Improvement of Adhesion and Continuity of Polypyrrole Thin Films Through Surface Modification of Hydrophobic Substrates Namita Dutta Gupta, 1 Swati Das, 1 Nirmalya Sankar Das, 2 Diptonil Banerjee, 2 Debabrata Sarkar, 1 Kalyan Kumar Chattopadhyay 1,2 1 Thin Films and Nanoscience Laboratory, Department of Physics, Jadavpur University, Kolkata 700032, India 2 School of Material Science and Nanotechnology, Jadavpur University, Kolkata 700032, India Correspondence to: K. K. Chattopadhyay (E - mail: kalyan_chattopadhyay@yahoo.com) ABSTRACT: Conducting polymer polypyrrole is reported to have a poor adhesion to substrate which limits its applicability as thin films. In this article, we report synthesis of well-formed and continuous film of polypyrrole through treatment of hydropho- bic substrates. However, in place of the widely used organosilanes, the substrates were simply treated with surfactant cetyl trime- thylammonium bromide (CTAB) prior to vapor phase polymerization under controlled environment. Polypyrrole films formed on CTAB pretreated substrates were found to have improved adhesion and continuity compared to the films formed on untreated substrates. The improved adhesion results in better electronic properties as seen during Electron field emission studies. Based on contact angle analysis, we propose that CTAB molecules act as anchoring agents for the oxidant layer on the substrate and hence assist in the deposition of a more continuous polypyrrole film. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. Appl. Polym. Sci. 2014, 131, 39771. KEYWORDS: coatings; conducting polymers; surfactants Received 9 April 2013; accepted 15 July 2013 DOI: 10.1002/app.39771 INTRODUCTION Conducting polymers such as polypyrrole (PPy) have been extensively studied for their unique physical and chemical prop- erties and hence diverse application in various fields such as organic electronic devices, 1 chemical and biological sensors, 2 and electromagnetic shielding applications. 3 For novel device applications, it is desirable to synthesize PPy as thin films, on flexible hydrophobic substrates like PET (Polyethylene tereph- thalate), polyester, and other different fabrics. Thin films of PPy are usually prepared by chemical process (and a subsequent process such as spin coating) or by electrochemical method, both the methods being in liquid phase. 4–6 In addition to these two processes, a new method of polymerization of pyrrole monomers on the substrate surface, directly from vapor phase has also been recently reported. 7–10 This technique has a lot of advantages over the other method of deposition of PPy. For example, in liquid phase, the presence of a transport medium increases the probability of particle agglomeration. In vapor phase, however, such probability does not exist and hence the use of dispersants or stabilizers is not necessary. Moreover, in vapor phase, polymerization can occur in different types of sub- strates in contrast to electrochemical method, where only con- ducting substrates can be used. One of the major obstacles for PPy film formation is the poor adhesion of PPy molecules to the substrate surface. 11 Though polymerization of pyrrole does not depend on the substrate, the polarity of the substrates has an important bearing on the adhe- sion of the polymer. The adhesion is worse for substrates with- out polar groups. 12 In order to overcome the problem of adhesion, the substrate surface is usually pretreated with an adhesive promoter layer, such as different types of organosi- lanes 13,14 or polymer (PVA and PFO) containing oxidants 10,15,16 before exposing to pyrrole vapors. These adhesion promoter molecules are appropriately functionalized organic molecules which allow anchoring of the polymer molecules on the sub- strate surface. For example, the adhesion promoter molecules like 3-((pyrrol-1yl) propyl trimethoxysilane, 17,18 6-(pyrrol-1-yl)- n-hexyl trichlorosilane, 19 and other pyrrole substituted organo- silane monolayers 20,21 consist of an adhesive group to the substrate, an alkyl spacer, and a terminal pyrrole group, 22 the last acting as nucleation sites of PPy films with good adhesion. Many authors have also proposed plasma treatment of the sub- strates as an alternative to increase the adhesion between the substrate and conducting polymer. 23–25 Plasma modification is reported to increase the wettability of the substrate due to increase of their surface energy. V C 2013 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2014, DOI: 10.1002/APP.39771 39771 (1 of 10)