Directed Assembly of Nanostructures

1. Directed Assembly of Nanostructures Directed Assembly addresses the fundamental scientific issues underlying the design and synthesis of new nanostructured materials, structures, assemblies, and devices with dramatically improved capabilities for many industrial and biomedical applications. It focuses on discovering and developing the means to assemble nanoscale building blocks with unique properties into functional structures under well-controlled, intentionally directed conditions. Directed assembly is the fundamental gateway to the eventual success of nanotechnology. It is based upon well-integrated research efforts that combine computational design with experimentation to discover novel pathways to assemble functional multiscale nanostructures with junctions and interfaces between structurally, dimensionally, and compositionally different building blocks. These efforts are leading to new methodologies for assembling novel functional materials and devices from nanoscale building blocks that will lead to novel applications of nanotechnology to spur industry into the 21st century.

2. Center for Directed Assembly of Nanostructures NSF NSEC at Rensselaer Polytechnic Institute in partnership with the University of Illinois at Urbana-Champaign, Los Alamos National Laboratory, Industry, and New York State. MISSION: We will integrate research, education, and technology dissemination, and serve as a national resource for fundamental knowledge and applications, in directed assembly of nanostructures • Combine computational design with experimentation to discover novel pathways to assemble functional multiscale nanostructures with junctions and interfaces between structurally, dimensionally, and compositionally different nanoscale building blocks • Excite and educate a diverse cadre of students of all ages from K-12 through postdoctorate in nanoscale science and engineering • Work hand-in-hand with industry to develop nanotechnology for the benefit of society

3. Structure and Properties of Nanoparticle Gels Figure: Scaled dimensionless elastic moduli (at 1 Hz) as a function of polymer concentration scaled by its value at the fluid-gel transition for a 40% volume fraction nanoparticle suspension and several values of the polymer-to-particle size ratio, Rg/R. The line indicates the theoretical prediction based on a cluster diameter of ~ five particle diameters. The structural and viscoelastic properties of high volume fraction nanoparticle-polymer suspensions have been systematically studied experimentally in both the equilibrium fluid and nonequilibrium gel states The low frequency elastic modulus grows rapidly with increasing depletion attraction near the gel boundary, but becomes a dramatically weaker function of polymer concentration as the gel state is more deeply entered. A novel microscopic statistical mechanical theory has been developed and shown to be in good agreement with experiment for both equilibrium collective nanoparticle structure over all length scales and the location of the gel boundary. The theory predicts a universal type behavior for the gel elastic modulus as a function of attraction strength (polymer concentration) and spatial range (polymer size) which has been experimentally verified. Based on the experimentally deduced non-equilibrium cluster size of roughly five nanoparticle diameters (see Figure),the no-adjustable-parameter calculations are in excellent agreement with the modulus measurements. (A. Shah, Y. L. Chen, K. S. Schweizer and C. F. Zukoski, J.Chemical Physics 119, 8747, 2003).

4. Carbon Nanotube Based Gas Sensor Based on MWNT Arrays Figure 1. Schematic of carbanion formation and subsequent initiation of polymerization (a) section of SWNT sidewall showing sec-butyllithium addition to a double bond and (b) the carbanion attacks the double bond in styrene and transfers the negative charge to the monomer. Successive addition of styrene results and a living polymer chain is formed. Figure 2. Aligned multiwalled carbon nanotube arrays (inset image; scale bar is 100 microns) used as electrode (anode) in a device (schematic shown on the right) that was used as a breakdown sensor. Recent collaborative work of P. M. Ajayan and N. Koratkar at RPI. The idea of gas sensing here is based on an aligned carbon nanotube array electrode. Gases break down at specific voltages, but conventional breakdown sensors have bulky architectures, since very high voltages are needed for the breakdown of most common gases. Here, the nanotubes concentrate the electric field at their tiny tips and hence brings down (several fold; for example, from ~1000 volts for planar metal electrodes to ~100 volts for a nanotube electrode, for a set electrode separation) the value of the applied voltage needed for breakdown. The use of nanotube electrodes could ultimately lead to the fabrication of small portable breakdown gas sensing devices (A. Modi, et al., Nature 424, 171-174, 2003).

5. Working in Partnership with Industry • Unrestricted gifts received totaling $1 million annually (with $500K used as annual NSEC match) • Results are shared with industry partner on a royalty-free, non-exclusive basis • Funds company-named graduate and postdoctoral fellows and distinguished lectures in Materials Science and Engineering at Rensselaer Polytechnic Institute Electrical behavior of polymer nanocomposites Mechanical behavior of polymer nanocomposites Eastman Kodak Optical/mechanical multifunctional coatings Nanocomposites for microelectronics Nanoscale biomaterials Nanoscale catalysts Nanostructured intermetallics

6. m m m Nanoparticle Control of Polymer Supermolecular Morphology A collaborative effort between L.S. Schadler, R.W. Siegel, Y. Akpalu (RPI) and ABB focuses on using nanoparticles to control the supermolecular morphology of semicrystalline polymers and their properties. The figure shows the effect of 20 nm diameter TiO2 nanoparticles dried or coated with N-(2-aminoethyl)3-aminopropyl-trimethoxysilane (AEAPS) on low-density polyethylene (LDPE). There is no change in unit cell dimension, degree of crystallinity, average lamellar thickness, or average spherulite size. The supermolecular structure, however, is impacted. Neat LDPE and the dried sample exhibit a well-defined, impinging, banded spherulite structure. The nanoparticles are embedded between the lamellae. In great contrast, no well-developed banded spherulites are observed in the AEPS sample, in which nanoparticles segregate to inter-spherulitic regions. This supermolecular structure is critical in controlling electrical breakdown strength in LDPE. Figure: AFM tapping mode images of the supermolecular structures of (a) neat LDPE (b) LDPE filled with more compatible dried TiO2 nanoparticles and (c), LDPE filled with non-compatible AEAPS coated TiO2 nanoparticles.

7. Educating the Scientists and Engineers of Tomorrow BOAST at UIUC Bouchet Outreach and Achievement in Science and Technology Junior Museum of Troy The Molecularium Stimulating academically at-risk children's interest in science, and serving as a national resource for hands-on science and Internet lessons. Introducing 5-9 year olds to the wonders of the molecular scale world, much the way that they have been learning about the wonders of the Universe and Solar System. Undergraduate Research Collaboration with Colleges MountHolyoke Providing opportunities to undergraduates in nanotechnology and to develop a pipeline for a diverse set of graduate students.