Four workshop participants, Jennifer Sinclair Curtis of the University of Florida, Michael Postek of the National Institute of Standards and Technology (NIST), Pierre Ricou of Arkema, and Richard Conroy of the National Institute for Biomedical Imaging and Bioengineering (NIBIB) at the National Institutes of Health (NIH), were asked to provide closing comments. Chosen for their diverse perspectives, each panelist discussed what he or she heard during the workshop and what some next steps might be. The panel comments were followed by an open discussion period when all workshop participants were given the opportunity to respond to the panelists and raise additional issues.
Jennifer Curtis heard three main topics discussed during the workshop: implications, understanding complex processes, and new characterization techniques for small particles. She said that health and environmental implications seem to motivate much of the work in characterizing and modeling small particles. Given that motivation, there is a need for greater understanding of fine particles and the dynamics of their behavior. There is another need to define the methods that are capable of distinguishing between single nanoparticles and agglomerates.
A key takeaway message for Curtis was that the modeling community faces some validation challenges related to the lack of detailed experimental data. She believed it would be useful to the field to compile a database of the available characterization techniques and their key features in terms of the type of material they can handle and the characteristics and properties that they measure. Such a database may increase the use of these powerful techniques in areas beyond those for which they were developed.
Mike Postek was struck by the obvious need to make multiple measurements on the types of complex that represent nanomaterials found in the real world. He noted the development of a wide range of new tools for nanomaterial characterization and the continuing advances being made with instrumentation, such as the applications of the soft x-ray tomography, the cryogenic light aberration-corrected transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and in situ TEM. He also raised the need for a database of available technologies.
Postek expressed a worry that cuts to research and development budgets, particularly in industry, are hampering technology development at a time when need in the nanocharacterization field is growing. However, he also noted that a great deal of advanced characterization technology is available at the national laboratories and at NIST, along with investigators who are more than willing to collaborate and cooperate in this area.
Modeling also touches on complexity, Postek said. Industry needs tools to model complex composites for use in high-performance applications. The potential cost savings from having models capable of predicting material performance would be huge, as it would be if models were available to predict the effect that process variables have on the properties of materials with complex surfaces and surface chemistries.
Pierre Ricou’s impression was that small-scale characterization is a focal point for many different parts of the nanotechnology world. From industry’s perspective, there is a need to characterize and understand the properties of materials to cre-
ate complex materials that can meet a wide range of demands. From an environmental scientist’s perspective, there is a need to characterize materials to understand what happens to those materials when they enter the world outside of the laboratory or factory. Although each group is tackling different issues, they are united by a need to characterize the properties and behaviors of complex materials in complex environments.
Ricou was also impressed by the wide range of technologies that are now available for characterizing nanoscale materials. He reiterated the importance of creating a database of technologies, and he stated that instrument vendors should hear more about the challenges facing those who need to better characterize nanomaterials. He would like to see development of the ability to perform spectroscopy on dynamic systems at the nanoscale to better understand how the chemistry of a nanomaterial changes over time, which would benefit many aspects of nanocharacterization.
Richard Conroy said that he came away from the presentations with two questions:
- Should we study function first or structure first?
- Should we measure something just because we can?
This second question is particularly important from the NIH perspective, because many measurements correlate weakly with outcomes, and thus it is not always clear that the measurements are useful when considering the research that has gone into them. He added that consideration of the question of safety and efficacy is also important, in terms of the comparative effectiveness and safety of nanotechnology-based products versus bulk materials.
Conroy provided a quick overview of some of the funding opportunities at NIH. Part of NIH’s current mission is to bridge the life and physical sciences, and, in that regard, he thought the nanomaterial characterization community would be interested in a number of initiatives. Most of the initiatives are funded by NIBIB or the National Institute of General Medical Sciences (NIGMS), with NIBIB focusing more on the clinical side and NIGMS focusing more on basic research. One new initiative is aimed at applying technologies from the physical sciences to life sciences problems. A significant feature of this initiative, the grant review panel includes experts from both NIH and the National Science Foundation (NSF), with the latter providing a physical science perspective to the NIH review process. A partner initiative aims to translate ideas from the physical sciences into the clinical arena.
Another NIBIB initiative is the bioengineering research partnership program that encourages investigators to form a partnership between the life and physical sciences to translate a concept, technique, or tool from the demonstration to the biomedical application phase. NIBIB also offers fellowships that are designed to create time for mid-career researchers in the physical or quantitative sciences to develop projects in the life sciences.
Conroy said that all of the other NIH institutes have similar initiatives, and NIBIB also supports Small Business Innovation Research (SBIR) grants in the area of bioengineering in nanotechnology.
Characterizing Aggregates—Trading Detail for Utility
Jim Litster said he was amazed by what he heard during the workshop about the ability to measure individual small particles. He added, however, that because the of the nanoparticles in use depends very much on the structures in which they are embedded, there is still a need for techniques that are just as powerful at characterizing the state of dispersion or aggregation. Developing the techniques and instrumentation to attack that problem is the logical next step for the field.
Doug Ray agreed that there is not as much capability in the area of concentrated liquids and solids. He asked, “Is it because it is just really hard and the community is not there yet, or is it because we have elected somehow to not focus in that arena?” He does not know the answer but thinks it is an interesting question to consider.
Mark Barteau added that work in this area might focus on “diagnostic,” meaning that it may not be necessary to know all the details of how nanoparticles behave in a matrix. It might be enough now to characterize these complex according to a certain number of reduced parameters or “lumped” parameters. He is aware of some movement in that direction, but the emphasis on incredible levels of detail and expensive instruments does not match the degree found in nanoscale imaging. He wondered, however, if looking at more complex systems at lower levels of detail that are still diagnostic might be where the field makes the biggest impact. Ray added that the atmospheric sciences are starting to move from a more detailed view to one that reduces the amount of information and creates useable models.
Conroy noted that NIH is interested in where the field is going on this matter. He believes that the relevant question relates to how much detail on specific characteristics is needed to predict biological outcomes. Ricou agreed with this idea but stressed the importance of understanding these systems in fine detail to know what is important when trying to predict relevant behavior.
Chemistry and Stability
Levi Thompson pointed out that many of the particles that were discussed at the workshop are semiconductors and
wondered if the properties of those particles are influenced by exposure to light. He asked if anybody had performed the requisite studies to determine whether photocatalytic or photolytic processes are important to particle reactivity. Satya Kuchibhatia from the Pacific Northwest National Laboratory answered that his group has looked at cerium oxide nanoparticles and found that exposure to light definitely influences the transformations happening on the nanoparticles. He also explained that how a nanoparticle responds to light changes over time and that his group has noticed changes between the times when a particle is received from a vendor and when it is studied. Where the particles are manufactured also makes a difference, which is likely due to the humidity of the manufacturing location.
Finlayson-Pitts said that the field of atmospheric chemistry is starting to pay attention to the photochemical properties of nanoparticles. The photochemistry of small particles can be quite different from the photochemistry of larger particles, primarily because of differences in surface-to-volume ratios. As an example, she described differences in the photolysis of nitrate ion that occurs when it is surrounded by a solvent shell on a bulk surface compared to when it is at an interface. “The whole issue of photochemistry at interfaces is certainly one that is getting increasing attention in the atmospheric community,” she said. Thomson added that researchers who study catalysis, photocatalysis, and electrocatalysis have been considering these issues for many years, and it might be an intersection that can be probed more.
What’s the Focus?
One participant commented that while the presentations were very informative, there was a lack of focus in terms of an industrial driver, that is, how at the end of the day will this research help to develop new products.
Kuchibhatia and his colleagues at the Pacific Northwest National Laboratory are encouraged that the field is moving beyond the excitement of getting a good TEM image to search for details about surface chemistry with an eye on developing nanoparticles with specific properties. The goal, he said, has gone from seeing structure to combining structure with a desired chemical property. “At the end of the day, it is the chemistry that is going to make the magic, not just the structure,” he said.
Postek added that a roadmap created by the semiconductor industry years ago has guided the industry since the 1980s and has allowed instrument manufacturers to build the measurement tools that the industry has needed as it meets its technology goals. Nothing like that exists for nanotechnology. He acknowledged that creating such a consortium to define what is happening in nanotechnology would be difficult given the disparate nature of this community. “Perhaps several of these kinds of consortia are needed to help shape this field and get people together to talk about what their needs happen to be,” he suggested.
Rhonda Stroud believes that having a focus is great, but it does not necessarily have to be on commercial applications alone. As a civil servant, her customer is the American public, and she asks herself, “Can I justify working on space particles to the taxpayer?” She believes that the common issue is really quality of life. Everyone is producing information and products that improve the quality of life. This is what air quality, new drug treatments, and astronomy have in common. They may not all have immediate commercial applications, but they can be important to the American people nonetheless. Therefore, a roadmap should look at what the impact of knowledge as well as products will be on the average person.
A participant agreed that the ultimate goal is to serve the people, but, at the end of the day, the commercial aspect is important because it is the means to get to that goal. For example, catalysis is very important for many applications. Researchers will make useful and environmentally benign catalysts from ruthenium or rhodium. However, those materials are expensive, so in poorer countries that same reaction will be carried out without the catalyst and will use excess reagent that gets dumped into waterways because pollution control standards are lax. Ultimately, if knowledge does not make money or save money, no matter how useful it is, people will not use it.
Ray replied that while certain sectors, such as energy or pharmaceuticals, are driven by commercial interests, other sectors such as the defense industry are not. He believes that there are sectors where commercial drivers are in place and are appropriate, and there are other sectors where they are not. The nation supports research in areas such as astronomy, not for an immediate commercial benefit but for quality-of-life issues and the long-term benefits that the research might produce. Stroud pointed out that the Department of Defense does a significant amount of work on the development or the advancement of catalysts and energetic materials where the driving force is not the immediate bottom line, but the need to protect the American people.
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