Composite Films with Ordered Carbon Nanotubes and Cellulose

Apr 6, 2017 - For example, interconnected CNT networks are preferred in energy storage,(8) while optimal bundling and anisotropy of CNT matrixes are n...
16 downloads 11 Views 5MB Size
Download PDF
Article pubs.acs.org/JPCC

Composite Films with Ordered Carbon Nanotubes and Cellulose Nanocrystals Jinhuan Sun,† Caihong Zhang,† Zaiwu Yuan,*,† Xingxiang Ji,† Yingjuan Fu,† Hongguang Li,*,‡ and Menghua Qin§ †

Key Laboratory of Fine Chemicals in Universities of Shandong, Qilu University of Technology, Jinan 250353, China State Key Laboratory of Solid Lubrication & Laboratory of Clean Energy Chemistry and Materials, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China § Laboratory of Organic Chemistry, Taishan University, Taian 271021, China ‡

S Supporting Information *

ABSTRACT: Composite films with oxidized carbon nanotubes (o-CNTs) incorporated in the chiral nematic liquid crystals (CNLCs) formed by cellulose nanocrystals (CNCs) were fabricated for the first time. Induced by solvent evaporation, the isotropic aqueous dispersion containing oCNTs and CNCs gradually forms lyotropic CNLCs, and the framework of the CNLCs can be retained in the final solid films, confirmed by polarized optical microscopy observations and scanning electron microscopy observations. During this evaporation-induced self-assembly process, the predispersed oCNTs were spontaneously integrated in the liquid crystal matrix. It is found that the incorporation of a trace amount of o-CNTs (∼1.5 wt %) can induce obvious structural changes of the films. The reflection spectrum shifts to higher wavelengths with increasing content of o-CNTs, resulting in a continuous increase of the helical pitch of the CNLC phase. Confined in the liquid crystal matrix, the randomly oriented o-CNTs in the aqueous dispersion are forced to adopt a higher degree of order. This ordered arrangement of o-CNTs combined with the intrinsic anisotropy of the CNLCs impart the composite film anisotropic conductivity as proved by the electrical resistance measurements. This new type of CNTs/CNCs composites could find applications in various fields such as sensors and photoelectronics.

■

INTRODUCTION As the most abundant natural resource in the Earth, cellulose has received great attention nowadays due to the increasing demand on the green and sustainable development of society. Specifically, cellulose nanocrystals (CNCs), which were obtained from hydrolysis of cellulose, have received considerable attention due to their good dispersibility, anisotropic properties, and interesting self-assembly behavior.1,2 CNCsbased composite materials by complexing with gold or silver nanoparticles, organic dyes, and polymers have been reported.3−6 From a viewpoint of self-assembly, one fascinating aspect of CNCs could be the formation of chiral nematic liquid crystals (CNLCs), which can be easily obtained via evaporation-induced self-assembly (EISA). Besides exploration of their interesting structures, CNLCs formed by different CNCs have been successfully used as templates for the prepartion of various inorganic and organic functional materials which find great potential applications in different fields.7 Since their discovery, carbon nanotubes (CNTs) have received considerable interest due to their excellent mechanical, electronic, and photonic properties. It is known that specific © 2017 American Chemical Society

orientation of CNTs is required in practical applications, especially for those related to electronics and photonics. For example, interconnected CNT networks are preferred in energy storage,8 while optimal bundling and anisotropy of CNT matrixes are needed in plastic electronics and display technologies.9−11 Unfortunately, most of the as-prepared CNTs are randomly oriented, which significantly hindered their promising applications in optoelectronics. To effectively align CNTs, different methods have been proposed, including direct growth and postgrowth approaches.12,13 Specifically, alignment of CNTs templated by liquid crystals (LCs) is a popular way and has received considerable attention during the past decades.14−21 It is generally accepted that the tubes will adopt arrangements mainly toward the director of the LC phase, which is also consistent with the predictions for other one-dimensional anisotropic particles.22 However, as the viscosities of the LCs Received: February 16, 2017 Revised: April 6, 2017 Published: April 6, 2017 8976

DOI: 10.1021/acs.jpcc.7b01528 J. Phys. Chem. C 2017, 121, 8976−8981

Article

The Journal of Physical Chemistry C

crossed polarizers under a transmission or reflection mode. UV−vis reflectance spectra of the samples were obtained from a UV−vis 2600 (Shimazduo, Japan) spectrophotometer. Scanning electron microscopy (SEM) experiments were conducted on a Quanta 200 (FEI, USA) electron microscope with samples sputter-coated by gold. X-ray diffraction (XRD) patterns were obtained from a D8-ADVANCE (Bruker, Germany) diffractometer equipped with a Cu Kα X-ray source. Transmission electron microscopy (TEM) observations were carried out on a JEM-2100 (JEOL, Japan) at an acceleration voltage of 200 kV. For negative-staining TEM observations, the samples were stained with an aqueous solution of phosphotungstic acid (2 wt %). For o-CNTs/CNCs composite films, two sample preparation methods were adopted before observations. In the first method, the film was treated by an aqueous solution consisting of 10 mol·L−1 H2SO4 at 98 °C for 18 or 24 h. After that, the film was rinsed alternatively with a solution of piranha (30 wt % H2O2/98 wt % H2SO4, 1:3 by volume) and water until it is colorless. Then, the film was washed with a large amount of deionized water and dried for subsequent characterizations. In the second sample preparation method, the composite film was subjected to calcination at 540 °C for 5 h under nitrogen. After cooling to room temperature, the solid was cracked in liquid nitrogen and the fragments were ready for the observation. Ohm measurements were performed on a SENIT VC890D Ohmmeter (Shenzhen, China) with a diameter of the tip around 0.8 mm. The pressure applied to the tip during measurements is ∼3.9 N. For each distance within the same circle (see Figure 6A), five measurements in total were carried out and the values were averaged. Finally, the averaged values from the three circles were further averaged.

are high, a heating process is normally needed to mix the CNTs and the LC matrix, which can lead to severe aggregation of the dispersed CNTs. Previously, Xin et al. have reported that surfactants and predispersed CNTs can spontaneously form lyotropic LCs during a phase separation process induced by hydrophilic polymers.19,20 Using this method, the heating process can be avoided and CNTs/LC composites with high qualities can be obtained, highlighting the advantage of utilizing a dynamic process for the integration of CNTs with LCs. As unique chiral LC phases which form through a dynamic process (i.e., EISA), the CNLCs formed by CNCs could be ideal candidates to accommodate and align CNTs. Bearing this in mind, herein we report for the first time that CNCs films with ordered CNTs inside can be facilely prepared via EISA from dilute CNTs/CNCs aqueous dispersions. As the solvent evaporates, CNCs gradually form CNLCs, during which the predispersed, randomly oriented CNTs are spontaneously integrated with CNLCs. The changes of the structures and properties of the CNCs-based films induced by the integration of CNTs have been investigated in detail. The morphologies and arrangement of CNTs inside the LC matrix have also been explored. Our work provides a new strategy to prepare CNTs/ LCs composites with great potential applications.

■

MATERIALS AND METHODS Chemicals and Materials. Cellulose nanocrystals (CNCs) were prepared through hydrolysis of bleached kraft softwood pulp using 64 wt % sulfuric acid (Laiyang, China) following the procedures described in the literature.23 CNTs (XianfengNano, Nanjing, China) were produced by the CVD method and have a purity of >95%. The diameters of the CNTs are 10−30 nm, and the lengths are 1−3 μm. The ratio of the intensity of the D peak to the G peak (ID/IG) of the CNTs from the Raman spectrum provided by the supplier is ∼0.22. Before use, the CNTs were oxidized in a solution of 98% sulfuric acid and 70% nitric acid (Laiyang, China) in a volume ratio of 3:1. In brief, 5 g of CNTs was added to 500 mL of mixed acids and mixed by stirring with a glass rod. The mixture was then heated to 50 °C and sonicated at 900 W for 2 h. After storage for 72 h, the mixture was further subjected to alternative centrifugation and washing with deionized water until the pH is neutral. The oxidized CNTs are denoted as o-CNTs. Its ID/IG increased to 1.07 (Figure S1), indicating the successful functionalization of the graphitic surfaces by the oxidation. Sample Preparation Method. For the preparation of oCNTs/CNCs aqueous dispersions, the o-CNTs were first dispersed in water under mild sonication. Different amounts of o-CNTs aqueous dispersion were then taken out and added to the CNCs aqueous solution with a concentration of 3 wt %. The mixtures were sonicated at 900 W for 3 s each with a duration of 5 s and a total sonication time of 5 min. After that, the mixture was centrifuged at 2500 rpm for 10 min to remove large tube bundles. The o-CNTs/CNCs composite films were prepared by slowly drying the aqueous dispersions of o-CNTs/ CNCs in a polystyrene Petri dish with a diameter of 3.5 cm at ambient conditions. The total evaporation time is about 1 day. Characterizations. Thermogravimetric analysis (TGA) was carried out on a TGA/SDTA851e system (Mettler-Toledo, Swiss). The temperature was increased from 10 to 900 °C at a rate of 10 °C·min−1 under nitrogen. The contents of o-CNTs in the composite films were calculated based on the weight loss at 900 °C. Polarized optical microscopy (POM) observations were performed on a Nikon Y-TV55 microscope (Japan) with

■

RESULTS AND DISCUSSION Preparation of the CNTs/CNCs Composite Films. The as-prepared CNCs were dispersed in water, and their morphologies were checked by negative-staining TEM observations. A typical image is given in Figure 1a, from

Figure 1. (a) A typical image from negative-staining TEM observations for the aqueous dispersion of CNCs (3 wt %, the photo is given in the inset). (b) A typical TEM image of the aqueous dispersion of CNCs after the introduction of o-CNTs. The content of o-CNTs was later determined to be 0.075 wt % by TGA.

which CNCs with diameters of 15−25 nm and lengths of 130− 200 nm have been clearly detected. To obtain CNCs-based composite materials with high qualities, a good compatibility between the guests and the CNLCs matrix of CNCs is needed. To improve the affinity between the tube surfaces and CNCs, CNTs were first oxidized to o-CNTs by mixed acids to have similar hydrophilic functional groups with CNCs. The asprepared o-CNTs can be facilely dispersed in water. However, 8977

DOI: 10.1021/acs.jpcc.7b01528 J. Phys. Chem. C 2017, 121, 8976−8981

Article

The Journal of Physical Chemistry C

Figure 2. (a, b) Polarized optical microscopy (POM) images operated in transmission mode of a concentrated o-CNTs/CNCs aqueous dispersion and the resulting solidified film after total drying. (c, d) POM images operated in reflection mode at different magnifications of the solid film formed by o-CNTs and CNCs (o-CNTs/CNCs-1). (e) Photos of the solidified films of CNCs with different contents of o-CNTs, which are (from left to right) 0, 1.5, 1.8, and 2.5 wt %, respectively.

gradual precipitation of o-CNTs from the aqueous dispersion occurs ∼1 h after preparation, indicating that o-CNTs themselves are lacking long-term stability. After being integrated with 3 wt % CNCs aqueous solution (for details, see the Materials and Methods section), homogeneous dispersions can be obtained which can be stable for up to months (inset of Figure 1b). TEM observations revealed the presence of randomly oriented tubes, as can be seen from a typical image shown in Figure 1b. Due to the strong filmforming ability of CNCs upon drying during the sample preparation process for TEM, it was found that the tubes are normally embedded in a mass of CNCs, and the number of individual tubes is relatively small (Figure S2). The o-CNTs/CNCs dispersion is isotropic, and no birefringence can be detected by polarized optical microscopy (POM) observations (Figure S3). When the o-CNTs/CNCs dispersion was open to the air for solvent evaporation, however, spherulite-like texture appears, as can be seen from a representative POM image shown in Figure 2a. This phenomenon is indicative of the formation of the lyotropic CNLCs, despite the presence of o-CNTs. The texture becomes more and more obvious with continuous evaporation of the solvent and finally is retained in the solidified film (Figure 2b). By POM observations operated in the reflection mode, a regular texture with protruding lattices was revealed for the oCNTs/CNCs composite film (Figure 2c,d). In contrast, the film formed solely by CNCs shows a relatively smooth morphology (Figure S4). The content of o-CNTs in the solidified composite film was calculated to be ∼1.5 wt % (this film is denoted as o-CNTs/CNCs-1 hereafter) based on thermogravimetric analysis (TGA, Figure S5). By adjusting the amount of o-CNTs in the o-CNTs/CNCs dispersions, the other two composite films can be obtained (Figure 2e) where the contents of o-CNTs were calculated to be 1.8 wt % (denoted as o-CNTs/CNCs-2) and 2.5 wt % (denoted as oCNTs/CNCs-3), respectively. Structural Changes of the LC Matrix Induced by the Incorporation of o-CNTs. We first checked the morphology of the composite film at micro- and nanometer length scales by scanning electron microscopy (SEM) observations with oCNTs/NCC-1 as a typical example. For comparison, observations on the film formed solely by CNCs were also carried out. From the typical images shown in Figure 3, one can

Figure 3. SEM images of the cross sections of the solid films formed by CNCs (a) and o-CNTs/CNCs-1 (b), respectively. Insets are illustrations of the chiral nematic structures formed solely by CNCs or o-CNCs/CNCs hybrid.

see that both films show layered chiral nematic structures. This indicates that the incorporation of o-CNTs did not destroy the matrix of the CNLCs, which is consistent with the conclusion obtained from POM observations where textures still exist in the solidified films. On the other hand, from the photos shown in Figure 2e, it is also evidenced that the o-CNTs/CNCs composite film displays a more pronounced iridescence under common white light illumination at an increased content of o-CNTs. This change indicates that, although the matrix of the CNLCs remains in the composite film, subtle structural changes might also be induced by the introduction of o-CNTs. Having periodically varied refractive index along the axis of the helix, CNLCs formed by CNCs can be viewed as one-dimensional photonic crystals which can reflect light with specific wavelengths. The wavelength of the reflecting light (λ) can be related to the helical pitch of the chiral nematic structure (P) through the Vries formula given below (eq 1)24 λ = navg P sin θ

(1)

where navg is the average refractive index, which is ∼1.54 for cellulose-based films, and θ is the angle between the surface of the liquid crystal and the incident light. Specifically, when the incident light is parallel to the helical axis (i.e., θ = 90°), sin θ becomes 1 and the reflecting light gains the maximum intensity (the corresponding wavelength is denoted as λmax). P can thus be calculated through eq 2: 8978

DOI: 10.1021/acs.jpcc.7b01528 J. Phys. Chem. C 2017, 121, 8976−8981

Article

The Journal of Physical Chemistry C

Figure 4. Reflection spectra of the solid films formed by CNCs (a), o-CNTs/CNCs-1 (b), o-CNTs/CNCs-2 (c), and o-CNTs/CNCs-3 (d), respectively. The values of the wavelengths at which the reflection gains the maximum intensity are also included inset. The dotted lines are guides for the eyes.

P = λmax /navg

(Figure 5a,b). The interlayer distance was determined to be ∼70 nm, which is much smaller than that obtained from the

(2)

To get details of the structural changes of the CNLCs induced by the incorporation of o-CNTs, the reflection spectra for the films with varying amounts of o-CNTs were recorded, and the results are summarized in Figure 4. It was found that the intensity of the reflection decreases continuously with increasing content of o-CNTs, which should be caused by the strong absorption of o-CNTs within a wide range of wavelengths from the UV to the NIR region. From Figure 4, it can be also seen that λmax of the composite film shifts to higher values with increasing content of o-CNTs. This corresponds to an increase of P, which is calculated to be 314, 368, 379, and 405 nm for the films formed by CNCs, oCNTs/CNCs-1, o-CNTs/CNCs-2, and o-CNTs/CNCs-3, respectively. Thus, the incorporation of o-CNTs swells the matrix of CNLCs. This phenomenon can be partially ascribed to the filling effect of o-CNTs which causes an increase of P. On the other hand, as o-CNTs were simultaneously integrated into the composite film through a dynamic process (i.e., EISA), it could also be possible that the predispersed o-CNTs nucleate a specific LC structure of CNCs, which then dominates the whole system after further nucleation. This assumption seems reasonable especially considering that the content of the introduced o-CNTs in the whole system is quite small (≤2.5 wt %). Morphologies of o-CNTs within the LC Matrix. A key concern for CNTs/LC composites is the morphologies and/or organization of the tubes in the LC matrix. To probe the internal structure of the o-CNTs/CNCs composite films as well as to try to figure out the arrangement of the tubes inside the CNLCs matrix, TEM observations were performed. As the composite films are mainly composed of CNCs, however, to directly view the arrangement of the tubes embedded in the films is difficult. Attempts on the as-prepared samples failed, as no electrons can successfully across the thick films. To facilitate TEM observations, we adopted an acidolysis treatment to uncover the film by removing most of the CNCs. The acidolysis process was monitored by X-ray diffraction (XRD) measurements, which shows a significant decrease of CNCs for o-CNTs/CNCs-1 after being heated in 10 mol·L−1 H2SO4 to 98 °C for 18 h (Figure S6). However, TEM observations only give rigid stripe-like patterns with a jagged streak at the ends (Figure S7). We thus extended the time of acidolysis to 24 h, and images showing the well-patterned layers were obtained

Figure 5. (a−c) Typical TEM images for the film of o-CNTs/CNCs-1 after being treated with 10 mol·L−1 H2SO4 at 98 °C for 24 h. (d) A typical TEM image for the film of o-CNTs/CNCs-1 after calcination at 540 °C for 5 h.

reflection spectra. This observation indicates that structural changes of the CNLCs induced by the acidolysis occurred. In Figure 5b, a tube with a diameter of ∼11 nm can be observed (along the arrowheads), which aligns preferentially toward the direction of the layers. In the regions where excessive acidolysis occurs, more tubes could be found (Figure 5c). We have also tried an alternative way to remove the CNCs by calcination (for details, see the Materials and Methods section). In this case, large amounts of amorphous carbon were found, which should be produced by the calcination of the CNCs. Even though, the presence of the tubes can be still distinguished (Figure 5d, Figure S8). From Figure 5c,d, it can be seen that most tubes have a dominant direction to align themselves and the number of the 8979

DOI: 10.1021/acs.jpcc.7b01528 J. Phys. Chem. C 2017, 121, 8976−8981

Article

The Journal of Physical Chemistry C

Figure 6. (A) A schematic diagram that denotes the method of electrical resistance measurements applied on the composite film (o-CNTs/CNCs1). Values between different endpoints are also included. The arrows denote the possible preferential direction of the alignment of the o-CNTs. (B) Plots of electrical resistance obtained between different endpoints (averaged from three measurements).

structural changes of the CNLCs induced by the incorporation of o-CNTs have been revealed, which indicated an increase in the helical pitch. The morphologies of the o-CNTs inside the CNLCs have been demonstrated with imaging studies by acidolysis or calcination of the composite film, where proofs pointing to an ordered arrangement of the tubes could be found. The intrinsic anisotropy of the LC matrix and the ordered arrangement of the embedded tubes result in anisotropic conductivity of the composite film. This work provides a new strategy to prepare CNTs/LCs composites where the integration of CNTs with LCs occurs during a spontaneous process. This is different from the methods reported previously where a heating process or strong stirring is needed. The composite films exhibit interesting optical and electronic properties, opening the door for their potential applications in a wide range of fields such as sensors and optoelectronics.

tubes deviating from the main direction is quite limited. Indeed, theoretical predictions indicate that the number of the anisotropic particles perpendicular to the main director of the LC matrix, if there is any, is less compared to that aligning along the main director.22 Thus, it can be speculated that the oCNTs have an ordered arrangement in the matrix. This conclusion has been widely adopted in CNTs/LCs composites, and proofs from optical techniques such as polarized Raman spectroscopy25,26 and transmittance measurement27 have been presented in certain circumstances. Anisotropic Conductivity of the Composite Film. It has been demonstrated that the introduction of a trace amount of CNTs can significantly change the property of the hybrid films28−30 or bulk composites.31 The film formed solely by CNCs is insulating. After incorporation of a small amount of oCNTs, however, the composite film becomes conductive. More importantly, anisotropic conductivity of the composite film was found, as confirmed by ohm measurements schematically shown in Figure 6A on the representative film, i.e., o-CNTs/ CNCs-1. A series of data of electrical resistance (ER) in different directions between the two endpoints with a 1 cm distance were obtained by measuring the top surface of the film. In total, three different regions were selected for the measurement. In all the cases, it was found that the ER values for the segments with the same vector directions are quite similar (Figure 6B). Within the four series of segments, the lowest ER values were obtained along OB and OB′, which corresponds to the highest conductivity (indicated by the arrows). This anisotropic conductivity of the composite film may partially come from the intrinsic anisotropy of the CNLCs matrix. However, the ordered alignment of the embedded oCNTs should also make contributions. Although previously it has been demonstrated that CNCs can be used to disperse CNTs in aqueous solutions with a high efficiency,32 and an SWNTs/CNCs composite film was constructed via a layer-bylayer method,33 the tubes were found to align randomly. The current work represents the first example addressing the alignment of CNTs in CNCs-based composites, which highlights that the CNLCs of CNCs can be ideal hosts to accommodate CNTs for potential applications in electronic devices.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b01528. Raman spectrum of o-CNTs (Figure S1), TEM and POM images of the dilute o-CNTs/CNCs aqueous dispersion before solvent evaporation (Figures S2, S3), POM image operated in reflection mode for the solid film formed solely by CNCs (Figure S4), TGA curves of the solid films formed by CNCs incorporated by different amounts of o-CNTs (Figure S5), XRD patterns between 10° and 30° for different films after acidolysis at 98 °C for 18 h (Figure S6), TEM image of the composite film after acidolysis at 98 °C for 18 h (Figure S7), and TEM image of the composite film after calcination (Figure S8) (PDF)

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Tel: +86 531 89631208. Fax: +86 531 89631111 (Z.Y.). *E-mail: [email protected]. Tel: +86 931 4968829. Fax: +86 931 4968163 (H.L.).

■

CONCLUSIONS In summary, we have demonstrated that the CNLCs formed by CNCs can be ideal hosts to accommodate o-CNTs via a spontaneous process induced by solvent evaporation. The

ORCID

Hongguang Li: 0000-0002-5773-5003 Notes

The authors declare no competing financial interest. 8980

DOI: 10.1021/acs.jpcc.7b01528 J. Phys. Chem. C 2017, 121, 8976−8981

Article

The Journal of Physical Chemistry C

■

Separation in the Presence of a Hydrophilic Polymer. Langmuir 2010, 26, 3562−3568. (20) Xin, X.; Li, H.; Kalwarczyk, E.; Kelm, A.; Fiałkowski, M.; Gorecka, E.; Pociecha, D.; Hołyst, R. Single-Walled Carbon Nanotube/Lyotropic Liquid Crystal Hybrid Materials Fabricated by a Phase Separation Method in the Presence of Polyelectrolyte. Langmuir 2010, 26, 8821−8828. (21) Wang, L.; Xin, X.; Guo, K.; Yang, M.; Ma, X.; Yuan, J.; Shen, J.; Yuan, S. Ordered carbon nanotubes−n-dodecyl tetraethylene monoether liquid crystal composites through phase separation induced by poly(ethylene glycol). Phys. Chem. Chem. Phys. 2014, 16, 14771− 14780. (22) Yadav, S. P.; Singh, S. Carbon nanotube dispersion in nematic liquid crystals: An overview. Prog. Mater. Sci. 2016, 80, 38−76. (23) Wang, Q.; Zhao, X.; Zhu, J. Y. Kinetics of Strong Acid Hydrolysis of a Bleached Kraft Pulp for Producing Cellulose Nanocrystals (Cncs). Ind. Eng. Chem. Res. 2014, 53, 11007−11014. (24) de Vries, Hl. Rotatory Power and Other Optical Properties of Certain Liquid Crystals. Acta Crystallogr. 1951, 4, 219−226. (25) Scalia, G.; Lagerwall, J. P. F.; Schymura, S.; Haluska, M.; Giesselmann, F.; Roth, S. Carbon Nanotubes in Liquid Crystals as Versatile Functional Materials. Phys. Status Solidi B 2007, 244, 4212− 4217. (26) Zhao, W.; Wang, J.; He, J.; Zhang, L.; Wang, X.; Li, R. Preparation and Characterization of Carbon Nanotubes/Monotropic Liquid Crystal Composites. Appl. Surf. Sci. 2009, 255, 6589−6592. (27) Lisetski, L. N.; Minenko, S. S.; Fedoryako, A. P.; Lebovka, N. I. Dispersions of Multiwalled Carbon Nanotubes in Different Nematic Mesogens: The Study of Optical Transmittance and Electrical Conductivity. Phys. E 2009, 41, 431−435. (28) Sun, Y.; Li, L.; Wen, D.; Bai, X.; Li, G. Bistable electrical switching and nonvolatile memory effect in carbon nanotube-poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) composite films. Phys. Chem. Chem. Phys. 2015, 17, 17150−17158. (29) Mariano, L. C.; Salvatierra, R. V.; Cava, C. E.; Koehler, M.; Zarbin, A. J. G.; Roman, L. S. Electrical Properties of Self-Assembled Films of Polyaniline/Carbon Nanotubes Composites. J. Phys. Chem. C 2014, 118, 24811−24818. (30) Liu, J.; Sun, J.; Gao, L. A Promising Way To Enhance the Electrochemical Behavior of Flexible Single-Walled Carbon Nanotube/Polyaniline Composite Films. J. Phys. Chem. C 2010, 114, 19614−19620. (31) Basu, R.; Garvey, A. Insulator-to-Conductor Transition in Liquid Crystal-Carbon Nanotube Nanocomposites. J. Appl. Phys. 2016, 120, 164309−1−5. (32) Mougel, J. B.; Adda, C.; Bertoncini, P.; Capron, I.; Cathala, B.; Chauvet, O. Highly Efficient and Predictable Non Covalent Dispersion of Single-Walled and Multi-Walled Carbon Nanotubes by Cellulose Nanocrystals. J. Phys. Chem. C 2016, 120, 22694−22701. (33) Olivier, C.; Moreau, C. l.; Bertoncini, P.; Bizot, H.; Chauvet, O.; Cathala, B. Cellulose Nanocrystal-Assisted Dispersion of Luminescent Single-Walled Carbon Nanotubes for Layer-by-Layer Assembled Hybrid Thin Films. Langmuir 2012, 28, 12463−12471.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 31570570, No. 31370581, No. 61474124). The authors would like to thank Dr. Qingrui Fan for the helpful POM measurements.

■

REFERENCES

(1) Eyley, S.; Thielemans, W. Surface Modification of Cellulose Nanocrystals. Nanoscale 2014, 6, 7764−7779. (2) Habibi, Y. Key Advances in the Chemical Modification of Nanocelluloses. Chem. Soc. Rev. 2014, 43, 1519−1542. (3) Tercjak, A.; Gutierrez, J.; Mondragon, G.; Mondragon, I. Cellulose Nanocrystals and Au Nanoparticles Well-Dispersed in a Poly(styrene-b-ethylene oxide) Block Copolymer Matrix. J. Phys. Chem. C 2011, 115, 22180−22185. (4) Chu, G.; Yin, H.; Jiang, H.; Qu, D.; Shi, Y.; Ding, D.; Xu, Y. Ultrafast Optical Modulation of Rationally Engineered Photonic− Plasmonic Coupling in Self-Assembled Nanocrystalline Cellulose/ Silver Hybrid Material. J. Phys. Chem. C 2016, 120, 27541−27547. (5) Zhao, L.; Li, W.; Plog, A.; Xu, Y.; Buntkowsky, G.; Gutmann, T.; Zhang, K. Multi-responsive cellulose nanocrystal−rhodamine conjugates: an advanced structure study by solidstate dynamic nuclear polarization (DNP) NMR. Phys. Chem. Chem. Phys. 2014, 16, 26322− 26329. (6) Samir, M. A. S. A.; Alloin, F.; Gorecki, W.; Sanchez, J.-Y.; Dufresne, A. Nanocomposite Polymer Electrolytes Based on Poly(oxyethylene) and Cellulose Nanocrystals. J. Phys. Chem. B 2004, 108, 10845−10852. (7) Giese, M.; Blusch, L. K.; Khan, M. K.; MacLachlan, M. J. Functional Materials from Cellulose-Derived Liquid-Crystal Templates. Angew. Chem., Int. Ed. 2015, 54, 2888−2910. (8) Das, R. K.; Liu, B.; Reynolds, J. R.; Rinzler, A. G. Engineered Macroporosity in Single-Wall Carbon Nanotube Films. Nano Lett. 2009, 9, 677−683. (9) Cao, Q.; Han, S.-j.; Tulevski, G. S.; Zhu, Y.; Lu, D. D.; Haensch, W. Arrays of Single-Walled Carbon Nanotubes with Full Surface Coverage for High-Performance Electronics. Nat. Nanotechnol. 2013, 8, 180−186. (10) Ishikawa, F. N.; Chang, H.-K.; Ryu, K.; Chen, P.-C.; Badmaev, A.; Gomez De Arco, L.; Shen, G.; Zhou, C. Transparent Electronics Based on Transfer Printed Aligned Carbon Nanotubes on Rigid and Flexible Substrates. ACS Nano 2009, 3, 73−79. (11) Opatkiewicz, J.; LeMieux, M. C.; Bao, Z. Nanotubes on Display: How Carbon Nanotubes Can Be Integrated into Electronic Displays. ACS Nano 2010, 4, 2975−2978. (12) Iakoubovskii, K. Techniques of Aligning Carbon Nanotubes. Cent. Eur. J. Phys. 2009, 7, 645−653. (13) Shekhar, S.; Stokes, P.; Khondaker, S. I. Ultrahigh Density Alignment of Carbon Nanotube Arrays by Dielectrophoresis. ACS Nano 2011, 5, 1739−1746. (14) Mauter, M. S.; Elimelech, M.; Osuji, C. O. Stable Sequestration of Single-Walled Carbon Nanotubes in Self-Assembled Aqueous Nanopores. J. Am. Chem. Soc. 2012, 134, 3950−3953. (15) Badaire, S.; Zakri, C.; Maugey, M.; Derré, A.; Barisci, J. N.; Wallace, G.; Poulin, P. Liquid Crystals of DNA-Stabilized Carbon Nanotubes. Adv. Mater. 2005, 17, 1673−1676. (16) Dierking, I.; Scalia, G.; Morales, P.; LeClere, D. Aligning and Reorienting Carbon Nanotubes with Nematic Liquid Crystals. Adv. Mater. 2004, 16, 865−869. (17) Jiang, W.; Yu, B.; Liu, W.; Hao, J. Carbon Nanotubes Incorporated within Lyotropic Hexagonal Liquid Crystal Formed in Room-Temperature Ionic Liquids. Langmuir 2007, 23, 8549−8553. (18) Weiss, V.; Thiruvengadathan, R.; Regev, O. Preparation and Characterization of a Carbon Nanotube−Lyotropic Liquid Crystal Composite. Langmuir 2006, 22, 854−856. (19) Xin, X.; Li, H.; Wieczorek, S. A.; Szymborski, T.; Kalwarczyk, E.; Ziebacz, N.; Gorecka, E.; Pociecha, D.; Hołyst, R. Incorporation of Carbon Nanotubes into a Lyotropic Liquid Crystal by Phase 8981

DOI: 10.1021/acs.jpcc.7b01528 J. Phys. Chem. C 2017, 121, 8976−8981