The Electroactive Materials Characterization group research focuses on processing-microstructure-property relationships in smart materials with the goal of developing new materials with unique combinations of mechanical, electrical, and coupled properties for uses that range from advanced electronic devices and autonomous system concepts to the aerospace, automotive, medical and consumer industries. The main research thrusts of the group are active polymers and polymer nanocomposites; processing and characterization of polymer nanocomposites.
Active polymers and polymer nanocomposites
Nanotechnology offers opportunities to reenergize the area of smart materials by addressing current shortfalls and expanding the scope of available material space. For example, by following the nanocomposite route, one can address current state-of-the-art challenges in smart materials such as high actuation voltage, low electromechanical coupling coefficients and low blocked stress. For this reason, a large part of the group research effort is concerned with elucidating critical aspects of the resulting nanostructured materials to determine limitations of nanoparticle-based enhancement of performance and to enable novel sensing, actuation and energy harvesting. Through the group’s work, we have shown that nanoparticles (NPs) interact strongly with polar functional groups in polymers. The direct implication is that presence of NPs enhances the piezoelectric response and leads to improved performance of polymeric sensors and actuators. Our research goals include:
- Developing robust sensing, actuation, and energy harvesting constitutive relationships for active nanocomposites;
- Determining limitations of nanoparticle-based enhancement of performance;
- Enabling integration in future system design.
Processing and characterization of polymer nanocomposites
We are taking a path toward realizing these advanced nanocomposites in the design of engineered materials by probing the link between control of nanoparticle (NP) distribution and resulting properties and performance. Through controlled dispersion of NPs, such as ceramic nanopowders, graphene platelets, carbon nanofibers, oxide nanotubes and carbon nanotubes, we have shown that property enhancements are not limited to just mechanical and electrical responses. We have identified potential challenges that our future work must address, among which include:
- Controlling NP dispersion and distribution;
- Maintaining composite processibility with addition of NPs;
- Elucidating NP-polymer interaction;
- Relating anisotropy in physical properties to NP distribution.
Our efforts have resulted in developing fundamental understanding of the dispersion of the nanoparticles, and characterization methodologies that span from the nano to macro length scales. Our investigations in response to these challenges promise to increase our understandings of the mechanisms involved, particularly as related to NP-polymer interaction and to develop correlations to properties and how processing can lead to unique microstructures and performance. Our increased understandings, in turn, would allow us to tailor the polymer nanocomposites to yield desired performance in terms of low actuation voltage, high electroactive strain, and improved response time (by modifying dipole moiety, NP content, and NP distribution, for example). We have shown that the presence of NPs affect polymer morphology, where nanoclays and carbon nanotubes enhance the formation of the polar beta phase in PVDF. We have also shown that NPs interact strongly with polar functional groups in polymers. The direct implication of such interaction is that the presence of NPs enhances the piezoelectric response and leads to improved performance of polymeric sensors and actuators. More recently, we have developed a methodology to manipulate and pattern nanotubes and nanofibers in polymers using electrokinetic interactions with dramatic changes in electrical and stress coupling. We are also focusing our attention on the development of experimental and analytical methodologies to determine the materials parameters that affect E-field alignment of NPs in polymers. By optimizing NP alignment, we have determined that the anisotropy of physical properties parallels that of morphology—a big step closer to our goal of spatially engineering and designing nano-composite material systems for prescribed performances. An important outcome of this work is that it will help establish a tool set for control of nanoparticle distribution, hence moving the community from nano-filled systems with random morphology to spatially engineered and designed nano-composite material systems.
Characterization of polymer nanocomposites includes mechanical, electrical and dielectric measurements through Dynamic Mechanical Analysis (DMA) and dielectric spectroscopy. Their morphology is also studied through X-Ray measurements, Polarized Light Microscopy, Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR).
