A Thermal-, Water-, and Near-Infrared Light-Induced Shape Memory

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Applications of Polymer, Composite, and Coating Materials

A thermal-, water- and near-infrared light-induced shape memory composite based on polyvinyl alcohol and polyaniline fibers Yongkang Bai, Jiwen Zhang, and Xin Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 13 Apr 2018 Downloaded from http://pubs.acs.org on April 13, 2018

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ACS Applied Materials & Interfaces

A thermal-, water- and near-infrared light-induced shape memory composite based on polyvinyl alcohol and polyaniline fibers Yongkang Bai*, Jiwen Zhang, and Xin Chen* School of Chemical Engineering and Technology, Shaanxi Key Laboratory of Energy Chemical Process Intensification, Institute of Polymer Science in Chemical Engineering, Xi’an Jiao Tong University, Xi’an, Shaanxi 710049, China

ABSTRACT A multi-responsive shape memory composite was prepared by incorporating polyaniline (PAn) fibers into polyvinyl alcohol (PVA), where in situ polymerization assisted by surfactant was used to homogeneously disperse PAn fibers in PVA matrix. The PAn fibers not only increased physical cross-linking points in the system, but also served as photothermal conversion reagents, resulting in excellent water-, thermaland near-infrared (NIR) light-induced shape memory properties of the composites, where its light-induced shape recovery ratio and speed could be enhanced via the increase of PAn loading percentage and light power density. Moreover, the composites possessed high mechanical properties with tensile strength over 83 MPa. Based on these dramatic mechanical properties and shape memory properties, the composites could show high recovery stress over 6.0 MPa, which increased with the increase of temperature and PAn loading percentage. This presented composite could be a great candidate as actuator element for various applications. KEYWORDS: shape memory composites, polyaniline, polyvinyl alcohol, infrared light, freezing-thawing 1. INTRODUCTION Shape memory materials have that ability of undergoing large scale shape change upon exposing to an external stimulus due to the concomitant the cross-linking points and molecular switches1, which have been used for various application, such as actuator and biomedicine devices.2-4 Compared to conventional shape memory materials made by metals, shape memory polymers (SMPs) have caught more and more attention due to its larruping advantages, including cost-effective, light weight,

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good processability, high flexible strain and diverse stimuli methods.5-8 So far, most of the SMPs use heat as a stimulus due to its high accessibility, where the shape change results from thermally induced phase transformation. However, direct heating process is not available for heat-sensitive environments, especially in bio-medical application. Thus other stimuli have been considered, such as inherent biological stimuli (water and pH) and highly penetrative extrinsic stimulus (near-infrared light). Among these stimuli, near-infrared (NIR) light provides many distinctive advantages, such as remote and accuracy control, high-level integrity and safety for living body

9-10

, which has been considered as a promising candidate to

design better SMPs. One of the most common and efficient approaches to prepare NIR light-induced SMP is mixing heat-induced SMP with photothermal conversion reagents, including organic dyes, carbon nano-materials, metal nano-particles, rare earth organic complexes and conjugated polymers.11-16 For example, Viva17 utilized a solution mixing process to prepare carbon nanotubes/polyurethanes based shape memory composite (SMC) which could show effective light-induce shape memory effect. Similarly, Haibao Lu18 reported a NIR light-induced SMC by introducing carbon nanotube and boron nitride, which took 60 s to recall its original shape. However, this physical blending method also suffers a significant problem, which is the poor compatible of photothermal conversion fillers in polymeric materials. It results in a dilemma that low doping percent of the fillers leads to weak light actuation efficiency, while increasing the doping percent would lead to the aggregation of the fillers, which have a negative impact on the shape memory property and mechanical performances of SMC. To solve the conflict, some optimized methods have been reported. For instance, Yongsheng Chen’ group19 increased the homogenous doping percent of graphene to 1 wt % in polyurethane by chemical modification. Similarly, Wei Feng’s group15 reported a NIR light-induced SMC by incorporating with 1 wt % of sulfonated reduced graphene oxide/ carbon nanotube mixed fillers. Moreover, the surfactant is also a choice to improve the dispersion of filler which has been reported by Javey and Arenas.20-21 However, the doping content of this method is still limited ACS Paragon Plus Environment

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and the cost of graphene or carbon nanotube is too high for practical applications in large-scale. Because the aggregation of photothermal conversion reagents is the main issue to limit the application of these NIR light-induced SMPs, inhibiting the aggregation is required. While in conventional solution casting method, aggregations of the fillers are easy to form during drying process in high concentration, even after modification to enhance the compatibility, due to the free move of these fillers.22 Considering that the freeze-drying method could preserve the original morphology of material, we predicted the aggregations could be reduced by freezing the fillers during drying process, which may be an easy solution to fabricate NIR light-induced shape memory materials with both great shape memory property and dramatic mechanical performances. Herein polyaniline (PAn) fibers were used as the photothermal conversion fillers to prepare NIR light-induced SMC due to its low cost and ease of preparation. Polyvinyl alcohol (PVA) was chosen as the polymer matrix due to its high water solubility and its shape memory performance has been reported in previous studies.23-24 To improve the dispersion of PAn fibers, freezing-thawing method25 combined with in situ formation of PAn fibers was used. In the procedure, PAn fibers were prepared by in situ polymerization of aniline in PVA aqueous solution, then PVA composites with homogeneous dispersion of PAn fibers were prepared by stepwise freezing, thawing and drying. The PAn fibers could increase the physical cross-linking points in composites through hydrogen bond interaction meanwhile serve as photothermal agent, endowing the composites with outstanding water-, thermal- and NIR-induced shape memory performances and high mechanical properties, which show great potential in developing novel generation of mechanical devices with stimuli responsiveness. 2. EXPERIMENTAL SECTION 2.1 Material Polyvinyl alcohol (PVA 1799) was purchased from Aladdin Industrial Corporation. Aniline was received from Sinopharm Chemical Reagent Co., and ACS Paragon Plus Environment


distilled before use. Ammonium persulphate (APS), sodium dodecyl sulfate (SDS), hydrochloric acid were purchased from Tianjin Chemical Reagents Company. 2.2 Preparation of PVA/PAn composites The PVA composites with different doping percent of PAn fibers were prepared by in situ polymerization and drying of hydrogel, which were named as PVA-PAn-x (x represented the weight ratio of PAn to PVA). The detailed process of PVA-PAn-10 was given as an example. Firstly, there solutions were prepared: 4 g PVA in 20 mL water, 0.4 g aniline and 0.04 g SDS in 5 mL HCl (5 M), and 0.24 g APS in 15 mL HCl (1 M). Then the latter two solutions were added to PVA solution successively and the reaction continued for another 12 h. After that, the solution was transferred to a Teflon plate and frozen at -20°C for10 h. After melting at room condition (20°C and relative humidity about 35%), the PVA/PAn hydrogel was obtained and washed by water to remove the residual aniline, APS and other impurity. At last, the hydrogels were dried at room condition for three days to afford the PVA/PAn composite films. The thickness of all the films was controlled by the casting volume. The preparation process of the composites was shown schematically in Scheme 1.

Scheme 1 Preparation process of PVA/PAn composites 2.3 Characterization The thermal-mechanical properties were investigated by dynamic mechanical analysis (DMA), which was performed on a DMA 242E (NETZSCH, Germany). The temperature was heated from 25°C to 150°C at a heating rate of 5 °C min-1. The original dimensions of the specimens were about 20 × 3 × 0.1 mm3. Fourier ACS Paragon Plus Environment

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transformed infrared (FTIR) spectra were carried out on a Nicolet iS50 IR spectrophotometer (America) with an ATR mode.

The fractured surface were

analyzed by a scanning electron microscope (SEM, TESCAN MALA3 LMH, Czech Republic ) and all specimens were coated with gold by sputtering before testing. A universal testing machine (WANCE ETM 103B-TS, China) was used to measure the mechanical properties at a strain rate of 5 mm min-1. The samples were cut to a dog bone type (ISO 527-2/1BB) and each sample was tested at least five times. The swelling behavior of composites was investigated by swelling experiments in water for 5 days. The degree of swelling (Q) and remained weight percent (R) were calculated according to following equations. Wherein, m0 and m1 are the weight of samples before and after immersing in water for 5 days, while m2 is the weight of sample re-drying at 60°C for 24 h. Q = (m1- m0) / m0 × 100% (1) R = m2 / m0 × 100%

(2)

A bend-recover test was used to investigate the NIR light-induced shape memory performance and at least three specimens were tested. The original samples were bended in half (180°) at 80°C and the temporary angle (θ1) was obtained by cooling to room temperature under external stress. Then the samples were exposed to different power density of NIR light (wavelength of 808 nm) and a digital camera was used to record the whole recovering process. The residual angle was defined as θ2. The shape fixity ratio (Rf) and shape recovery ratio (Rr) of light-induced shape memory effect were evaluated according to following formula:18, 26 Rr = (θ1-θ2) / θ1 × 100%

(3)

Rf = θ1 / 180 × 100%

(4)

The recovery stress was investigated by DMA 242E in an isostrain mode. The samples for tests were cut to about 20 × 1.5 × 0.1 mm3. The isostrain experiments were performed at 100% strain and heated from 25°C to 150°C with a heating rate of 5 °C min-1, while contraction forces were measured. The composites begin to decompose above 150°C.



3. RESULTS AND DISCUSSION 3.1 Preparation of PVA/PAn composites A series of PVA composites with different doping percent of PAn were prepared and the structural information of the composites was investigated by FTIR, swelling tests and DMA. As shown in Fig. 1(A), the peaks around 1590 and 1260 cm-1 appeared on the composites curves was belong to the characteristic stretching vibration of C=N and C-N+, which demonstrated the formation of PAn.27-28 The broad peak around 3262 cm-1 was the characteristic stretching vibration peak of O-H for PVA, and it decreased to a lower wavenumber with the increase of doping percent, which was showed more clearly in Fig. 1(B). The red shift of the peak was attributed to the increase of hydrogen-bond interaction in the polymer networks, indicating that PAn could form physically crosslinking interaction with PVA chains.29 This physically crosslinking network was also a key factor for PVA to realize shape memory effect.

Fig. 1 (A) FTIR spectra of PVA/PAn composites: (a) PVA, (b) PVA-PAn-2.5, (c) PVA-PAn-5, (d) PVA-PAn-10, (e) PVA-PAn-20. (B) The –OH characteristic peaks of PVA/PAn composites. To further confirm the formation of physically crosslinking structure, a swelling test was performed and the results were shown in Table 1. Due to the weak crosslinking interaction, pure PVA was dissolved in water after swelling for 5 days. With the introduction of PAn, the remained weight percent (R) of composites all exceeded 93%, indicating the strong crosslinking interaction of composites. With the increase of PAn loading, the degree of swelling (Q) decreased from 187.6% to


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135.5%, demonstrating the increase of crosslinking interaction. Table 1 Degree of swelling and storage modulus of PVA and composites Sample

Q(%)

R(%)

E’25(MPa)

E’80 (MPa)

PVA

dissolved

dissolved

3500

239

PVA-PAn-2.5

187.6±21.6

93.0±3.4

3750

443

PVA-PAn-5

156.84±7.5

96.9±1.0

4316

477

PVA-PAn-10

141.2±5.3

93.3±6.4

4345

532

PVA-PAn-20

135.5±4.9

97.2±0.5

4415

550

Fig. 2 (a) Loss factor and (b) storage modulus curves of PVA and composites. Dynamic mechanical analysis (DMA) was utilized to investigate the influence of PAn fibers on the thermal-mechanical properties of the composites. As observed in Fig. 2(a), pure PVA showed a typical peak around 62.5°C, which was considered as the glassy transition temperature (Tg) of PVA. The picture also showed that the Tg of PVA decreased slightly from 62.5 to 58.1°C with the increase of PAn loading, which may be attributed to the decrease of PVA chains regularity brought by PAn. Additionally, a broad peak around 100°C appeared more obviously with the increase of PAn, which may belong to the glassy transition of PAn chains.30 In Fig. 2 (b), the storage modulus (E’) at 25 and 80°C of the materials both increased with the increase of doping percent attributed to the reinforcement of PAn, and a high E’ at elevated temperature over transition temperature was beneficial to an increased recovery stress during shape recovery process.



3.2 Microstructure and mechanical properties of PVA/PAn composites The dispersion state of PAn fibers in composites was investigated by scanning electron microscopy (SEM). Firstly, PAn nano-fibers with diameter about 100 nm was confirmed by SEM image in Fig. S1. Then the microstructure of fracture surface of pure PVA and PVA/PAn composites were presented in Fig. 3. The pure PVA showed a smooth facture surface after fracturing in liquid nitrogen, while the introduction of PAn fibers increased the roughness of the fracture surface. This may be resulted from the increase of energy dissipation during fracturing process, indicating the reinforcing effect of PAn fibers.16 According to previous works, the white dots on the facture surface in SEM images were ascribed to the end of nano-fibers or nanotubes.31-32 From the distribution of the dots (as indicated in arrow in the pictures), a relatively uniform dispersion of 2.5, 5 and 10 wt% of the PAn fibers could be observed in SEM images, while some agglomerations were observe in PVA-PAn-20. It was also the reason why the roughness of the fracture surface decreased with the increase of doping percent from 10 to 20 wt%. In addition, a composite direct drying from PVA/PAn solution (10 wt%), absent of gelation process, was taken as a control sample (named as PVA-PAn-10-C). As shown in Fig 3 (f) and (i), the aggregations of PAn fibers could be observed clearly on the fracture surface of PVA-PAn-10-C. Therefore, the SEM results demonstrated that the method of drying from hydrogel was indeed beneficial to the dispersion of PAn fibers. The dispersion state would greatly impact the mechanical properties of the composites. In Fig. 4 (a), the tensile strength (σ) increased slightly with the increase of PAn loading from 2.5 to 10 wt%, while it decreased greatly to 63.9 MPa due to the partial agglomerations of PAn fibers in PVA-PAn-20. However, the elongation at break (ε) of composites reduced gradually from 93.6% to 17.2% with the increase PAn loading, resulting from the phase separation of composites. In addition, the control sample was also tested as shown in Fig. 4(b). It was found that the control sample was brittle with ε about 6%, which was far less than that of PVA-PAn-10 drying from hydrogel.


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Fig. 3 SEM analysis of (a) PVA, (b) PVA-PAn-2.5, (c) PVA-PAn-5, (d) PVA-PAn-10, (e) PVA-PAn-20 and (f) PVA-PAn-10-C at the cross-section; SEM images of (g) PVA-PAn-5 (h) PVA-PAn-10 (i) PVA-PAn-10-C with high magnification.

Fig. 4 (a) Elongation at break (ε) and tensile strength (σ) of PVA/PAn composites; (b) Stree-strain curves of PVA-PAn-10 and its control sample



Fig. 5 Water-induced shape memory effect of (a) PVA-PAn-2.5, (b) PVA-PAn-5, (c) PVA-PAn-10, (d) PVA-PAn-20. 3.3 Water-induced shape memory performance As being a water soluble polymer, PVA could endow the composites with water responsive shape memory performance. Fig. 5 showed the shape recovery of composites upon immersing into water. The original size of specimens was about 20 × 3 × 0.1 mm3. The original straight specimens were bent to “m” shape at 80°C and fixed this shape at room temperature (20°C) under external load. Then the deformed specimens were immersed into water to observe the water-induced shape recovery process. With a weak crosslinking interaction, pure PVA showed poor shape memory performance in accordance with previous studies.23, 29 With the introduction of PAn fibers, all the composites specimens could recover to the original shape after immersing for more than 26 min. In addition, the completed recover time prolonged with the increase of doping percent. These results clearly indicated that the shape memory effect of PVA can be realized after the introduction of PAn fibers. According to the results of FTIR spectrums, it has been shown that the hydrogen bond interaction could form between PAn fibers and PVA chains. Therefore, as the additional physically crosslinking points, PAn fibers can improve the shape memory performance of PVA. It is well known that the water-induced shape memory effect is mainly attributed to the plastication of water molecules, while the recovery speed ACS Paragon Plus Environment

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depends on the diffusion speed of water molecules in the polymer network.33-34 In this study, the diffusion speed of water molecules in PVA/PAn composites will decrease with the increase of crosslinking degree because of the reduced free volume in polymer networks.35 Thus, the recovery speed of PVA/PAn composites decreased with the increase of doping percent.

Fig. 6 NIR light-induced shape memory behavior of PVA-PAn-10 in different power density of NIR light irradiation. 3.4 NIR light-induce shape memory behavior As a photothermal conversion material, the introduction of PAn fiber also endowed the composites with NIR light-induce shape memory effect and the results were presented in Fig. 6, Fig. 7 and Fig. S2 to S5. A bending-recovery test was used to explore the light-induced shape memory performance of the composites. The straight samples were folded in half at 80°C and the temporary shape was fixed by external load at room temperature. The original size of specimens was about 20 × 1.5 × 0.1 mm3. Then the deformed specimens were exposed to a NIR light (wavelength of 808 nm) and the light-induced recovery behavior was recorded using a digital camera. In Fig.6, PVA-PAn-10 was taken as an example to show the shape recovery process under different power density of NIR light. It is clearly observed that the shape



recovery ratio and speed were both improved by the increasing power density of NIR light. At a power density of 4.2 W cm-2, the sample could recover to its original straight shape within 5 s. In addition, the light-induced shape memory properties of composites were quantitatively assessed by the shape fixity ratio (Rf) and shape recovery ratio (Rr). As presented in Fig. S5, all samples exhibited a high Rf due to the remarkable change of E’ between two temperatures, which was affected little by the doping content of PAn. Extracting the data from Fig.7 (a), it is clearly observed that the Rr increased with the increase of PAn loading under each power density of NIR light. This may be attributed to two functions brought by the PAn fibers, including photothermal conversion efficiency and cross-linking density. The first one was apparent that the terminal temperature of a sample would increase with the increase of doping percent due to the enhancement of photothermal conversion efficiency, leading to a higher Rr. Based on the two-segment theory of SMP, Rr mainly depended on the cross-linked structure.36 In this study, PAn fibers, as additional physically crosslinking points, could improve the shape memory effect of composites. Therefore, the PVA-PAn-10 or -20 with a higher doping percent exhibited better shape memory properties than other two composites. In Fig. 7(a), it was also found that the Rr of each composite increased with the increased power density of NIR light irradiation, which was also attributed to the terminal temperature of samples. Irradiating by a higher power density of NIR light, the samples could reach a higher temperature and more reversible deformation could be recovered. Fig. 7(b) showed the thermal-infrared images of PVA-PAn-10 under 1.6 and 2.9 W cm-2 of NIR light. Irradiating by a low power density of 1.6 W cm-2, the sample presented an apparent temperature about 60°C, while it increased to 85°C (higher than its Tg) irradiating by 2.9 W cm-2. Therefore, the Rr of PVA-PAn-10 increased dramatically from 42.1% to 95.8% with the increase of power density.


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Fig. 7 (a) Shape recovery ratio of composites under different power density of NIR light irradiation; (b) thermal-infrared images of PVA-PAn-10 under 0.25 W and 0.47 W of NIR light irradiation. 3.5 Application of NIR light-induced shape memory performances Comparing to thermal and water-induced SMP, local and remote control of shape recovery process are the particular advantages for light-induced SMP, which are also presented in Fig. 8. The temporary “m” shape samples were obtained through the same process as above. In Fig. 8(a), the sample was placed on a thermal platform at 80°C and its original shape could be recovered within 13 s, indicating its good thermal-induced shape memory performance. In contrast, the NIR light-induced shape recovery process in Fig. 8(b) showed that the original straight shape was recovered in three steps by locally irradiating the sample. In addition, a 3D shape structure (cube) was used to demonstrate the local control of NIR light- shape recovery process. In Fig. 8(c), it was obvious that the cube structure could be recovered in steps by irradiating the edge of the cube in sequent. These results demonstrate the application prospect of the composites as actuators, whose shape change need precise and remote control.



Fig. 8 (a) Thermal-induced shape recovery of PVA-PAn-10 at 80°C; (b) and (c) NIR light-induce shape memory behavior of PVA-PAn-10 under 2.9 W cm-2 of NIR light irradiation. Because of superior mechanical properties and high storage modulus, the composites also exhibited outstanding heavy-lift capability. In Fig. 9, the original dimension of samples was about 20 × 1.5 × 0.1 mm3 and the weight of each specimen was about 0.005 g. All specimens were stretched to a strain of 200% before the tests. As demonstrated in Fig. 9 (a), in 2.9 W cm-2 of NIR light irradiation, the sample could lift up one binder clip by 1.4 cm, which was about 580 times heavier than the sample’s own weight. The Rr with one binder clip was about 70% due to the limitation of recovery stress, while it decreased to about 35% with increase of load as shown in Fig. 9(b). But the sample was still able to lift up the load by 0.7 cm, which was about 1160 times heavier than its own weight. In addition, the recovery stress of composites at 100% strain was quantified by DMA in an isostrain mode. Fig 9(c) showed that the recovery stress of composites increased with an increased temperature due to the increase of activated polymer chains. For example, the recovery stress of PVA-PAn-10 could reach about 6.4 MPa at 100°C, which was higher than the results reported by previous studies (such as 1.2 MPa in Wei Feng’s15, 3.8 MPa in Ortega’s37 and 4.2 MPa in Denis Lourdin’s38). It also showed that the recovery stress of PVA-PAn-10 was higher than that of composites with low PAn loading, resulting from


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the increase of cross-linking points.39 Therefore, the composites may also possess great application prospect in artificial muscles with convenient control.

Fig. 9 NIR light-induced heavy-lift capability of PVA-PAn-10 at different load (a) 2.9 g and (b) 5.8 g; (c) Recovery stress-temperature curves of composites carried out by and isostrain experiment at 100% strain. 4. CONCLUSION In summary, a multi-responsive shape memory composite was prepared by homogeneously dispersing PAn fibers into PVA though the stepwise in situ polymerization, freezing-thawing and drying methods. The PAn fibers could serve as additional physically cross-linking points in composites through hydrogen bond interaction, which endowed the composites with excellent water- and thermal-induced shape memory performances. In addition, the composites exhibited outstanding NIR light-induced shape memory properties through the photothermal effect of PAn fibers. For example, it only took 5 s for PVA-PAn-10 to recover its original shape under irradiation of NIR light (4.2 W cm-2). These results also showed that the light-induced shape recovery ratio and recovery speed all enhanced with the increase of PAn loading percent or light power density. Moreover, the composites exhibited high recovery stress over 6.0 MPa, which increased with the increase of temperature and PAn loading percentage. Combining with the superior mechanical properties, the composites possess tremendous application prospect in actuator element and artificial muscles.



ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: SEM image of PAn, NIR light-induced shape memory behavior of PVA/PAn composites, NIR light-induced shape memory properties of PVA/PAn composites. AUTHOR INFORMATION Corresponding Authors *Email: [email protected]; *Email: [email protected] ORCID Yongkang Bai: 0000-0003-3541-9349 Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was supported by China Postdoctoral Science Foundation (2017M613126 to YKB), the Postdoctoral Science Foundation of Shaanxi Province (2017BSHEDZZ04 to YKB), the National Natural Science Foundation of China (81601606 to XC), the "Young Talent Support Plan" of Xi'an Jiao Tong University (XC), the Technology Foundation for Selected Overseas Chinese Scholar of Shaanxi Province (XC), the Fundamental Research Funds for the Central Universities (2016qngz02 to XC), and the One Hundred Talents Program of Shaanxi Province (XC). We thank Jiamei Liu at instrument Analysis Center of Xi’an Jiao Tong University for her assistance with DMA test.

References (1) Chen, Y.; Peng, L.; Liu, T.; Wang, Y.; Shi, S.; Wang, H. Poly(vinyl alcohol)– Tannic Acid Hydrogels with Excellent Mechanical Properties and Shape Memory Behaviors. ACS Appl. Mater. Inter. 2016, 8, 27199-27206. (2) Miriyev, A.; Stack, K.; Lipson, H. Soft Material for Soft Actuators. Nat. Commun. 2017, 8, 596.


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(3) Haines, C. S.; Lima, M. D.; Li, N.; Spinks, G. M.; Foroughi, J.; Madden, J. D. W.; Kim, S. H.; Fang, S.; Jung de Andrade, M.; Göktepe, F.; Göktepe, Ö.; Mirvakili, S. M.; Naficy, S.; Lepró, X.; Oh, J.; Kozlov, M. E.; Kim, S. J.; Xu, X.; Swedlove, B. J.; Wallace, G. G.; Baughman, R. H. Artificial Muscles from Fishing Line and Sewing Thread. Science 2014, 343, 868-872. (4) Liu, X.; Zhao, K.; Gong, T.; Song, J.; Bao, C.; Luo, E.; Weng, J.; Zhou, S., Delivery of Growth Factors Using a Smart Porous Nanocomposite Scaffold to Repair a Mandibular Bone Defect. Biomacromolecules 2014, 15, 1019-1030. (5) Hearon, K.; Singhal, P.; Horn, J.; Small, W.; Olsovsky, C.; Maitland, K. C.; Wilson, T. S.; Maitland, D. J. Porous Shape-Memory Polymers. Polym. Rev. 2013, 53, 41-75. (6) Wang, W.; Liu, Y.; Leng, J. Recent Developments in Shape Memory Polymer Nanocomposites: Actuation Methods and Mechanisms. Coordin. Chem. Rev. 2016, 320, 38-52. (7) Hardy, J. G.; Palma, M.; Wind, S. J.; Biggs, M. J. Responsive Biomaterials: Advances in Materials Based on Shape-Memory Polymers. Adv. Mater. 2016, 28, 5717–5724. (8) Zhou, S.; Wang, L.; Yang, X.; Chen, H. M.; Yang, G.; Gong, T.; Li, W. B., Multi-Stimuli Sensitive Shape Memory Poly(vinyl alcohol)-Graft-Polyurethane. Polym. Chem. 2013, 4, 4461-4468. (9) Chan, B. Q. Y.; Low, Z. W. K.; Heng, S. J. W.; Chan, S. Y.; Owh, C.; Loh, X. J. Recent Advances in Shape Memory Soft Materials for Biomedical Applications. ACS Appl. Mater. Inter. 2016, 8, 10070-10087. (10) Liu, L.; Liu, M.; Deng, L.; Lin, B.; Yang, H. Near-Infrared Chromophore Functionalized Soft Actuator with Ultrafast Photoresponsive Speed and Superior Mechanical Property. J. Am. Chem. Soc. 2017, 139, 11333-11336. (11) Zheng, Y.; Li, J.; Lee, E.; Yang, S. Light-Induced Shape Recovery of Deformed Shape Memory Polymer Micropillar Arrays with Gold Nanorods. RSC Adv. 2015, 5, 30495-30499. (12) Kohlmeyer, R. R.; Chen, J. Wavelength-Selective, IR Light-Driven Hinges Based on Liquid Crystalline Elastomer Composites. Angew. Chem. Int. Edit. 2013, 52, 9234-9237. (13) Fang, L.; Fang, T.; Liu, X.; Ni, Y.; Lu, C.; Xu, Z. Precise Stimulation of Near-Infrared Light Responsive Shape-Memory Polymer Composites using Upconversion Particles with Photothermal Capability. Compos. Sci. Technol. 2017, 152, 190-197. (14) Fang, L.; Chen, S.; Fang, T.; Fang, J.; Lu, C.; Xu, Z. Shape-Memory Polymer Composites Selectively Triggered by Near-Infrared Light of Two Certain Wavelengths and Their Applications at Macro-/Microscale. Compos. Sci. Technol. 2017, 138, 106-116. (15) Feng, Y.; Qin, M.; Guo, H.; Yoshino, K.; Feng, W. Infrared-Actuated Recovery of Polyurethane Filled by Reduced Graphene Oxide/Carbon Nanotube Hybrids with High Energy Density. ACS Appl. Mater. Inter. 2013, 5, 10882-10888. (16) Casado, U. M.; Quintanilla, R. M.; Aranguren, M. I.; Marcovich, N. E., Composite Films Based on Shape Memory Polyurethanes and Nanostructured



Polyaniline or Cellulose–Polyaniline Particles. Synthetic. Met. 2012, 162, 1654-1664. (17) Koerner, H.; Price, G.; Pearce, N. A.; Alexander, M.; Vaia, R. A. Remotely Actuated Polymer Nanocomposites Stress-Recovery of Carbon-Nanotube-Filled Thermoplastic Elastomers. Nat. Mater. 2004, 3, 115-120. (18) Lu, H.; Yao, Y.; Huang, W. M.; Leng, J.; Hui, D. Significantly Improving Infrared Light-Induced Shape Recovery Behavior of Shape Memory Polymeric Nanocomposite via a Synergistic Effect of Carbon Nanotube and Boron Nitride. Compos. Part B-Eng. 2014, 62, 256-261. (19) Liang, J.; Xu, Y.; Huang, Y.; Zhang, L.; Wang, Y.; Ma, Y.; Li, F.; Guo, T.; Chen, Y. Infrared-Triggered Actuators from Graphene-Based Nanocomposites. J. Phys.Chem. C 2009, 113, 9921-9927. (20) Zhang, X. B.; Pint, C. L.; Lee, M. H.; Schubert, B. E.; Jamshidi, A.; Takei, K.; Ko, H.; Gillies, A.; Bardhan, R.; Urban, J. J.; Wu, M.; Fearing, R.; Javey, A. Optically- and Thermally-Responsive Programmable Materials Based on Carbon Nanotube-Hydrogel Polymer Composites. Nano. Lett. 2011, 11, 3239-3244. (21) Arenas, M. C.; Sánchez, G.; Martínez-Álvarez, O.; Castaño, V. M. Electrical and Morphological Properties of Polyaniline–Polyvinyl Alcohol in situ Nanocomposites. Compos. Part B-Eng. 2014, 56, 857-861. (22) Sattar, R.; Kausar, A.; Siddiq, M. Thermal, Mechanical and Electrical Studies of Novel Shape Memory Polyurethane/Polyaniline Blends. Chinese J. Polym. Sci. 2015, 33, 1313-1324. (23) Qi, X.; Yao, X.; Deng, S.; Zhou, T.; Fu, Q. Water-Induced Shape Memory Effect of Graphene Oxide Reinforced Polyvinyl Alcohol Nanocomposites. J. Mater. Chem. A 2014, 2, 2240-2249. (24) Du, H. Y.; Zhang, J. H. Solvent Induced Shape Recovery of Shape Memory Polymer Based on Chemically Cross-Linked Poly(Vinyl Alcohol). Soft Matter 2010, 6, 3370-3376. (25) Zhang, H.; Xia, H.; Zhao, Y. Poly(vinyl alcohol) Hydrogel Can Autonomously Self-Heal. ACS Macro Lett. 2012, 1, 1233-1236. (26) Chan, B. Q. Y.; Heng, S. J. W.; Liow, S. S.; Zhang, K.; Loh, X. J. Dual-Responsive Hybrid Thermoplastic Shape Memory Polyurethane. Mater. Chem. Front. 2017, 1, 767-779. (27) Hu, R.; Zheng, J. Preparation of High Strain Porous Polyvinyl Alcohol/Polyaniline Composite and Its Applications in All-Solid-State Supercapacitor. J. Power. Sources 2017, 364, 200-207. (28) Coskun, E.; Martinez-Ramirez, S. M.; Antunez-Flores, W.; Hernandez-Escobar, C. A.; Zaragoza-Contreras, E. A. Improving Polyaniline Processability by Grafting Acrylic Copolymer. Synthetic. Met. 2012, 162, 344-351. (29) Yang, G.; Wan, X.; Liu, Y.; Li, R.; Su, Y.; Zeng, X.; Tang, J., Luminescent Poly(vinyl alcohol)/Carbon Quantum Dots Composites with Tunable Water-Induced Shape Memory Behavior in Different Ph And Temperature Environments. ACS Appl. Mater. Inter. 2016, 8, 34744- 34754. (30) Chen, S. A.; Lee, H. T., Structure And Properties of Poly(acrylic acid)-Doped Polyaniline. Macromolecules 1995, 28, 2858-2866.


Page 18 of 20

Page 19 of 20 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


(31) Du, F.; Ye, E.; Yang, W.; Shen, T.; Tang, C.Y.; Xie, X.; Zhou, X.; Law, W. Electroactive Shape Memory Polymer Based on Optimized Multi-Walled Carbon Nanotubes/Polyvinyl Alcohol Nanocomposites. Compos. Part B-Eng. 2015, 68, 170-175. (32) Du, F.; Tang, C.; Xie, X.; Zhou, X.; Tan, L. Carbon Nanotube Enhanced Gripping in Polymer-Based Actuators. J. Phys. Chem. C 2009, 113, 7223-7226. (33) Liu, Y.; Li, Y.; Yang, G.; Zheng, X.; Zhou, S. Multi-Stimulus-Responsive Shape-Memory Polymer Nanocomposite Network Cross-Linked by Cellulose Nanocrystals. ACS Appl. Mater. Inter. 2015, 7, 4118-4126. (34) Du, H.; Yu, Y.; Jiang, G.; Zhang, J.; Bao, J. Microwave-Induced Shape-Memory Effect of Chemically Crosslinked Moist Poly(vinyl alcohol) Networks. Macromol. Chem. Phys. 2011, 212, 1460-1468. (35) Bai, Y.; Chen, Y.; Wang, Q.; Wang, T., Poly(vinyl butyral) Based Polymer Networks with Dual-Responsive Shape Memory and Self-Healing Properties. J. Mater. Chem. A 2014, 2, 9169-9177. (36) Hu, J.; Zhu, Y.; Huang, H.; Lu, J. Recent Advances in Shape–Memory Polymers: Structure, Mechanism, Functionality, Modeling and Applications. Prog. Polym. Sci. 2012, 37, 1720-1763. (37) Ortega, A. M.; Yakacki, C. M.; Dixon, S. A.; Likos, R.; Greenberg, A. R.; Gall, K., Effect of Crosslinking and Long-Term Storage on the Shape-Memory Behavior of (Meth) Acrylate-Based Shape-Memory Polymers. Soft Matter 2012, 8, 7381-7392. (38) Véchambre, C.; Buléon, A.; Chaunier, L.; Gauthier, C.; Lourdin, D., Understanding the Mechanisms Involved in Shape Memory Starch: Macromolecular Orientation, Stress Recovery and Molecular Mobility. Macromolecules 2011, 44, 9384-9389 (39) Hornat, C. C.; Yang, Y.; Urban, M. W., Quantitative Predictions of Shape-Memory Effects in Polymers. Adv. Mater. 2017, 29, 1603334-1603341.



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A Thermal-, Water-, and Near-Infrared Light-Induced Shape Memory

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