Multifunctional super-aligned carbon nanotube/polyimide composite film heaters and actuators

doi:10.1016/j.carbon.2018.08.011

Carbon

Volume 139, November 2018, Pages 1136-1143

https://doi.org/10.1016/j.carbon.2018.08.011 Get rights and content

Abstract

Polyimide (PI) is a high-performance polymer with ultrahigh heat stability while carbon nanotube (CNT) possesses high mechanical strength, excellent electrical and thermal conductivity. Here we report a facile and low-cost method free from CNT pre-dispersion for fabricating super-aligned carbon nanotube (SACNT)/PI composite film which combines the advantages of both SACNT and PI. Flexible and scratch-resistant composite film with high CNT content, uniform dispersion of CNTs, and controlled patterned CNT structures can be fabricated easily via in situ imidization. The SACNT/PI composite film exhibits improvement in mechanical strength, Young's modulus, electrical conductivity compared with pristine PI, and shows good thermal stability. Thanks to these superb properties, a flexible, stable, addressable, electromagnetic wave permeable, and high-temperature fast-response multifunctional heater as well as a thermo-mechanical actuator based on SACNT/PI composite film have been demonstrated in this paper. And it also shows great potential in a variety of applications such as flexible/wearable electronics, RFID, other thermo-related devices and so on.

Graphical abstract

Introduction

Carbon nanotube (CNT) has been stimulating great interests since the report by Sumio Iijima in 1991 [1]. Because of its unique physical properties such as flexibility, light weight, high mechanical strength, excellent electrical and thermal conductivity, CNT is believed to be an ideal material to improve the performance of polymers [[2], [3], [4], [5]]. Among the diverse polymer materials, polyimide (PI) possesses ultrahigh thermal stability (with a glass transition temperature ranging from 248 °C to 446 °C), resistance to radiation and solvent, as well as excellent mechanical and dielectric properties [[6], [7], [8], [9]]. It has been found that the CNT/PI film's properties can be improved by combining the extraordinary properties of CNT and PI together. For instance, 5 wt% of CNTs can improve the electrical conductivity of CNT/PI composite by 12 orders of magnitude [10], and the tensile strength by 40% compared with pristine PI [11]. The combination of high mechanical strength, ultrahigh flexibility, light weight, high thermal stability, and good electrical conductivity can meet the demands of applications in many fields ranging from microelectronics to aeronautics and astronautics.

A variety of methods for CNT/polymer composites have been developed including solution blending [[12], [13], [14], [15], [16]], melt blending [17,18] and buckypaper polymerization [19,20]. These traditional methods require pre-dispersion of CNTs in which case CNT content and dispersion uniformity are limited due to the large viscosity of resin, which restricts the performance of composites and increases the complexity of fabrication process. Based on the solution blending method, efforts have been made to improve the fabrication process. Dual-material aerosol jet printing method was developed to fabricate smart nanocomposite with tailorable and controllable intra-part varying CNT loading [21]. Inkjet printing method (directly printing the carbon nanotube polyimide suspension on a flexible polyimide substrate) was used to generate patterned electrical conductive nanocomposite thin films [22]. A three-dimensional porous PI/CNT composite aerogels were formed by freeze-drying method [23]. These methods still need the pre-dispersion of CNTs and are not environmentally friendly. Therefore, it is still a challenge to simultaneously achieve high content, uniform dispersion, and orientation-controlled patterning of CNTs in composite films with a low-cost method. CNT/PI composites with high CNT fraction and high degree orientation were fabricated by infiltration-winding method [24]. Super-aligned CNT (SACNT) film is ultrathin, transparent, flexible, stretchable, and highly conductive, which is a suitable candidate for fabricating composite since the CNTs are parallel-aligned and uniformly distributed in it [[25], [26], [27]]. Moreover, the SACNT film can be patterned simply by laser cutting [28], which enables flexible and scratch-resistant composite films with controlled patterned CNT structures.

Here we report a facile and low-cost fabrication method for SACNT/PI composite, which shows improved properties and great potential for a wide range of applications. Several thermo-related applications such as serving as a heater and an actuator have been demonstrated in this paper. Commercial PI film heater is usually made by copper foil or nickel-chromium alloy plate electrodes embedded in PI film. Compared with it, SACNT/PI composite film heater we develop has the advantages of low cost, simple fabrication process, fitting more closely together with heated objects, being freely cut after being fabricated and other special functions such as high-temperature fast response, controllability under PID unit, addressability and RF permeability. Besides, SACNT/PI composite film can work as actuators, showing its potential application in soft robots. It is expected that more and more applications of SACNT/PI composite film will be developed in the future.

Section snippets

Synthesis of Poly(amic acid) (PAA)

2.0024 g of ODA (10 mmol) is placed in a three-neck flask containing 30.68 mL of anhydrous DMAc under nitrogen purge at room temperature. After ODA is completed dissolved in DMAc, 2.1812 g of PMDA (10 mmol) is added in one portion. Thus, the solid content of the solution is ∼12%. The mixture is stirred at room temperature under nitrogen purge for 12 h to produce a viscous PAA solution. The viscosity of the resultant PAA estimated from Cone Plate Viscometer is 7046 cp.

SACNT/PI composite preparation

We have used the XPS

Morphology and structure characterization

Microscopic morphology and structure of SACNT/PI composite film are characterized by scanning electron microscope (SEM, FEI Nova Nano 450), focused ion beam-scanning electron microscope (FIB-SEM, FEI Helios G4 CX) and atom force microscope (AFM, Seiko SPA 300HV). The surface morphology of SACNT/PI composite film (shown in Fig. 1e) clearly demonstrates that CNTs distribute uniformly on the surface. However, after gold-plating on the surface of sample, CNTs are almost invisible, as shown in Fig. 1

Conclusion

In this paper, SACNT/PI composite films with high content of well-dispersed and orientation-controlled patterned CNT structures are obtained via a simple approach without prior CNT dispersion. Not only can the self-dispersed and self-supported SACNT films simplify the preparing of composite film, but also they can work as patterned transparent electrically and thermally conductive networks to improve the properties of composite film. The SACNT/PI composite film exhibits improvement in

Acknowledgements

This work is financially supported by the NSFC (51727805, 51672152, 51472141), the National Basic Research Program of China (2014CB643604), The National Key Research and Development Program of China (2017YFA0205800). This work is supported in part by the Beijing Advanced Innovation Center for Future Chip (ICFC).

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Citation Excerpt :
Carbon-based nanostructures, such as carbon nanotubes (CNTs) and graphene, have also drawn wide interest owing to their flexibility and excellent electrical conductivity. Flexible heaters based on CNT/polyimide composites (Ning et al., 2018), CNT-heaters prepared on PET substrates (Liu et al., 2011), washable graphene papers (Guo et al., 2017), and stretchable graphene-based heaters (Zhang et al., 2020) are just a few examples. Generally poor processability of carbon nanostructures in aqueous media, weak bonding to common flexible substrates, and poor device-level electrical conductivity owing to large junction resistance and defects, however, have hampered their adoption.
The emergence of wearable devices over the recent decades has motivated numerous studies aimed at developing flexible or stretchable materials and structures for their electronic or optoelectronic functionalities. Like in conventional devices, electronic and optoelectronic components in wearable devices must be kept within certain temperature ranges to ensure reliability, performance, and/or functionality. But this must be accomplished without requiring any bulky heat sinks or other heat transfer augmentation elements. At the same time, the proximity of wearable devices to the human skin poses additional requirements of thermal comfort and safety. A growing body of literature is now focusing on the thermal management or control of wearable devices and related development of new materials and structures. The present article aims to provide a broad overview of such materials and structures and offer suggestions for future research directions.

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¹: These authors contributed equally to this work.

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Multifunctional super-aligned carbon nanotube/polyimide composite film heaters and actuators

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of Poly(amic acid) (PAA)

SACNT/PI composite preparation

Morphology and structure characterization

Conclusion

Acknowledgements

Curr. Opin. Solid State Mater. Sci.

Carbon

Polymer

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

Compos. Sci. Technol.

Polymer

Prog. Polym. Sci.

Adv. Colloid Interface Sci.

Compos. B Eng.

Mater. Res. Bull.

Compos. Appl. Sci. Manuf.

Carbon

Compos. Sci. Technol.

Compos. Sci. Technol.

Carbon

Carbon

Prog. Solid State Chem.

Helical microtubules of graphitic carbon

Nature