Thinking Small: Properties of Nanomaterials and Nanostructures
It has been understood for a long time that the origins of defects in materials are typically of atomic scale. Moreover, many physical, chemical, electronic, magnetic, and mechanical properties are traced to atomic structure and its evolution. At the same time, it is also widely appreciated from a materials science perspective that there are numerous intermediate or mesoscopic length scales of material microstructure that relate to process path and material heterogeneity — these mesoscopic structures often control properties at the macroscopic scale, in conjunction with atomic scale structure and nature of defects.
In this sense, we may consider that understanding mechanical properties requires not only a fundamental understanding of nanoscale structure and processes but also of the multiscale nature of materials and material structure-property relations. The Mechanical Properties Research Lab (MPRL) is heavily involved in modeling ranging from atomistic simulations to continuum methods, and experiments ranging from tens of nanometers (e.g., AFM-tip nanoindentation) to hundreds or thousands of microns.
Nanostructured materials and devices may be regarded as having scale-dependent properties or characteristics that enable new desirable functionality. For example, nanometer scale grain-size alloys processed using electrodesposition or extensive shear deformation offer exceptionally high strength (and sometimes also ductility) relative to traditional micron scale grain-size alloys. Patterned surfaces with nanometer-scale feature size and spacing can be useful in advanced electronics and optoelectronics applications. Nanoparticles may by useful for chemical detection or other catalytic reaction enhancement due to high surface area to volume ratio, or they may be useful for unique scattering behavior as pigments or reinforcement phases in nanoscale-reinforced composite materials.
In some cases, nanostructured materials also have unusual mechanical properties. The figure below from the group of Min Zhou shows how a nanowire of Face-centered cubic (FCC) copper is predicted to exhibit remarkable reversible pseudoelastic shape memory strain. Since many medical devices, for example arterial stents, employ shape memory alloys, these nanowires may provide fundamental advances.
We are still in the exploration stage of applications and potential fruitful areas for nanotechnology to improve quality of life in terms of consumer products, health care, alternative energy, and environmental protection. It is a technology in its infancy.