4
Challenges
INTRODUCTION
The chemical sciences provide the underpinnings for most, if not all advanced technologies that we use today. Fundamental chemical sciences research creates the infrastructure that supports technologies that are key to the health and well-being of our communities. Just as our current research efforts are built on the knowledge gained by our predecessors, tomorrow’s innovations will be based on today’s research. (Sidebar 4.1).
MAJOR RESEARCH CHALLENGES
Fundamental chemical science research efforts can be linked to several areas that can immediately be seen to impact each individual, namely, water, energy, food, and air. Coupled to these necessities, development of chemistry to address environmental concerns is a significant grand challenge. As the standard of living improves worldwide, environmental concerns in developing nations grow proportionately. Chemistry could provide the means to decouple environmental impacts from this growth in the standard of living. Examples of areas in which the chemical sciences research can play a role include the following:
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Allocation of diminishing resources
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Remediation of existing environmental problems
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Finding or developing replacements for strategic materials
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Decentralization of power supplies
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SIDEBAR 4.1 Turning Lead into Golda The dream of making valuable things from cheap ones dates back thousands of years and has lost none of its appeal in modern times. Many important advances in modern materials science can be described in such terms, and many can be traced to new methods of chemical synthesis and new methods of catalyzing chemical change. A half-century ago, Karl Ziegler in Germany discovered a Ti/Al catalyst and Giulio Natta in Italy found that it could convert cheap, gaseous ethylene or propylene into valuable solid materials that are now made in quantities of billions of pounds per year. More recently, revolutionary advances in transition metal chemistry have made the olefin metathesis reaction—previously unpredictable and difficult to control—an important route to valuable polymers and specialty chemicals. New developments in controlled free-radical chemistry are providing new routes to specialty polymers, with commercial impact just a few years away. In all of these examples, the ability of chemists to devise new catalysts has been essential. Biocatalysis—especially catalysis by protein enzymes—has long been a special source of inspiration for chemists, since living systems routinely accomplish difficult chemical reactions under the mildest of conditions. An especially exciting recent development is the possibility of engineering these systems to perform reactions that do not occur naturally. Chemists are already developing synthetic schemes that exploit the power and selectivity of natural enzymes, but result in materials that could never be obtained in a direct means from nature. One of the most appealing aspects of using biocatalysis is the prospect of making materials that are not only tough and durable, but also carry information. We’re already good at the first part—we can make bulletproof vests—but we’re a long way from encoding the human ge |
For instance, research in the chemical sciences is critical to the development of new materials technologies that might enable affordable clean energy. This could be accomplished through the design and development of a high-capacity reversible energy storage medium or the identification and development of alternative energy sources. Chemistry is unquestionably critical to the development of photovoltaics and hydrogen-based fuel cells. In the area of nuclear energy, it is also chemistry that must lead in the design of new processes for improved handling of nuclear wastes.
Another issue related to the environment is the development and implementation of sustainable routes to materials and the development of new recyclable and biodegradable materials. In addition, the concepts of energy and materials
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nome into a piece of plastic. Macromolecular systems (systems that consist of long molecular chains) have the capacity to carry information at very high density and to read information in and back out. DNA works by encoding information in the sequence of its monomeric building blocks. An important challenge for chemistry is to devise synthetic materials systems that can carry information at high density. Exciting progress has been made in recent years in devising molecular systems that can serve as switches and thereby move us toward information storage at the molecular level. There’s a long way to go before this approach will be practical, but the early signs are encouraging. Still another way to create valuable materials systems from inexpensive building blocks is to “teach” them how to sense their environment and respond to it in some useful fashion. Such systems are often described as “smart” materials (a term that by analogy would make the information-laden systems discussed above into “educated” materials). In a recent development of this kind, an inexpensive epoxy matrix was engineered to carry microcapsules filled with a healing agent.b As a crack propagates through the matrix, the microcapsules open and mix the healing agent with a catalyst, causing rapid polymerization in the crack. Materials of this kind regain most of their initial toughness, without any “active” repair, following fracture. Such “self-healing” materials might add greatly to the safety of transportation and other systems that are subject to catastrophic materials failure. |
efficiency must be pervasive. The use of toxic materials and the emission of harmful materials must be minimized to the greatest extent possible.
The efficient use of limited natural resources must be maximized. It is only through the application of fundamental principles and insights of the chemical sciences that environmentally benign materials and applicable manufacturing process technologies can be developed.
A major research challenge in materials chemistry is to create new materials utilizing the insights obtained by studying biological structures. Could cells and biomolecules be functionally integrated into materials? As a first step, we must understand how to both spatially and temporally control chemical systems. We are just beginning to understand how molecules self-assemble on short-length
scales. This understanding must be extended to appreciate how to design molecules and facilitate self-assembly on a macroscopic scale. Such spatial and temporal control of chemical systems might enable one to envisage and build a multifunction sensor in just one step.
The concept of self-assembly could be broadly looked at as the seamless manipulation of matter and information from molecular to macro scales through understanding of interconnects, synthesis, and dynamics. There must be understanding of interconnection issues between materials at all length scales coupled with understanding of how materials properties change in the transition from the nano- to the micro- and the macroscales. These transitions must be modeled to provide understanding and facilitate materials design from the molecular level up. To control matter at all length scales, there must be fundamental understanding of all steps in the self-assembly processes. This includes the mechanisms for self-assembly and crystallization, non-equilibrium steps or structures, protein folding, and how to control macromolecules.
Although the importance of self-assembly processes to biological systems is generally understood, their impact on advanced technologies such as electronics and communications is likely to be equally significant. Active and passive photonic materials are the cornerstones of the telecommunications infrastructure. For any given application, the goal is to design and build the desired material through fundamental knowledge of materials properties and function from the atomic scale through the macroscale. Such understanding and control requires the development of requisite process control methodologies and the ability to predict materials properties from the nano- to the macroscale. Molecular-level structure or property process control is an absolute requirement. Even the smallest defects and impurities must be identified. Developing a tool for high-resolution, three-dimensional element-specific mapping that is nondestructive and provides real-time information on both crystalline and noncrystalline materials on multiple length scales would be a worthwhile research challenge. In the area of analysis, diagnostic tools that allow for in situ process control are critical for future materials manufacturing.
Having the design and synthesis methodologies in place along with advanced analytical capabilities allows the next question to be addressed, namely, what should be made. The answer requires accurate design of materials with a road map of how to make them, not only on a laboratory scale, but more importantly on the manufacturing scale. On some level, the latter will be driven by cost, but through theory and modeling come an understanding of structure (at all length scales) and concomitant ability to develop affordable materials for a given technology application. Figure 4.1 schematically shows the interplay between each of the above components.
As we move further into the twenty-first century, many of the most exciting developments are occurring at the interfaces between disciplines. Ever more frequently, chemical scientists and engineers work with biologists, physicists, elec
FIGURE 4.1 The interplay of competing interests in the design of new materials.
trical or mechanical engineers, device engineers, and/or computer scientists to address significant scientific and technological challenges. It is these interchanges that will create new opportunities in the chemical sciences.
Significant research efforts focus on improving the health and well-being of our society. Much of the ongoing biomaterials research is aimed at restoration and enhancement of the function of living materials. Such efforts encompass not only work aimed at restoring lost organ function and expression of the human genome but also the development of miniaturized, multifunctional biosensors and human-computer interfaces. Researchers, while maintaining their own specific expertise, must increasingly be trained to work in multidisciplinary environments. New device concepts require precise design of materials at the molecular level as well as fabrication processes that allow for complete control of structure and defects. For biosystems, understanding of biological function and how materials designs will either influence or be influenced by the environment is critical.
Although only a few examples of multidisciplinary research problems have been presented, each of these relates to high-performance materials developed for specific functionalities. (For example, see Siedebar 4.2.) A design methodology that effects ease of processing and scaling must be developed. Conceivably, such materials will also be bio-inspired.
Additional interfaces that will create challenges for the chemical scientist, relate to the development of analytical or characterization methodologies. Some examples are the detection of hydrogen in metal or local analysis of materials; identifying and understanding the effects of “impurities” in alloys and metals; and developing accelerated test methods. Are all critical to the development of advanced materials technologies and manufacturing methodologies. The ability to visualize nanoscale interactions between chemical systems could greatly advance miniaturization of devices, whether electronic, photonic, catalytic, or biologically compatible. The ability to visualize or characterize nanoscale interactions could in turn lead to the development of principles and theory for the
self-assembly of materials and thus ultimately allow the truly rational design of materials with defined functionality.
SUMMARY AND FINDINGS
Finding: Advances in materials chemistry will be essential to improving our standard of living while also improving environmental quality.
Almost every materials- and chemistry-related issue and technology that has been discussed or can be envisioned is likely to have a direct impact on environmental challenges. As a result, environmental concerns must remain at the center of developing new materials and manufacturing technologies. New materials technologies are also needed to enable affordable clean energy, such as energy storage media, and materials to enable the use of alternative energy sources.
Finding: Major research challenges for the chemical sciences include the design of tailor-made materials with defined performance attributes, such as synthetic materials systems that can carry information at high density, utilizing the insights obtained by studying biological structure to design and make new materials.
To achieve complete control of material properties, knowledge of the processes that affect spatial and temporal control of chemistry is required. Resources are needed to explore self-assembly processes that could lead to the seamless manipulation of matter and information from the molecular through the macromolecular scale. For example, high-density information systems may be devised using DNA encoding as a model, where information is built up on the macromolecular scale through monomeric building blocks (Sidebar 4.2). Interconnection issues between materials at all length scales must be understood, and this understanding must be coupled to an understanding of how materials properties change in the transition from nano- to micro- to macroscales.
The acquisition of biomimetic approaches to materials design and synthesis will both lead to an understanding of natural processes and provide insight into value-added ways to design materials with new functionalities and enhanced performance. In effect, a “tool box” is required that will provide understanding and facilitate materials design from the molecular level up, where that design will be for an intended technology application.
Finding: New analysis techniques will be required to enable significant progress in materials chemistry.
Methodologies are required to visualize nanoscale interactions between chemical systems; these could greatly advance the miniaturization of devices— whether those devices are photonic, electronic, catalytic, or biologically compatible. This ability could in turn lead to the development of a set of principles and theory for self-assembly of materials and thus ultimately allow truly rational design and manufacture of materials with defined functionality.
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SIDEBAR 4.2 Materials Needs for Defense and Energya In responding to the needs of both the Department of Defense (DoD) and the Department of Energy (DOE), researchers are often called upon to develop new materials and novel applications for existing materials. Materials needs for DoD consist of structural materials, materials for energy and power, electronic and photonic materials, and functional organic as well as biological materials. All of the services desire complete defense systems based on materials that require less maintenance. In order to develop these materials to meet long-term DoD needs, a wide range of scientific advances will be necessary. Meanwhile, DOE has sought breakthroughs in materials research to address issues related to its missions—the stewardship of an aging arsenal of nuclear weapons, nonproliferation of weapons of mass destruction, and issues related to the supply and management of energy. While a new material or process may be very promising in the laboratory it may be completely inappropriate for mission needs because it is not manufacturable. Materials and process scientists must ensure that production of the material or component can be scaled to a level appropriate for its end use. Yield must be high and defect density low, so there is little or no waste or inefficiency. The end product must be able to be inspected and characterized either through rigorous process-based quality approaches or via more standard inspection. The product must also be manufacturable at an acceptable cost. As the demand grows for increased functionality at lower volume, weight, and cost, the need to understand and develop new materials on the molecular scale will increase. Strategies must be developed to incorporate nanomaterials into structures, to use self-assembly to build structures with order on multiple length scales, and to develop nanotechnology into a manufacturable technology. |
