Self Assembly in Biologically Synthesized Electrospun Electroactive Polymers
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Self Assembly in Biologically Synthesized Electrospun Electroactive Polymers A. Bishop and P. Gouma Materials Science and Engineering - 314 Old Engineering SUNY Stony Brook University Stony Brook NY, 11794 ABSTRACT The processing parameters of polyaniline (PANI) dictate the desired morphology and overall structural stability of the deposited polymer for biological and chemical sensor applications. Electrospun composites of leucoemeraldine based PANI (LEB-PANI) has exhibited effective separation of aggregates inherent in LEB-PANI powder as a result of charge separation induced on the composite matrix during electrospinning. However it appears the encapsulation of biologicals (enzyme-Urease E.C.3.5.1.5) in the electrospun matrix intensifies the self assembly process. An investigation of the changes in morphology as an effect of electrospinning and enzyme immobilization is discussed. INTRODUCTION Due to its stability and the nature of its charge transfer mechanisms, polyaniline has been exploited for applications ranging from organic batteries to sensing. In recent years correlations between processing conditions and PANI morphology have been addressed. It has been well established that the oxidation state of PANI dictates its chemical and electronic nature. Oxidation states of PANI range from leucoemeraldine to emeraldine to pernigraniline (or emeraldine salt). These states represent the insulating, semiconducting, and fully conducting forms of polyaniline respectively [1]. In the past decade it has been observed that PANI particles may self-assimilate as a consequence of synthesis. Angelopoulos et. al. observed that interchain interactions between amine (benzenoid) and imine (quinoid) nitrogen centers were the basis of aggregation in the emeraldine base form. [2]. Hydrogen bonds formed along the backbone of PANI, at nitrogen sites, supported the interchain reactions and thus promotes assembly of PANI particles. Moreover the authors noted that as the oxidation state of PANI was reduced the aggregation yield also diminished. LEB-PANI is the reduced form of polyaniline, amorphous, and insulating. In essence, due to lack of imine centers it is not supposed to endure aggregation because H-bonding between the amine centers is not energetically favorable [2]. Further processing conditions are carried out on polymerized PANI to create a system apt for various applications. Electrospinning is a technique employable for processing polyaniline mats. Charged PANI films constructed using this process may inhibit the self-assembly mechanism. The intensity of the charges on both the fibrous jet and electrospun mat [3-4] may be high enough to overcome the hydrogen bonds formed along the PANI backbone that trigger self assembly. Moreover, appropriate selection of a base polymer may also promote de-aggregation. Polymeric stabilizers such as poly-
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vinyl-pyrrolidone (PVP) [5] can be absorbed on the surface of PANI forming a solvated steric barrier around PANI particles preventing aggregation [6]. This res
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