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

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-paramete
r 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
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
Mount Holyoke
Providing opportunities to undergraduates in
nanotechnology and to develop a pipeline for a
diverse set of graduate students.