Gelation, Electrical Conductivity and Elasticity of PAM- MWNT
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Gelation, Electrical Conductivity and Elasticity of PAM- MWNT Gulsen A. Evingur1 and Önder Pekcan2 1 2
İstanbul Technical University, 34469, Maslak, İstanbul, TURKEY Kadir Has University, 34320, Cibali, İstanbul, TURKEY
ABSTRACT Polyacrylamide- Multiwalled carbonnanotube (PAM- MWNT) composites were prepared via free radical crosslinking copolymerization with different amounts of MWNT varying in the range between 0.1 and 15 wt. %. PAM- MWNT composite gels were characterized by fluorescence, dielectric spectroscopy and the tensile testing technique. A small content of doped nanotubes dramatically changed gelation time, conductivity and young modulus, respectively. The gel fraction exponent, E of PAM- MWNT composite gels were measured for various monomer and MWNT concentrations and observed that the gel fraction exponent E agrees best with the percolation theory for various amounts of PAM- MWNT. These polymer systems which are initially of an isolator character are doped with carbon nanotubes of nano dimensions and when the amount of this addition exceeds a critical value (0.3 wt. % MWNT) known as the percolation threshold, then composite gel systems with carbon nanotubes become electrically conducting structures with a critical exponent around rൌ2 which is close to the theoretical prediction of this value in 3D percolated system as known random resistor network. The observed elasticities are decreased above 3 wt. %MWNT with critical exponent around y=0.72 which is indicative of a transition from liquid-like to solid-like viscoelastic behavior.
INTRODUCTION Polymer composites with carbon nanotube additions are one of the research subjects which have attracted a lot of attention in recent years. The first polymer nanocomposites using carbon nanotubes as filler were reported in 1994 by Ajayan et al.[1]. Hydrogel- carbon nanotubes (CNT) nanocomposites were demonstrated for potential applications such as sensors and actuators with DC electric field as the stimulus. They are being pursued in sensor applications for the detection of a variety of biomolecules including ethanol, glutamate, and glucose[2]. In this work, the universalities on gelation, electrical conductivity and elasticity of PAMMWNT composites were presented.
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THEORETICAL
Gelation Percolation offers a particularly simple and yet detailed picture through which one may seek to understand gelation [3-5]. In the language of percolation, one may think of monomers as occupying the vertices of a periodic lattice, and the chemical bonds as corresponding to the edges joining these vertices, at any given moment, with some probability p. Then, the gel point can be identified with the percolation threshold pc, where, in the thermodynamic limit, the incipient infinite cluster starts to form. Identifying the weight average degree of polymerization DPW with the average cluster size Sav and the gel fraction G with the probability Pf of an occupied site belonging to the incipient infinite cluster, one can predict the scaling behavior of these and related quantities n
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