Electric-Field-Induced Nonlinear Conduction Behavior Of Unsaturated Polyester Resin/Hcl-Doped Polyaniline Conducting Composites

In this study, Percolative behavior, reversible nonlinear conduction behavior and irreversible nonlinear conduction behavior of unsaturated polyester resin (UPR)/HCl-doped polyaniline (HCl-PANI) conducting composites have been primarily investigated and percolative behavior and reversible nonlinear conduction behavior in UPR/HCl-PANI conducting composites have been preliminarily compared with ones in EPR/GN conducting composites.UPR/HCl-PANI conducting composites have been fabricated via in-situ polymerization with the application of ultrasonic irradiation. Empirical method and excluded volume theory are applied to explain the critical volume fraction (percolation threshold: Pc = 27.83%) and the latter can interpret this critical volume fraction better. The simulated value of the conductivity critical exponent is not accordance with classical percolation theory but can be well explained by tunneling conduction theory. Furthermore, preliminary studies on the influence of HCl-PANI on the thermal stability of the host (unsaturated polyester resin) have been performed.Nonlinear conduction behavior of UPR/HCl-PANI conducting composites close to percolation threshold from above under application of electric field has been investigated. Nonlinear conductance measurement as a function of electric field has been made. All samples show the nonlinear conduction behavior. Experimental results exhibit that the crossover current Ic at which nonlinear conduction process occurs scales with the linear conductanceΣ1 as Ic ~Σ1x, with x≈1.20, and the second-order conductance,Σ2, also scales withΣ1 asΣ2 ~Σ1y, with y≈0.99. Through analysis of j-E curves, it is true that two classical models, nonlinear random resistor network model (NLRRN) and dynamic random resistor network model (DRRN), cannot fully explain the nonlinear current-voltage characteristics in present case and thus four categories of conduction processes and their combinations are examined.EPR/GN conducting composites with a low percolation threshold, owing to particular geometry of GN with the high aspect ratio, were fabricated. The nonlinear conduction behavior of EPR/GN conducting composites close to percolation threshold from above by the action of variable DC electrical field was investigated. For specimens, the current density or current reduces with decreasing graphite nanosheets concentrations and the J-E curves are well fitted by a cubic term, J =σ1 E +σ3 E 3. Moreover, the crossover current density Jc, at which nonlinearity takes place, scales with the linear conductivityσ1 as Jc ~σ1x, with x≈1.390. And the third-order conductivity,σ3, also scales with Jc as Jc ~σ3y, with y≈1.175. Through the discussion of the nonlinearity within the framework of two theoretical models, the nonlinear random resistor network (NLRRN) and the dynamic random resistor network (DRRN), it is indicated that neither of these two models can fully explain our experimental results. Taking into account the microscopic structures and conduction processes of the composites, it is likely that a combination of these two models may explain the nonlinear characteristics better. Furthermore, percolative behavior and reversible nonlinear conduction behavior of UPR/HCl-PANI conducting composites by way of in-situ polymerization with the application of ultrasonic irradiation have been in contrast with EPR/GN conducting composites by way of the same in-situ polymerization with the application of ultrasonic irradiation.The irreversibly nonlinear behavior of UPR/HCl-PANI conducting composites under applied voltage was investigated. A specimen suffers breakdown when the field is too large. It is found that the crossover voltage U R= R0where resistance of the specimen is restored to the linear or zero-field resistance scales with the linear or zero-field resistance as a power law R = R0 ~ R0y, with y0≈0.420 and the breakdown voltage Ub scales with the linear or zero-field resistance as a power law Ub ~ R0yb, with yb≈0.422. The latter is consistent with modeling the breakdown process in terms of hot spots (singly connected bonds, SCBs) within errors. It is also discovered that the ratio of the breakdown resistance to the zero-field resistance assumes a fixed value Y = Rb/R0≈4.00 at breakdown whether under transient or stable electrical breakdown measurement. This fixed value, Y, is independent of HCl-PANI fraction but depends on the intrinsic nature of the conducting filler.