This grant provides funding for developing a series of chemically-stable conductive polymer nanocomposites (cPNCs) to tackle a central problem, corrosion of conductive metals, facing metallic electronic devices. Two strategies will be carried out. One is to use conductive fillers to make insulating polymers conductive. Two different types of conductive filling materials, soft and hard, in three combinations will be explored. The commercial hard nanofillers will be modified for better compatibility with the polymer matrix. The conductive polymer soft nanofillers (particle and fiber) and conductive polymer coated particles will be fabricated. The other strategy is to use the doped conductive polymer as the hosting matrix. The nanofillers will introduce the desired functionalities. Different filler shapes will be utilized to disentangle the intrinsic properties of the cPNCs. The fundamental science of the project will involve developing composites preparation techniques, manipulating the component and structure of the nanofillers and their surface characterization, disclosing the properties under static and dynamic conditions, and correlating their properties to the intrinsic structure especially under mechanical dynamic situation. The dynamic performance of the cPNCs will be predicted from the percolation theory under different mechanical deformation conditions and compared with experimental results.
If successful, the results of this research will make a significant impact to the rapidly developing field of polymer-based conductive nanostructural materials. The cPNCs either from combining different conductive nanofillers into insulating polymer or from utilizing the conductive polymer matrix bring prospects of organic-based devices with reduced weight density, increased integration, and multi-functionality. The collaboration with industries will facilitate the possible commercialization of the newly developed cPNCs. The results of the proposed work will create many noteworthy opportunities for education and training. The education of underrepresented groups will be highly emphasized during this project. K-12 education, curriculum development, and international outreach will also be established and improved.
This 3-year project supports the PIs and the team to study the conductive polymer nanocomposites (PNCs) with different nanofillers including soft and hard materials. The soft fillers include conductive polyaniline and polypyrrole. And the hard nanofillers include the magnetic iron oxides, silica and silicon. The combined soft and hard nanofillers include the core-shell structural nanofillers were studied for nanofillers. The researchers have systematically studied all the nanofillers and some major discoveries with detailed examples are provided: Example 1: with soft nanofillers. For the liquid epoxy nanosuspensions with both fibril and spherical polypyrrole (PPy) nanostructures, a stronger PPy nanofibers/epoxy interaction and more temperature stable behavior with a lower flow activation energy of nanosuspensions with nanofibers (54.34 kJ/mol) than that with nanopsheres (71.15 kJ/mol) were revealed by the rheological studies. Except the common enhancing mechanism of limiting crack propagation in the polymer matrix, the nanofibers further initiated the shear bands in the epoxy resin to give a higher tensile strength (90.36 MPa) than that of pure epoxy (70.03 MPa) and even that of the epoxy nanocomposites with nanospheres (84.53 MPa). The real permittivity was observed to increase with increasing the PPy nanofiller loading, and the enhanced permittivity was interpreted by interfacial polarization. The filler shape effect on the mechanical properties is illustrated in Figure 1. Example 2: with hard nanofillers. (A) Carbon coated iron (Fe@C) nanoparticles have successfully served as nanofillers for obtaining magnetic epoxy resin PNCs. A reduced viscosity was observed in 1.0 wt% Fe@C/epoxy resin liquid suspension samples and the viscosity was increased with further increasing the Fe@C loading. The dynamic storage and loss modulii were studied together with the glass transition temperature (Tg) being obtained from the peak of tand. Enhanced storage modulus was observed in the PNCs with 20.0 wt% Fe@C nanoparticles. The percolation thresholds of the Fe@C nanoparticles were identified with the study of tensile strength and electrical conductivity, and due to the cavities initiated by the nanoparticles, the PNCs with 5.0 wt% Fe@C nanoparticles showed an increased tensile strength up to 60% compared with pure epoxy. The Fe@C nanofillers could efficiently increase the electrical conductivity of the epoxy matrix, and the particle chain observed in the SEM image of fracture surface indicated the formation of percolated Fe@C nanoparticles in the epoxy matrix. Finally, the Fe@C nanoparticles become magnetically harder after dispersing in epoxy due to the decreased interparticle dipolar interaction. Figure 2(A) illustrates the detailed effect of these core-shell type nanofillers. (B) Graphene nanosheets coated with iron nanoparticles Magnetic grapheme (Gr) nanocomposites (Gr nanosheets coated with iron core iron oxide shell nanoparticles, named Gr/Fe@Fe2O3) have successfully served as nanofillers for obtaining magnetic epoxy resin PNCs to be compared with the nanocomposites with pure grapheme. A reduced viscosity was also observed in 1.0 wt% Gr–epoxy resin liquid nanosuspensions. In the TGA test, although the introduction of both nanofillers caused lower onset decomposition temperature of the PNCs, the Gr/Fe@Fe2O3 was found to favor the char formation from the epoxy resin. The enhanced char residue was also observed during the flammability tests. The dynamic storage and loss modulii were studied together with the glass transition temperature (Tg) obtained from the peak of tand. The tensile strength observed in the PNCs with 1.0 wt% Gr/Fe@Fe2O3 is 58% higher than that of the pure epoxy, and was attributed to the high stiffness of Gr. Both nanofillers could increase the electrical conductivity of the epoxy matrix. The magnetic properties of the PNCs with Gr/Fe@Fe2O3 are studied and the value of Hc is observed inversely proportional to the loading of Gr/Fe@Fe2O3 in the PNCs. Figure 2(B) illustrates the detailed effect of these protruding nanoparticles on the graphene nanosheets. Example 3: with soft coating on the hard nanofillers. The new function of PPy to serve as a coupling agent has been demonstrated in preparing conductive epoxy resin nanocomposites with PPy coating on the magnetite (f-Fe3O4) nanoparticles. Compared with pure epoxy suspension, a reduced viscosity was observed in epoxy nanosuspensions with 5.0 wt% f-Fe3O4 nanoparticles, and the viscosity increased with further increasing the f-Fe3O4 nanoparticle loading. The increased glass transition temperature (Tg) and enhanced mechanical tensile strength were observed in the cured solid epoxy PNCs with f-Fe3O4 nanoparticles. The volume resistivity of the PNCs with 30.0 wt% f-Fe3O4 nanoparticles was decreased almost 7 orders of magnitude compared with the cured pure epoxy (1.6×1013 ? cm). The PNCs exhibited good magnetic properties. The synergism between the nanofillers and the hosting epoxy matrix has been disclosed with detailed examples. The results have been published involving graduates, undergraduates and researchers/professors from outside institute and would have generated broad impact. In the future, the highly conductive polymers, and the property compatibility between the doped acid and the used curing agent will be needed for further pursuing to enhance the electricity and other properties.
