Multi-Stimuli Responsive Carbon Nanotube Incorporated Polysiloxane

Jan 14, 2016 - In this work, aiming to combine thermal-induced LC-to-isotropic phase transition effect, azobenzene's trans–cis tautomerization effec...
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Multi-Stimuli Responsive Carbon Nanotube Incorporated Polysiloxane Azobenzene Liquid Crystalline Elastomer Composites Meng Wang, Sayed Mir Sayed, Ling-Xiang Guo, Bao-Ping Lin, Xue-Qin Zhang, Ying Sun, and Hong Yang* School of Chemistry and Chemical Engineering, Jiangsu Province Hi-Tech Key Laboratory for Bio-medical Research, Jiangsu Optoelectronic Functional Materials and Engineering Laboratory, Southeast University, Nanjing, 211189, China S Supporting Information *

ABSTRACT: In this work, aiming to combine thermal-induced LC-toisotropic phase transition effect, azobenzene’s trans−cis tautomerization effect and the photothermal effect into one liquid crystalline elastomer (LCE) system to prepare a heat/UV/near-infrared(NIR) triple-stimuli-responsive LCE material, we design and synthesize a polysiloxane-based side-chain sideon azobenzene-containing LCE matrix embedded with 1 wt % single-walled carbon nanotubes, through Finkelmann’s two-step cross-linking process coupled with a uniaxial stretching technique. The multistimuli responsive behaviors of this LCE/CNT composite film are investigated under different external stimuli (heat, UV, NIR). The composite film can realize a reversible deformation between contraction and extension under heating/cooling cycles. Moreover, the composite film can perform an impressive threedimensional deformation (bending) under UV-light irradiation. On the contrary, long wavelength light (NIR laser) forces the composite film into shrinking instead of bending. Most importantly, the shape transformations (three-dimensional bending vs two-dimensional shrinking) of this novel shape memory material can be tuned by the light wavelength (UV vs NIR), which might endow this LCE material with potential applications in control devices and logic gate devices, etc.

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INTRODUCTION Stimuli-responsive polymeric materials possess many inherent advantages such as lightweight, good processability, biomimetic responses to external stimuli, and have been categorized into an important branch of smart materials with widespread applications in sensors,1 drug delivery,2 and robotics technology,3 etc. Among them, liquid crystalline elastomers (LCEs) have received tremendous scientific attention4−11 due to their reversible anisotropic dimensional shape responses to applied stimuli (heat,12−16 light,17−21 electric,22−25 or magnetic field,26 etc.), which can dramatically impact the microscopic orders or molecular structures of uniaxial-aligned liquid crystal mesogens and further change the macroscopic shapes of the whole LCE materials. These unique characters endow LCE materials with potential applications as mechanical actuators,27 artificial organs,28 smart surfaces,29−31 and microrobots,32 etc. Most of traditional LCE materials are designed using heat or light stimulus. The thermal-responsive LCEs usually perform significant contraction/expansion deformations related to the temperature-determining LC-to-isotropic phase transitions, while the macroscopic transformations of light-responsive LCEs are much more complicated, depending on either the molecular structure changes of the incorporated chromophores or the photothermal effect induced LC-to-isotropic phase transitions. For example, azobenzene-containing LCE materials can show an impressive three-dimensional deformation © XXXX American Chemical Society

(i.e., bending) relying on the trans−cis variations of azobenzene chromophores triggered by ultraviolet (UV) irradiation (λ < 400 nm) or visible/near-infrared (vis/NIR) light source (λ > 760 nm) which can be converted into low-wavelength lights by doping inorganic or organic up-conversion materials.33−35 Another type of light-responsive LCEs takes advantage of the photothermal effect of thermal conductive fillers (carbon nanotubes,36−41 gold nanoparticles42,43 or organic dyes44−46) to transform photons into heat which further induce the LC-toisotropic phase transition and thus make the LCE materials shrink/expand. Although thermal-responsive LCEs and lightresponsive LCEs have been intensively investigated, there was rare example of multistimuli responsive LCE materials. The objective of this work is to combine thermal-induced LC-toisotropic phase transition effect, azobenzene’s trans−cis tautomerization effect and the photothermal effect by embedding carbon nanotubes (CNTs) into azobenzene-containing LCE matrix, to prepare a heat/UV/NIR triple-stimuli-responsive LCE material, which might have a potential application in control devices and logic gate devices, etc. Furthermore, an ideal material which can execute different shape responses Received: November 3, 2015 Revised: December 29, 2015

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Figure 1. (A) Molecular structures of monomers V444, A44 V6 and cross-linker 11UB used for preparing SWCNT/PMHS-V444-A44 V6 composite films. (B) Schematic illustration of a two-step cross-linking coupled with a uniaxial stretching process of preparing SWCNT/PMHSV444-A44 V6 composite films.

(bending47 vs shrinking12) toward different stimulus (UV vs NIR) is highly desirable. In 2010, Terentjev group described a main-chain azobenzenecontaining LCE/CNT composite decorated with pyrene

moieties which greatly enhanced the solubility of CNT in LCE matrix, and studied its NIR-responsive behavior, while the UV-responsive behavior was however left unexplored.48 Two years later, Yu and colleagues reported the second example of B

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azobenzene LCE/CNT composite material.49 On the contrary, they studied the alignment effect caused by a CNT array and UV-induced bending behavior of the LCE film, while the NIRresponsive phenomenon was left unexplored possibly due to the high clearing points of the polyacrylate-backbone LCEs requiring high thermal energy to achieve LC-to-isotropic phase transition which is a difficult task for such an indirect photoactuation. Inspired by all the above works, we herein choose polysiloxane LCE matrix because polysiloxane systems possess highly flexible backbones, excellent thermal/mechanical stabilities, low glass phase transition temperatures (Tg) and relatively low LC-toisotropic phase transition temperatures, etc.50−55 As shown in Figure 1, we design and synthesize a side-chain side-on azobenzene-containing LCE system, instead of intensively investigated side-chain end-on LCE matrixes. Poly(methylhydrosiloxane) (PMHS) is mixed with a vinyl-terminated side-on mesogen56,57 V444 and a vinyl-terminated side-on azobenzenecontaining mesogen A44 V6 whose acrylate-analogue was first invented by keller58,59 and the silane-analogue was later developed by Hammond,60,61 the cross-linker 11UB, Pt catalyst and single-walled CNTs (SWCNTs). Then, the famous two-step cross-linking process introduced by Finkelmann52,53 is used to prepare the CNT-incorporated polysiloxane azobenzene LCE composites successfully. The heat/UV/NIR triple-stimuliresponsive behaviors of such a CNT/LCE composite material are investigated herein.

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into an ice cooled solution of phenol 4 (1.00 g, 2.16 mmol), 5-hexen1-ol (0.43 g, 2.72 mmol) and triphenylphosphine (TPP) (0.85 g, 3.24 mmol) in CH2Cl2 (15 mL). The mixture was stirred at room temperature overnight. After evaporation of the solvent, the residue was purified by column chromatography on silica gel using cyclohexane/ethyl acetate (90/10) as eluent. The product was recrystallized from absolute ethanol (yellow crystals); yield 0.90 g (69%). 1H NMR (500 MHz, CDCl3) δ: 8.15 (d, J = 8.9 Hz, 2H), 7.90 (d, J = 8.9 Hz, 2H), 7.74 (d, J = 8.8 Hz, 1H), 6.99 (dd, J = 8.9, 2.1 Hz, 5H), 6.87 (dd, J = 8.8, 2.2 Hz, 1H), 5.84 (m,, 1H), 5.14−4.84 (m, 2H), 4.18 (t, J = 6.4 Hz, 2H), 4.06 (t, J = 6.5 Hz, 4H), 2.17 (m, 2H), 2.01−1.88 (m, 2H), 1.88−1.73 (m, 4H), 1.73−1.60 (m, 4H), 1.53 (m, 4H), 1.00 (t, J = 7.4 Hz, 6H). 13C NMR (75 MHz, CDCl3) δ: 163.7, 138.6, 132.3, 124.8, 117.6, 114.7, 114.4, 114.1,108.3, 69.8, 68.1, 33.4, 31.2, 28.6, 25.4, 19.2, 13.8. Phase sequence and transition temperatures: Cr−45.1 °C−N−107.3 °C−Iso (on heating, determined by POM), Iso−104.1 °C−N−36.1 °C−Cr (on cooling). Preparation of SWCNT/PMHS-V444-A44 V6 Composite Film. As shown in Figure 1B, the synthesis procedure of SWCNT/PMHSV444-A44 V6 composite film was using the two-stage cross-linking coupled with a uniaxial stretching process. PMHS (24.0 mg, 0.400 mmol Si−H groups), V444 (141.0 mg, 0.250 mmol), A44 V6 (45.7 mg, 0.084 mmol), 11UB (13.6 mg, 0.033 mmol) and SWCNTs (2.4 mg, 1.0 wt %) were solved in 1.5 mL of toluene. The mixture was high-power ultrasonicated for 3 min to ensure homogeneous dispersion. After adding 40 μL of 2% Pt(dvs) dissolved in xylenes, the mixture solution containing SWCNTs was cast into a polytetrafluoroethylene (PTFE) rectangular mold (2.0 cm long × 2.0 cm wide × 1.0 cm deep). The PTEF mold was high-power ultrasonicated for 5 min to remove the bubbles in the mixture solution and heated in an oven at 60 °C for 8 h to accomplish the first cross-linking stage. After cooling to room temperature, the polydomain LCE sample was then carefully removed from the PTEF mold, dried overnight, and cut into a stripe (2.0 cm long × 0.5 cm wide, the thickness is ca. 0.2− 0.3 mm). The stripe film was slowly uniaxial-stretched to ca. 160% of the original length by loading a weight (ca. 1.0 g). Then the stretched LCE film with the load was heated at 60 °C in an oven for 48 h to complete the second cross-linking stage.

EXPERIMENTAL SECTION

General Considerations. The molecular structures of monomers and the cross-linker are shown in Figure 1A. The monomer V444 was synthesized following our previous report.42,62,63 The cross-linker 11UB was prepared following literature protocol.62 All the detailed synthetic procedures, 1 H NMR spectra and instrumentation descriptions are listed in the Supporting Information. Synthesis of monomer A44 V6. Intermediate 5 was prepared following literature protocol.58 As shown in Scheme 1, diisopropyl azodicarboxylate (DIAD) (0.56 g, 3.24 mmol) was added dropwise C

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Figure 2. 1H NMR spectra of (A) V444, (B) A44 V6, and (C) PMHS-V444-A44 V6.

Figure 3. DSC curves of (A) monomer V444, (B) monomer A44 V6, (C) PMHS-V444-A44 V6 film, and (D) SWCNT/PMHS-V444-A44 V6 composite film during the first cooling scan and the second heating scan at a rate of 10 °C/min under nitrogen atmosphere. K = crystalline, G = glass phase, N = nematic, and I = isotropic.

Figure 4. One-dimensional WAXS patterns of (A, B) PMHS-V444A44 V6 film and (C, D) SWCNT/PMHS-V444-A44 V6 composite film.

RESULTS AND DISCUSSION Syntheses and Mesomorphic Properties of Monomers and Elastomers. As shown in Figure 1A, we designed and synthesized a side-on vinyl-terminated monomer V444 and a side-on vinyl-terminated azobenzene-containing monomer A44 V6. The synthetic protocol of monomer V444 was reported previously.42,62,63 The other monomer A44 V6 was inspired by Keller’s methacrylate analogue.58 As illustrated in Scheme 1, 4-butoxyaniline (1) was first transformed in its diazonium salt

(2), which further reacted with resorcinol to give the intermediate 3. After a regioselective DCC coupling reaction between compound 3 and 4-butoxybenzoic acid, followed by a Mitsunubo etherification reaction with 5-hexen-1-ol, the side-on vinyl-terminated azobenzene monomer A44 V6 was successfully prepared. A hydrosilylation reaction was performed to graft two mesogens V444 and A44 V6 onto PMHS backbone with a designed molar ratio of 3:1. We intentionally set azobenzene monomer

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Figure 5. POM images of (A, B) PMHS-V444-A44 V6 film and (C, D) SWCNT/PMHS-V444-A44 V6 composite film recorded at 50 °C. (E, F) SEM images of the surface of SWCNT/PMHS-V444-A44 V6 composite film.

of polymer chains in the LCE materials is very important. The protocols of preparing monodomain LCEs can be divided into two general strategies. One widely used method is applying surface anchoring effects of antiparallel surface-rubbed LC cells to align the mesogens uniaxially and further prepare the monodomain LCE films by a convenient in situ polymerization of low viscous small molecules. However, the disadvantage of this strategy is that the thicknesses of prepared LCE films are limited to 20−100 μm and dispersing inorganic fillers in LCE matrix is extremely difficult. Another widely used method is the two-step cross-linking process introduced by Finkelmann.52,53 Although this protocol completely overcomes the disadvantages of the former strategy, the traditional preparation setup is much more complicated. Recently, Li et al.39,64 reported a simplified protocol, which performed the first-cross-link step of LCE samples in a mold, then evaporated off the solvent inside the precross-linked LCE films, and stretched out the precrosslinked LCE films by loading a weight in an oven to complete

A44 V6 as the minority of the laterally attached mesogenic groups in order to force the corresponding LCE films into bending instead of shrinking under UV illumination. The 1H NMR spectra of V444, A44 V6, and PMHS-V444-A44 V6 are shown in Figure 2. After the hydrosilylation reaction, the terminal vinyl protons of V444 and A44 V6 originally locating at ∼5.0 and ∼5.7 ppm, disappear completely on the 1H NMR spectrum of PMHS-V444-A44 V6. It is confirmed that the vinyl-terminated mesogenic monomers, both V444 and A44 V6, have been successfully grafted onto PMHS backbones. However, it is difficult to accurately estimate the graft density of mesogenic monomers by calculating the integral ratio of aromatic protons and CH3−Si protons, due to the existence of internal standard reference tetramethylsilane (TMS) contained in CDCl3 solvent presenting at ∼0 ppm. Macroscopic shapes of LCEs are actuated by the order deformations of polymer chains induced by the anisotropic-toisotropic transitions. Thus, to achieve a good uniaxial-alignment E

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PMHS-V444-A44 V6 film and SWCNT/PMHS-V444-A44 V6 composite film. As shown in Figure 5 and Videos S1 and S2, the lowest transmittances of two LCE films appear when the stretching directions of the films are perpendicular or parallel to one polarizer. Rotating the films with an interval of 45 o, the transmittances reach maximum. Because of the existence of SWCNTs, the ideal full extinction of birefringence has not been observed in SWCNT/PMHS-V444-A44 V6 composite sample. Nonetheless, the anisotropic alignments of mesogenic units in both LCE films are quite good. Furthermore, through scanning electron microscope (SEM) investigation, the SWCNTs are well dispersed in SWCNT/PMHS-V444-A44 V6 film, and are moderately aligned along the stretching direction as shown in Figure 5E,F. Thermal-Induced Shrinking Behavior of SWCNT/ PMHS-V444-A44 V6 Composite Film. The thermalactuation properties of SWCNT/PMHS-V444-A44 V6 composite films were first investigated on a hot stage. It is wellknown that when monodomain LCE samples are heated above or cooled down below their Tni, the mesogenic orders change, the cross-linking points provide elastic strains and forces, and thus the spontaneous uniaxial shrinking or extending behaviors of LCE materials along the molecular director can be realized. As shown in Figure 6A-B and Video S3, the prepared SWCNT/ PMHS-V444-A44 V6 composite film was heated from room temperature up to 120 °C and an obvious shrinking phenomenon with the maximal shrinkage ratio of ca. 60%, was observed. After cooled back to room temperature, the LCE composite film fully expanded to its original length. The reversible contraction and expansion were repeatedly observed under several heating/cooling cycles. In order to further study the shrinking behavior of SWCNT/ PMHS-V444-A44 V6 composite film, the uniaxial thermal expansion (L/Liso) of film along the director axis is plotted in Figure 6C, where Liso is the minimum length of LCE film at its isotropic state, and L is the length of the film at any specific temperature during the heating and cooling cycles. In the heating process, the LCE film performs a gentle contraction deformation below 85 °C, and suddenly shrinks sharply when the temperature is higher than 90 °C due to the anisotropy-toisotropy transition, finally reaches to the maximum deformation at 120 °C. After cooled back to room temperature, a reversible expansion and a full recovery of the original shape of the LCE film are also observed in a relaxation manner. UV-Induced Bending Behavior of SWCNT/PMHSV444-A44 V6 Composite Film. As shown in Figure 7, the UV−vis spectra of SWCNTs, azobenzene monomer A44 V6, PMHS-V444-A44 V6 film and SWCNT/PMHS-V444-A44 V6 composite film dispersed in THF with a concentration of ca. 0.0001 mol/L were obtained using a TU-1810 ultraviolet−visible spectrophotometer. Similar to the A44 V6/THF solution sample, both PMHS-V444-A44 V6 film and SWCNT/ PMHS-V444-A44 V6 composite film have a strong absorption peak in the UV region centered at 365 nm. In the visible and NIR region, both SWCNTs and SWCNT/PMHS-V444-A44 V6 composite film dispersed in THF show broad absorptions while PMHS-V444-A44 V6 sample has no absorption at all. In other words, SWCNT/PMHS-V444-A44 V6 composite film can absorb photons in both UV and NIR regions. The UV-triggered photoactuation behavior of LCE composite film was studied using a 365 nm UV-light (LUYOR LP-20A). As shown in Figure 8 and Video S4, SWCNT/PMHSV444-A44 V6 film could bend toward to the UV irradiation

Figure 6. Images of SWCNT/PMHS-V444-A44 V6 composite film heated at (A) 25 °C and (B) 120 °C on a hot stage. (C) Shape deformation L(T)/Liso of SWCNT/PMHS-V444-A44 V6 composite film along the stretching direction during heating and cooling circles. Heating rate = 1 oC/min.

Figure 7. UV−vis spectra of SWCNTs, A44 V6, PMHS-V444-A44 V6 film and SWCNT/PMHS-V444-A44 V6 composite film dispersed in THF with a concentration of ca. 0.0001 mol/L.

the second-cross-link process. Inspired by their work, we herein successfully prepared the desired SWCNTs incorporated polysiloxane azobenzene LCE composite film as described in the Experimental Section. In Figure 3, we recorded the DSC curves of two monomers V444, A44 V6, as well as two LCE films PMHS-V444-A44 V6 and SWCNT/PMHS-V444-A44 V6 containing 0 and 1.0 wt % SWCNTs, respectively. Monomers V444 and A44 V6 both show an enantiotropic nematic (N) phase in the temperature ranges of 97.2−107.5 °C and 45.1−107.3 °C respectively. Onedimensional wide-angle X-ray scattering (WAXS) patterns of PMHS-V444-A44 V6 and SWCNT/PMHS-V444-A44 V6 samples both present one diffuse peak in wide-angle regions and no peak in low-angle regions (Figure 4), which are characteristics of nematic phase. Compared with PMHS-V444A44 V6 sample, although SWCNT/PMHS-V444-A44 V6 LCE film possesses almost same phase transitions, its nematic-toisotropic phase transition temperature (Tni) is slightly lower (ca. 3 °C) than the Tni of PMHS-V444-A44 V6 film due to the embedded 1 wt % SWCNTs. The polarized optical microscope (POM) was used to evaluate the uniaxial alignment effect of the mesogens in F

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Figure 8. A 365 nm UV-light has been illuminated on SWCNT/PMHS-V444-A44 V6 composite film for (A) 0 min and (B) 20 min. (C) The schematic description of tangent angle θ. (D) UV illumination time vs tangent angle θ diagram of SWCNT/PMHS-V444-A44 V6 composite film.

source. After removing the UV light, the LCE composite film returned to its original state under heating or visible-light illumination. The molar absorption coefficient of azobenzene is very high under 365 nm UV-light, and the trans-azobenzene in the surface absorbed the photons to form its geometric isomer, cis-azobenzene. As hypothesized by prior research,21 the shrinking behavior only occurs in the surface of the film, and the rest parts of the film do not change under UV-light irradiation, so the composite film bends under the drive of internal stress. When performing heating or visible light irradiation, the cis-azobenzene returns to trans-azobenzene, and the bent film returns to the original state. As shown in Figure 8C, the tangent angle θ is measured and recorded to show the bending rate of SWCNT/PMHS-V444-A44 V6 films under the irradiation of UV light. The θ is the included angle of line l1 and l2, where l1 and l2 are the tangent lines to left end point and right end point, respectively. The film started bending under irradiation for 2 min and performed a continuous bending behavior in the next 15 min (Figure 8D). Correspondingly, the θ reached the maximum (ca. 55°) in 20 min. Considering that the above experiment has taken place at 25 °C, we further investigated the effects of temperature variation on the LCE film’s UV-response rate. As shown in Figure 9A, dramatically accelerated film bending speeds have been recorded at various elevated environmental temperatures. Particularly at 60 °C, the composite film could realize a much faster response with bending maximally in 2 min (Figure 9B). Nevertheless, the UV-response speed is not as fast as the samples described in some previous literatures.65,66 The possible reason might be that the thickness of those previous reported films prepared by LC cells are limited to several decade micrometers thick, which are much thinner than our sample, meanwhile the embedded CNTs acting like longitudinal reinforcing bars, might disfavor the bending transformation. NIR-Induced Shrinking Behavior of SWCNT/PMHSV444-A44 V6 Composite Film. An NIR-light source (Output power: 8W, Center wavelength: 808 ± 3 nm) was

used to investigate the NIR-light-triggered photoinduced actuation characteristics of PMHS-V444-A44 V6 film and SWCNT/PMHS-V444-A44 V6 composite film. As one of the applied thermal conductive fillers,36−47 SWCNTs show high photothermal transition ratio in IR region. The monodomain SWCNTs-containing LCE samples can be heated above their Tni by the absorbed photon energy, and consequently the spontaneous uniaxial shrinking behavior of LCE materials along the molecular director induced by the anisotropic-to-isotropic transition can be observed. As shown in Figure 10A,B and Video S5, the prepared SWCNT/PMHS-V444-A44 V6 composite film conspicuously shrunk after being exposed to NIR-light irradiation and reached the maximum contraction in 20 s. After the NIR source was removed, the LCE composite film fully recovered to its initial length. In contrast, PMHSV444-A44 V6 film almost remained an intact shape under the NIR irradiation in the first 20 s, and a slight shrinking behavior was recorded in the next 30 s. In order to further examine the shrinking behavior of these two LCE samples, the surface temperature changes of PMHSV444-A44 V6 and SWCNT/PMHS-V444-A44 V6 films under the NIR-light illumination were directly recorded by a thermal imager (FLUKE Ti90), as shown in Figure 10C. The temperature of SWCNT/PMHS-V444-A44 V6 composite film rose within 9 s from room temperature to about 91 °C, which was higher than its Tni, and eventually reached to ca. 120 °C. When NIR-light was switched off, the film’s temperature decreased from 120 to 50 °C in 10 s. In contrast, the temperature of PMHS-V444-A44 V6 film only reached to 57 °C in the first 10 s, which is far below its Tni, and got to 82 °C eventually. These data indicate that although the applied NIR laser source dramatically release heat, SWCNTs can efficiently absorb and convert photons into thermal energy, which is the key factor of raising the temperature of SWCNT/PMHS-V444A44 V6 composite film to achieve the anisotropic-to-isotropic transition. Taking into account the significant NIR response rate difference between PMHS-V444-A44 V6 film and SWCNT/PMHS-V444-A44 V6 film, it is confirmed that the G

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Figure 9. UV illumination time vs tangent angle θ diagram of SWCNT/PMHS-V444-A44 V6 composite film irradiated at (A) varied temperatures and (B) 60 °C specifically.

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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/acs.macromol.5b02388. Materials and instrumentation, detailed synthetic procedures of monomer A44 V6, V444 and cross-linker 11UB, 1 H NMR and 13C NMR spectra (PDF) Video S1: Rotation of PMHS-V444-A44 V6 film under polarized optical microscopy (AVI) Video S2: Rotation of SWCNT/PMHS-V444-A44 V6 film under polarized optical microscopy (AVI) Video S3: Shrinking phenomenon of prepared SWCNT/ PMHS-V444-A44 V6 composite film during heating (AVI) Video S4: Bending of SWCNT/PMHS-V444-A44 V6 film toward to the UV irradiation source (AVI) Video S5: Shrinking of prepared SWCNT/PMHS-V444A44 V6 composite film after NIR−light irradiation (AVI)

Figure 10. Images of SWCNT/PMHS-V444-A44 V6 film (on the left) and PMHS-V444-A44 V6 film (on the right) under NIR illumination for (A) 0 and (B) 30 s. (C) The NIR illumination time vs temperature diagram of SWCNT/PMHS-V444-A44 V6 film and PMHS-V444-A44 V6 film.

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AUTHOR INFORMATION

Corresponding Author

*(H.Y.) Telephone: 86 25 52090620. Fax: 86 25 52090616. E-mail: [email protected].

shrinking behavior of SWCNT/PMHS-V444-A44 V6 composite film under the NIR-irradiation derives from SWCNTs’ photothermal effect.

Notes

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The authors declare no competing financial interest.

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CONCLUSION In this work, we successfully prepared multistimuli responsive SWCNTs incorporated, polysiloxane-based, azobenzene-containing LCE composite films SWCNT/PMHS-V444-A44 V6 via a two-step cross-linking process coupled with a uniaxial stretching technique. Taking advantage of thermal-induced LC-to-isotropic phase transition effect, azobenzene’s trans−cis tautomerization effect and the photothermal effect induced by embedding CNTs, the LCE/CNT composite film can perform a fully reversible shrinking/expanding response toward heat or NIR light stimulus, and a fully reversible bending behavior under UV irradiation. To the best of our knowledge, this is the first example of LCE materials performing two different fully reversible transformations (three-dimensional bending vs twodimensional shrinking) under illuminations of two light sources in different wavelength bands (UV vs NIR), which might endow this novel shape memory LCE material with potential applications in control devices and logic gate devices, etc. Further research about optimization and miniaturization of this multistimuli-responsive LCE composite material is under investigation.

ACKNOWLEDGMENTS This research was supported by National Natural Science Foundation of China (Grant No. 21374016) and Priority Academic Program Development of Jiangsu Higher Education Institutions.

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Macromolecules

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DOI: 10.1021/acs.macromol.5b02388 Macromolecules XXXX, XXX, XXX−XXX