Controllable and Stable Deformation of a Self-Healing Photo

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Controllable and stable deformation of a self-healing photo-responsive supramolecular assembly for an optically actuated manipulator arm Qianyu Si, Yiyu Feng, Weixiang Yang, Linxia Fu, Qinghai Yan, Liqi Dong, Peng Long, and Wei Feng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b08025 • Publication Date (Web): 26 Jul 2018 Downloaded from http://pubs.acs.org on July 27, 2018

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ACS Applied Materials & Interfaces

Controllable and stable deformation of a self-healing photo-responsive supramolecular assembly for an optically actuated manipulator arm †

Qianyu Si , Yiyu Feng*,

†, § , ‖

†

Peng Long†, Wei Feng †

‡

§

†

†

†

, Weixiang Yang , Linxia Fu , Qinghai Yan , Liqi Dong , †, ‡ , § , ‖

School of Materials Science and Engineering, Tianjin University, PR China

Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, PR China

Key Laboratory of Advanced Ceramics and Machining Technology, Ministry of Education, PR China ‖

Tianjin Key Laboratory of Composite and Functional Materials, Tianjin 300072, PR

KEYWORDS : azobenzene, multiple hydrogen bonds, photo-responsive, manipulator arm, selfhealing

ABSTRACT: It is highly challenging to achieve an optically deformable polymer with good controllability, stability and self-healability for fabricating an optically controlled micro robotics. Here, we present a photo-responsive self-healing supramolecular assembly crosslinked by

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tertracarboxylated azobenzene (t-Azo) enabling the controllable and stable deformation. The network (PAA-u) of polyacrylic acid (PAA) grafted with 2-ureido-4[1H]-pyrimidinone (UPy) is formed via multiple intermolecular hydrogen bonds (H-bonds) between UPy and t-Azo moieties. Molecular H-bonds stabilizes the cis-isomer, enables stress transfer at the interface and also contributes to fast healability. The PAA-u/t-Azo assembly shows a green-light-induced bending deformation, which recovers its shape under the irradiation of UV light. Based on this controllable and reversible deformation, the PAA-u/t-Azo “hand” realizes reversible light-driven grabbing, and releasing of an object by optimizing bending and recovery. The assembly also shows a fast and excellent self-healing performance irradiated by green light during the deformation. The multiple-H-bonding-crosslinked assembly with stable deformation and fast self-healability can be used for the development of a multitude of advanced micro robotics.


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INTRODUCTION

A photo-responsive polymer is one of the important candidates for optical actuators or micro robotics owing to its ability to convert light into mechanical power based on shape deformation.1,2 Azobenzene chromophores (Azo) can undergo photo-induced reversible trans (E) - cis (Z) isomerization, causing changes in the structure at the molecular length scale, steric configuration, and the interaction with the surrounding materials.3,4 Based on these changes, a variety of Azo derivatives has been prepared and incorporated into polymers for light-to-work transduction.5-7

Controllability and stability of light-driven deformation of Azo-based polymers are of significant importance for their potential application.8-11 However, the deformation induced by E-to-Z isomerization is often found to recover uncontrollably owing to the Z-to-E reversion of Azo moieties. Thus, this uncontrollable shape recovery limits its use in optical actuators or micro robotics. Ikeda pioneered the study on photo-induced macroscopic deformation of the liquidcrystalline Azo-polymer film.12 The fast Z-to-E isomerization leads to a short-term deformation. Many researchers tried to restrict the fast Z-to-E transformation of Azo in the polymer matrix after the deformation.13-15 However, this effect also lowers the rate and the degree of E-to-Z isomerization, resulting in a slow and small deformation.16-18

A promising method to improve the deformation stability of Azo-polymers is inducing the deformation by Z-to-E isomerization. Compared to the Z-isomers, the stable E-isomers is able to keep the deformation for a long time due to good thermodynamic stability.19 Unfortunately, in many cases, the resultant Azo molecules usually show E-rich states with a high content of > 93% before the deformation.20,21 As a result, a low amount of the Z-isomers in the matrix reduces its


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photo-responsivity (shape deformation). Hydrogen bonds (H-bonds) have been used to affect the degree and rate of the photo-isomerization by cross-linking the Azo with polymers to form a supermolecular network.5,7,18 Compared with single H-bond, the multiple-H-bond-crosslinking network not only has the potential for stabilizing the Z-isomers based on limited structural transformation, but also endows the photo-responsive film with self-healing performance.22-24 To our knowledge, there are few studies on a stable photo-induced deformation of Azo-polymers based on Z-to-E isomerization.25-31 Such Azo-polymers combining controllability and stability of the light-driven deformation and fast healability is one of ideal candidate materials for optical actuators or micro robotics.

In this study, we prepare a photo-responsive supramolecular assembly of polyacrylic acid (PAA) grafted with 2-ureido-4[1H]-pyrimidinone (UPy) (referred as PAA-u) and 3,3’,5,5’azobenzenetetracarboxylic acid (t-Azo) by crosslinking them via multiple molecular H-bonds. After the irradiation, the Z-isomers in the assembly are stabilized by intermolecular H-bonds. The Z-to-E isomerization of the t-Azo crosslinkers induces bending deformation under the irradiation of green laser driven by the stretching force along the cross-section of the film. The deformation not only shows high stability but also is able to recover the shape under UV irradiation. The deformation rate (response time) is also tuned by the intensity of the incident light. We realize cyclic grabbing and releasing of the object using PAA-u/t-Azo arms by controlling bending and recovery of the “hand”. The assembly also has a fast self-healability induced by the green-light irradiation during the deformation. The healing efficiency can be controlled by the irradiation intensity.


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MATERIALS AND METHODS

2-(6-Isocyanatohexylaminocarbonylamino)-6-methyl-4[1H] pyrimidinone (UPy-NCO), t-Azo and PAA-u were synthesized according to the literature respectively.32-34 Materials and the preparation details (Scheme S1) are shown in supporting information.

Preparation of PAA-u/t-Azo film. PAA-u and t-Azo were dissolved in DMF at a concentration of 1.2 mg/mL and 0.275 mg/mL respectively. Then, the PAA solution was added dropwise to the t-Azo solution. The mixture was heated to 80 ºC for 1 h and then cooled to room temperature followed by stirring overnight to get PAA-u/t-Azo assembly. A quartz glass (7 cm × 2 cm) was cleaned by ultrasonication with acetone, DI-water, and alcohol successively and dried by nitrogen gas at room temperature. The concentrated solution of the PAA-u/t-Azo supramolecular assembly was dip-coated on the quartz glass, then the solution was irradiated by UV light for 48h at room temperature. Finally, a free-standing PAA-u/t-Azo film was released from the substrate.

Instruments and Measurements. FTIR spectra was recorded on a Bruker Tensor 27 spectrometer using discs of KBr with the compound to be analyzed. Differential scanning calorimetry (DSC TA Q20) was carried out to analyze the hydrogen bonding. The detail is shown in Supporting Information. A Hitachi 330 UV-vis spectrophotometer was used to record the time-evolved UV-vis absorption spectra for investigating the isomerization. The samples were first irradiated by a 532 nm green laser (STOEMT 2–5). Then, the film was irradiated by 365 nm UV light (LED-200).

Photo-induced Deformation. The PAA-u/t-Azo film was cut into a strip (7cm× 0.5cm), and then one side of the film was clamped by tweezers. The outside of film was irradiated by green


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laser at different intensities (80, 127, 310 and 563 mW/cm2) to induce bending deformation for different shapes. Then the film kept the deformation for 240 h at the temperature of 25 ºC. The curved positions were irradiated by UV light (25, 30, 62, 102 mW/cm2) for shape recovery. The bending angles and rates were controlled by irradiation time and light-intensity.

Manipulator arm. Two strips (20mg, 7 cm × 0.5 cm) square-crossed at the center were held vertically with its center tied with a rope to make a “hand” with four “fingers”. The strips were held above an object. The green laser was irradiated at the position where was 0.5cm from edge of four “fingers” one by one to make “knuckle” in front of “finger”. Then the four “fingers” were irradiated to 90° using green laser to grasp object. Then the whole manipulator arms with object were lifted by rope. After staying for 480 h, the “finger” was irradiated by UV light to release the object. The bent “finger” shows reversible shape recovery. The cycling performance of manipulator arm was also investigated by the irradiation of green laser and UV light alternatively.

Photo-induced driving force. The clamped strip (7 cm × 0.5 cm) was placed above a precision balance at a distance of 3 cm. The strip was irradiated by the green laser or UV light at different intensities respectively at a position 2 cm from the tweezers. The force is read by the precision balance when the bent film touches it.

The driving force for different rates of bending

deformation or shape recovery is tuned by irradiation intensity. The weight of the film and bending time were also recorded. Schematic illustration of the measurement of driving forces is shown in Figure S1.

Self-healing performance. The PAA-u/t-Azo film was damaged by a razor blade to attain a well-defined scratch with a depth of approximately 30–50% of its thickness. The scratch was


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near the deformation point. Then, the film was exposed to green laser (310 mW cm-2) for 20 s. At the same time, another film was also cut into two pieces, then the pieces were brought into contact firmly and irradiated by green laser (80, 127, 310 and 563 mW/cm2) for 2-20min. In order to measure the healing efficiency, the original and healed samples were cut into strips with a width of 0.5 cm and length of 20 mm. Samples were carried out at 25 ºC at a strain rate of 5%/min on TA Instruments Model Q800 dynamic mechanical analyser. The tensile strength of the film with E- and Z-rich t-Azo are measured to investigate the self-healing efficiency. The temperature of the PAA-u/t-Azo film under green laser was also tracked using a high-resolution IR thermal imaging camera (resolution: ±0.03 0C). The healing process was recorded on Olympus BX51 microscope equipped with DP72 digital camera to get optical microscopy images.

RESULTS AND DISCUSSION Multiple H-bonding network We designed a stable, self-healing, and photo-deformable Azo-polymeric supramolecular architecture, which is assembled via multiple intermolecular H-bonds (Figure 1). Multiple molecular H-bonds in the PAA-u/t-Azo network are characterized by Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). The covalent grafting of UPy on PAA is confirmed by the disappearance of the band at 2270 cm-1 corresponding to -NCO.34 New bands originate at 1246 and 1658 cm−1 corresponding to the bending vibration of the N-H group of UPy and stretching mode of the amide C=O group. The presence of two bands at 1500 and 3260 cm-1 suggests the formation of self-complementary H-bonds. A detailed analysis is provided in Figure S2. The grafting density is found to be one UPy molecule grafted on every


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eight PAA monomer units on average, as determined by X-ray photoelectron spectroscopy (XPS) (Table S1 and Figure S3). Compared to t-Azo and PAA-u, the PAA-u/t-Azo assembly shows shift of the C=O band (1637 cm-1) to a higher wavenumber (1658 cm-1)35 and enhanced band of N---H at 1500 cm-1.36 These features indicate the formation of multiple H-bonds between UPy, tAzo, and PAA or between themselves in the matrix (Figure 2a). The formation of multiple H-bonds is further confirmed by DSC analysis (Figure 2b). All three derivatives, PAA-u/t-Azo, PAA, and t-Azo, show an endothermic peak between 92 and 102 ºC owing to the breakdown of the molecular H-bonds during the heating cycle. PAA-u/t-Azo exhibits a higher temperature (97 ºC) of the endothermic peak and absorbs more energy (0.6725 J/g) for breaking the H-bonds than PAA (95 ºC, 0.3786 J/g) and t-Azo (95 ºC, 0.3122 J/g). The assembly also shows an exothermic peak at 65 ºC (Figure S4), owing to the formation of Hbonds during the cooling cycle.37 The crosslinked assembly is also demonstrated by the improvement in the mechanical strength (Figure 2c). PAA-u/t-Azo film shows a maximum tensile stress of 26 MPa with a strain of 1.9%. The stress is higher than that of PAA film (11.6 MPa, 1.22%) and PAA-u film (20 MPa, 1.7%), respectively, owing to the crosslinking via multiple H-bonds. Thus, the H-bonding-crosslinked assembly has a great potential as a material amenable to stable photo-induced deformation compared to a single-H-bonded structure.38-40 At the same time, after cross-linking, the PAA-u/tAzo film is only soluble in N,N-dimethylformamide (DMF), as opposed to the good solubility of t-Azo in several solvents such as ethyl alcohol, acetone, N-methyl-2-pyrrolidinone (NMP), and DMF (Figure 2d).

Isomerization of PAA-u/t-Azo film


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The photomechanical behavior of Azo-polymers depends on the degree and rate of E-Z isomerization of the t-Azo cross-linker.41 The as-prepared Azo molecules usually show a low amount (< 7%) of Z-isomers.20,21,42 The content of Z-isomers in the molecules or in the assembly film is calculated by the change in 8.26, 7.86, 7.76, 7.39 ppm 1H-NMR and also tracked by the change in intensity of the π-π* transition (340 nm) in absorption spectra.14 The pristine t-Azo molecule has 15% Z-isomers, and time-evolved absorption spectra indicates that the content becomes 4% and 40%, after the irradiation of green light (20 s) and UV (180 s) light respectively ((Figure S5a) and (Figure S6)). At the same concentration (0.07 mg/mL) of t-Azo, the intensity at 340 nm shows a clear linear increase with the content of Z-isomer (Figure S5b).

To enhance the ratio of Z-isomers, we prepared the PAA-u/t-Azo film by irradiating UV light during the formation. As indicated by Figure S7, PAA shows no characteristic peak in the range from 300 nm to 400 nm and the PAA-u/t-Azo assembly correspondingly has 25% Z-isomers (10% higher than the as-prepared t-Azo molecule) before the irradiation of green light according to Figure 3a and S5. Importantly, the Z-isomer of t-Azo exhibits good stability in the PAA-u matrix due to multiple H-bonding at the interface. The stable H-bonding-crosslinked network and the relatively limited movement of PAA chains below the glass transition temperature (Tg =106℃, Figure S4) restrict steric transformation (reversion) in the matrix, thus stabilizing the Zisomer.43 Figure 3c and S5b indicate that only 6% Z-t-Azo in the PAA matrix spontaneously isomerizes to E-state in darkness after 40 h. The half-life of Z-isomer is 120 h in darkness (Figure 3c), which is comparable or longer than that in many previous studies (Table 1).9,10,25-31

We also can accelerate the Z-to-E isomerization induced by green light. Under green-light irradiation, the PAA-u/t-Azo assembly shows a decreasing content of Z-isomers. When


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irradiating for 60 s, the Z-isomers reach 12%, which is 13% lower than that before the irradiation. And E-to-Z isomerization induced by UV irradiation (240 s) results in a 15% increase (from 12% to 27%) in Z-isomers of t-Azo in the film. The reversibility of the photoisomerization was also verified through alternative irradiation with green laser (1 min) and UV light (4 min). As shown in Figure S8, the assembly shows excellent cycling performance up to 100 cycles without decay.

Both E and Z-rich t-Azo crosslinkers enable the reversible

isomerization in the network. This result offers a great potential for photo-responsive and stable deformation of the PAA-u/t-Azo film.

Controllable and stable shape deformation

The as-prepared PAA-u/t-Azo film with 25% Z-isomers potentially enables a large degree of Zto-E isomerization compared with previous studies.21,44,45 We use a green-light point source to induce light-driven shape deformation controlled by an intrinsic stress along the cross-section of the film. This stable deformation shows the shape recovery irradiated by UV light.

The light-driven reversible bending of the PAA-u/t-Azo film (7 cm × 0.5 cm) is induced by a green laser. The deformation of the bent film is evaluated by the bending angles (α, β and γ) at different positions. As shown in Figure 4a, the film can be optically actuated into different shapes (“L” “N” and “M”) with good stability by controlling the direction of the irradiation. We demonstrate the bending process by selecting the “M”-shaped film as an example. A strip of the film is shaped into “M” by performing photo-induced bending of the film three times at three appropriate locations (Figure 4b). When irradiated by the green laser, the film bends at the irradiation point on the side opposite to that irradiated. The continuous bending under continued irradiation (4 s) increases the bending angle. The deformation is induced by the intrinsic


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stretching force based on Z-to-E isomerization. The bending rate can be controlled by the intensity of irradiation light (Figure 4c). The bent film does not shrink or recover its original shape in 480 h due to the stability of E-isomer of t-Azo, which outperforms other Azo-polymer films.46-48 We also realize the recovery of the film by bending the film in the opposite direction by irradiating with UV light (5 s). After the recovery, the film (13% Z-isomer) shows no shape change in 120 h because of an extremely low Z-to-E isomerization, which enables stress relaxation based on the movement of the chains in the film. Moreover, the film also shows excellent reversible bending ability over 100 cycles (Figure S8).

We also control the bending rate by changing the intensity of irradiation light (green and UV light) (Figure 4c and 4d). It can be seen that the high-intensity irradiation facilitates fast deformation and recovery. When irradiated by green light (563 mW/cm2) and UV (102 mW/cm2) with high intensity, the film reaches the bending deformation up to 135° and recovers its shape for 4 s and 5 s, respectively. The rates of deformation are 33.75 °/s (green laser) and 27 °/s (UV light). The bending or recovery times of the PAA-u/t-Azo film become longer at a relatively lowintensity incident light. This feature indicates that t-Azo crosslinker needs to absorb enough light for isomerization to drive the deformation, which is to some degree restricted by the H-bonding network in the polymer matrix.

Mechanism of shape deformation

The photo-induced bending deformation of the PAA-u/t-Azo film depends on the stretching or contraction along the cross-section caused by the isomerization of the t-Azo cross-linker (Figure 5). When exposed to green laser, the bent-shaped Z-Azo cross-linkers isomerize to rod-like Eform with their length increasing from 5.5 to 9.0 Å.49,50 Because of the large absorption


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coefficient of t-Azo,51 the front surface facing the green light absorbs more energy than the back surface.52 As a result, the E-Azo crosslinkers at the front surface undergo a faster and higher degree of isomerization than those at the back. The asymmetric Z−E isomerization rate between the lower and upper surfaces continuously generates an intrinsic stretching force along the crosssection of the film, which decreases from the lower to the upper surface.53,54 The shape recovery is also induced by UV irradiation on the same area. The bent Z-t-Azo crosslinkers in the front surface rapidly isomerize to the rod-like E-form to generate a similar contraction force along the cross-section of the film.

We measure the green-induced stretching force55,56 (Hm, 3.2 × 10-6 - 1.7 × 10-5) and UV-induced contraction force (Hm’ , 1.6 × 10-6 - 1.1 × 10-5) for bending deformation and shape recovery respectively. The details and schematic illustration of the measurement of photo-induced driving forces are shown in experimental section and Figure S1. As shown in Table S2, the highintensity irradiation results in an increase in driving force based on a fast isomerization. The difference between the stretching and contraction force is attributed to different degrees of isomerization in the cross-section direction. The moment of the force (Mm) driving the deformation and shape recovery are 2.8 × 10-10- 6 × 10-10 N m and 3.4 × 10-11- 8 × 10-10 N m respectively. The increasing moment of the driving force enables a fast bending deformation, consistent with the controllable bending rate in Figure 4c and 4d.

Manipulator arms

We prepared optically actuated manipulator arms using the PAA-u/t-Azo film assembly to realize grabbing and releasing of an object by optimizing the “finger” shape of the “hand”57 (Movie S1). The process (three stages) (Figure 6) demonstrates the applicability and


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controllability of the optically actuated arms. The square-cross-shaped “hand” is prepared by crossing two strips of the film (20 mg, 7 cm × 0.5 cm) at the center. The object (100–150 mg) is placed under the “hand”. In the first stage, four “fingers” of the “hand” are bent one after the other to different angles, with a “knuckle” formed in front of the “finger” (Figure 6, a,b) via the irradiation of the cross with the green laser. For example, we formed a knuckle at the front of the “finger” (the distance between light and the edge of finger (d) is 0.5 cm, the angle θ is 60°) and bent the “finger” by 90° (δ) (Figure 6,c,d) using green-light irradiation at different positions. As a result, the hand is manipulated to grab the object using the finger. We lift and move the object (the second stage) (Figure 6e) and the deformed “finger” supports the object in 480 h due to good stability (Figure 4b). In the third stage, the finger is induced to release the object by irradiating the “finger” with UV light. And the finger (Figure 6f) continues to rises up to the angle δ of 70° under UV irradiation, and as a result, the object drops out of its grasp under gravity. Moreover, the hand can also be used for the next optical actuation cycle (Figure 6g-i). The “hand” is induced to repeatedly grab and release the object up to 40 times by alternately irradiating with green laser and UV light (Movie S2). The arm shows 15% decline of bending angle (δ) upon 40 cycles (Figure 6j). The stability of the bending “finger” is attributed to the Erich t-Azo cross-linker via multiple H-bonds. The optically-controlled reversible deformable arm can be developed for micro robotics by further optimizing its deformation and recovery.

Self-healability

A fast self-healability is one of the important characteristics for optical actuators or micro robotics, in particular, during the “operation”. The assembly crosslinked by multiple-H-bonding shows self-healing property during Z-to-E deformation (green laser).24 Before the self-healing,


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the PAA-u film with Z-rich Azo (25%) shows a tensile strength of 26 MPa, which is 8% lower than the film (28 MPa) with as-prepared E-rich Azo (95%) (Figure S9). The decrease in strength arises from the contraction force.58-60 Before the bending deformation, the “finger” is scratched to a depth of 3–4 µm (30% of the thickness) using a razor blade. Thus, multiple “wounds” were made at the position of the “finger” to be irradiated. The self-healing properties of the PAA-u/tAzo “fingers” during the manipulation were monitored by optical microscopy. The optical images (Figure7) show that the 4-µm-deep scratch of the “finger” disappears after irradiation of the area with green light (310 mW/cm2) for 20 s. The healability is further investigated by stress– strain tests. The sample shows an increasing stress (σ) and strain (ε) when the irradiation time increases. The “injured” PAA-u/t-Azo “fingers” (25 MPa) recover 98% of the tensile strength (25.5 MPa) after the irradiation for 20 s (Figure 8a).

The fast self-healability of the PAA-u/t-Azo “fingers” arises from the reversible interaction (formation and breakdown) of multiple H-bonds at the Azo crosslinkers.61-63 The irradiation not only induces the Z-to-E isomerization of the Azo unit from the bent shape to the rod-like isomer of increased length but also heats the irradiated area. The irradiation generates a stretching force at the break points to facilitate the contact, while the temperature of the “fingers” increases to 72ºC, according to the high-resolution IR image (Figure S10). As indicated by DSC measurements (Figure S4), multiple intermolecular H-bonds re-arrange to form a stable network upon cooling, thereby healing the “wound”. The H-bonds mainly come from the interaction of N–H and C=O according to Figure 2a. This analysis is confirmed by the FT-IR spectra (Figure 8c) at different temperatures. Two bands at 1726 cm-1 and 1656 cm-1 corresponds to stretching vibration of C=O group, and bands at 1448cm-1 and 1385cm-1 is attributed to bending vibration of the N-H group. Their intensity can recede during the heating and strengthen during the cooling


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process, suggesting that the interaction of the H-bonding is reversible (Table 2). The dissociation and re-formation of H-bonds contribute to the fast self-healing properties.

The finger is able to self-heal its shape under green-light irradiation even it is bisected. The arm recovers 94-97 % of the strength when the facture surface is irradiated by green light (80-563 mW/cm2) for 6-20 min (Figure 8b).We can further improve the self-healing efficiency by irradiating green light at a high-intensity or for a long time (Figure 8d). As shown in Figure 8d, the “finger” reaches 95 % of the original strength after the irradiation for 6 min at 563 mW/cm2, which is much higher than that (87 %, 60 % and 50 %) for irradiated by the light at 310 mW/cm2 (7 min), 127 mW/cm2 (6 min), and 80 mW/cm2 (8 min).

The excellent self-healing performance arises from multiple H-bonds favoring the interaction between two adjacent polymer chains at a high temperature (58-80 oC tracked by IR) (Figure S11). The increasing temperature facilitates the interaction, resulting in the fast and efficient selfhealing. According to previous studies, most supramolecular polymers showed self-healing properties at the temperature higher than their Tg because the relatively free movement of chain favors the re-formation of H-bonds.22,24,61-67 Based on multiple H-bonds, PAA-u/t-Azo enables the fast recovery and high healing efficiency at a low temperature (65oC), which is much lower than its Tg (106 oC). The self-healing performance is better than most previous polymers (Table 3). The self-healable and photo-responsive PAA-u/t-Azo “fingers” broadens a multitude of application of the optically actuated manipulator arm in complicated or harsh environment.

CONCLUSION


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We prepared a stable, self-healing, and photo-deformable PAA-u/t-Azo supramolecular assembly via multiple intermolecular H-bonds. The cross-linked network not only stabilizes Zisomers with a half-life of 120 h but also enables E-Z isomerization of t-Azo induced by green and UV light. PAA-u/t-Azo with Z-rich states shows light-driven bending deformation caused by stretching force based on Z-to-E isomerization. The deformation shows high shape persistence in 480 h because of stable E-isomers in the assembly, and the shape recovery is also obtained by irradiating UV light to generate the contraction force along the cross-section of the film. PAAu/t-Azo film exhibits stable and reversible bending deformations with controllable angles (90°170°) and rates (green: 33.75 °/s) and (UV: 27 °/s). We further increase the bending rate and angle of the film by irradiating it using the high-intensity light. Based on this deformation, an optically actuated manipulator arm enables cycling grabbing and releasing an object upon optimizing the “finger” shape of the “hand”. Moreover, this manipulator arm also shows a fast self-healing performance under green-light irradiation. The multiple-H-bond-crosslinking assembly shows controllable, and stable and reversible light-driven deformation and fast selfhealing properties, which can be developed for advanced optically controlled micro robotics.


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Figure 1. Chemical structures of t-Azo, and PAA-u.


17


Page 18 of 40

Figure 2. Characterization of H-bonds (a) FT-IR spectra of PAA-u, t-Azo, PAA-u/t-Azo. (b) DSC curves of PAA-u/t-Azo, PAA, and t-Azo. (c) The relationship between the stress and strain of the films of PAA-u/t-Azo, PAA-u, and PAA . (d) Photographs of t-Azo (A-D) and PAA-u/tAzo films (a-d) in different solvents: ethyl alcohol, acetone, NMP, DMF (from left to right).


18

60s 45s 30s 10s 0s

1.54 1.54 1.52 1.52 1.50

1.50

green laser

1.48

1.48

1.46

1.46

320 320

0s 15s 50s 90s 120s 180s 240s

1.56 (b)

330 340 350 360 330 340 340 350 350 360 330 Wavelength(nm) Wavelength (nm)

1.54 1.52 1.50

UV light

1.48 1.46

320

330 340 350 Wavelength (nm)

initial 120h 40h 0h

1.56 (c) Absorbance (a.u.)

1.56 1.56 (a) Absorbance(a.u.) Absorbance(a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Absorbance (a.u.)

Page 19 of 40

360

1.54 1.52 1.50

in darkness

1.48 1.46

320

330 340 350 Wavelength (nm)

360

Figure 3. Time evolution of the absorption spectra of a free-standing PAA-u/t-Azo film under the irradiation of (a) green laser at 532 nm, (b) UV light at 365 nm after the irradiation with the green laser, and (c) in darkness after the irradiation by UV light.


19


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Figure 4. (a) Photographs showing multiple light-driven deformations of strips of the PAA-u/tAzo film to shape it into letters, L, N, and M. One side of the film (7 cm × 0.5 cm) was clamped by tweezers. The green laser is switched on during deformation and the UV light is switched on during the recovery.(upper one is the schematic drawing, bottom one is the optical image). (b) Time-dependent bending angles of PAA-u/t-Azo film with green laser irradiation and the shape recovery process under UV light. Time-dependent bending angles irradiated by (c) green light, and (d) UV light at different intensities.


20

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Figure 5. Schematic illustration of the light-driven deformation and shape recovery of a PAAu/t-Azo film (a) original film, (b) irradiated by green laser, (c) irradiated by UV light.


21


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Figure 6. Photographs show the cyclic process of grabbing and releasing an object by the optically actuated manipulator arms. (a) Manipulator arms crossed at the center were held vertically with its center tied with a rope, (b-d) the finger bents with a knuckle induced by green light, (e) The object grabbed by the finger is lifted, (f) The finger releases the object induced by


22

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UV light, (g-i) the same process to b-d under the irradiation alternatively to control the deformation and recovery. (j) The cycling bending angle of PAA-u/t-Azo film controlled by alternative irradiation.


23


Page 24 of 40

Figure 7. Optical microscopic images of the “finger” (a) before, (b) during, and (c) after the exposure to green laser.


24

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Figure 8. (a) The stress & strain of the PAA-u/t-Azo “finger” after healing the scratched “wound”. (b) The stress & strain of the PAA-u/t-Azo “finger” after healing fracture by irradiating green light (563 mW/cm2). (c) The FTIR spectra trances of PAA-u/t-Azo film at various temperature upon the heating process. (d) The healing efficiency of the “finger” irradiated by green light for different times.


25


Page 26 of 40

Table 1. The Z-to-E thermal isomerization kinetics of PAA-u/t-Azo and a comparison with other azo-based polymers at 25 ºC Monomer

Polymer

Half of life (t1/2)

Reference

2,2',6,6'–Tetrafluoro–4,4'diacetamidoazobenzene

agarose

8s

[25]

Poly{1−4[4-(3-carboxy-4hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl sodium salt}

poly(acrylic acid)

8days

[26]

4-4’-diaminoazobenzene

Polyimides

16h

[27]

Monomer 1

Poly-1

10h

[9]

4-(dimethylamino) azobenzene

microcrystal

30min

[28]

4-Bromo-40-hydroxy-2-methyl azobezene

9-bromo-1-nonanol

1s

[29]

disperse Red 1

polyvinyl alcohol

40min

[10]

diphthalimidobis- (azobenzene)

poly(amic acid)

36h

[30]

Disperse Red 1

poly(acrylic acid)

2min

[31]

t-Azo

poly(acrylic acid)

120h

This paper


26

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Table 2. The variation of the transmittance at 1726cm-1 and 1448cm-1 at different temperatures.

C=O

N-H

stretching vibration

bending vibration

30

0.518

0.256

50

0.507

0.255

70

0.491

0.248

90

0.483

0.227

Temperature (ºC)


27


Page 28 of 40

Table 3. The self-healing performance of a PAA-u/t-Azo assembly and other supramolecular polymers Materials Supramolecular polymers Butyl acrylate/6-(4((4butylphenyl)diazenyl) phenoxy)

Tg

25 ºC

Self-healing

Cross-linker

Temperature

time

Healing efficiency

References

UPy

40 ºC

48h

76%

[22]

polytetramethyl eneglycol

12.8 ºC

di-(1-hydroxyundecyl) diselenide

35 ºC

48 h

85%

[64]

poly(dimethylsiloxane)

-123 ºC

Fe(III)-2,6butylpyridinedicarboxa mide

RT

48 h

93%

[65]

cis-1,4-polyisoprene-g-3amino-1,2,4-triazole

-50 ºC

Zn-triazole

70 ºC

24 h

74%

[24]

2,2’-hydroxy ethyldisulfide/isophorone diisocyanate with polyethylene glycol

29.8 ºC

triethanolamine

UV

24 h

92%

[61]

polystyrene -b-poly(nbutyl acrylate)

45.5 ºC

barbiturate

30 ºC

24 h

98%

[66]

pyrenemethylurea endcapped polymer

-30 ºC

chain-folding polyimide

100 ºC

10 h

95%

[62]

Amidoethyl imidazolidone

8 ºC

Di(amidoethyl) urea

40 ºC

6h

84%

[63]

Polyglycidols

17.9 ºC

diaminotriazine

NIR at 60 ºC

1h

100%

[67]

GL at 80 ºC

6 min

95%

PAA-u

106 ºC

t-Azo & UPy GL at 65 ºC

10 min

97%

This paper

RT stands for room temperature; NIR stands for near-infrared light; GL stands for green laser. Healing efficiency = σhealing / σoriginal


28

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ASSOCIATED CONTENT Supporting Information. Supporting Information Available: This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] . ORCID W. Feng: 0000-0002-5816-7343 Y. Y. Feng: 0000-0002-1071-1995 Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by National Key R&D Program of China (No. 2016YFA0202302), National Natural Science Funds for Distinguished Young Scholars (No. 51425306), the State Key Program of National Natural Science Foundation of China (No. 51633007), and National Natural Science Foundation of China (No. 51573125 and 51773147).


29


Page 30 of 40

REFERENCES (1) Cheng, F. T.; Zhang, Y. Y.; Yin, R. Y.; Yu, Y. L. Visible Light Induced Bending and Unbending Behavior of Crosslinked Liquid-crystalline Polymer Films Containing Azotolane Moieties. J. Mater. Chem. 2010, 20, 4888-4896. (2) Gelebrat, A. H.; Mulder, D. J.; Varga, M.; Konya, A.; Vantomme, G.; Meijer, E. M.; Selinger, R. L. B.; Broer, D. J. Making Waves in A Photoactive Polymer Film. Nature 2017, 546, 633-635. (3) Iamsaard, S.; Aßhoff, S. J.; Matt, B.; Kudernac, T.; Cornelissen, J. J.; Fletcher, S. P.; Katsonis, N. Conversion of Light into Macroscopic Helical Motion. Nat. Chem. 2014, 6, 229. (4) Priimagi, A.; Saccone, M.; Cavallo, G.; Shishido, A.; Pilati, T.; Metrangolo, P.; Resnati, G. Photoalignment and Surface-Relief-Grating Formation are Efficiently Combined in LowMolecular-Weight HalogenBonded Complexes. Adv. Mater. 2012, 24, OP345–OP352. (5) Yu, Y. L.; Nakano, M.; Ikeda, T. Directed Bending of A Polymer Film by Light. Nature 2003, 425, 145. (6) Hosono, N.; Fukushima, T.; Ito, K.; Sasaki, S.; Takata, M.; Aida, T. Large-area ThreeDimensional Molecular Ordering of A Polymer Brush by One-step Processing. Science 2010, 330, 808. (7) Zeng, H.; Wani, O. M.; Wasylczyk, P.; Priimagi, A. Light-Driven, Caterpillar-Inspired Miniature Inching Robot. Macromol. Rapid Commun. 2017, 39, 1700224.


30

Page 31 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(8) K, D. Y.; Shin, S.; Yoon, W. J.; Choi, Y. J.; Hwang, J. K.; Kim, J. S., Lee, C. R.; Choi, T. L.; Jeong, K. U. From Smart Denpols to Remote-Controllable Actuators: Hierarchical Superstructures of Azobenzene-Based Polynorbornenes. Adv. Funct. Mater. 2017, 27, 1606294. (9) Hu, Y.; Li, Z.; Lan, T.; Chen, W. Photoactuators for Direct Optical‐to‐Mechanical Energy Conversion: From Nanocomponent Assembly to Macroscopic Deformation. Adv. Mater. 2016, 28, 10548–10556. (10) Wani, O. M.; Zeng, H.; Priimagi, A. A light-Driven Artificial Flytrap. Nat. Commun. 2017, 8, 15546. (11) Huang, C. L.; Lv, J. A.; Tian, X. J.; Wang, Y. C.; Yu, Y. L.; Liu, J. Miniaturized Swimming Soft Robot with Complex Movement Actuated and Controlled by Remote Light Signals. Sci. Rep. 2015, 5, 17414. (12) Mamiya, J.; Yoshitake, A.; Kondo, M.; Yu, Y. L.; Ikeda, T. Is Chemical Crosslinking Necessary for The Photoinduced Bending of Polymer Films? J. Mater. Chem. 2008, 18, 63. (13) Ruslim, C.; Tchimura, K. Conformation-Assisted Amplification of ChiralityTransfer of Chiral Z-Azobenzenes. Adv. Mater. 2001, 13, 37-40. (14) Yang, Y.; Hughes, R. P.; Aprahamian, I. Visible Light Switching of a BF2-Coordinated Azo Compound. J. Am. Chem. Soc. 2012, 134, 15221-15224. (15) Jerca, F. A.; Jerca, V. V.; Anghel, D. F.; Stinga, G.; Marton, G.; Vasilescu, D. S.; Vuluga, D. M. Novel Aspects Regarding the Photochemistry of Azo-Derivatives Substituted with Strong Acceptor Groups. J. Phys. Chem. C 2015, 119, 10538–10549.


31


Page 32 of 40

(16) Dugave, C.; Demange, L. Cis−Trans Isomerization of Organic Molecules and Biomolecules: Implications and Applications. Chem. Rev. 2003, 103, 2475–2532. (17) Calbo, J.; Weston, C. E.; White, A. J. P.; Rzepa, H. S.; Contreras-García, J.; Fuchter, M. J. Tuning Azoheteroarene Photoswitch Performance through Heteroaryl Design. J. Am. Chem. Soc. 2017, 139, 1261−1274.

(18) Iamsaard, S.; Anger, E.; Aßhoff, S. J.; Depauw, A.; Fletcher, S. P.; Katsonis, N. Fluorinated Azobenzenes for Shape-Persistent Liquid Crystal Polymer Networks. Angew. Chem. Int. Ed. 2016, 55, 9908 –9912. (19) Weston, C. E.; Richardson, R. D.; Haycock, P. R.; White, A. J. P. Arylazopyrazoles: Azoheteroarene Photoswitches Offering Quantitative Isomerization and Long Thermal HalfLives. J. Am. Chem. Soc. 2014, 136, 11878–11881. (20) Samanta, S.; Beharry, A. A.; Sadovski, O.; McCormick, T. M.; Babalhavaeji, A.; Tropepe, V.; Woolley, G. A. Photoswitching Azo Compounds in Vivo with Red Light. J. Am. Chem. Soc. 2013, 135, 9777−9784. (21) Robertus, J.; Reker, S. F.; Pijper, T. C.; Deuzeman, A.; Browne, W. R.; Feringa, B. L. Kinetic Analysis of the Thermal Isomerisation Pathways in An Asymmetric Double Azobenzene Switch. Phys. Chem. Chem. Phys. 2012, 14, 4374–4382. (22) Ni, B.; Xie, H. L.; Tang, J.; Zhang, H. L.; Chen, E. Q. A Self-healing PhotoinducedDeformable Material Fabricated by Liquid Crystalline Elastomers Using Multivalent Hydrogen Bonds as Cross-linkers. Chem. Commun. 2016, 52, 10257.


32

Page 33 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Cui, J. X.; Campo, A. D. Multivalent H-bonds for Self-healing Hydrogels. Chem. Commun. 2012, 48, 9302-9304. (24) Liu, J.; Liu, J.; Wang, S. An Advanced Elastomer with an Unprecedented Combination of Excellent Mechanical Properties and High Self-Healing Capability. J. Mater. Chem. A 2017, 5, 25660–25671. (25) Xiong, Y. B.; Zhang, L. D.; Weis, P.; Naumov, P.; Wu, S. A Solar Actuator Based on Hydrogen-bonded Azopolymers for Electricity Generation. J. Mater. Chem. A 2018, 6, 3361– 3366. (26) Zhang, Y.; Ma, Y.; Sun, J. Reversible Actuation of Polyelectrolyte Films: ExpansionInduced Mechanical Force Enables cis–trans Isomerization of Azobenzenes. Langmuir 2013, 29, 14919-14925. (27) Lee, K. M.; Wang, D. H.; Koerner, H.; Vaia, R. A.; Tan, L.-S.; White, T. J. Enhancement of Photogenerated Mechanical Force in Azobenzene-Functionalized Polyimides. Angew. Chem. Int. Ed. 2012, 51, 4117−4121. (28) Koshima, H.; Ojima, N.; Uchimoto, H. Mechanical Motion of Azobenzene Crystals upon Photoirradiation. J. Am. Chem. Soc. 2009, 131, 6890−6891. (29) Wu, W.; Yao, L. M.; Yang, T.; Yin, R.; Li, F.; Yu, Y. NIR-LightInduced Deformation of Cross-Linked Liquid-Crystal Polymers Using Upconversion Nanophosphors. J. Am. Chem. Soc. 2011, 133, 15810−15813.


33


Page 34 of 40

(30) Wang, D. H.; Wie, J. J.; Lee, K. M.; White, T. J.; Tan, L. S. Impact of Backbone Rigidity on the

Photomechanical

Response

of

Glassy,

Azobenzene-Functionalized

Polyimides.

Macromolecules 2014, 47, 659−667. (31) Vapaavuori, J.; Laventure, A.; Bazuin, G.; Lebel, O.; Pellerin, C. Submolecular Plasticization Induced by Photons in Azobenzene Materials. J. Am. Chem. Soc. 2015, 137, 13510−13517. (32) Brigitte, J. B. F.; Sijbesma, R. P.; Versteegen, R. M.; Rijt, J. A. J. v. d.; Meijer, E. W. Supramolecular Polymer Materials: Chain Extension of Telechelic Polymers Using a Reactive Hydrogen-Bonding Synthon. Adv. Mater. 2000, 12, 874-878. (33) Qin, C. Q.; Feng, Y. Y.; An, H. R.; Han, J. K.; Cao, C.; Feng, W. Tetracarboxylated Azobenzene/Polymer Supramolecular Assemblies as High-Performance Multiresponsive Actuators. ACS Appl. Mater. Interfaces 2017, 9, 4066−4073. (34) Keizer, H. M.; Kessel, R. V.; Sijbesma, R. P.; Meijer, E.W. Scale-up of The Synthesis of Ureidopyrimidinone Functionalized Telechelic Poly (ethylenebutylene). Polymer 2003, 44, 5505–5511. (35) Wei, M.; Zhan, M.Q.; Yu, D. Q.; Xie, H. M.; He, Jie.; Yang, K. K.; Wang, Y. Z. Novel Poly(tetramethylene ether)glycol and Poly(ε-caprolactone) Based Dynamic Network via Quadruple Hydrogen Bonding with Triple-Shape Effect and Self-Healing Capacity. ACS Appl. Mater. Interfaces 2015, 7, 2585−2596. (36) Zhu, D.; Ye, Q.; Lu, X.; Lu, Q. Self-healing Polymers With PEG Oligomer Side Chains Based on Multiple H-bonding And Adhesion Properties. Polym. Chem. 2015, 6, 5087–5088.


34

Page 35 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(37) Zhang, J. J.; Niu, Y. C.; Huang, L.; Xiao, L. P.; Chen, Z. T.; Yang, K. K.; Wang, Y. Z. Selfhealable and Recyclable Triple-shape PPDO–PTMEG Co-network Constructed Through Thermoreversible Diels–Alder Reaction. Polym. Chem. 2012, 3, 1390-1393. (38) Suzuki, T.; Shinkai, S.; Sada, K. Supramolecular Crosslinked Linear Poly(Trimethylene Iminium Trifluorosulfonimide) Polymer Gels Sensitive to Light and Thermal Stimuli. Adv. Mater. 2006, 18, 1043–1046. (39) Medvedev, A. V.; Barmatov, F. B.; Medvedev, A. S.; Shibaev, V. P.; Ivanov, S. A.; Kozlovsky, M.; Stumpe, J. Phase Behavior and Photooptical Properties of Liquid Crystalline Functionalized Copolymers with Low-molecular-mass Dopants Stabilized by Hydrogen Bonds. Macromolecules 2005, 38, 2223–2229. (40) Camacho-Lopez, M.; Finkelmann, H.; Palffy-Muhoray, P.; Shelley, M. Fast Liquid-crystal Elastomer Swims into The Dark. Nat. Mater. 2004, 3, 307–310. (41) Kondo, M.; Yu, Y. L.; Ikeda, T. How Does the Initial Alignment of Mesogens Affect the Photoinduced Bending Behavior of Liquid-Crystalline Elastomers? Angew. Chem. Int. Ed. 2006, 45, 1378. (42) Zhao, X. Z.; Feng, Y. Y.; Qin, C. Q.; Yang, W. X.; Si, Q. Y.; Feng, W. Controlling Heat Release from a Close-Packed Bisazobenzene–Reduced-Graphene-Oxide Assembly Film for High-Energy Solid-State Photothermal Fuels. Chem. Sus. Chem 2017, 10, 1395 – 1404. (43) Chan, W. W.; Lo, S. F.; Zhou, Z. Y.; Yu, W. Y. Rh-Catalyzed Intermolecular Carbenoid Functionalization of Aromatic C–H Bonds by α-Diazomalonates. J. Am. Chem. Soc. 2012, 134, 13565−13568.


35


Page 36 of 40

(44) Samanta, S.; Beharry, A. A.; Sadovski, O.; McCormick, T. M.; Babalhavaeji, A.; Tropepe, V.; Woolley, G. A. Photoswitching Azo Compounds in Vivo with Red Light. J. Am. Chem. Soc. 2013, 135, 9777.9784. (45) Wang, J. L.; Wang, S. H.; Zhou, Y. Q.; Wang, X. G.; He, Y.N. Fast Photoinduced Large Deformation of Colloidal Spheres from a Novel 4-arm Azobenzene Compound. ACS Appl. Mater. Interfaces 2015, 7, 16889−16895. (46) Yamada, M.; Kondo, M.; Miyasato, R.; Naka, Y.; Mamiya, J.; Kinoshita, M.; Shishido, A.; Yu, Y. L.; Barrettc, C. J.;

Ikeda, T. Photomobile Polymer Materials—Various Three-

Dimensional Movements. J. Mater. Chem. 2009, 19, 60–62. (47) Cheng, F. T.; Yin, R. Y.; Zhang, Y. Y.; Yen, C. C.; Yu, Y. L. Fully Plastic Microrobots Which Manipulate Objects Using Only Visible Light. Soft Matter 2010, 6, 3447–3449. (48) Lu, X.; Guo, S. W.; Tong, X.; Xia, H. S.; Zhao, Y. Tunable Photocontrolled Motions Using Stored Strain Energy in Malleable Azobenzene Liquid Crystalline Polymer Actuators. Adv. Mater. 2017, 29, 1606467. (49) Yu, Y. L.; Ikeda, T. Photodeformable polymers: A New Kind of Promising Smart Material for Micro‐and Nano‐Applications. Macromol. Chem. Phys. 2005, 206, 1705.

(50) Brown, C. J. A Refinement of The Crystal Structure of Azobenzene. A Refinement of The Crystal Structure of Azobenzene. Acta. Cryst. 1966, 21, 146. (51) Liu, F.; Urban, M. W. Recent Advances and Challenges in Designing Stimuli-Responsive Polymers. Prog. Polym. Sci. 2010, 35, 3.


36

Page 37 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(52) Toshchevikov, V.; Saphiannikova, M.; Heinrich, G. Light-Induced Deformation of Azobenzene Elastomers: A Regular Cubic Network Model. J. Phys. Chem. B 2012, 116, 913. (53) Lee, K. M.; Smith, M. L.; Koerner, H.; Tabiryan, N.; Vaia, R. A.; Bunning, T. J.; White, T. Photodriven, Flexural–Torsional Oscillation of Glassy Azobenzene Liquid Crystal Polymer Networks. Adv. Funct. Mater. 2011, 21, 2913. (54) Lee, K. M.; White, T. J. Photochemical Mechanism and Photothermal Considerations in The Mechanical Response of Monodomain, Azobenzene-Functionalized Liquid Crystal Polymer Networks. Macromolecules 2012, 45, 7163. (55) Chen, M. L.; Xing, X.; Liu, Z.; Zhu, Y. T.; Liu, H.; Yu, Y. L.; Cheng, F. T. Photodeformable Polymer Material: Towards Light-Driven Micropump Applications. Appl. Phys. A 2010, 100, 39–43. (56) Bin, J.; Oates, W. S. A Unified Material Description for Light Induced Deformation in Azobenzene Polymers. Nat. Commun. 2015, 5, 14654. (57) Biyani, M. V.; Foster, E. J.; Weder, C. Light-Healable Supramolecular Nanocomposites Based on Modified Cellulose Nanocrystal. ACS Macro.Lett. 2013, 2, 236−240. (58) Toshchevikov, V.; Petrova, T.; Saphiannikova, M. Kinetics of Ordering and Deformation in Photosensitive Azobenzene LC Networks. Polymers 2018, 10, 531.

(59) Kozanecka-Szmigiel, A.; Antonowicz, J.; Szmigiel, D.; Makowski, M.; Siemion, A.; Konieczkowska, J.; Trzebicka, B.; Schab-Balcerzak, E. On Stress - Strain Responses and Photoinduced Properties of Some Azopolymers. Polymer 2018, 140, 117-121.


37


Page 38 of 40

(60) Loebner, S.; Lomadze, N.; Kopyshev, A.; Koch, M.; Guskova, O.; Saphiannikova, M; Santer, S. Light-Induced Deformation of Azobenzene-Containing Colloidal Spheres: Calculation and Measurement of Opto-Mechanical Stresses. J. Phys. Chem. B. 2018, 122, 2001−2009.

(61) Xu, W. M.; Rong, M. Z.; Zhang, M. Q. Sunlight Driven Self-Healing, Reshaping and Recycling of A Robust, Transparent and Yellowing-Resistant Polymer. J. Mater. Chem. A 2016, 4, 10683–10690. (62) Burattini, S.; Greenland, B. W.; Merino, D. H.; Weng, W.; Seppala, J.; Colquhoun, H. M.; Hayes, W.; Mackay, M. E.; Hamley, I. W.; Rowan, S. J. A Healable Supramolecular Polymer Blend Based on Aromatic π− π Stacking and Hydrogen-Bonding Interactions. J. Am. Chem. Soc. 2010, 132, 12051–12058. (63) Cordier, P.; Tournilhac, F.; Soulie-Ziakovic, C.; Leibler, L. Self-Healing and Thermoreversible Rubber from Supramolecular Assembly. Nature 2008, 451, 977–980. (64) Ji, S. B.; Cao, W.; Yu, Y. L.; Xu, H. P. Visible ‐ Light ‐ Induced Self ‐ Healing Diselenide‐Containing Polyurethane Elastomer. Adv. Mater 2015, 27, 7740–7745.

(65) Li, C. H.; Wang, C.; Keplinger, C.; Zuo, J. L.; Jin, L. H.; Sun, Y.; Zheng, P.; Cao, Y.; Lissel, F.; Linder, C.; You, X. Z.; Bao, Z. N. A Highly Stretchable Autonomous Self-Healing Elastomer. Nature Chemistry 2016, 8, 622. (66) Chen, S.; Mahmood, N.; Beiner, M.; Binder, W. H. Self‐Healing Materials from V‐and H‐Shaped Supramolecular Architectures. Angew. Chem. Int. Ed. 2015, 54, 10188 –10192.


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(67) Noack, M.; Merindol, R.; Zhu, B. L.; Benitez, A.; Hackelbusch, S.; Bechert, F.; Seifert, S.; Mülhaupt, R.; Walther, A. Light‐Fueled, Spatiotemporal Modulation of Mechanical Properties and Rapid Self‐Healing of Graphene‐Doped Supramolecular Elastomer. Adv. Funct. Mater. 2017, 27, 1700767.


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Controllable and Stable Deformation of a Self-Healing Photo

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