Investigation of Polyetherimide Melt-Extruded Fibers Modified by Carbon Nanoparticles

The fibers based on thermoplastic partially crystalline polyetherimide R-BAPB modified by vapor grown carbon nanofibers (VGCF) were prepared by melt extrusion, exposed to orientational drawing, and crystallized. All of the samples were examined by scanning electron microscopy, X-ray scattering, and differential scanning calorimetry to study how the carbon nanofiller influences on the internal structure and crystallization behavior of the obtained R-BAPB fibers. The mechanical properties of the composite R-BAPB fibers were also determined. It was found that VGCF nanoparticles introduced into R-BAPB polyimide can act as a nucleating agent that leads, in turn, to significant changes in the composite fibers morphology as well as thermal and mechanical characteristics. VGCF are able to improve an orientation degree of the R-BAPB macromolecules along the fiber direction, accelerate crystallization rate of the polymer, and enhance the fiber stability during crystallization process.

Changes in Electrical Conductance of Polymer Composites Melts Due to Carbon Nanofiller Particles Migration

In this work, the results of investigation of the effect of polymer composite melts electrical conductance increase with time are presented. The conductance time dependencies were obtained for composites based on polypropylene filled with carbon nanoparticles of different types. The dependencies were analyzed to demonstrate the possibility of correlation of the conductance kinetics with different composite parameters, such as the filler geometry. Additional studies were carried out, such as electron microscopy study, conductance measurements after consecutive surface layer removal, and composite melt conductance measurements using a three-electrode scheme. The results showed that the increased electrical conductance of the composite materials can be attributed to the formation of an enriched with the filler particles surface layer, which happens during the stay of the composite in a melt state. Analysis of the experimental data, along with the results of numerical modeling, allowed to suggest a possible filler distribution transformation scheme. The physical premises behind the investigated effect are discussed.

A computational exploration of the effect of alignment and aspect ratio on alternating current conductivity in carbon nanofiber–modified epoxy

Carbon nanofiller–modified polymers have been the subject of intense study for years due to their potential use in diverse and far-reaching applications. The effect of nanofiller network parameters on macroscale direct current electrical transport has been thoroughly elucidated by extensive nano-to-microscale modeling. As a result, we now have great insight into how the conductive and piezoresistive properties of nanocomposites can be tailored through judicious control of the underlying nanofiller network. It is also well-known that carbon nanofiller–modified polymers possess frequency-dependent alternating current electrical properties. Even though work has been done to understand the alternating current properties of nanocomposites via experimental characterization and through the development of macroscale equivalent circuit models, much less has been done to understand how macroscale alternating current conductivity depends on microscale effects such as nanofiller alignment and aspect ratio. This is an important knowledge gap because, like direct current conductivity, the underlying nanofiller network ultimately gives rise to macroscale alternating current transport in these materials. To this end, we herein present an alternating current microscale percolation model for carbon filler–based polymer nanocomposites. After calibration against experimental complex impedance data from randomly ordered carbon nanofiber–modified epoxy, this model is used to explore the effect of carbon nanofiber alignment and aspect ratio on alternating current conductivity. These simulations show that alternating current conductivity generally increases with increasing alignment and with aspect ratio; however, the competing effects of alternating current and direct current percolation give rise to substantial variation in alternating current conductivity at low frequencies and with poor percolation. The methodology presented in this article provides a modeling tool by which nanocomposites with highly optimized alternating current properties can be developed through careful control and tailoring of nanofiller network properties for the realization of exotic, next-generation material functionality.

Cyclic piezoresistive effect in poly(dimethylsiloxane)/carbon nanofiber composites for large strain Sensing applications

Adding conductive one-dimensional carbon nanomaterials to poly(dimethysiloxane) can form bio-compatible composites with significant electromechanical (piezoresistive) response. This effect can be effectively tuned by controlling the carbon nanofiller size, concentration, and distribution. However, to be applied as strain sensors, the composite material has to meet mechanical, sensitivity, temperature stability, and reliability requirements. Here we report on the study of cyclic electromechanical behaviors of poly(dimethysiloxane)/carbon nanofiber composites under different temperatures. Through mechanical training, reproducible and sensitive piezoresistive response suitable for large strain sensing can be obtained.