Synthesis and Self-Assembly of Amphiphilic Nanoparticles Based on Block Copolymers of Functionalized Vinylbenzocyclobutenes

University Of Akron, Akron OH

Investigators

Abstract

TECHNICAL SUMMARY Nanoparticles must be ordered into complex arrays with the control and reproducibility of biological systems for both nano- and biotechnology applications. Although asymmetrically functionalized nanoparticles are expected to self-assemble directly into complex structures without the need for template assistance, most nanoparticles are spherical in shape with isotropic surfaces. A new route is therefore proposed to synthesize relatively rigid, amphiphilic organic nanoparticles with rod or dumb-bell and tripod shapes for self-assembly into 1-D, 2-D, and/or 3-D superstructures, using amphiphilic block copolymers based on 1-functionalized vinylbenzocyclobutenes in which each of the vinylbenzocyclobutene-containing blocks undergoes isomerization at a significantly different temperature. The amphiphilic nanoparticles will therefore be fabricated step-wise by separate intramolecular crosslinking steps under pseudo-high dilution conditions in solvents that selectively solvate the non-crosslinking block(s). The lengths of the blocks will control the size of the lobes, and the nanoparticles are expected to be in the 5-20 nm size range. The intramolecular crosslinking reaction will be monitored by the disappearance of the resonances of the benzocyclobutene rings by NMR spectroscopy, and the change in the size and shape of the polymers/nanoparticles will be followed by gel permeation chromatography, light scattering, transmission electron microscopy (TEM), and/or atomic force microscopy (AFM) of samples prepared by a "fossilized liquid assembly" technique. Atomic force microscopy of "fossilized" samples will be used to determine the shapes of individual nanoparticles, and variations in their chemical composition as well as shape will be determined by TEM, scanning TEM and surface-enhanced raman spectroscopy; these techniques will also be used to characterize their self-assembled structures at a liquid-liquid interface or on a solid substrate. NON-TECHNICAL SUMMARY Particles that are small enough to be considered nanoparticles have unique properties compared to larger particles. These unique properties are leading to unique applications, which has led to the field of "nanotechnology". However, to make major advances in nanotechnology applications, the nanoparticles must be able to order into complex structures. Although complex structures can be generated by placing the nanoparticles on a surface with that complex pattern already built into it, computer studies have shown that nanoparticles should be able to order on a non-patterned surface if the particles themselves have complex shapes and/or complex surface properties. For example, if half of the nanoparticle surface likes water and the other half repels water, those two parts of the particle will only interact with similar parts on surrounding particles, such that their organization is directed or restricted by their similarities and differences. A new route is therefore proposed to create nanoparticles that have complex shapes, such as dumbbell and tripod shapes, in which each of their lobes have different surface properties. The different parts of the nanoparticle will be created stepwise using chemistry that reacts at a different temperature for each of the different lobes. These new nanoparticles will provide real materials to test theories that predict how nanoparticles organize when they have unusual shapes and varying surface properties. The proposed research will train student researchers in the increasingly important area of nanotechnology, simultaneously with requiring mastery of fundamental chemistry and physics. Undergraduate students will participate in this research program during the summer through an REU (research experience for undergraduates) position, in the NSF-sponsored REU Site for Polymer Science and Engineering at The University of Akron. In addition, a Special Interest Fair will be established for K-5 students at King Elementary School in Akron.