4.6. Multifunctional Materials and Their Impact on Sustainability
Multifunctional materials are the materials that perform multiple functions in a system due to their specific properties. Multifunctional materials can be both naturally existing and specially engineered.
For example, some traditional materials that provide, for instance, high mechanical strength can be modified at the nanoscale to attain other properties such as energy absorption, self-healing, etc. The applications of such new "smart" materials include energy, medicine, nanoelectronics, aerospace, defense, semiconductor, and other industries.
Numerous examples of multifunctional materials can be found in nature. Bio-materials routinely contain sensing, healing, actuation, and other functions built into the primary structures of an organism. For example, the human skin consists of many layers of cells, each of which contains oil and perspiration glands, sensory receptors, hair follicles, blood vessels, and other components with functions other than providing the basic structure and protection for the internal organs. Through biological evolution, these structures were seamlessly integrated into the body to serve their functions (Nemat-Naser et al., 2005).
The ability for materials to respond to their environment in a useful manner has broad technological impact. Such "smart" systems are being developed in which material properties (such as optical, electrical, or mechanical characteristics) respond to external stimuli. Materials of this kind have tremendous potential to impact new system performance by reducing size, weight, cost, power consumption, and complexity while improving efficiency, safety, and versatility. The multifunctionality of materials often occurs at scales from nano through macro and on various temporal and compositional levels (Nemat-Nasser et al., 2005).
Innovative advanced materials make a direct and positive impact on economic growth, the environment, and quality of life. They allow for improved processes and products and create several avenues to increasing sustainability.
Note the following areas of impact:
- reducing environmental effects
- increasing efficiency of processes
- lightening the weight of products
- lowering power consumption
- reducing system size
- reducing system weight
- reducing system cost
- reducing complexity
- increasing safety
- increasing fuel flexibility
- increasing versatility
Most of these impacts may result in higher efficiency of the system and cost savings.
Examples of advanced materials studies
The following are several examples of sustainable solutions through improved materials chemistry or using alterative innovative materials.
A. Power-generating structural composites
"Researchers at ITN Energy Systems and SRI International have integrated a power-generating function into ﬁber-reinforced composites. Individual ﬁbers are coated with cathodic, electrolytic, and anodic layers to create a battery. The use of the surface area of ﬁbers as opposed to that of a foil in a thin ﬁlm battery allows greater energy outputs, measured on the order of 50 Wh/kg in a carbon ﬁber-reinforced epoxy laminate. These batteries may be deposited on various substrates, including glass, carbon, and metallic ﬁbers."
Source: Nemat-Nasser, S., et al., Multifunctional Materials, Figure 12.2. in Biomimetics: Biologically Inspired Technologies, Bar-Cohen, Y., Ed., CRC Press, 2005. (This book is available online through the Penn State Library system.)
B. Thermostructural materials for gas turbines
Gas turbines are a core technology in aero-propulsion and industrial power generation. Technological progress in this area depends on advances in thermo-structural materials. The requirements to reduce emissions, increase fuel flexibility, and resist environmental attack call for development of new material systems with multifunctional properties. University of California Santa Barbara researchers employ a holistic approach that embraces and integrates all critical aspects of materials technology, including alloys, coatings, and composites, processing, and simulations to create the thermostructural materials that combine mechanical strength and exceptional thermal stability. Materials issues relevant to the high-pressure turbine include higher temperature single crystal alloys that act in concert with coatings, advanced bond coat alloys for environmental protection with improved thermo-chemical and thermo-mechanical compatibility with the load-bearing alloy, and thermal barrier oxides with new compositions that enhance temperature capabilities. Ceramic matrix composites (CMCs) and associated environmental barrier coatings are also incorporated in next generation engines, especially for combustors.
C. Nanoparticle assembly using DNA strands
"Scientists at the U.S. Department of Energy's Brookhaven National Laboratory have developed a general approach for combining different types of nanoparticles to produce large-scale composite materials with special properties. The approach takes advantage of the attractive pairing of complementary strands of synthetic DNA—based on the molecule that carries the genetic code in its sequence of matched bases known by the letters A, T, G, and C. After coating the nanoparticles with a chemically standardized "construction platform" and adding extender molecules to which DNA can easily bind, the scientists attach complementary lab-designed DNA strands to the two different kinds of nanoparticles they want to link up. The natural pairing of the matching strands then "self-assembles" the particles into a three-dimensional array consisting of billions of particles. Varying the length of the DNA linkers, their surface density on particles, and other factors gives scientists the ability to control and optimize different types of newly formed materials and their properties."
Source: Brookhaven National Laboratory
D. Organic batteries provide better recyclability
A typical battery consists of two electrodes - anode and cathode, electrolyte layer, separator, and current collectors. Most of traditional battery technologies use metals or metal oxides as electrode-active materials, and metals are not renewable resources. This study describes the use of organic materials as electrodes. The advantage of such organic-based batteries over Li-ion batteries in terms of sustainability is improved recyclability, safety, adaptability to wet fabrication process, and extraction of starting material from less limited resources. One recently developed type of organic battery is based on organic radical polymers - "aliphatic or nonconjugated redox polymers with organic robust radical pendant groups as the redox site". The organic batteries have lower energy density compared to Li-ion technology, but this limitation is expected to be overcome in the near future.
Source: Anastas, P.T., Zimmerman, J.B., Innovations in Green Chemistry and Green Engineering, Chapter 8, pp. 235-246. Springer 2013. (This book is available online through the Penn State Library system.)