Particle-based Functional Materials
Research Experience for Undergraduates

PFM Example Projects

The research conducted in the PFM-REU will focus on two distinct applications of "particles" within functional materials: functional particles, and particle-mediated functional materials. As discussed briefly below, these two classes of functional materials impact energy, biomedical engineering/biotechnology, sustainability, manufacturing, and nano-science and materials.

Functional particles

In the area of functional particles, we will address (among others) biomedical aspects of functional particles, and the use of functional particles in process engineering as well as energy applications:

Biomimetic particle design: With respect to the physiological milieu, human cells are an impressive example of a functional particle that can encode information via spatially and temporally varying surface-bound and soluble-secreted signals. Importantly, this overall context is completely lost in bulk, systemic administration of therapeutic drugs. Recently, we have developed the necessary tools to mimic both surface-bound and soluble-secreted signaling in a degradable, autonomous polymeric particle that is the size of a living cell. More specifically, we have developed the first mathematical models capable of rationally designing a desired release profile for any given secreted factor. We have also developed new surface labeling strategies the allow us to not only bind bioactive materials in the correct orientation, but also spatially pattern these materials. Ongoing research will continue to explore functional particles that present combinations of micro-fabricated patterns of receptors and temporal presentation of secreted factors on living cells.

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Synthesis and Application of Hierarchically Structured Functional Particles: Hierarchically structured particles consisting of building blocks in multiple length scales at different levels, with the higher levels having a control or precedence over the lower levels, are of great interest for both fundamental research and technological applications. The design and synthesis of hierarchical structures provide the capability to tailoring material properties through tuning the accessibility of functional components, the curvature of interfaces, and the structure of the internal organizations. None of these parameters can be designed or controlled by traditional material engineering in a single length scale. Current projects include the use of these particles to make super water and oil repellent surfaces, remove toxic metals from water, and construct efficient and inexpensive bioassays.

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Nanomaterials for energy applications: Research in our laboratory focuses on the synthesis, characterization, and evaluation of nanomaterials for energy-related applications, such as clean combustion, hydrogen production, and catalytic fuel processing. While the vast potential of nanomaterials for this class of applications has been sufficiently demonstrated to-date, most of these nanomaterials suffer from insufficient stability at realistic technical conditions, severely limiting their prospects for real life application. A focus of the research in our laboratory is hence on the design of high-temperature stable, robust nanomaterials. We are investigating the design of ceramic matrices that allow stabilization of embedded metal nanoparticles without compromising their accessibility, and the modification of metal nanoparticles via alloying in order to enhance thermal stability. In this way, we have been able to stabilize metal nanoparticles up to temperatures as high as 900C. In parallel, we are investigating the exciting potential that simultaneous tailoring of the size, shape, and composition of nanostructured mixed oxides offers for engineering catalytic function. For example, we have been able to demonstrate the tailoring of reducibility of mixed Ce/La-oxide nanoparticles and nanorods for water-gas shift, a key reaction in the production of hydrogen and liquid fuels from fossil and renewable resources. Finally, we are starting a collaboration with researchers at the University of Pittsburgh Medical Center to investigate the toxicity of metallic nanoparticles, and how this toxicity is affected by size, shape, and encapsulation of these nanoparticles. All described activities involve a wide range of wet-chemical synthesis methods, a broad spectrum of techniques for materials characterization, and the evaluation of these materials in different test environments (from fixed-bed reactors to zebra fish), exposing undergraduate students to a broad range of experiences. At the same time, experience with undergraduate researchers in our laboratory has shown that each area (synthesis, characterization, and application/test) offers ample opportunities for a quick start through simple, basic steps, which can be expanded as the individual progress of the student allows.

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Particle-mediated functional materials

Particle-mediated functional materials have the potential to impact essentially any area of engineering practice. In the PFM research program, we will examine (among other topics):

Particle-stabilized foams: Polymer foams are commonly used for insulation, cushioning, or for reducing the weight and cost of plastic parts. Bubble coalescence during foaming places significant constraints on the range of plastics that can be foamed. We have developed a new mechanism of stabilizing polymer foams against coalescence, viz. inducing particles to adsorb on the surface of foam bubbles. Such interfacially-adsorbed particles form solid-like "shells" that protect bubbles against coalescence. Using this new mechanism, foams may be realized from plastics that are conventionally regarded as unfoamable. We aim to expand this research to foams based on clay nano-composites. The hypothesis is that by suitably engineering the surface chemistry of the clay nano-particles, foams of unprecedented low densities can be realized. We also aim to use particles with specific properties to realize foams with unusual functionalities. For example, by using metal nano-particles -- even at a very low loading -- we will develop electrically-conducting foams. Other ongoing research projects in our lab includes using particles to control the morphology of polymer blends; particle "jamming" in two dimensions; and thin films of highly charged particles that form photonic crystals.

Biomimetic functional materials: Responsive membranes can be designed such that their interactions with inclusions can be controlled through the application of an external stimulus. For example, by exploiting the interactions between a lipid bilayer and Janus nanoparticles, we can design a synthetic membrane with stable pores that can be controllably opened and closed. This leads to design rules for creating nanoparticle-bilayer assemblies where the pores open and the cargo is released only when local environmental conditions reach a critical value. Ongoing research will continue to explore designing artificial membranes, whereby one can explicitly introduce certain reactive or responsive components into the bilayers and determine how to activate these components through the appropriate choice of external stimuli.

Examples of Student "Internships" for PFM-REU

The purpose of the internships is both to increase the breadth of the students' hands-on experience as well as to enhance the integrative thinking of the students by showing them how seemingly disparate topics still exhibit commonality. As such, the students will be assigned --- in teams --- to work on internships that are widely separated from their summer research project. For example, two students working on experimental aspects of biomimetic functional materials may be asked to perform an internship on computational modeling of particle flow in process engineering. Each internship team will be assigned both a faculty and a graduate student or post-doc mentor in much the same way as they are for the research project.

The internship problems are comprised of very well-defined and short-lived (3-4 days) exercises. While the problems are not technically research in that the answers to the questions are likely known, they will introduce the students to important techniques and give them valuable "cross-training" experience.

Evaluating the wettability of particles: Numerous practical applications of particles require knowledge of their critical surface energy. Yet, direct evaluation of the surface energy is often difficult, since unlike for flat solid surface, it is not possible to directly measure the contact angle on a particle surface. Critical surface energy may be measured by testing whether the particles sink or float on the surface of a liquid of known surface tension; if they sink, the critical surface energy of the particle is presumed to be higher than the surface tension of the liquid. By repeating this test on a series of liquids of decreasing surface tension, the critical surface energy can be determined as the highest surface tension that can wet the particles. While easy to implement, this method is fraught with potential experimental errors associated with particle agglomeration, gravitational effects (dense particles tend to sink regardless of their wettability), and reproducibility of the way particles are deposited on the liquid surface.

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The goal of this project is to evaluate the accuracy of the float/sink method test. Experiments will be conducted using particles of materials (e.g. various polymers, or metals) whose surface properties are well-known. The critical surface tension measured by the float/sink test will be compared against known values for a variety of particle sizes, preparation methods, and deposition methods.

Drug delivery via erodable particles: Students will do a brief "internship" in the Little Labs by performing a simple design, fabrication, and release assay. We will first acquaint students with our novel model construct and the general concepts associated with rational design of drug delivery vehicles. Focus will be placed upon potential applications for their controlled release vehicle. Students will then "choose" their own design from a pre-set number of options (single injection vaccine, sustained medication, etc.) , and consequently, the fabrication parameters that they will implement. Students will then make their chosen formulation with a representative "drug" (fluorescently labeled Bovine Serum Albumen) as to facilitate easy detection. After the student's formulation is complete, students will detect the release of their "drug" using our fluorescent plate reader to determine if they achieved their design criterion.

Nano-structured membrane separation: We have developed codes to model flow of fluids through carbon nanotube membranes. We are currently investigating desalination of sea water with carbon nanotube membranes using various functional groups on the tube ends and nanotubes of various diameters. An undergraduate student will be able to run the existing code, modify the conditions of the simulation (pressure drop, temperature, salt concentration, nanotube diameters, etc.) and observe the resultant water flux, salt rejection rate, and so forth. Students will be able to analyze the simulation results using the VMD visualization package.

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