Investigation of polyaniline-based microwave absorbing nanocomposites

Microwave absorbing properties of polyaniline-based nanocomposites in polyurethane matrix were studied. Measurements of absorbing properties were performed in the broad frequency range from 8 to 36 GHz in a waveguide system. Metal-backed samples exhibit a reflectivity about -30 dl3. Results obtained show that microwave absorbing properties can be tuned easily with mass fraction of nanocomposite in the matrix. Conjugated polymers, especially polyaniline and its derivatives, have a variety of potential application in microwave absorbing materials [ 11. Polyaniline and polyaniline-based composites are inexpensive to produce, relatively lightweight, corrosion-resistant and exhibit good adhesion and environmental stability. Aside from their superior properties relative to traditional microwave absorbing materials, the ability to tailor the properties offers the flexibility required in the design of high-loss materials and multilayer structures. We have developed methods of synthesis of polyaniline-based nanocomposites with low concentration of structural inhomogeneities. The composites were synthesized by chemical oxidative polymerization of aniline on dispersible centers such as carbon black, silicates, clays and graphite. The dc conductivity of samples is in the range from 1 to 10 Ohm-lcm-l. Materials for microwave measurements were prepared by blending composites with an elastomer (polyurethane) and other polymeric matrices with different mass fraction (lo%, 20%, 30%, 40%). Structures obtained are stable porous, flexible sheets with good adhesion. All reflection measurements were obtained from samples backed with a metallic plate. Measurements were camed out in a rectangular waveguides over broad frequency band (8-36 GHz) Fig.l shows the dependency of reflectance (in dB) on the concentration of nanocomposite in the matrix. The broadening of the reflection peak is attributed to the high dielectric loss of the composite inclusions. It can also be seen in Figure 1 that the increase of the concentration shifts the peak towards lower frequencies.