Using Nanoparticles to Confine Molecular Self-Assembly

Wayne State University, Detroit MI

Investigators

Abstract

CBET-0755654 Mao The project is at the interface of two active research areas: nanoparticle arrays and organic thin films. Self assembled monolayers of amphiphiles are relevant to biological processes and in lubrication, colloidal stabilization, and detergency. Nanoparticle arrays are applicable to thin film devices. The overall objective of this proposal is to explore the possibility of nucleating molecular nanorods on inorganic nanoparticle surfaces in order to explore the nanoconfinement effect in templated crystallization and to generate a unique hybrid nano architecture. Experimental and theoretical evidence in non epitaxial seed mediated nucleation suggests that a critical seed size and the presence of other confinement effects are necessary for the selective formation of rod like nanoclusters attached to the nanoparticle seeds. To test this hypothesis, gold nanoparticles of various sizes will be used and physicochemical experiments will be conducted to characterize and understand the underlying molecular self assembly mechanisms of the hybrid architectures. The proposed study will continue a preliminary investigation of co-deposited cadmium selenide nanoparticles with eicosanoic acid, by using gold nanoparticles of varying sizes immobilized on solid substrates as models. Additionally, our ability to regulate the overall geometry of the hybrid by controlling seed shape, and our ability to impart electrical conductivity to the organic component, will be explored. The kinetics of crystallization will be probed by in situ AFM experiments. In addition to ongoing collaboration with Dr. Helmuth Mohwald at the Max Planck Institute of Colloids and Interfaces, the proposal will seek to characterize the hybrid ultrathin film structure by neutron diffraction/scattering through collaboration with Dr. Stuart M. Clarke at the University of Cambridge. Intellectual Merit. Shape restrictive nucleation stems from the high curvature of a nanoparticle surface, which imposes unsustainable strains for tangential crystal growth. Other alternative controls for nanoparticle mediated nucleation of nanorods will be explored, which may include high supersaturation, favorable wetting of seed by nucleus, 1D growth habit, and seed surface defects. The seed mediated nucleation represents an alternative approach to nanoparticle and nanorod integration. Unlike previous work using seeds of the same building blocks as the nuclei, the proposed work will investigate the formation of the nanoparticle/nanorod architecture using heterogeneous and non epitaxial seed mediated nucleation, i.e. the nucleus is made of different building blocks (organic) than those of the seed (inorganic). The confinement control for small molecules at molecular length scales, 0.11 nm, is more difficult than the confinement by polymer length scales, 10100 nm. To date, very few reliable measurements of microscopic mechanisms and kinetics of molecular crystal formation at early stages have been made. If successful, the solutionbased, room temperature approach will facilitate divergent combinatorial and scalable chemistry for the construction of branched nano objects. The hybrid nanostructure allows the size dependent properties of each component to be tuned independently. Broader Impacts. Crystallization confined to nano media impacts a number of emerging technologies including thin film and high throughput screening devices. From a human resources perspective, U.S. students will gain international research experience by working with world leading institutions in interfacial materials research. Underrepresented undergraduate students will be recruited from the Michigan Louis Stokes Alliance for Minority Participation Program to participate in this global research training.