Scalable Growth of Colloidal Crystalline Materials and their Inverses
Abstract
A vast array of particles with different shapes (spheres, cubes, hexagons, octahedra, disks, rods, and tubes), dimensions from (nanometers to microns), and with diverse chemical compositions have emerged during the last two decades. They exhibit properties not found in bulk variants of the same materials and can be ÒtunedÓ by varying particle size. Thin films made by the colloidal assembly of these particles have shown collective interactions that can manipulated through particle selection and by packing structure, resulting in new states of condensed matter with novel thermal, mechanical, electromagnetic, and optoelectronic properties and functionalities. Even in the absence of phenomena associated with quantum confinement and ultra-high specific surface area, colloidal crystal thin films exhibit novel photonic, phononic, thermal, electrical and other (e.g. thermoelectric) properties, and hold promise for a new class of ultralight structural material. However, concepts for the assembly of particles into macroscale materials with long-range order are not as developed as methods for particle synthesis. The objective of this international collaborative proposal between the Universities of Cambridge (UK) and Virginia is to investigate novel processes for the scalable growth of bulk colloidal crystals and their metal and ceramic inverses by understanding the assembly of small diameter spherical polymer and/or silica particles, and then using this insight to explore novel scalable processing concepts. The hypothesis to be tested is that the defect populations formed during assembly of model spherical particles to form close packed crystals is controllable via the application of oscillatory shear and compressive forces, permitting the growth of close-packed (crystalline-like) materials with controllable defect populations. Our fundamental approach seeks to understand the mechanisms of formation of defects such as stacking faults, vacancies, grain boundaries, dislocations, regions of non-close packed structure, and other void or crack-like flaws. This insight will be used to guide design of assembly processes that enable defect population control during processing. The proposed program uses a granular mechanics to understand the assembly process during the processing of macroscale close packed crystals and their inverses. The objective is to identify relationships between the defect populations formed during assembly (low volume fraction regions, grain boundaries, stacking defects, dislocations and vacancies) and the stress, assembly rate and second phase (solvent, polymer or composite) properties. A Task 1 effort led by Vikram Deshpande (University of Cambridge) will develop simulation methodologies, validated by small-scale experiments, to create a fundamental understanding of the assembly of colloidal systems comprising micro/nano sized particles. A key output provides process design guidance to the University of Virginia for their work on the processing of close packed materials. The UVa led Task 2 component of the program will modify vertical and horizontal particle sedimentation techniques (developed in an earlier one-year duration exploratory ARO supported effort) to enable the assembly of macroscale polymer and silica opal-like materials and their inverses. This will include an investigation of a model nickel inverse opal. It will also explore the processing of inverse opals by a route where the eventual inverse structure material is incorporated during opal assembly. Task 3, beginning in year 2, consists of a fundamental study conducted jointly both the two groups to unravel the mechanisms of defect formation and their influence upon mechanical properties.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 14, 2019
- Source ID
- W911NF1910075
Entities
People
- H.N.G. Wadley
Organizations
- Army Contracting Command
- United States Army
- University of Virginia