Catalytic motors are a novel class of nano- and microscale particles and assemblies that convert chemical energy to mechanical energy. The proposed work builds on the initial experimentation in the area of catalytic motors an existing collaboration between the PIs Darrell Velegol and Ayusman Sen in the Departments of Chemical Engineering and Chemistry at The Pennsylvania State University. These catalytic motors are multiphase nanoparticles that catalyze reactions resulting in their motion through solution. These motions can be influenced by chemical gradients and by light. Individually the motors move in a random direction at speeds of tens of microns/sec, and the transport physics has been studied and modeled by the research groups. Collectively, the motors give complex behaviors similar to the chemotaxis, phototaxis, or even predator-prey phenomena normally seen only in biological systems. This is apparently the first observation of this phenomenon outside living systems.
Because of the continuous input of energy due to the catalytic reaction, these are driven systems that operate far from equilibrium. Thus, hierarchical or dynamic pattern formation can result within the collection of particles. The PIs have done sufficient prior work to demonstrate that they do observe very interesting collective motion of the particles. These motions are of a variety of different types and are of potential use in building both static and dynamic nanostructures. The proposed work makes use of novel nanoparticle syntheses and measurements of particle motion, combined with electrokinetics modeling of the motion, in order to predict behavior.
The PIs state the overarching goal is to establish principles for manipulating energy and information on the nano- and micron scales to create patterns of materials, leading toward technologies with capabilities perhaps even rivaling those of living things. This allows the PIs to pose questions such as: Can we design particle systems from which complex patterns emerge? Can we use patterns to quickly assess the quality/variability of individual catalysts? Can we pattern materials that change dynamically in time? Velegol and Sen have done a very nice job of relating their observations to types of motions and collective behaviors observed in microbial systems, which adds to the attractiveness of the project.
Since the work has high visual impact as well as significant fundamental content, the subject provides powerful outreach opportunities including graduate student education, undergraduate participation, and involvement with the Upward Bound Math and Science program at Penn State, which does outreach to urban school districts. The undergraduates seem to have a very positive research experience and this has resulted in a number of them attending some of the best graduate programs in the country. The PIs have demonstrated excellent ability to work together and to encourage their research groups to work together. The work will gain broad exposure in premier materials, chemistry, and physics journals, and through presentations at major scientific conferences.
Interdisciplinary research. This project combines cutting edge colloidal chemistry - including the synthesis,fabrication,functionalization and catalysis - with cutting edge colloidal physics - including auto-electrokinetic phenomena and simulations. This research also impacts both graduate and undergraduate students by requiring highly multidisciplinary work. Students will learn cutting-edge techniques employed in chemistry, chemical engineering, and nanofabrication, as well as modeling strategies for dynamic systems. Velegol and Sen propose a project which exemplifies the interdisciplinary nature of modern advanced fundamental science programs.
Over the past three years, we have made important discoveries with colloidal motors. These motors are micron size – about 100 times smaller than a human hair – and move spontaneously in various water solutions. They were first discovered in 2004, and a website that has numerous examples of videos exists at http://research.chem.psu.edu/axsgroup/supporting_information.html. Our research has Intellectual Merits. First, we have found that the small motors move in solutions that have dissolving calcium carbonate – this is just ordinary bathtub scale! We are aiming to use this science for important applications, for instance pumping in "dead end pores". It is difficult to pump fluids out of dead-end pores; one might imagine trying to use a straw to drink out of a cup, if the straw is closed at one end! Developing the science involved in pumping in dead-end pores is among the triumphs of this research. Second, another important Intellectual Merit is that we have developed the chemistry to produce the small motors and pumps, using for instance advanced catalysis techniques. Other Intellectual Merits include important discoveries in colloidal assembly, optical plasmonics, pump-triggering mechanisms, and more. Our research has also produced Broader Impacts. After graduation, our PhD students – a diverse group of highly-educated scientists and engineers – have gone on to work with an array of American companies. The graduates not only understand chemistry and physics well, they understand professionalism and how to utilize what they know. Second, the work with dead-end pores is being examined for impact in petroleum recovery. A large amount of petroleum exists in dead-end pores, which cannot be readily accessed by conventional methods. Colloidal motors and pumps have shown an ability to pull oil out of pores, and replace that fluid with water.
