NER: Large Scale Synthesis and Assembly of Micro- and Nanoparticles with Dipolar Charge and Anisotropic Shape

North Carolina State University, Raleigh NC

Investigators

Abstract

Abstract CTS-0403462 O. Velev, North Carolina State University Micro- and nanometer sized polymer particles possessing specific directional interactions can be assembled into advanced "smart" materials and consumer products, however such particles are not readily available to date. Two new techniques for large-scale synthesis of novel classes of polymer particles with anisotropic charge or shape are extended here. The first class of particles will have permanent dipolar and/or quadrupolar moments. The synthesis technique is based on polymerization (or solidification) of emulsions and microemulsions in the presence of constant or alternating electric field. These particles will exhibit dipole-dipole interactions that will make them directionally self-assemble into structures with long-range orientation. The second new class of particles that will be fabricated are cylindrical polymer microrods. The PI has discovered a scalable process for making such cylindrical particles by shearing and "drying" of emulsified droplets from polymer solution. Fabrication of colloid rods of different aspect ratios will allow controlling their orientational, entropic and induced dipolar interactions. These anisotropic particles will be used for the assembly of a variety of advanced materials such as ion- and pH sensitive gels, colloidal liquid crystals, photonic crystals of uncommon symmetry and electrorheological fluids. Intellectual merit of the proposed activity. Two original concepts for fabrication of new classes of particles with fundamentally novel properties and interactions are extended. The orientation dependent non-DLVO surface forces between electrically anisotropic particles in water could be of interest to a wide community of academic and industrial researchers. Access to these particles could lead to new fundamental insights into non-DLVO forces. The rod-like particles make possible fundamental research in new phenomena of entropic self-organization. New types of micro- and nanostructures will be formed by engineered assembly of these particles. These structures include "colloidal" liquid crystals from particles instead of molecules, photonic crystals with novel symmetries, strongly interacting water-based electrorheological fluids and materials where the particles assemble or disassemble in response to changes in their environment. Broader impacts resulting from the proposed activity. This project will for the first time allow the large-scale, efficient and inexpensive fabrication of colloidal particles with anisotropic shape and/or directional interactions. Undergraduate student research projects, an outreach course for industrial scientists, and national and international collaborations are also planned. Potential beneficiaries of the resulting novel materials and technologies include the chemical, pharmaceutical and biomedical industries, and companies making displays, photonics and optoelectronic devices. Some possible applications are in multi-million dollar industries, such as replacing the molecular liquid crystals in displays with colloidal liquid crystals, and developing new polymer "latex" paints with higher viscosity and better optical properties. Photonic crystals and water-based electrorheological fluids could find application in emerging high technologies. Novel "smart" ion-sensitive or biomolecule-sensitive gels for medical applications could also be fabricated. This will lead to scalable and efficient manufacturing processes at the nanoscale.