Harnessing Coulombic Forces to Guide Colloidal Self-Assembly
Abstract
The goal of this research program is to harness elementary electrostatic forces between charged colloidal particles, to synthesize complex single crystals on a macroscopic scale. Colloidal self-assembly is a delicate balancing act of attraction and repulsion, where multiple components adequately position themselves to form complex architectures. A necessary requirement is that particles avoid a proximity where van der Waals attraction causes them to aggregate uncontrollably. This objective is often achieved by using suspensions of like-charged colloids that repel electrostatically. In this context, target architectures are encoded by specific attractive forces built to task: from simple entropic forces to highly tailored supra-molecular interactions. As the simple idea of mixing suspensions of oppositely charged components intuitively defies colloidal stability, electrostatic attraction is rarely used in colloidal self-assembly. In this proposal, we described a radically different scenario where virtually any charged particle can act as a model ion, assembling with oppositely charged partners into crystal structures that were previously accessible only to DNA-coated colloids. We propose a chemistry-free approach to colloidal self-assembly, which we refer to as polymer attenuated Coulombic self-assembly (PACS), where only a few basic ingredients are required to grow macroscopic colloidal single crystals. Briefly, by holding colloidal particles separated at specific distances by neutral polymer spacers, the attractive overlap between oppositely charged electrical double layers can be systematically tuned, directing the particles to disperse, crystallize, or become permanently fixed on demand. We plan to assemble centimeter-scale colloidal single crystals using a variety of seeded growth techniques borrowed from molecular crystal engineering. For example, preassembled seed crystals will be mounted and introduced into particle suspensions tuned, using PACS, for growth on the crystalline substrate. Continually replacing the particle background will allow the crystal to grow indefinitely. In another experiment, epitaxial growth will be carried out by utilizing crystalline monolayers as seeds. These monolayers will be produced in large areas and with different motifs, allowing a variety of bulk crystal structures to grow to macroscopic length scales. We plan to increase the structural complexity of the crystals that can form via PACS by utilizing colloidal ions with non-spherical shapes and anisotropic material compositions. We also plan to explore the assembly of nano-sized colloidal ions where the Debye screening length is commensurate with the size of the particles. In these nano-systems, particles not in direct contact can influence one another, leading to an array of anisotropic clusters, and ultimately open lattices. The relationship between particle size and interaction range will provide a unique structural tuning knob that we will exploit to assemble complex crystalline architectures such as zinc blende and ABX3 perovskite lattices. We will use computer simulations to investigate the enormous phase space of shape and size combinations. New structures will be predicted and targeted by surveying the multitude of experimentally available shapes. Furthermore, through a combination of experimental and simulated efforts, questions such as the ideal dimensions and conditions for building blocks to assemble into target crystal structures will be answered. This research program will yield the fundamental understanding and technical know-how to develop a general microfabrication technology, where elementary colloidal forces replace chemistry.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 02, 2020
- Source ID
- W911NF2110011
Entities
People
- Stefano Sacanna
Organizations
- Army Contracting Command
- New York University
- United States Army