Controlling the Morphology of Poly(N-cyanoethylpyrrole) Georgina Fabregat, †,‡ Carlos Alema ́ n,* ,†,‡ Maria T. Casas, † and Elaine Armelin* ,†,‡ † Departament d’Enginyeria Química, ETSEIB, Universitat Polite ̀ cnica de Catalunya, Av. Diagonal 647, 08028, Barcelona, Spain ‡ Center for Research in Nano-Engineering, Universitat Polite ̀ cnica de Catalunya, Campus Sud, Edifici C’, C/Pasqual i Vila s/n, Barcelona E-08028, Spain * S Supporting Information ABSTRACT: The morphology of poly(N-cyanoethylpyrrole) has been controlled through the polymerization process. This polymer has been prepared by anodic polymerization, chemical oxidative polymerization in emulsion medium, and layer-by-layer templating polymerization. Anodic polymerization using LiClO 4 as supporting electrolyte provides compact films, in which the oxidation degree is controlled through the thickness, useful for the microdetection of dopamine. Chemical polymerization using FeCl 3 as oxidant agent results in very well-defined microspheres with porous internal structure, which may be useful in molecular loading and transport processes. Finally, the layer-by-layer templating technique produces core-shell particles of controlled size and thickness. Moreover, these core-shell particles can be easily converted in hollow microspheres by removing the template. ■ INTRODUCTION Many of the nanostructured materials currently under develop- ment draw their inspiration from the structures found in nature. 1-3 Highly sophisticated morphologies and functions have been achieved using supramolecular architectures of polymer structures. 4 Within this context, micro- and nano- structures based on conducting polymers (CPs) is a field of current interest. CPs are a class of important materials with many potential applications because of their low density, large specific area, high stability and surface permeability, and good electrochemical properties. In general, the structure of CPs is moderately affected by the experimental conditions used in the polymerization process. For example, the roughness, regularity, and porosity of the spongy morphology of electrochemically produced poly(3,4- ethylenedioxythiophene), an extensively studied CP with very important technological applications, 5,6 are known to depend on factors such as the applied potential, polymerization time (i.e., the thickness of the sample), the solvent, the supporting electrolyte that acts as doping agent, and the substrate used for polymer deposition. 7-13 Much higher variability can be obtained using an alternative synthetic process based on templates. These approaches are typically described as the one- step electrochemical generation of CP in a solid substrate assisted by a solid or soft template mechanism. Thus, the generation of CP micro- and nanostructures can be carried out using solid templates with well-defined shapes (e.g., porous alumina membranes or polystyrene colloidal nanoparticles) limiting the size of the materials, 14,15 or “soft” templates formed by assemblies of molecules (e.g., surfactants and gases). 16,17 This approach has been used to prepare microspheres, microcrocks, microbowls, microbarrels, micropunpkins, micro- bottles, and microdoughnuts of polypyrrole and poly(N- methylpyrrole), abbreviated PPy and PNMPy, respec- tively. 18-23 In this work, we show how to exert a drastic control on the structure and morphology of poly(N-cyanoethylpyrrole), here- after abbreviated PNCPy (Scheme 1), through the polymer- ization method. More specifically, we report the very different morphologies and microstructures found for this material when it is prepared by anodic polymerization, oxidative polymer- ization in emulsion medium, and layer-by-layer (LbL) templating technique. PNCPy was found to be highly sensitive to dopamine, presenting a very fast and effective response even when the concentration of such neurotransmitter is of 100 μM only (i.e., the concentration of dopamine in the synaptic region is 1.6 mM). 24 However, despite such promising biomedical application, the number of studies devoted to examine the structure of this CP is very scarce. Thus, although PNCPy has been obtained and characterized using anodic polymerization Received: January 26, 2012 Revised: March 16, 2012 Published: April 13, 2012 Scheme 1 Article pubs.acs.org/JPCB © 2012 American Chemical Society 5064 dx.doi.org/10.1021/jp3008688 | J. Phys. Chem. B 2012, 116, 5064-5070