Room temperature self-healing and recyclable conductive composites for flexible electronic devices based on imine reversible covalent bond

https://doi.org/10.1016/j.jallcom.2021.162433Get rights and content

Highlights

  • Room temperature self-healing and recyclable conductive composites based on imine reversible covalent bond.

  • The composites have excellent room temperature self-healing properties, mechanical strength and the electrical resistivity.

  • The composites can be recovered by solution recovery and hot pressing.

Abstract

With the development of flexible electronic devices, various requirements for flexible conductive materials have been put forward to. However, the self-healing, mechanical and conductive properties of the flexible materials are poor. Therefore, it is important to prepare self-healing materials with good mechanical and conductive properties. In this paper, room temperature self-healing and conductive composites based on imine reversible covalent bond were prepare by introducing of the carbon nanotube and carbon black. The self-healing, mechanical and conductive properties of the composites were studied. And the structure of the composites was also characterized. The experimental results showed that the mechanical strength and the electrical resistivity of composites were 6.6 MPa and 108 Ω·m, respectively. The composites have excellent room temperature self-healing properties through the reversible exchange of imine bond, and the healing efficiency of mechanical properties and the electrical properties can reach 96% and 93%, respectively. At the same time, the self-healing mechanism was put forward to. In addition, the composites can be recovered by solution recovery and hot pressing.

Introduction

Polymer material is widely used in the automotive industry, energy, aviation, electronics and other fields, due to its excellent mechanical properties, biocompatibility and processing properties [1], [2]. With the development of flexible electronic devices, many conductive flexible materials have been developed. To this end, many researchers have done a lot of work to improve the conductivity of polymer material. Conductive polymer nanocomposites are composite multiphase systems with unique conductive properties, which are formed by mixing conductive nano-fillers into insulating polyurethane matrix in a certain proportion to form a uniformly distributed continuous conductive network. Conductive polymer nanocomposites have many excellent properties. For example, the electrical and mechanical properties of the materials can be controlled by changing the content, type and matrix properties of the conductive fillers, or by physical or chemical modification of the conductive fillers [3], [4], [5], [6], [7]. It has been widely used in anti-static [8], [9], electro-magnetic shielding [10], [11], [12], [13], [14], [15], [16], [17], strain sensor [18], [19], temperature control sensor [20], [21] and volatile organic gas monitoring [22], [23] and other fields. Generally, the electrical conductivity of polymer material is obtained by adding conductive fillers to the polyurethane matrix. Conductive filler can be mainly divided into two kinds, one of them is inorganic filler, mainly refers to metal [24], metal oxides [25] and carbon materials, another one is conductive polymer such as polyaniline. And carbon materials include graphene [26], carbon nanotubes [27], carbon black [28], carbon fiber [29], etc.

But conductive flexible polymer can be easily damaged, the development of new-generation materials that can repair damages on themselves to restore the electrical conductivity as well as mechanical properties has drawn more and more attentions because materials with self-healing capacity not only can significantly decrease maintenance costs and make the materials safer, longer lasting, more durable, and reliable during usage, but can effectively reduce the severely detrimental influence on resource consumption and environmental pollution [30], [31], [32]. Therefore, self-healing materials are widely used in various fields, such as biomedicine, electronic sensing, and artificial skin [33], [34], [35]. Kim S. M. et al. prepared a transparent and easily processable thermoplastic polyurethane (TPU) with the highest reported tensile strength and toughness (6.8 MPa and 26.9 MJ*m−3, respectively), This TPU can conveniently heal within 2 h through facile aromatic disulfide metathesis engineered by hard segment embedded aromatic disulfides. And the film has potential applications in the wearable electronics industry [34]. The healing of intrinsic healable materials mainly relies on non-covalent interactions and dynamic covalent interactions. In the last decade or so, many kinds of non-covalent interactions were applied in self-healing materials, such as hydrogen bonding [36], [37], host-guest interaction [38], metal-ligand coordination [39], π-π stacking [40], and other supramolecular interaction. Dynamic covalent interactions have bigger bond energy than non-covalent interactions, theoretically the self-healing materials with dynamic covalent interactions theoretically have better self-healing efficiency. In recent years, a lot of dynamic covalent interactions self-healing materials based on disulfide bonds [41], Schiff base [42], boroxine bond [43], cycloaddition reactions [44] and so on were reported. Pepels et al. prepared a self-healing gel containing disulfide bonds according to the reaction of pentaerythritol tetra-3-mercaptodiacid and polysulfide groups. The gel system can achieve multiple self-healing under mild conditions [45]. Peng Wang et al. reported a self-healing transparent polydimethylsiloxane elastomer based on imine bonds. The polydimethylsiloxane elastomer can repair damages in 6 h at room temperature [46]. Guadagno, L et al. prepared a self-healing conductive composite based on Reversible Hydrogen Bonds (RHB), different percentages of rubber phase covalently linked to the epoxy precursor, and functionalized multiwalled carbon nanotubes (MWCNTs) were added to the composites [47]. Wang HM et al. reported a conductive self-healing film, the electrical and mechanical self-healing of the film is derived from the electrical reconnection of carbon nanotubes and transesterification-induced topology change of the network, respectively. And they further demonstrated soft actuators and high-performance supercapacitors based on the prepared self-healing conducting films [48].

However, there are two problems need to be solved for self-healing materials. Firstly, materials used to make reversible covalent bonds are expensive. Secondly, the tensile strength of most self-healing materials is very weak, especially for the polymers with room-temperature self-healing capacities. It is usually a trade-off between excellent mechanical properties and efficient self-healing ability because the healing of intrinsic self-healable materials strongly relies on the high mobility of polymer chains and high-reversible dynamic cross-linkages [49]. In order to reduce the cost of materials, imine bonds are used as reversible covalent bonds because of the low cost of raw materials (terephthalaldehyde and diamine). Conductive nanomaterials can not only improve the mechanical strength of self-healing materials but also make them conductive, it’s an effective method to make self-healing materials have more practical uses.

Because of its high aspect ratio, high strength and modulus, CNT can be used as an excellent polymer reinforcement additive. When the load applied to the composite material can be effectively transferred to CNT, the composite material will obtain very good mechanical properties, such as high strength and modulus. Load transfer depends on the interfacial interaction between CNT and polymer matrix, and high interfacial shear stress can achieve effective load transfer in a short distance. There are three mechanisms of load transfer from matrix to CNT, the first is micromechanical interlocking between CNT and matrix. Due to the smooth surface of CNT, this method is difficult to achieve; The second is the chemical bond between CNT and matrix, which make a very high interface interaction between CNT and matrix, and effectively transfer load; The third is the van der Waals force interaction between CNT and matrix [50]. As a conductive material, CNT can be used as a conductive agent, and it can be added to the polymer to improve the conductivity of composite materials. The conductivity of CNT can be evaluated by percolation threshold, which is the minimum packing concentration of conductive filler to form a three-dimensional conductive path network in the matrix [51]. The role of carbon black in composites is about the same as that of carbon nanotubes. Because the price of carbon black is much lower than that of carbon nanotubes, carbon black is more used as a conductive filler in industrial production, although its efficiency of improving the electrical conductivity and mechanical properties is lower than that of carbon nanotubes.

Herein, we prepared a conductive self-healing polyurea. Graft modified carbon nanotubes(0.5 wt%) and carbon black(2–10 wt%) were filled into polyurea matrix as the conductive filler. The modified carbon nanotubes can form hydrogen bond with polyurea molecular chain, it can be as a skeleton in the nanocomposite. But the carbon nanotubes are expensive, more and cheaper carbon black were used to improve electrical conductivity and mechanical properties. The imine bond is prepared by the reaction of amino-terminated polyurea prepolymer and terephthalaldehyde. Dynamic reversible imine bonds and hydrogen bonds make the conductive material restore mechanical properties and electrical conductivity after material was damaged. At last, these dynamic interactions within the polyurea also enabled the materials with excellent recycling and reshaping ability by hot-pressing or dissolution/casting process.

Section snippets

Materials

Hexamethylene diisocyanate (HDI, 99%), poly (propylene glycol) bis (2-aminopropyl ether) (PEA, Mn = 400), terephthalaldehyde (TA, 98%), dibutyltin dilaurate (DBTDL, 95%) and propylamine were purchased from Aladdin Chemical Co., Ltd. Tri-methylolpropane tris[poly(propylene glycol), amine terminated] ether (Tri-PEA, Mn = 400) were purchased from Huntsman Chemical Trading (Shanghai) Co., Ltd. Hydroxyl functionalized multi-walled carbon nanotubes (OH-g-MWCNTs, outer diameter: 10–20 nm, length:

Characterization

Carbon nanotubes (CNTs) are widely used in polymer modification due to their excellent mechanical, electrical and thermal properties. But unmodified carbon nanotubes are difficult to disperse in the polymer because of their high specific surface.

Area, π-π stacking effects and high aspect ratio. In order to improve the dispersion of carbon nanotubes in polymers, the MWCNTs was modified with urea groups in this paper. The modified MWCNTs showed better dispersion in solvents, as shown in the Fig.

Conclusion

In summary, we prepared a room temperature self-healing flexible TB-PUI nanocomposite using a simple method. A powerful reversible nanocomposite network is formed through the reversible imine covalent bond and hydrogen bonds. Under the condition of room temperature for 48 h or 60 ℃ for 3 h, the mechanical properties of the self-repair efficiency reached 85%−96%, electrical properties of the self-repair efficiency reached 82%−93%. A small amount of modified carbon tubes and a large amount of

CRediT authorship contribution statement

Jinbiao Min: Investigation, Formal analysis, Data curation, Conceptualization, Validation, Visualization, Methodology, Writing − original draft. Zhaoxi Zhou: Investigation, Data curation, Validation. Qihui Chen: Data curation, Resources. Maochun Hong: Writing − review & editing. Hainan Wang, Heqing Fu: Supervision, Writing − review & editing, Project administration, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We appreciate the financial support from the STS project of Chinese Academy of Sciences and Fujian Province under grant No. 2019T31020029.

References (52)

  • L.H. Wang et al.

    Piezoresistive effect of a carbon nanotube silicone-matrix composite

    Carbon

    (2014)
  • S.D. Zheng et al.

    Investigation on the piezoresistive behavior of high-density polyethylene/carbon black films in the elastic and plastic regimes

    Compos. Sci. Technol.

    (2014)
  • S.P. Bao et al.

    Effect of mechanical stretching on electrical conductivity and positive temperature coefficient characteristics of poly(vinylidene fluoride)/carbon nanofiber composites prepared by non-solvent precipitation

    Carbon

    (2011)
  • S. Isaji et al.

    Electrical conductivity and self-temperature-control heating properties of carbon nanotubes filled polyethylene films

    Polymer

    (2009)
  • K. Dai et al.

    Tuning of liquid sensing performance of conductive carbon black (cb)/polypropylene (pp) composite utilizing a segregated structure

    Compos. Part a-Appl. Sci. Manuf.

    (2013)
  • P. Slobodian et al.

    Multi-wall carbon nanotube networks as potential resistive gas sensors for organic vapor detection

    Carbon

    (2011)
  • M. Eswaran et al.

    One-step preparation of graphitic carbon nitride/polyaniline/palladium nanoparticles based nanohybrid composite modified electrode for efficient methanol electro-oxidation

    Fuel

    (2019)
  • J.R. Lloyd et al.

    Biotechnological synthesis of functional nanomaterials

    Curr. Opin. Biotechnol.

    (2011)
  • A. Schrofel et al.

    Applications of biosynthesized metallic nanoparticles − a review

    Acta Biomater.

    (2014)
  • Y. Konishi et al.

    Direct determination of oxidation state of gold deposits in metal-reducing bacterium shewanella algae using x-ray absorption near-edge structure spectroscopy (xanes)

    J. Biosci. Bioeng.

    (2007)
  • J.H. Yoon et al.

    Highly self-healable and flexible cable-type ph sensors for real-time monitoring of human fluids

    Biosens. Bioelectron.

    (2020)
  • L. Yang et al.

    Diels-alder dynamic crosslinked polyurethane/polydopamine composites with nir triggered self-healing function

    Polym. Chem.

    (2018)
  • P. Wang et al.

    A self-healing transparent polydimethylsiloxane elastomer based on imine bonds

    Eur. Polym. J.

    (2020)
  • W.Z. Tang et al.

    Melt processing and mechanical property characterization of multi-walled carbon nanotube/high density polyethylene (mwnt/hdpe) composite films

    Carbon

    (2003)
  • T. McNally et al.

    Polyethylene multiwalled carbon nanotube composites

    Polymer

    (2005)
  • T.K. Das et al.

    Review on conducting polymers and their applications

    Polym. -Plast. Technol. Eng.

    (2012)
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