2023 Research Article Received: 21 November 2013 Revised: 25 February 2014 Accepted article published: 7 May 2014 Published online in Wiley Online Library: 10 June 2014 (wileyonlinelibrary.com) DOI 10.1002/pi.4756 Core – shell polypyrrole nanoparticles obtained by atmospheric pressure plasma polymerization Miguelina Vasquez-Ortega, a Mauricio Ortega, a Juan Morales, b M Guadalupe Olayo, c Guillermo J Cruz c and Roberto Olayo b* Abstract Polypyrrole hollow nanoparticles were prepared by atmospheric pressure plasma polymerization. The structure of the nanopar- ticles was studied using Fourier transform infrared and X-ray photoelectron spectroscopies, thermogravimetric analysis, scan- ning and transmission electron microscopies and atomic force microscopy. In contrast to low-pressure plasma polymerization of pyrrole, which can produce films and solid nanoparticles, we obtained two types of hollow nanoparticles: a fraction with sin- gle spherical core and another with a core composed of small bubbles. Thermal characterization allowed us to determine that the nanoparticles are composed of highly crosslinked polymer. A mechanism that explains the formation of both types of hol- low nanoparticles as well as solid nanoparticles is proposed. Chemical characterization shows that, in addition to the expected chemical structures due to pyrrole polymerization, the high energy of the plasma at atmospheric pressure produces intense dehydrogenation and oxidation processes. The fluorescence spectrum of the nanoparticles, however, shows a peak at 482 nm indicating that some degree of -conjugation is present in the material. © 2014 Society of Chemical Industry Keywords: core – shell; plasma polymerization; nanoparticles; fluorescence; polypyrrole INTRODUCTION When particles are of the order of nanometers in diameter, their high surface area and small size increase the possibilities of their application. Hollow nanoparticles are especially interesting due to their possible use in drug delivery and waste removal among other applications. 1 – 3 Polypyrrole (PPy) has been widely explored as a shell material in core–shell nanoparticles due to its electrical conductivity and biocompatibility properties. 4 Hol- low PPy particles have been prepared by multistep templating procedures using Au, 2,5 SiO 2 , 3,6,7 AgCl, 8 Fe 2 O 3 , 9 and polystyrene particles 10 as templates. Similarly, PPy hollow spheres con- taining silica nanoparticles inside have been prepared using SiO 2 @polystyrene@PPy core–double-shell particles followed by removal of the polystyrene intermediate shell. 11 The main disad- vantage of templating methods is their use of sacrificial materials which adds to the cost of hollow nanoparticle preparation. An alternative method for the production of nanoparticles is plasma polymerization. 12 This technique is free of organic solvents and environmentally friendly. Nanoparticles prepared by plasma polymerization are generally synthesized in a low-pressure reactor introducing the monomer as a vapor which ionizes in the reac- tor chamber and polymerizes via complex mechanisms. 13,14 Poly- mers produced by plasma polymerization are not as chemically regular as conventional polymers, but are rich in functional groups which may be useful as chemical anchors or to facilitate interac- tions with other materials including biological media. For example, our group has shown that the surfaces of PPy films prepared by plasma polymerization have a diversity of functional groups such as primary amine, small aliphatic chain, carbonyl and hydroxyl groups. 15 – 17 The concentration of functional groups on the sur- face can be tuned by changing the plasma polymerization pro- cess variables. 15 Because of this richness in functional groups, PPy prepared by plasma polymerization can interact with various cell types allowing their anchorage, differentiation and proliferation, 18 and has been shown to even promote regeneration. 19 Recently, we reported the preparation of iodine-doped PPy nanoparticles by plasma polymerization with chemical function- ality diversity similar to that of thin films. 14 Also, Yang et al. 20 have reported the fabrication of PPy nanoparticles in atmospheric plasma. These nanoparticles, however, did not have the same chemical functionality due to the low residence time of the mate- rial in the plasma, but they showed fluorescence which suggests that the milder conditions used in the synthesis reduces the ∗ Correspondence to: Roberto Olayo, Departamento de Física, Área de Polímeros, Universidad Autónoma Metropolitana, Unidad Iztapalapa, Av. San Rafael Atlixco 186, Col, Vicentina, CP 09340, DF, México. E-mail: oagr@xanum.uam.mx a Departamento de Ingeniería Eléctrica, Sección de Electrónica del Estado Sólido, Centro de Investigación y Estudios Avanzados del Instituto Politécnico Nacional, Av. Instituto Politécnico Nacional 2508, Col, San Pedro Zacatenco, CP 07360, DF, México b Departamento de Física, Área de Polímeros, Universidad Autónoma Metropoli- tana, Unidad Iztapalapa, Av. San Rafael Atlixco 186, Col, Vicentina, CP 09340, DF, México c Departamento de Física, Instituto Nacional de Investigaciones Nucleares, Km. 36.5 Carretera México-Toluca, Ocoyoacac, Edo. Mex, CP 52750, México Polym Int 2014; 63: 2023–2029 www.soci.org © 2014 Society of Chemical Industry