Ordered porous materials hold promise for enhanced performance in a variety of fields. Often this class of materials are fabricated through a process called self-assembly, whereby the component parts of a macroscopic material spontaneously arrange themselves into a desired structure. While self-assembly of materials that are ordered at the nano-scale has recently captured the interest and imagination of scientists and engineers, the self-assembly of larger, meso- and macro- scale components can also have a dramatic impact on tissue engineering, microelectronics, energy, and 3-D visual displays. Nevertheless, despite these technical drivers, self-assembly at these larger scales has received little focus from the scientific and engineering communities and this area remains in its infancy. This award supports the study and development of methods of self-assembly that are amenable to the fabrication of ordered porous materials constructed of building blocks that are considerably larger than nano-materials (that is, in the tens to hundreds or micrometer size range). In addition to opening the approach of self-assembly to a whole new range of building blocks, a successful project in this area will also allow a combination of the new techniques with existing nano-scale methods to ultimately lead to the fabrication of materials that are ordered over an unprecedented range of size scales. It is expected that this new class of materials can lead to advances in applications ranging from tissue engineering (scaffolds) to fuel cell/battery electrode fabrication to pharmaceuticals, thus, results from this research will benefit the U.S. economy and society as a whole. This research involves combining expertise in chemistry, physics, engineering, and materials science. The multi-disciplinary approach will help broaden participation of underrepresented groups in research and positively impact engineering education.
Colloidal crystallization is a staple of nano-scale particle self-assembly, however, until recently is has been a technique that was essentially unused at scales beyond several microns. This is due, in part, to the fact that the underlying thermal effects (i.e., Brownian motion) at these larger meso- and macro- scales are small enough that components become kinetically arrested in non-equilibrium states. The research team plans to use a combination of experimentation and modeling (coupled Discrete Element and Lattice Boltzmann methods) in order to further develop a promising series of new materials processing strategies that exploit recently uncovered instabilities of dilute fluid-particle systems at large (10s to 100s of microns) scales. Theoretical and scaling arguments will be used to determine the criteria necessary to induce the required instabilities. These new strategies will open particle crystallization techniques to a range of particle sizes that are typically well beyond the colloidal limit. Then, a combination of existing (colloidal) techniques with the new approaches can be used to fabricate novel hierarchically-ordered structures that mimic those found in nature (both in pore distribution as well as stoichiometry) and can ultimately form the basis of novel materials processing methods.
