Polymer Nanocomposite Materials. Группа авторов

Чтение книги онлайн.

Figure 2.2 (a, b) The PEO/DNA nanofiber webs containing 5% DNA-dispersed DWNTs. (c) Stress–strain curves for nanofiber webs of pure PEO, PEO/DNA, and PEO/DNA/DWNT. Source: (a)–(c) Reproduced with permission. [57] Copyright 2013, American Chemical Society.

      2.2.3 In Situ Polymerization

      In situ polymerization was firstly proposed by Imai et al. where polyimide (PI)/CB composite was obtained by dispersing the CB into the polymer salt monomer [66]. In fact, this is a unique solution based processing technology for preparing the CPCs, and chemical reaction is usually involved during the polymerization [67, 68]. The efficient polymer-chain graft onto the filler surface could form a perfect interface interaction between the filler and polymer matrices, which also improves the homogeneous dispersion of the fillers in the polymer matrix and influences the crystallization of polymer chains to some extent [69–71]. As a result, CPCs with a high weight content of the nanofillers can be obtained by this method [69, 72].

      Zhu and coworkers prepared reduced graphene oxide (r-GO)/PI composites with different loadings of GO by in situ polymerization and the maximum content of GO can reach 30 wt%. During polymerization, a relatively high temperature was set to reduce GO into conductive r-GO in the polymer matrix. The electrical property of the obtained r-GO/PI was greatly enhanced, because of the conductive network formed by r-GO in the composite film and the conductivity could reach as high as 1.1 × 10¹ S m⁻¹, which is about 10¹⁴ times that of pure PI film [73]. The mechanical properties of GO/PMMA composites fabricated by in situ polymerization were also tested by Potts et al. [74]. It is found that the elastic modulus and tensile strength of the GO/PMMA composites could be improved even with 1 wt% loading of fillers.

2.3 Morphologies

      Different fabrication techniques may lead to different morphologies of conductive networks in CPCs, which significantly influence the electrical properties of these composites [30]. Various morphologies including uniform dispersion of nanofiller in the polymer matrix, segregated structure, and selective decoration of the nanofiller on the skeleton of porous polymer materials are reported [75].

      2.3.1 Random Dispersion of Nanofiller in the Polymer Matrix

The most straightforward and popular strategy to fabricate CPCs is the incorporation of conductive fillers (e.g. graphene, CNTs) in the polymer matrix by either melting or solution method. Naturally, the nanofillers are randomly located in the polymer matrix, and some of them may be squeezed out to polymer surface in particular at a high filler concentration [76]. The nanofillers can be uniformly distributed in the fibers, film, and three-dimensional polymer materials, depending on the processing technology used. Wet-spinning [77, 78] and electrospinning [75, 79] are two most common means to prepare one dimensional CPCs. Yu et al. [80] have successfully prepared conductive poly(styrenebutadiene-styrene) (SBS)/CNT fiber through wet-spinning the mixed solution of CNT and SBS elastomer. The schematic diagram of the fabrication procedure of SBS/CNT and the pictures of flexible SBS composite with different content of CNTs are shown in Figure 2.3a. Figure 2.3b–d show the SEM micrographs of fracture SBS/CNT fibers with a content of 0.5%, 0.75%, and 1%, respectively. Uniformly dispersed CNTs in SBS matrix can be observed even at a CNT content of 1%. Also, the conductivity of the obtained 1-D conductive fiber composite improves with the increase of CNT content (Figure 2.3e).