Macroscopic objects such as fibers and films formed from a combination of nanocarbon materials and polymers have promising electrical [1], thermal [2], thermoelectric [3], and mechanical [4] properties. In particular, composites of nanocarbon and conductive polymers revealed that they can constitute key parts of batteries [1] and thermoelectric generators [3]. In literature, it is possible to find many synthesis methods of this type of material. One of the most common approaches is electrochemical, wherein monomers are polymerized onto the nanocarbon surface due to its highly conducting nature [5]. Polyaniline (PANI) is the oldest and still one of the most popular conductive polymers used in this area. That is because PANI is relatively simple to manufacture at low cost and effort. Moreover, it has good mechanical strength and tunable electrical conductivity, which depend on the kind of PANI. This polymer has three forms: pernigraniline – fully oxidized (purpure/red), emeraldine – partially oxidized (blue/violet), and leucoemeraldine – fully reduced (black) [6]. Emeraldine achieves the highest conductivity when doped with Brøstead acids such as HCl, H₂SO_4, HBF₄ [7].

The goal of this study was to exploit the phenomenon of the hydrophilic surface of carbon nanostructure caused by thermal annealing, described by us previously [8], to electropolymerize aniline onto free-standing films from nanocarbon. The films were manufactured by the wet method [8] using single-walled nanotubes (SWCNTs) exclusively and SWCNTs/graphene nanoplatelet composite. Electropolymerization was used to synthesize PANI on the surface of these materials. To establish the parameters of synthesis of different forms of PANI, voltage ranges between [(-1.6 V) – (1.6 V)] were investigated. The films were tested as a counter and a working electrode in this process. After the synthesis, the composites were investigated by optical and Scanning Electron Microscopy, Raman spectroscopy, Atomic Force Microscopy. Moreover, water contact angles, electrical conductivity values, and Seebeck coefficients were determined. Composites containing all three PANI forms have been synthesized and thoroughly analyzed to elucidate the structure-property relations. Consequently, correlations between the forms of PANI and the characteristics of nanocomposites were established. Depending on the amount and type of PANI on the surface, the character of the nanocarbon films was affected considerably. For example, coating of the material with emeraldine salts enhanced the electrical conductivity of the films by about 60% [9], while simultaneously making the material much stronger.

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[2] Z. Duan, Y. Luo, Z. Luo, W. Yu, C. Liu, S. Fan, The influence of charging and discharging on the thermal properties of a carbon nanotube/polyaniline nanocomposite electrode, RSC Adv. 9 (2019) 7629–7634. doi:10.1039/C9RA00151D.

[3] R. Wu, H. Yuan, C. Liu, J. Le Lan, X. Yang, Y.H. Lin, Flexible PANI/SWCNT thermoelectric films with ultrahigh electrical conductivity, RSC Adv. 8 (2018) 26011–26019. doi:10.1039/c8ra04863k.

[4] M.R. Saeb, P. Zarrintaj, Polyaniline/graphene-based nanocomposites, Fundam. Emerg. Appl. Polyaniline. (2019) 165–175. doi:10.1016/B978-0-12-817915-4.00010-5.

[5] C. Oueiny, S. Berlioz, F.X. Perrin, Carbon nanotube–polyaniline composites, Prog. Polym. Sci. 39 (2014) 707–748. doi:10.1016/J.PROGPOLYMSCI.2013.08.009.

[6] S.C. Rasmussen, The Early History of Polyaniline: Discovery and Origins, An Int. J. Hist. Chem. Subst. 1 (2017) 99–109. doi:10.13128/substantia-30.

[7] Q. Qin, Y. Guo, Preparation and characterization of nano-polyaniline film on ITO conductive glass by electrochemical polymerization, J. Nanomater. 2012 (2012). doi:10.1155/2012/519674.

[8] D. Janas, G. Stando, Unexpectedly strong hydrophilic character of free-standing thin films from carbon nanotubes, Sci. Rep. 7 (2017) 12274. doi:10.1038/s41598-017-12443-y.

[9] G.Stando, P. Stando, P. Chulkin, M. Salhman, M. Lundström, D. Janas, Electropolymerization of aniline onto hydrophilic nanocarbon films (in preparation)

G.S. and P.S. would like to thank the Ministry of Science and Higher Education of Poland for financial support of research (under Diamond Grant, grant agreement 0036/DIA/201948). G.S. also would like to thank European Union for thanks for financing the costs of the conference (European Social Fund, grant nr POWR.03.05.00-00-Z305) and National Agency for Academic Exchange of Poland (under the Iwanowska program, grant agreement PPN/IWA/2019/1/00017/UO/00001) for financial support during the stay at the University of Pittsburgh in the USA. G.S. and H.L. acknowledge NSF (CBET-2028826) for partial support of this work. P. S. acknowledges the National Agency for Academic Exchange of Poland (under the Academic International Partnerships program, grant agreement PPI/APM/2018/1/00004) for supporting training in the Aalto University. G.S, P.S and D.J. would like to thank the National Centre for Research and Development, Poland (under the Leader program, grant agreement LIDER/0001/L-8/16/NCBR/2017).