Nanoscale Fluctuations in Disordered Materials

Northeastern University, Boston MA

Investigators

Abstract

Non-Technical Abstract Both exotic and ordinary materials exhibit unexpected behavior when they are used to build ultra-small machines. Normal properties, such as their mechanical strength and electrical conductivity, may in fact vary dramatically in such objects that are a few billionths of a meter in size. Understanding of spatial heterogeneity and temporal fluctuations is important for nanotechnology. Disordered solids (glasses), plastics, and advanced metals with extraordinary springiness are prototype examples of materials that are technologically important. When a materials is undergoing a change from a liquid to a glassy state, nano-properties are believed to fluctuate wildly in different locations. Using powerful new microscopic techniques, these fluctuations will be imaged and studied, and used for testing new theories of glass formation. The ultimate goal of this work will be to predict the properties of the nano-material building blocks of nanotechnology, as well as new classes of disordered materials. Undergraduate students will participate in this project through research and a new course that incorporates the latest techniques. Technical Abstract Complex materials may exhibit variations in their properties on the nanoscale. Understanding these fluctuations will be increasingly important for nanotechnology. Near the glass transition, disordered materials are believed to have large spatial and temporal fluctuations (dynamical heterogeneity), which play a central role in glassy phenomena such as slow, non-exponential relaxation and aging. Using new nanoscale imaging techniques based on ultra-high-vacuum electric force microscopy, the real-time spatio-temporal fluctuations as well as local dielectric response functions will be studied in polymers and simple liquids near the glass transition. These studies will enable the visualization of the pattern and statistical properties of dynamical heterogeneity, thereby testing promising new models of the glass transition. By studying fluctuations and responses following a temperature quench, new ideas in non-equilibrium statistical mechanics will be tested. Undergraduate students will be trained in nano-science by their participation in this research and through a new experimental course for advanced undergraduate and graduate students which incorporates the latest measurement techniques.