Insight into a Fast-Phototuning Azobenzene Switch for Sustainably Tailoring the Foam Stability Shaoyu Chen, Yanyan Zhang, Kunlin Chen, Yunjie Yin, and Chaoxia Wang* Key Laboratory of Eco-Textile, Ministry of Education, College of Textile & Clothing, Jiangnan University, 1800 Lihu Road, Wuxi 214122, People’s Republic of China S Supporting Information *

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−1 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 cisOTAEAzo, resulting in the foam stabilization effects of trans-OTAEAzo (t1/2 = 2.58 min) and the destabilization effects of cisOTAEAzo (t1/2 = 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. KEYWORDS: azobenzene, fast foam switch, low CMC, photoisomerization, surface activity

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INTRODUCTION Foams, a thermodynamically metastable system, are abundantly exploited in varied fields including the food, froth flotation, manufacturing metal materials, detergent, cosmetic, and textile industries.1−3 In some applications like cosmetics and food, foams are required to remain stable for a long time. Generally, foam stabilizers can be surfactants, polymers, and solid particles.4−6 They cover the gas−liquid interfaces, improving the foam film stability or increasing the viscosity, which result in slowing foam drainage, coarsening, and coalescence.7−10 In contrast, foams are desired to be quickly ruptured in areas such as froth flotation and wastewater treatment. Stable foams are also expected to be destroyed fast and controllably at the end of the process because of the clean difficulty and large space occupation of these residual foams. In this case, the addition of chemical agents (e.g., defoaming agents11) is usually required. Unfortunately, both foam stabilizers and defoaming agents are not good choices because the foam properties cannot be reversibly tuned, which is unsustainable and not environmentally friendly. In view of the desire for sustainable tuning of the foam stability, switchable foam is a novel toolbox. Switchable foam means that the foam stability can be reversibly switched with external stimuli12 such as the pH,13 light, temperature, CO2, oxidants, electricity, and enzymes.14 Light is of green, renewability, and tunable properties, becoming a promising trigger candidate.15,16 The approaches for obtaining switchable foams are based on the foam liquid © 2017 American Chemical Society

channel modifications or the interfacial layer responsiveness. For example, emulsion is introduced in the liquid films and its stability is broken by external stimuli, leading to foam destabilization.17 The latter approach without the presence of complex reorganizations in the foam liquid channels is simpler and more effective, which can be obtained from responsive surfactants. Photoresponsive surfactants usually contain photochromic moieties, which exhibit reversible structural changes by light stimuli, notably azobenzene, stilbene, anthracene, and norbornadiene.18,19 Particularly, azobenzene is a promising moiety because of its uniquely reversible and highly sensitive photoisomerization capability.20 Azobenzene isomerization can be triggered by light, electric field, or thermal stimulation.21 They have been abundantly explored in fields such as energy storage materials,19,20,22,23 conductance switches,24,25 shapechanging materials26,27 and responsive wettability surfaces,28,29 while they are seldomly reported to obtain switchable foams. In our previous work, photoresponsive azobenzene molecules with three types of alkyl chain lengths had been synthesized as foam switches.30 These azobenzene molecules showed a rapid photoisomerization speed. Because of the poor solubility, their foamability was unsatisfying. In order to improve the solubility, 4-butoxy-4′-[(trimethylamino)ethoxy]Received: February 11, 2017 Accepted: March 28, 2017 Published: March 28, 2017 13778

DOI: 10.1021/acsami.7b02024 ACS Appl. Mater. Interfaces 2017, 9, 13778−13784

Research Article

ACS Applied Materials & Interfaces

been described in our previous work.31 All measurements were repeated three times, following the calculation of the average value.

azobenzene (BTAEAzo) was synthesized and showed excellent foamability and foam-switch capability at the concentration beyond its critical micelle concentration (CMC; 1.84 g·L−1).31 The photoisomerization speed was slow in such a high concentration because of the steric crowding of the azobenzene molecules, which meant that BTAEAzo was an inefficient foam switch.32 Encouraged by the reports that the surfactant CMC decreases with an increase of the hydrophobic tail length,33 an azobenzene cationic surfactant with a longer alkyl chain length, 4-octoxy-4′-[(trimethylamino)ethoxy]azobenzene (OTAEAzo) was synthesized for the development of a fast foam switch. OTAEAzo was hypothesized to be endowed with low CMC, and it could show foamability with a small dosage, which facilitated a rapid photoisomerization process. Therefore, the photoisomerization properties of OTAEAzo, including the isomerization speed and reversibility, were analyzed using ultraviolet (UV) adsorption spectra. In order to gain insight into the foam switch mechanism of OTAEAzo, the surface properties such as the CMC, equilibrium surface tensions, and surface excesses of trans- and cis-OTAEAzo were investigated. Besides, the foam properties of OTAEAzo alternately irradiated with UV- and visible (Vis)-light were also investigated to confirm its foam-switch capability. The study aims at obtaining an azobenzene surfactant with low CMC and demonstrating its mechanism of foam phototuning capability, which is anticipated to achieve a fast foam switch, opening a gate for sustainably and efficiently tailoring the foam stability.

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RESULTS AND DISCUSSION Isomerization Analysis. The azobenzenes own the capability of reversible photoisomerization because of the rearrangement of their two π-conjugated arms induced by UVand Vis-light stimuli. The rearrangement results in two molecular configurations, i.e., the trans and cis isomers, which present significant differences in both their dipole moment and geometry.34,35 Owing to the azo group transition moments, the isomerization process can be investigated by UV−vis absorption spectroscopy.36 Therefore, the UV−vis absorption spectra of OTAEAzo are recorded to investigate its isomerization properties, as shown in Figure 1. In Figure 1, a strong

EXPERIMENTAL SECTION

Materials. OTAEAzo was homemade. The synthesis and characterization of OTAEAzo are presented in the Supporting Information. Bromooctane (C8H17Br; >98.0%), 1,2-dibromoethane (>99.0%), a trimethylamine solution (>33.0%), potassium carbonate (K2CO3; >99.0%), potassium hydroxide (KOH; >99.0%), ethanol (EtOH; >99.7%), anisole (>98.0%), ethyl acetate (EtOAc; >99.5%), petroleum ether (60−90 °C, 99%), and silica gel (FCP) were bought from Sinopharm Chemical Reagent Co., Ltd. 4,4′-Dihydroxyazobenzene (DHAzo; >98.0%) and potassium iodide (KI; >99.0%) were purchased from Tokyo Chemical Industry Co., Ltd. and Aladdin Industrial Inc., respectively. Deionized water was used in all experiments. Photoisomerization Property Measurement. UV−vis absorption spectra recorded with an UV spectrophotometer (Cary 50, Varian, USA) were used to monitor the isomerization process of OTAEAzo. The OTAEAzo solution was irradiated by an UV lamp (Intelli-ray 600, Uvitron International Inc., USA) or a Vis lamp [YG(B)982X, Wenzhou Darong Textile Instrument Co., Ltd., China], simultaneously recording the change of UV−vis absorption spectra until the spectra remained unchanged after prolonged light irradiation, which meant that they reached a photostationary state, i.e., the finish of photoisomerization. Surface Tension Measurement. The equilibrium surface tension of an OTAEAzo solution in a photostationary state was measured by a drop-shape analysis system (DSA100, Krüss GmbH, Germany), which is based on the fitting of the pendant drop shape of the solution with the Young−Laplace equation of capillarity. The samples of trans- and cis-OTAEAzo were exposed to UV- or Vis-light until they reached a photostationary state prior to measurement. The measurement was performed at 25 °C, and the average value of the equilibrium surface tension was calculated after the measurement was repeated at least three times. Foam Preparation and Property Measurement. Foams was prepared as in our previous report.31 Foamability and foam stability are the two main foam properties of a surfactant solution, which are evaluated by the foaming ratio (R) and foam half-life (t1/2). The definition and measurement of the foaming ratio and half-life also have

Figure 1. Photoisomerization of OTAEAzo (0.02 g·L−1). (a) (a) UV−vis absorption spectra exposed to UV-light. (b) UV−vis absorption spectra exposed to Vis-light. (c) Schematic diagram of isomerization and photographs of the OTAEAzo solution before (left) and after (right) UV-light irradiation.

peak and a weak peak appear at about 350 and 450 nm in the trans-OTAEAzo absorption spectra, and after UV-light irradiation, the peak located at 450 nm becomes stronger. The phenomenon conforms to the previous report that the trans-azobenzene absorption spectrum presents a strong UVband (λmax at 320 nm), corresponding to the π → π* transition, and exhibits a weaker band in the Vis-region (λmax at 450 nm), belonging to the n → π* transition. Conversely, cis-azobenzene shows weaker π → π* transitions (λmax at 250 and 270 nm) and a stronger n → π* transition (λmax at 450 nm).37 Compared to the azobenzenes, λmax of the OTAEAzo π → π* transition presents a bathochromic shift (from 320 to 350 nm) due to the electron-donating substituents through steric and electronic effects.37 In Figure 1a, a distinct decrease and a slight increase in the absorbance at around 350−400 and 450 nm are found after exposure to UV-light within 1 s. These absorbance values do not change, even prolonging the UV-light irradiation time, indicating that cis-rich photostationary states are reached. Figure 1b shows an inverse trend, revealing that reversible isomerization from cis to trans conformation occurs within a 3 min Vis-light irradiation. According to Figure 1a,b, OTAEAzo shows high sensitivity and reversible photoisomerization capability. 13779


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ACS Applied Materials & Interfaces Figure 1c illustrates the change of the OTAEAzo molecular configurations and OTAEAzo solution photographs in the isomerization process. Four pathways, including rotation, inversion, concerted inversion and inversion-assisted rotation, have been regarded as azobenzene isomerization mechanisms. The accuracy of the mechanism may vary after taking into account factors such as isomeric forms, excitation modes, substituents, solvent, irradiation wavelength, pressure, and temperature.37 OTAEAzo solutions undergo the isomerization process when they are exposed to UV- or Vis-light at room temperature. Its isomerization mechanism may be interpreted as follows: S1 ← S0 (S0 = electronic ground state; S1 = n−π* state) and S2 ← S0 (S2: π−π* state) excitations are triggered by light radiation, and then S2 → S1 → S0 and S1 → S0 relaxation happen in which the isomerization process occurs along the rotation pathway.38 Because of the shift of λmax after isomerization, the color of the OTAEAzo solution reversibly changes between light yellow and light orange. Besides, it is shown in Figure 2 that the light irradiation time remains 1 s

Figure 3. Effect of the OTAEAzo concentration on the photoisomerization speed: (a) trans-to-cis photoisomerization triggered by UV-light; (b) cis-to-trans photoisomerization triggered by Vis-light.

slow photoconversion speed. Besides, a dilute monomer molecular state facilitates photoisomerization compared to a dense aggregation state.41 With an increase of the OTAEAzo concentration, van der Waals and π-stacking interactions, resulting from the alkyl chains and azobenzene aromatic rings, cause dense parking of the OTAEAzo molecule, leading to a dense aggregation state.42,43 Such a steric crowding state lacks “free volume”, which hinders isomerization.32,42 Surface Activity Analysis. The surface acticity of a surfactant is crucial with regard to its utilization. As for a foaming agent, the foamability and foam stabilization effects are decided by the surface activity of the surfactant. Because of the photoisomeraization capability, OTAEAzo has two molecular configurations, i.e., the trans and cis isomers. The different dipole moment and geometry of these two configurations could lead to the surface activity differences. For the sake of analysis of the surface activity of trans- and cis-OTAEAzo, their surface tensions depending on the concentrations were investigated. It is worth noting that in Figure 4 the surface tension of the trans isomer solution progressively decreases until about 41 mN·m−1 at a concentration of 2.5 × 10−4 mol·L−1, revealing that the CMC of trans-OTAEAzo is 2.5 × 10−4 mol·L−1 and its equilibrium surface tension is 41 mN·m−1. Similarly, the CMC and equilibrium surface tension of cis-OTAEAzo are 5.7 × 10−4 mol·L−1 and 52 mN·m−1. The surface tension mainly depends on the packing density of the surfactant molecules in the interface. It is widely believed that trans-azobenzenes show an order and dense adsorption at the gas−liquid interface because of the π-stacking forces of the azobenzene rings, while cisazobenzenes exhibit a rapid decrease of the molecular density owing to the irregular and random structures. Therefore, the equilibrium surface tension of trans-OTAEAzo is lower than that of cis-OTAEAzo. Compared to cis-OTAEAzo, the surface tension of a trans-OTAEAzo solution decreases more quickly

Figure 2. Cycle properties of a OTAEAzo solution (0.02 g·L−1) photoisomerization: (a) isomerization speed; (b) absorbance at 350 nm upon alternating UV- and Vis-light irradiation over 20 cycles.

(UV-light) and 180 s (3 min of Vis-light) for isomerization, and the absorbance values of the photostationary states are stable at about 0.60 (trans-rich) and 0.27 (cis-rich) after 20 isomerization cycles, demonstrating the high fatigue resistance of OTAEAzo. Figure 3 presents the relevance between the concentration and photoisomerization speed of OTAEAzo. As shown in Figure 3, a lower OTAEAzo concentration clearly facilitates a faster photoisomerization process. The UV-time decreases from 36 to 1 s and the Vis-time decreases from 21.5 to 3.0 min as the concentration decreases from 0.2 to 0.02 g·L−1. It has been reported that the photoisomerization efficiency of azobenzene derivatives depends on the bulk solution photoconversion and molecule parking density.39,40 The solution absorbance increases at a higher OTAEAzo concentration, resulting in a 13780


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Amin, the minimum area per surfactant molecule at the surface, can be estimated on the basis of Γmax and Avogadro’s number (NA) following the formula A min =

with increasing concentration, meaning that trans-OTAEAzo owns high surface activity. In addition, in order to confirm that the CMC of OTAEAzo is much lower than the CMC of BTAEAzo, the surface tensions depending on the BTAEAzo concentrations were also investigated (shown in Figure S4). From Figure S4, the CMCs of trans- and cis-BTAEAzo are 42.2 × 10−4 and 59.7 × 10−4 mol·L−1, which are more than 10 times higher than the CMC of OTAEAzo. According to the curve of the surface tension, the surface excess concentration (Γ) of trans- and cis-OTAEAzo was calculated by the Gibbs adsorption equation: c ⎛ dγ ⎞ ⎜ ⎟ RT ⎝ dc ⎠T

(1) −1

(2)

Amin of trans- and cis-OTAEAzo as well as other surface activity parameters including CMC, γCMC, and Γmax are summarized in Table 1. Amin of trans-OTAEAzo is 1.36 × 10−8 nm2 and Amin of cis-OTAEAzo is 2.95 × 10−8 nm2, suggesting that the steric hindrance of trans-OTAEAzo is smaller and it can park at the interface densely. As listed in Table 1, the surface activities of trans- and cis-OTAEAzo vary distinctly, which may result in significant differences in the foamability and foam stabilization effects. Fast-Phototuning Foam Switch. The different surface activities of trans- and cis-OTAEAzo enable OTAEAzo to become a foam switch by UV- and Vis-light stimuli. The investigation of the surface activities of OTAEAzo and BTAEAzo demonstrated that the CMC of OTAEAzo was much lower than that of BTAEAzo, indicating that OTAEAzo could prepare foam in a much smaller dosage. In order to compare the foamability of OTAEAzo and BTAEAzo, three samples, i.e., 2 mL solutions of OTAEAzo (0.2 g·L−1) and BTAEAzo (0.2 and 2.0 g·L−1), are foamed by bubbling N2 at the same flow rate, as shown in Video S1. From Video S1, a BTAEAzo solution (0.2 g·L−1) fails to prepare foam, while a BTAEAzo solution (2.0 g·L−1) and a OTAEAzo solution (0.2 g· L−1) present approximately equal foam heights, revealing similar foamability. According to the investigation about the effects of the concentration on the photoisomerization speed, the photoisomerization of a BTAEAzo solution (2.0 g·L−1) could be much slower than the photoisomerization of a OTAEAzo solution (0.2 g·L−1). As shown in Figure 3, trans-tocis and cis-to-trans isomerizations of a OTAEAzo solution (0.2 g·L−1) occur by UV-light irradiation for 36 s and Vis-light irradiation for 21.5 min, respectively, while Figure S5 reveals that a BTAEAzo solution (2.0 g·L−1) undergoes trans-to-cis and cis-to-trans photoisomerization by UV-light irradiation for 88 s and Vis-light irradiation for 35 min, respectively. Therefore, OTAEAzo with low CMC shows excellent foamability at a lower concentration and a more rapid photoisomerization speed at the foaming concentration compared to BTAEAzo, verifying that OTAEAzo is a highly efficient foam switch. To analyze the foamability, the foaming ratios of OTAEAzo solutions varying from 0.30 to 0.40 g·L−1 are determined, as shown in Figure 6a. The foaming ratio increases from 3.87 to 6.32. This is ascribed to the difference of bubble breakup. The surface tension and bubble breakup determine the foamability of surfactant solutions. Low surface tension and a slow bubble breakup process are a benefit to improving the foamability.44 As for OTAEAzo, its CMC is 2.5 × 10−4 mol·L−1 (ca. 0.12 g·L−1), and the surface tension is almost invariant in the concentration range of 0.30−0.40 g·L−1. It is obvious that the foam half-life increases with an increase in the concentration in Figure 6b, indicating a slow bubble breakup process. Therefore, the

Figure 4. Equilibrium surface tension of OTAEAzo.

Γ=−

1 NA Γmax

−1

where R is the gas constant of 8.3144 J·mol ·K , T is the measurement temperature (298.15 K), γ is the equilibrium surface tension, and c is the bulk surfactant concentration. The calculated values of Γ are plotted against the OTAEAzo concentration, as presented in Figure 5. Trans- and cis-

Figure 5. Surface excess of OTAEAzo.

OTAEAzo show maxima at 122.3 and 56.2 mol·m −2, respectively. Γmax refers to the maximum adsorbed surfactant per unit interface at surface saturation. The Γmax value of transOTAEAzo is higher than that of cis-OTAEAzo, demonstrating that more trans-OTAEAzo molecules absorb at the interface when the concentration exceeds the CMC. Table 1. Surface Activity Parameters of trans- and cis-OTAEAzo configuration

CMC (×10−4 mol·L−1)

γCMC (mN·m−1)

Γmax (mol·m−2)

Amin (×10−8 nm2)

trans isomer cis isomer

2.5 5.7

41 52

122.3 56.2

1.36 2.95

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and bulk viscosity is a critical factor on improving the foam stability.41,47,48 The foam half-lives after UV-light irradiation also increase with increasing OTAEAzo concentration. The half-life is tuned owing to conversion between the trans and cis configurations triggered by light so that an increase of the foam half-life after UV-light irradiation also confirms the slower photoisomerization speed with an increase in the concentration. Additionally, Figure 7 plots the foaming ratio and foam

Figure 6. Foam properties of OTAEAzo: (a) foamability; (b) foam half-life; (c) foam photograph of OTAEAzo (0.35 g·L−1) after foaming for 0.5 s and the phototuning mechanism.

foamability is improved when the concentration increases to 0.40 g·L−1. As presented in Figure 6b, foams prepared from a OTAEAzo solution exposed to Vis-light show a long half-life (e.g., t1/2= 2.58 min at 0.35 g·L−1), while the half-life of that prepared from the UV-light-irradiated solution is short (e.g., t1/2 = 0.38 min at 0.35 g·L−1), which unveils that the stability of the OTAEAzo foam is phototuning. After Vis-light irradiation, OTAEAzo is in a trans isomer that shows foam stabilization effects, while the trans isomer transforms to a cis isomer triggered by UV-light, which promotes foam rupture, as illustrated in Figure 6c. The phototuning capability of OTAEAzo can be interpreted by large changes in the equilibrium surface tension, molecular geometry, and absorption properties between the trans and cis isomers. First, the equilibrium surface tension of trans-OTAEAzo (ca. 41 mN·m−1) is much lower than that of cis-OTAEAzo (ca. 52 mN· m−1). According to the formula ΔE = γA, a lower surface tension, γ, will promote the formation of new surfaces, A, when the external energy, ΔE, is constant, suggesting that foams prepared from trans-OTAEAzo are more stable. Second, transOTAEAzo shows a nematic phase due to the high interactions and π-stacking forces of face-to-face azobenzene rings (as shown in Figure 6c).39,45 The strong attractive interaction can cause dense packing of trans-OTAEAzo, which improves the foam stability. On the contrary, cis-OTAEAzo occupies a higher surface area owing to its irregular and random structure, which leads to a loose packing at the gas−liquid interface. Third, it has been reported that the desorption constants of cis-azobenzenes are higher than those of trans-azobenzenes.46 Also, their surface excess (56.2 mol·m−2) is lower than the surface excess of trans isomers (122.3 mol·m−2). The trans-OTAEAzo molecules absorb at the interface, while they rapidly desorb after UVlight irradiation. The prominent desorption indicates a decrease of the OTAEAzo molecules at the interface, increasing the surface tension, which weakens the protection of a thin liquid film from coalescence. Besides, it is obvious that the foam halflife becomes longer with an increase in the OTAEAzo concentration. This may be interpreted by the increase of the bulk viscosity. Surfactants form micelles at the concentrations beyond the CMC, resulting in an increase in the bulk viscosity,

Figure 7. Cycle properties of the OTAEAzo capability for phototuning the foam at a concentration of 0.35 g·L−1: (a) foamability; (b) foam half-life.

half-life on the cycle times, showing that the foaming ratio and half-life of the OTAEAzo foam vary slightly after cycling five times. The foam properties during the cycle process depend on photoisomerization between the trans and cis conformations. These results are consistent with Figure 2, further confirming that OTAEAzo has excellent reversible photoisomerization capability. Figures 6 and 7 prove that OTAEAzo is a sustainable foam switch stimulated with UV- and Vis-light, bringing an environmental tool for reversibly tailoring the foam stability.

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CONCLUSIONS In order to obtain an environmental and sustainable foam switch for rapidly tuning the foam stability, a photoresponsive azobenzene cationic surfactant (OTAEAzo) with low CMC was synthesized. According to the UV−vis absorption spectra, OTAEAzo showed high sensitivity triggered by light stimuli. Trans-to-cis isomerization occurred within 1 s of UV-light irradiation, and cis-OTAEAzo underwent reversible isomerization after exposure to Vis-light for 3 min when the concentration of OTAEAzo was 0.02 g·L−1. The photoisomerization of OTAEAzo was reversible and of high fatigue resistance. The isomerization speed correlated with the OTAEAzo concentration and a lower concentration made for 13782


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Lamellar Liquid Crystal in Aqueous Systems of Diglycerol Fatty Acid Esters. Colloids Surf., A 2007, 293, 262−271. (6) Song, X. W.; Zhang, L.; Wang, X. C.; Zhang, L.; Zhao, S.; Yu, J. Y. Study on Foaming Properties of Polyoxyethylene Alkyl Ether Carboxylic Salts with Different Structures. J. Dispersion Sci. Technol. 2011, 32, 247−253. (7) Dickinson, E.; Ettelaie, R.; Kostakis, T.; Murray, B. S. Factors Controlling the Formation and Stability of Air Bubbles Stabilized by Partially Hydrophobic Silica Nanoparticles. Langmuir 2004, 20, 8517− 8525. (8) Georgieva, D.; Cagna, A.; Langevin, D. Link between Surface Elasticity and Foam Stability. Soft Matter 2009, 5, 2063−2071. (9) Bureiko, A.; Trybala, A.; Huang, J.; Kovalchuk, N.; Starov, V. Bulk and Surface Rheology of Aculyn 22 and Aculyn 33 Polymeric Solutions and Kinetics of Foam Drainage. Colloids Surf., A 2013, 434, 268−275. (10) Eugénie, S. d. P.; Fabrice, D.; Gérard, C.; Samir, M. Effect of Bulk Viscosity and Surface Tension Kinetics on Structure of Foam Generated at the Pilot Scale. Food Hydrocolloids 2014, 34, 104−111. (11) Denkov, N. D. Mechanisms of Foam Destruction by Oil-Based Antifoams. Langmuir 2004, 20, 9463−9505. (12) Fameau, A. L.; Carl, A.; Saint-Jalmes, A.; Von Klitzing, R. Responsive Aqueous Foams. ChemPhysChem 2015, 16, 66−75. (13) Chu, Z.; Feng, Y. PH-switchable Wormlike Micelles. Chem. Commun. 2010, 46, 9028−9030. (14) Brown, P.; Butts, C. P.; Eastoe, J. Stimuli-Responsive Surfactants. Soft Matter 2013, 9, 2365−2374. (15) Peng, S.; Guo, Q.; Hughes, T. C.; Hartley, P. G. Reversible Photorheological Lyotropic Liquid Crystals. Langmuir 2014, 30, 866− 872. (16) Zhao, Y. Light-Responsive Block Copolymer Micelles. Macromolecules 2012, 45, 3647−3657. (17) Salonen, A.; Langevin, D.; Perrin, P. Light and Temperature BiResponsive Emulsion Foams. Soft Matter 2010, 6, 5308−5311. (18) Eastoe, J.; Dominguez, M. S.; Wyatt, P.; Beeby, A.; Heenan, R. K. Properties of a Stilbene-Containing Gemini Photosurfactant: LightTriggered Changes in Surface Tension and Aggregation. Langmuir 2002, 18, 7837−7844. (19) Han, G. D.; Park, S. S.; Liu, Y.; Zhitomirsky, D.; Cho, E.; Dincă, M.; Grossman, J. C. Photon Energy Storage Materials with High Energy Densities Based on Diacetylene−Azobenzene Derivatives. J. Mater. Chem. A 2016, 4, 16157−16165. (20) Luo, W.; Feng, Y.; Cao, C.; Li, M.; Liu, E.; Li, S.; Qin, C.; Hu, W.; Feng, W. A High Energy Density Azobenzene/Graphene Hybrid: a Nano-Templated Platform for Solar Thermal Storage. J. Mater. Chem. A 2015, 3, 11787−11795. (21) Ferri, V.; Elbing, M.; Pace, G.; Dickey, M. D.; Zharnikov, M.; Samorì, P.; Mayor, M.; Rampi, M. A. Light-Powered Electrical Switch Based on Cargo-Lifting Azobenzene Monolayers. Angew. Chem. 2008, 120, 3455−3457. (22) Feng, W.; Li, S.; Li, M.; Qin, C.; Feng, Y. An Energy-Dense and Thermal-Stable Bis-Azobenzene/Hybrid Templated Assembly for Solar Thermal Fuel. J. Mater. Chem. A 2016, 4, 8020−8028. (23) Zhitomirsky, D.; Grossman, J. C. Conformal Electroplating of Azobenzene-Based Solar Thermal Fuels onto Large-Area and Fiber Geometries. ACS Appl. Mater. Interfaces 2016, 8, 26319−26325. (24) Basuki, S. W.; Schneider, V.; Strunskus, T.; Elbahri, M.; Faupel, F. Light-Controlled Conductance Switching in Azobenzene-Containing MWCNT-Polymer Nanocomposites. ACS Appl. Mater. Interfaces 2015, 7, 11257−11262. (25) Renuka, K. D.; Lekshmi, C. L.; Joseph, K.; Mahesh, S. Sustainable Electronic Materials: Reversible Phototuning of Conductance in a Noncovalent Assembly of MWCNT and BioresourceDerived Photochromic Molecule. ACS Appl. Mater. Interfaces 2017, 9, 1167−1172. (26) Meng, H.; Li, G. Reversible Switching Transitions of StimuliResponsive Shape Changing Polymers. J. Mater. Chem. A 2013, 1, 7838−7865. (27) Qin, C.; Feng, Y.; Luo, W.; Cao, C.; Hu, W.; Feng, W. A Supramolecular Assembly of Cross-Linked Azobenzene/Polymers for

a faster photoisomerization. The differences of the surface activity between trans and cis isomers including the CMC, equilibrium surface tension, maximum surface excess, and minimum area per surfactant molecule enabled OTAEAzo to become a foam switch. It presented excellent foamability at a low concentration so that the photoisomerization speed was rapid at the foaming concentration, indicating that OTAEAzo is a highly efficient foam switch. Trans-OTAEAzo showed foam stabilization effects, while cis-OTAEAzo promoted foam rupture. The half-life of OTAEAzo foam was reversibly tunable from 0.38 to 2.58 min, verifying that OTAEAzo is a sustainable foam switch. Therefore, OTAEAzo with low CMC, highly sensitive photoisomerization capability, and surface activity differences of the trans and cis isomers is an efficient and sustainable foam switch, which opens an environmental strategy for tailoring the foam stability.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b02024. Synthetic route of OTAEAzo, characterization of OTAEAzo (including FT-IR, LC-MS, and 1H NMR spectra), surface activity analysis of BTAEAzo, and photoisomerization of BTAEAzo (PDF) Video of the foamability comparison of OTAEAzo and BTAEAzo (AVI)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Chaoxia Wang: 0000-0001-6322-7606 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for financial support of the National Natural Science Foundation of China (Grant 21174055), the Fundamental Research Funds for the Central Universities (Grant JUSRP51724B), the Excellent Doctoral Cultivation Project of Jiangnan University, and the International Joint Research Laboratory for Advanced Functional Textile Materials of Jiangnan University.

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REFERENCES

(1) Stubenrauch, C.; Shrestha, L. K.; Varade, D.; Johansson, I.; Olanya, G.; Aramaki, K.; Claesson, P. Aqueous Foams Stabilized by NDodecyl-β-D-Maltoside, Hexaethyleneglycol Monododecyl ether, and Their 1:1 Mixture. Soft Matter 2009, 5, 3070−3080. (2) Astarita, A.; Carrino, L.; Franchitti, S.; Langella, A.; Paradiso, V. Manufacturing of Innovative Components Formed Using SPF Processes and Filled with Aluminum Metal Foams. Surf. Interface Anal. 2013, 45, 1638−1642. (3) Yu, H.; Wang, Y.; Zhong, Y.; Mao, Z.; Tan, S. Foam Properties and Application in Dyeing Cotton Fabrics with Reactive Dyes. Color. Technol. 2014, 130, 266−272. (4) Du, Z.; Bilbao-Montoya, M. P.; Binks, B. P.; Dickinson, E.; Ettelaie, R.; Murray, B. S. Outstanding Stability of Particle-Stabilized Bubbles. Langmuir 2003, 19, 3106−3108. (5) Shrestha, L. K.; Saito, E.; Shrestha, R. G.; Kato, H.; Takase, Y.; Aramaki, K. Foam Stabilized by Dispersed Surfactant Solid and 13783


Research Article

ACS Applied Materials & Interfaces a High-Performance Light-Driven Actuator. J. Mater. Chem. A 2015, 3, 16453−16460. (28) Petroffe, G.; Wang, C.; Sallenave, X.; Sini, G.; Goubard, F.; Péralta, S. Fast and Reversible Photo-Responsive Wettability on TiO2 Based Hybrid Surfaces. J. Mater. Chem. A 2015, 3, 11533−11542. (29) Sun, W.; Zhou, S.; You, B.; Wu, L. Polymer BrushFunctionalized Surfaces with Unique Reversible Double-Stimulus Responsive Wettability. J. Mater. Chem. A 2013, 1, 10646−10654. (30) Chen, S.; Wang, C.; Yin, Y.; Chen, K. Synthesis of PhotoResponsive Azobenzene Molecules with Different Hydrophobic Chain Length for Controlling Foam Stability. RSC Adv. 2016, 6, 60138− 60144. (31) Chen, S.; Zhang, W.; Wang, C.; Sun, S. A Recycled Foam Coloring Approach Based on the Reversible Photo-Isomerization of Azobenzene Cationic Surfactant. Green Chem. 2016, 18, 3972−3980. (32) Chen, K. Y.; Wezenberg, S. J.; Carroll, G. T.; London, G.; Kistemaker, J. C.; Pijper, T. C.; Feringa, B. L. Tetrapodal Molecular Switches and Motors: Synthesis and Photochemistry. J. Org. Chem. 2014, 79, 7032−7040. (33) Hong, C. R.; Park, S. J.; Choi, S. J. Influence of the Hydrophilic Head Size and Hydrophobic Tail Length of Surfactants on the Ability of Micelles to Stabilize Citral. J. Sci. Food Agric. 2016, 96, 3227−3232. (34) Tian, Z.; Wen, J.; Ma, J. Reactive Molecular Dynamics Simulations of Switching Processes of Azobenzene-Based Monolayer on Surface. J. Chem. Phys. 2013, 139, 014706. (35) Demirel, G. B.; Dilsiz, N.; Ç akmak, M.; Ç aykara, T. Molecular Design of Photoswitchable Surfaces with Controllable Wettability. J. Mater. Chem. 2011, 21, 3189−3196. (36) Feng, C. L.; Jin, J.; Zhang, Y. J.; Song, Y. L.; Xie, L. Y.; Qu, G. R.; Xu, Y.; Jiang, L. Reversible Light-Induced Wettability of FluorineContaining Azobenzene-Derived Langmuir-Blodgett Films. Surf. Interface Anal. 2001, 32, 121−124. (37) Bandara, H. D.; Burdette, S. C. Photoisomerization in Different Classes of Azobenzene. Chem. Soc. Rev. 2012, 41, 1809−1825. (38) Crecca, C. R.; Roitberg, A. E. Theoretical Study of the Isomerization Mechanism of Azobenzene and Disubstituted Azobenzene Derivatives. J. Phys. Chem. A 2006, 110, 8188−8203. (39) Chevallier, E.; Mamane, A.; Stone, H.; Tribet, C.; Lequeux, F.; Monteux, C. Pumping-Out Photo-Surfactants from an Air-Water Interface Using Light. Soft Matter 2011, 7, 7866−7874. (40) Smaali, K.; Lenfant, S.; Karpe, S.; Ocafrain, M.; Blanchard, P.; Deresmes, D.; Godey, S.; Rochefort, A.; Roncali, J.; Vuillaume, D. High On-Off Conductance Switching Ratio in Optically-Driven SelfAssembled Conjugated Molecular Systems. ACS Nano 2010, 4, 2411− 2421. (41) Hayashita, T.; Kurosawa, T.; Miyata, T.; Tanaka, K.; Igawa, M. Effect of Structural Variation within Cationic Azo-Surfactant upon Photoresponsive Function in Aqueous Solution. Colloid Polym. Sci. 1994, 272, 1611−1619. (42) Elbing, M.; Błaszczyk, A.; von Hänisch, C.; Mayor, M.; Ferri, V.; Grave, C.; Rampi, M. A.; Pace, G.; Samorì, P.; Shaporenko, A.; Zharnikov, M. Single Component Self-Assembled Monolayers of Aromatic Azo-Biphenyl: Influence of the Packing Tightness on the SAM Structure and Light-Induced Molecular Movements. Adv. Funct. Mater. 2008, 18, 2972−2983. (43) Han, M.; Honda, T.; Ishikawa, D.; Ito, E.; Hara, M.; Norikane, Y. Realization of Highly Photoresponsive Azobenzene-Functionalized Monolayers. J. Mater. Chem. 2011, 21, 4696−4702. (44) Karakashev, S. I.; Grozdanova, M. V. Foams and Antifoams. Adv. Colloid Interface Sci. 2012, 176-177, 1−17. (45) Yim, K. S.; Fuller, G. G. Influence of Phase Transition and Photoisomerization on Interfacial Rheology. Phys. Rev. E: Stat. Phys., Plasmas, Fluids, Relat. Interdiscip. Top. 2003, 67, 041601. (46) Chevallier, E.; Monteux, C.; Lequeux, F.; Tribet, C. Photofoams: Remote Control of Foam Destabilization by Exposure to Light Using an Azobenzene Surfactant. Langmuir 2012, 28, 2308−2312. (47) Oh, S. G.; Shah, D. O. Relationship between Micellar Lifetime and Foamability of Sodium Dodecyl Sulfate and Sodium Dodecyl Sulfate/1-hexanol Mixtures. Langmuir 1991, 7, 1316−1318.

(48) Lu, X. Y.; Jiang, Y.; Cui, X. H.; Mao, S. Z.; Liu, M. L.; Du, Y. R. NMR Study of Surfactant Micelle Shape Transformation with Concentration. Acta Phys-Chim. Sin. 2009, 25, 1357−1361.

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Insight into a Fast Photo-Tuning Azobenzene Switch for Sustainably

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