Characterization on the Electrical Properties of PDMS Nanocomposites by Conducting Polymer Nanowires
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Characterization on the Electrical Properties of PDMS Nanocomposites by Conducting Polymer Nanowires Ping Du, Xi Lin and Xin Zhang Department of Mechanical Engineering, Boston University, Boston, MA 02215, U.S.A. ABSTRACT Polydimethylsiloxane (PDMS) is one of the most used materials in bio-applications. However, previous works were mainly focus on the mechanical aspect. In this paper we presented a practical and efficient approach to enhance the electrical properties of PDMS by using conducting polymer nanowires (CPNWs). The nanowires were synthesized using template method and added in PDMS to form nanocomposites. The dielectric constants of the composites were characterized by impedance measurements, and the dielectric relaxation behavior and the volume fraction of CPNWs was investigated. Based on the percolation theory a much lower threshold (5.3 vol%) was achieved. INTRODUCTION PDMS plays an essential role in chemical and biological applications due to its optical transparency, mechanical compliance, chemical stability, bio-compatibility, and easy of fabrication [1]. However, being a non-conductive elastomer, PDMS has been limited to a structural material in most applications [2-5]. Hence there is an increasing demand to explore the multifunctionality of PDMS, such as electrical properties, to broaden the range of applications. A common approach is through adding inorganic or organic conductors as fillers to form composites. However, the phase separation of inhomogeneous particles [6] and high percolation threshold for large-sized particles limit the practical applications. Conducting polymer nanowires become a promising filler candidate because of the mechanical flexibility, elongated shape and much lower threshold concentration [7]. In this work, polypyrrole (PPy) nanowires were synthesized and added in PDMS to form the nanocomposites. The enhancement of dielectric constants of the composites was characterized, and the relationship to the volume fraction of CPNWs was investigated based on percolation theory. EXPERIMENT In this work the CPNWs were fabricated using porous membrane as the template [8-10]. Anopore porous alumina membranes (Whatman) with a pore diameter of 200 nm were used, and the electrochemical synthesis was carried out at a constant current density of 1 mA/cm2 (Figure 1(a)). The solution consisted of 0.1 M pyrrole monomer and 0.1 M sodium dodecylbenzene sulfonate (NaDBS, all from Sigma Aldrich). The length of the NWs was controlled by synthesis time. A typical 4 hour synthesis resulted in an average length of 49.12 Pm (Figure 1(b)). After synthesis, the seed layer was etched, followed by etching of the alumina membrane to free the nanowires. Subsequently centrifuge and ultrasonic stirring were applied for several times to replace the etchant solution by ethanol and obtain an evenly distributed CPNW
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dispersion. This dispersion was then mixed with PDMS and thermal cured to form the composites. (a)
(b)
200 nm
S1818 Au/Cu Alumina
60 Pm
PPy
Figure 1. (a) Schematic diagram of CPNW fabrica
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