Spherical Molecular Containers of Polypyrrole: From Discovery to Design to Drug Delivery Applications
S. Gupta, R.. Patel and E. Bohannan
University of Missouri, US
Conducting polymers, nanostructures, templateless, electrochemistry
Polypyrrole (PPy) in the family of -conjugated (or conducting) polymers is a potential candidate for building microscopic actuators, electrochromic devices, and recently as scaffolds for bio-implants and drug delivery systems. We present a controlled synthesis of polypyrrole nano/micro-containers by electro-generated H2 gas bubbles which act as template and their structural characterizations thus gaining an insight into the growth kinetics. The discovery of using gas bubbles to designing supramolecular architects is unique as it is template-free and dubbed as bubblology. We have used electrochemical technique to polymerize pyrrole onto stainless steel substrates from electrolytes (organic solvent, supporting electrolyte, and monomer) in a single compartment three-electrode cell on the polished stainless steel substrates as working and counter/auxiliary electrode. The reference electrode was a standard Ag/AgCl (saturated calomel electrode). Three different solutions were utilized: i) 0.25 M pyrrole and 0.4 M NaClO3 (sodium chlorate, 99% min ii) 0.25 M pyrrole and 0.4 M NaClO4 (sodium perchlorate, 99% min and iii) 0.25 M pyrrole and 0.4 M b-NSA (2-Naphthalenesulfonic acid, sodium salt 95%). While NaClO3 and NaClO4 act as an electrolyte, the b-NSA functions as an electrolyte and surfactant as well. Experimental results show that surfactant-mediated growth under controlled electrochemical biasing led to synthesis of micro/nanostructures ascribed to electrochemical polymerization of pyrrole around micelles. Depending upon the electrochemical conditions such as potential window, number of cycles, and scan rate, different types of structures were formed and the shapes of which were revealed using scanning electron microscopy. The films consisted of spherical globules, cup/bowl-like containers, which became lantern-like with increasing number of cycles. Their diameter and room temperature conductivity were ranged 50–2000 nm and 1–50 S cm-1, respectively. Analyses of these films were complemented with Raman spectroscopy to identify the oxidized PPy, polaron, and bipolarons besides XRD, HRTEM, XPS, and electrochemical impedance techniques to establish process-structure-property relationship. Their applications in tissue engineering and drug delivery will be discussed.
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Nanotech 2007 Conference Program Abstract