Patchy Colloids & Colloidal Molecules

New York University, New York NY

Investigators

Abstract

Non-Technical Abstract: This project addresses a central goal of contemporary materials science: to create methods for manipulating and assembling materials on the nanoscale. While chemists address such problems on a molecular scale, methods for designing and assembling small molecular aggregates known as "nanoparticles" or "colloids" are poorly developed. Such particles, 100 to 100,000 times smaller than the diameter of a human hair, are usually spherical with surfaces that either uniformly repel or stick to each other where they first happen to touch. However, to design organized useful structures, particles cannot simply stick where they first touch but need to have "hands" that grab onto each other only at specific points on their surfaces and only along certain directions. The goal of this project is to use newly developed nanoparticles that have sticky pads or "hands" arranged in such a way that the particles assemble into structures that have technologically useful optical, electrical, and mechanical properties. The research could lead to new materials for manipulating light, which could be used in optical circuits for enhanced communications and computing. This project, jointly funded by DMR and CBET, also provides a rich multifaceted training for students in the increasingly technologically important areas of colloidal and nanoparticle self assembly and photonic materials. Technical Abstract: The goal of this project is to develop and study self assembly of two new classes of non-spherical colloidal particles: "patchy colloids" and "colloidal molecules." Patchy colloids are nearly spherical particles having highly symmetric directional interactions, for example colloidal spheres with four attractive pads arranged with tetrahedral symmetry on the particle surface. Colloidal molecules are high-symmetry clusters made from colloidal spheres irreversibly linked together. These include dumbbells, triangles, tetrahedra, and octahedra, as well as more exotic clusters. The fundamental motivation is to understand the role of particle shape and directional interactions for self assembly at the micron scale and below. A long-term practical motivation is to develop colloidal crystals that are useful for making complex colloidal crystals and other structures such as photonic band gap crystals. Questions to be addressed include: (1) How can directionality, strength, range, and specificity of interparticle interactions be manipulated to create new colloidal structures? (2) How do particle shapes with lower symmetry than spherical change the phase diagram of condensed phases? (3) What is the effect of external fields on particles of reduced symmetry and how can they be used to manipulate and control the self assembly and structure of these new colloids? This project, jointly funded by DMR and CBET, also provides a rich multifaceted training for students in the increasingly technologically important areas of colloidal and nanoparticle self assembly and photonic materials.