Liquid-crystalline PANI

It is likely that stiffening of chains is a result of two effects. The first effect is due to electronic delocalization and the second to counterion crowding. The second effect has been discussed in detail in Section IV. The importance of the second effect was confirmed in Ref. 43 by dissolving PANi in concentrated sulfuric acid (which is of significantly smaller size). Electronic delocalization should be the same for both acids, but the crowding effect for CSA is higher. The existence of liquid crystalline PANi(CSA) solutions indicates a rodlike conformation of the polymer chains. 

Cao and coworkers reported that problems in processing of doped PANi could be solved by the use of functionalized protonic acids. Indeed, solutions of camphor-sulfonic acid doped with PANi in m-cresol show liquid crystallinity and high electrical conductivity, according to Smith and his coworkers. This prompted additional work with this and other polymers. Unfortunately, the conductivity of cast films of solutions of polypyrrole (PPy) doped with dodecyl benzene sulfonic acid in m-cresol is low (ca. 10 S/cm). 

Using a y-irradiation technique, hexagonal PANI nanoparticles have been prepared in the hexagonal lyotropic liquid crystalline phases of a non-ionic and biodegradable surfactant alkyl polyglucoside (GP215 CS UP) in water and/or medium and long chain alkanes, used as a template [421]. 

There are no reports about PANI composites with oxides of silver and gold because of the high redox reactivity of these oxides (e.g., Ag O and Au O can oxidize PANI), while PANI composites with copper oxides are known. Electrodeposition of mesoporous bilayers of PANI supported Cu O semiconducting films from lyotropic liquid crystalline phase has recently been reported by Xue et al. [16]. The control of size, morphology, and conductivity of PANI nanofibers (PANI-NFs) in PANI-NFs/CuO nanocomposites (Figure 2.1) was achieved by systematic variation of CuO loadings during the oxidative polymerization of aniline with mixture of oxidants [ammonium peroxydisulfate (APS) and sodium hypochlorite] in an acidic aqueous solution [17]. 

Till date, liquid-crystalline phases [51], colloidal particles [52], and structure-directing molecules [53[ as the soft-template have been employed to synthesize PANI nanostructures. Based on the traditional synthesis method of PANI, in particular, some simple approaches such as interfacial polymerization [54], mixed reactions [55], dilute polymerization [56] and ultrasonic irradiation [57] have also been employed to synthesize PANI. The interfacial polymerization method only allows the oxidative polymerization of aniline to take place at the interface of the organic/water phases and the product directly enters into the water phase, which could facilitate environmentally friendly processing. 

Electrical conductivity measurements have been reported on a wide range of polymers including carbon nanofibre reinforced HOPE [52], carbon black filled LDPE-ethylene methyl acrylate composites [28], carbon black filled HDPE [53], carbon black reinforced PP [27], talc filled PP [54], copper particle modified epoxy resins [55], epoxy and epoxy-haematite nanorod composites [56], polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) blends [57], polyacrylonitrile based carbon fibre/PC composites [58], PC/MnCli composite films [59], titanocene polyester derivatives of terephthalic acid [60], lithium trifluoromethane sulfonamide doped PS-block-polyethylene oxide (PEO) copolymers [61], boron containing PVA derived ceramic organic semiconductors [62], sodium lanthanum tetrafluoride complexed with PEO [63], PC, acrylonitrile butadiene [64], blends of polyethylene dioxythiophene/ polystyrene sulfonate, PVC and PEO [65], EVA copolymer/carbon fibre conductive composites [66], carbon nanofibre modified thermotropic liquid crystalline polymers [67], PPY [68], PPY/PP/montmorillonite composites [69], carbon fibre reinforced PDMS-PPY composites [29], PANI [70], epoxy resin/PANI dodecylbenzene sulfonic acid blends [71], PANI/PA 6,6 composites [72], carbon fibre EVA composites [66], HDPE carbon fibre nanocomposites [52] and PPS [73]. 

Amphiphilic behavior is related to conducting polymers and to mesomorphic polymers for several reasons. First, doping of PANi with surfactant molecules has been found to induce liquid crystallinity. Second, alkylation of semiflexible conducting polymers (PT and PANi) favors the formation of layered structures. Third, both rigid and flexible macromolecules with alkyl side chains may be considered as diphilic, in which case lyotropic behavior is to be expected. In the next section examples of mesomorphism and structural organization for macromolecules with flexible side groups will be given. 

Figure 2.20 Tunneling current vs. bias voltage for PANI nanoneedles (from Table of Contents of Reference 399). (Reprinted with permission from ACS Nano, Liquid/liquid Interfacial Polymerization to grow Single Crystalline Nanoneedles of Various Conducting Polymers by N. Nuraje, K. Su, N.-l. Yang and H. Matsui, 2, 3, 502-506. Copyright (2008) American Chemical Society)...

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