CBET Award Achievements
Notable Accomplishments from CBET Awards

Nanoparticle Stability by Quantum

Darrell Velegol & Milton Cole, The Pennsylvania State University

Background:  Many applications for nanoparticles (e.g., electronics, drug delivery, environmental agents) are hindered by a critical bottleneck: nanoparticles tend to clump together randomly, rather than remain dispersed or assemble in a controlled way.  Why do they clump?  The primary reason is the ubiquitous van der Waals (VDW) forces that cause non-specific and undesired aggregation of the particles.  These forces always exist between atoms and molecules, and they have been studied in various contexts for 75 years . . . but not for nanoparticles.  By studying VDW forces for nanoparticles systems, this work is providing intuition and quantitative results for controlling the VDW forces in real systems.

Results:  A primary result is the use of co-solvent systems to stabilize nanoparticles.  This result has been evaluated using the group’s “coupled dipole method”, the first method able to calculate accurate VDW forces between nanoparticles.  Why is this method accurate?  It accounts for every atom in the system, which is extremely important for nanoparticles, which can sometimes be only 10 atoms in diameter.  In contrast, previous methods have assumed “perfect spheres” or “perfect cylinders”, which do not exist with so few atoms.

Darrell Velegol Image
At the top of the image are
Stable Nanoparticles (groups of red atoms) with co-solvent "shield" (blue)
and at the bottom are Unstable (aggregated) Particles.

A primary result of this work is that nanocolloids can be more stable in solvent mixtures
(e.g., alcohol mixed with water).  One of the solvents selectively adsorbs to the particle surfaces,
giving a “bumper layer” that decreases the attractive van der Waals forces and gives better stability.
The research quantifies the van der Waals forces between particles in these solvent mixtures.

Credit:  Darrell Velegol & Milton Cole, The Pennsylvania State University

Scientific Uniqueness:  The unique point of Velegol and Cole’s method for calculating VDW energies and forces is that they solve the quantum mechanics and electrodynamics accounting for every atom in the system, in both particles and in the medium between.  No approximations about atomic position are made, as in models that assume perfect spheres or perfect cylinders.

Impact on Industry and/or Society:  This project is an important step in work on colloidal self-assembly, especially for nanoparticles, which is leading to colloidal devices and machines from the lab.  Nanoparticle aggregation has been a bottleneck problem industrially, and having an accurate model for VDW forces and energies enables the “design” of better stabilization methods.

This work is notable because it is the first to account properly for every atom in a nanoparticle system, for VDW force calculations.

This work is multidisciplinary. This project required the different perspectives of both a chemical engineering and a quantum physicist.  It took several years of working together before the primary result was achieved!  In addition, the group collaborated with experts in Belgium and India, as well as other researchers at Penn State, on published journal articles concerning this work.

This project addresses the NSF Strategic Goals of:  (1) Discovery and (2) LearningThe work promotes discovery in a field (nanotechnology) of tremendous transformative power.  By focusing on a broadly important yet very fundamental problem, the aim has been to be widely enabling.  This work contributed to the learning of two post-docs in an environment of international collaboration.  The "coupled dipole method" is now a clear, powerful method that contributes substantially to the research infrastructure not only at Penn State, but internationally.  This grant contributed to the training of two female post-docs, who are both now faculty members training their own students, including one at an HBCU (Historically Black Colleges & Universities).  This is good stewardship, using funds from one grant to promote diverse education more broadly.

This Nugget represents transformative research.  This research represents an important part of a transformation that is coming.  Scientifically the work is transformative for the VDW interaction problem; however, more broadly, by enabling the use of well-dispersed of controllably-assembling nanoparticles in actual technology, the work contributes to significant changes in the devices and machines that consumers will use in 10 years.

Program Officer:   Judy Raper
NSF Award Numbers:   0403646
Award Title:   NER: Nanoparticle Stability by Quantum Design of Van der Waals Forces
PI Name:   Darrell Velegol
Institution Names:   The Pennsylvania State University
Program Element:   1415

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This Nugget was Updated on 3 May 2007.