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Figure 7. Instantaneous view of a lattice Boltzmann method simulation of a liquid drop just prior to colliding with an array of fibers.

Figure 8. Ultrabright fluorescent silica particles, the brightest particles ever synthesized.  They are 170 times brighter than particles of a similar size made of quantum dots.

U.S. Army Research Project: Smart Responsive Nanocomposites for Soldier Protection

The $2M Army Research Office (ARO) project on Smart Responsive and Nanocomposite Systems continues at Clarkson University. The research is led by CAMP Director Professor S.V. Babu and CAMP Professors Sergiy Minko and Igor Sokolov. The whole team includes ten other CAMP Professors: Ahmadi, Cetinkaya, Li, Jha, McLaughlin, Moosbrugger, Morrison, Privman, Shipp, and Suni. Two goals of the project are to develop protective clothing and self-healing composites.

Modeling of Smart Nanocomposites for Soldier Protection

Professors John McLaughlin and Goodarz Ahmadi (members of the US Army Research project team) are developing computer simulation programs to simulate the movement of liquid drops in “gradient” clothing. The idea underlying the work is that, by blending fibers of different wettabilities in a multilayer fabric, one can produce a wettability gradient that will block aerosolized chemicals from reaching a soldier’s body while permitting perspiration to pass through to the outer surface and evaporate. In the current phase of the modeling effort, the emphasis is on lattice Boltzmann method simulations since the LBM permits one to directly control physical properties such as equilibrium contact angles. The results of these simulations will be used to test volume of fluid (VOF) programs that are developed with FLUENT. The latter programs will be used for larger scale simulations of more realistic geometries. Figure 7 shows an instantaneous view of a LBM simulation of a liquid drop, just prior to colliding with an array of fibers.

The same general approach is being used in the project on self-healing composites. This project involves dispersing glass nanocapsules filled with a healing agent into epoxy matrices. When a crack propagates through the material, the capsules break. The goal of the modeling is to determine conditions under which the healing agent can flow from the broken capsules into the crack.

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Micro- and Macro-Mechanical Modeling of Self Healing Composite Materials

Professors Jha, Cetinkaya, Ahmadi, and Sokolov are studying the mechanical properties of self healing materials for this Army funded project. The objectives are to provide a fundamental knowledge of the mechanical behavior of undamaged and healed materials. A multi-scale model will be used to predict the effects of “healing fiber” concentration, aspect ratio, and modulus on the mechanical properties of the composite material. The response of self-healing composite structures to quasi-static and dynamic loads will be investigated. The modeling will determine stress/strain concentrations, failure mechanisms, stress wave propagation, and healing efficiency.

Processing and Characterization of Advanced Materials

CAMP Professor Dipankar Roy’s research focuses on processing and the characterization of advanced materials that have applications in energy storage and conversion, catalysis, chemical sensor technology and semiconductor device fabrication. To study these materials, he combines optical methods such as surface plasmon resonance spectroscopy and second harmonic generation with electrochemical techniques such as impedance spectroscopy, amperometry and voltammetry. More information about Professor Roy’s current research can be found at: http://www.clarkson.edu/~samoy/.

Nanostructured Silica Particles

Clarkson University Physics Professor Igor Sokolov synthesizes ultra-bright fluorescent silica particles. See Figure 8. Sokolov, along with Ph.D. student Yaroslav Y. Kievsky (now a research fellow at the National Research Council of Canada) and Clarkson undergraduate student Jason M. Kaszpurenko, has created a process to physically entrap a large number of organic fluorescent molecules inside a nanoporous silica matrix. The fluorescence of these particles is 170 times brighter than any particles of similar size created so far. The previous record was reached using quantum dots. These nanostructured microscopic silica particles have potential applications in medicine, forensic science and for environmental protection and other uses. Eventually there will be particles that can change color in different acidities and during temperature changes. The next step is to create a particle that would be a whole laboratory, simultaneously detecting many chemical environment factors such as temperature, acidity, and metal ions.

Professor Sokolov’s other research interests include studying the mechanics of human cells with atomic force microscopy and investigating the forces between various particles and surfaces in liquids, self-healing materials, human skin, and the fundamentals of self-assembly.

Interfacial Science and Engineering in Biotechnology

CAMP Professor Ian Suni’s research group is working on a series of projects, that borderline between materials science, engineering and biotechnology. They involve understanding and controlling the behavior of proteins and cells at solid surfaces, with applications in the development of biosensors, medical implants, and artificial organs. This requires the proper choice of a biocompatible surface and an effective linker chemistry to control protein/cell activity.

In collaboration with Michael Pugia and James Profitt from Bayer HealthCare (now Siemens Medical), Professor Suni and Ph.D. student Jianbin Wang have demonstrated the use of Au nanoparticle amplification of antibody detection in an electrochemical biosensor based on impedance spectroscopy. Au nanoparticle amplification has been widely used in biotechnology for visualizing and tracking cellular processes, but has not been widely used for amplification in electrochemical biosensors. For portable and implantable applications, electrochemical biosensors generally have lower noise levels, and hence lower detection limits, than optical biosensors.

Professor Suni and M.S. student Sonya Havens are also working with Professor Michael Twiss, of Clarkson’s Biology Department, to develop methods for sensing and capturing E. coli K12, a non-pathogenic strain of the common food pathogen. This involves the use of both antimicrobial peptides and antibodies arrays immobilized onto solid surfaces. Detection methods include both electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM).

Model of Burst Nucleation in Solution
 
With postdoctoral researcher Dr. Daniel T. Robb, CAMP Professor Vladimir Privman recently completed a comprehensive theoretical modeling study of the phenomenon of burst nucleation in solution, in which a period of apparent chemical inactivity is followed by a sudden and explosive growth of nucleated particles from a solute species. Burst nucleation has been given a widely accepted qualitative explanation by LaMer and Dinegar.

CAMP researchers have analyzed for the first time a quantitative model of burst nucleation, under the assumptions of instantaneous rethermalization below the critical nucleus size, and irreversible diffusive growth above the critical size. The behavior of the model at large times was derived, with the result that the average cluster size, as measured by the number of atoms, grows linearly with time, while the width of the cluster size distribution grows as square root of time. See Figure 9. An effective numerical scheme was developed to integrate the equations of the model, and compare the large-time asymptotic expressions to results from numerical simulation. Physical effects were studied which might cause real nucleation processes in solution to deviate from the behavior of the burst-nucleation model. Burst nucleation of nanosize crystals is an important step in a two-step synthesis process of uniform polycrystalline colloid particles, which find numerous applications and are studied experimentally and theoretically in CAMP’s colloid group led by Professors Dan V. Goia, Egon Matijevic and Vladimir Privman. This research has been funded by the National Science Foundation.