CAREER: Colloidal Origami: Directing and Designing Complex Colloidal Assemblies Using Magnetic Fields

William Marsh Rice University, Houston TX

Investigators

Abstract

0955003 Biswal The aim of this proposal is to develop linear colloidal chains that fold into specific shapes using self and directed assembly. This colloidal origami will consist of chains of magnetic colloids that are linked together to form a bead spring bead structure. These chains will have welldefined chemical and physical properties that function to fold them into specific architectures. For example, by controlling the repulsive and attractive interactions along a flexible chain, a colloidal knot structure can be formed. Active exploration of diverse chemistries and connectivities in these polymer inspired colloidal assemblies will offer the potential for selforganized materials with greater chemical diversity and stability than current colloidal assemblies. Linking magnetic colloidal particles into flexible chains will be achieved by exploiting laminar flow characteristics in microfluidic devices. The first objective of this work is to create a chain with heterogeneous rigidity. These multi link chains, colloidal analogs of block copolymers, are composed of magnetic particles which have been linked together with polymers of different lengths. The second objective is to generate attractive and repulsive interactions along the backbone of a chain by introducing point dipoles and patterned charges. This includes synthesizing ferromagnetic particles with varying magnetic susceptibilities and creating chains composed of ferromagnetic and paramagnetic particles. The final objective is to understand the resulting chain structures that form with the goal of controlling the folding pathways of these chains. The intellectual merit of this proposal is the development of novel colloidal microstructures formed when magnetic particles are chemically patterned using microfluidic flows and magnetic fields. These microstructures are of great interest because they impart interesting material properties; for example, by switching from one microstructure to a closely related structure, one may alter the viscosity, elastic modulus, and optical properties of the material. This assembly concept is driven primarily by the desire to create materials that have the capacity for folding and self-assembly, but also possess the diversity of possible chemical functionalities. The educational plan in this proposal includes integrating the research proposed with interactions with local middle school and high school students. The PI's lab will host two female high school students in a project using magnetic colloidal assembly in microfluidic devices. These students will use this project to compete in the International Sustainable World Project Olympiad, an international science fair aimed at promoting awareness in science and technology. The plan also includes outreach to the community in the form of lab demos entitled Magnetic Gummy Worms for middle school children. The PI will also engage undergraduate and graduate students in scientific learning through research and the development of new curriculum and colloquia. This includes the development of an advanced level course entitled Directed Colloidal Assembly, that will be available to chemists, physicists, and engineers. This research proposal brings together methods from surface science and microfluidics to create new colloidal materials. The broader impact of this proposed work is to develop an integrated research and teaching program on colloidal origami that will advance the field of soft materials by leading to a better understanding of colloidal assembly and opening the door to new particle technologies.