Gradient Nano-Structures from Dissipative Nonequilibrium Self-Assembly of Block Copolymers
Abstract
Materials with porous structures offer immense value due to their applications in both industry and fundamental research in areas such as separation, adsorption, catalysis, energy-storage, sensing, etc. A particularly challenging goal is achieving hierarchical porous structures with specific structural gradients. By continually varying poresÕ dimensions, the sharp transition from one property to the next is avoided, greatly improving the materialÕs performance. However, with only a limited number of approaches to prepare such gradient porous structures, the pore-sizes are usually in the micrometer regime, with little control over their distribution. In particular, it becomes increasingly difficult to develop nanoscale gradient porous structures, especially in thin films, which is essential for effective light modulation or optical design. Self-assembly of block copolymers (BCPs) provides a unique platform for producing periodic and ordered soft materials on nanometer length scales, which may be functionalized or used as templates for the subsequent fabrication of structured inorganic materials. These nanoscale periodic structures are often difficult, if not impossible, to achieve using other materials or techniques. However, the normal equilibrium thermodynamic framework of BCPs limits the range of accessible morphologies and the tunability of pore size. It does not, for example, allow the formation of gradients or asymmetric hierarchies. The long-term goal here is to investigate the potential of using gradient nanostructured polymer films to mimic natureÕs own light modulation structures. This requires understanding the fundamental principles of how to controllably push polymer-based materials systems away from equilibrium towards the successful generation of gradient porous ordered asymmetric nanostructures. The objective of this project is to study the phase behaviors and self-assembly of the BCP/homopolymer system under a dissipative nonequilibrium or dynamic process, thereby advancing asymmetric porous nanostructures in thin films. The dissipative self-assembly depends on a constant influx of energy or disturbance. So far, the study has been limited to the systems of particle/micelle/peptides self-assembly. A delicate experimental design for precise control of energy input or waste removal will be critical to apply the dissipative self-assembly principle to block copolymers. The central hypothesis is that mixture solvent vapor that is applied to a perpendicular ordered BCP/homopolymer cylindrical structure in a stepwise or oscillating manner can adjust the homopolymer blends in the system to redistribute gradually across film thickness, resulting in non-native morphologies. This entails the rational design of the system based on homopolymer blends, interfacial energy, and mixture solvents. Completion of these aims will provide insights into the fundamental BCP self-assembly mechanisms under a dissipative nonequilibrium or dynamic process in order to achieve nonnative morphologies at different non-equilibrium states. This will pave the way for the realization of new conical frustum structure of BCPs to address important problems in the design of light modulation systems and optical lenses.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 04, 2021
- Source ID
- W911NF2110055
Entities
People
- Xiao Li
Organizations
- Army Contracting Command
- United States Army
- University of North Texas