Nanoparticle ionic fluids: interactions and transport properties

Cornell University, Ithaca NY

Investigators

Abstract

CBET-0756516 Archer Intellectual Merit: Nanoparticle-based ionic materials (NIMS) are a new class of hybrid materials recently discovered at Cornell. NIMS are created by covalent attachment of charged oligomers to the surface of nanoparticles. The charge on the oligomer is balanced by a counterion species that can vary from a compact molecular entity such as a chloride ion, to a more bulky organic species such as an Isosterate ion. Depending on the interactions between the components (core particles, attached oligomers, and associated counterions), physical properties of the materials can be tuned over a surprisingly wide range. On one end of the spectrum are materials with high core particle content, which display properties similar to glasses, stiff waxes, and gels. At the opposite extreme are systems that spontaneously form homogeneous particle-based ionic fluids, characterized by transport properties remarkably similar to simple Newtonian liquids comprised of molecular building-blocks. These nanoparticle ionic fluids resemble molecular ionic liquids in their ability to form zero vapor pressure, ?green?, solvents with high dielectric constants. Because they contain an inorganic particle core, however, a more exciting array of properties can be accessed. The proposed research uses a combination of experiment, theory, and computer simulations to understand the fundamental forces in NIMS and to determine how these forces influence their transport properties. Our preliminary studies indicate that nanoparticle ionic fluids are the first example of a system of particles of any size that can reach equilibrium without a solvent. These studies also indicate that two new types of interactions are important for understanding the stability of our fluids and for predicting their transport properties: (i) An entropic attraction force arising from attachment of the effective solvent to the core particles; and (ii) Electrostatic forces due to surface-attached, bendable dipoles on the cores. Broader Impacts: The NIMS core particle is an inorganic nanostructure. This open possibility for creating entirely new types of hybrid fluids based upon the vast library of available inorganic particle chemistries and shapes. The unique properties possible in such fluids makes them attractive for a host of applications, including high-conductivity heat-transfer liquids, inkjet printable semiconducting inks, stable electrolytes for high-temperature batteries, light-weight conformal armor for military and law-enforcement personnel, and high refractive index liquids for photolithograph. Most of these applications are inaccessible to fluids created from molecular building blocks. The proposed research is the first attempt to develop fundamental understanding of the interaction forces that control structure and properties of these types of fluids. We believe that our work will provide crucial guidance on how to select components (e.g. core particle size, shape, volume fraction, corona and counterion molecular weight, and chemistry), for the many applications targeted. Furthermore, because our fluids combine elements of colloids, polymers, and complex-fluid behavior in a single material, we believe that results from the proposed research will help expand and modernize the literature on colloidal phenomena and complex fluid flows. We believe a direct result of the range of applications that will be impacted by our materials, is that transfer of knowledge developed in the study to the classroom will be more rapid than normal for subjects in the field. The novelty of NIMS and their relevance to easily appreciated applications also provides new opportunities for attracting younger students (K-12) to science. Specifically, in collaboration with the Cornell Center for Materials Research (CCMR), we will develop demonstrations based on applications of the materials, e.g. as inkjet printable inks, conformal body armor, and high-index liquids for photolithography. Our goals for these demonstrations are to engage students at an early age to think about materials in terms of their fundamental units or building blocks, and to recognize the connection between physical properties and the forces between these units. We also believe that video demonstrations connecting flow transitions in NIMS to structural transitions revealed by scattering experiments will help advanced students appreciate relationships between transport properties of complex fluids and their interactions. We will use these video demonstrations in our undergraduate Fluid Mechanics (ChemE 323) and graduate Polymer Physics (ChemE 745) courses, and also plan to take advantage of the YouTube web portal to disseminate them to a broader audience.