Gary L. McPherson - US grants

This project is to research the synthesis of two classes of materials. The first is biominerals, in particular, calcium carbonate, a well defined model in biomineralization studies. The objective here is develop systems for the control of crystal size and morphology. The biomimetic environments selected are those that exert spatial and structural control of mineralization. Reversed micelles and Langmuir-Blodgett (LB) films will be used. In addition, the role of proteins that regulate mineralization through geometric and stereochemical lattice matching will be investigated. The second class of materials is semiconductor nanoclusters of zinc and cadmium sulfides and selenides. Synthesis will again be approached through the use of reverse micelle environments. Control in-situ is to be carried out by a novel approach using clathrate hydrate formation, and this project will examine the effects of hydrate formation on particle size and structure.

This Americas Program award will support continuation of a research collaboration between Dr. Gary L. McPherson of Tulane University and Dr I. A. Kawha of the University of the West Indies, Jamaica. The research focuses on the luminescence spectroscopy and excited state dynamics of a series of novel macrocyclic complexes containing pairs of rare earth ions. Although the luminescence properties of a number of the macrocyclic rare earth complexes have been examined, many of the most important features of excited state behavior have not been explored. This project will provide valuable new information about these complexes and their interactions. Preparation and structural characterization of these unusual materials will be accomplished by Dr. Kawha at the University of the West Indies, while the luminescence of the materials will be examined in the laser spectroscopy laboratories at Tulane. This project will also involve undergraduate and graduate students from both institutions.

ABSTRACT
CTS-9909912
John, Vijay/Tulane U.

We propose a collaborative project to develop new nanostructured materials by exploiting the potentially templating environment of a self-assembled surfactant gel phase. The novelty of the gel is the fact that it contains equal volumes of water and an oil phase, thus opening up several possibilities of synthesis in dual hydrophobic and hydropbilic microenvironments. Our hypothesis is that the spatial immobilization of the hydrophobic and the hydrophilic regions will allow the formation of extended structures that are organized over multiple length scales. Our research thus seeks to systematically understand the gel phase and to exploit its features for materials synthesis.

The gel mesophase is formed by adding lecithin (phosphatidylcholine) to AOT-in-isooctane reverse micelles and increasing the water content of the system. The gel is formed when the volume fractions of water and isooctane become approximately equal, and continues to be stable upon further increase of the water content. The gel is optically clear and rigid. Our objective therefore is to synthesize materials in the hydrocarbon and aqueous microphases, or to exploit the properties of an oil-water interface that is immobilized over large length scales, for interfacial synthesis, We propose the synthesis of (a) polymer and inorganic materials with extended nanostructures, (b) polymer-inorganic nanocomposites where the polymer is synthesized in the oil phase or at the oil-water interface, and the inorganic component is synthesized in the aqueous phase, and (c) polymer-polymer structured nanocomposites using hydrophobic and hydrophilic monomers. Four different examples of materials synthesis are chosen. If these can be successfully demonstrated, the conceptual framework for generating an array of other important materials will have been developed.

Together with materials synthesis, we will concurrently carry out extensive studies to understand the microstructure of the gel phase and to correlate the gel microstructure with the morphology of the materials synthesized in the gel. The proposed work will use the AOT reverse micellar system as a reference point and seek to understand the transition to the gel phase. The synthesis of nanoparticles in AOT reverse micelles has been well-studied and it will be of interest to follow morphology evolution as the system follows the composition trajectory to the gel phase. Thus the research will seek to provide an understanding of how materials morphology can be systematically changed by the microstructure evolution of the templating medium.

The research is a collaboration between researchers at Tulane University and the University of Rhode Island. It is anticipated that such collaboration will expose the students involved, to a broad range of scientific experimental techniques and expertise. The PIs will seek to integrate their research with education both at the graduate and at the undergraduate level.

John, Vijay T.
Tulane University

"Environmental Remediation through Self-Assembly and Applications to Environmental Sensor Development"

The objective of this research is to develop a process for environmental remediation of aqueous streams containing aromatic compounds. The process involves incorporating well-known technologies with new science. Surfactant micelles will be first used to concentrate organic contaminants (typically phenols and aromatic amines) in aqueous streams, in a version of the well-studied micellar enhanced ultrafiltration technology (MEUF). The next step will be to polymerize these contaminants within the micelles using oxidative enzymes such as horseradish peroxidase. The resulting conjugated polymers are themselves very useful in coatings technologies, and in applications to electrooptics. The third step is to encapsulate the micelle-polymer assembly within the pore structure of mesoporous silicas (and titanias). This will result in useful polymer-ceramic nanocomposites where functionality of the encapsulated materials can be utilized to develop robust sensor materials that are photoluminescent. The encapsulation of enzymes through this route will also be evaluated in the development of novel chemo-biosensors.

Broader impacts

Excellent interdisciplinary training for both undergraduates and graduate students will be provided. The combination of spectroscopy, microscopy and scattering techniques that the students will be exposed to, will be an invaluable research experience. Tulane University operates a unique Coordinated Instrumentation Facility where centralized instrumentation and expertise allow excellent student training. The PI's are fully committed to providing educational opportunities, and have a strong record of working towards such objectives with formalized programs such as the Louisiana Alliance for Minority Participation in Research (LAMP). The research is the continuation of a collaboration at Tulane that has produced several Ph.D. graduates and has provided undergraduate research experience to over 10 students. From a technical prospective, the exploratory research phase will evaluate the feasibility of transforming environmental contaminants to useful, high value products.

The process of enzyme entrapment in mesoporous silicas will be used to encapsulate phosphotriesterase. Thin films of such enzyme containing silicas will be used to develop a sensor for the detection of nerve agent surrogates such as paraoxon.

ABSTRACT
CTS-0438463
Vijay T. John/ Gary L. McPherson
Tulane University

Self-Assembly of a Novel Organogel and Applications to Nanostructured Materials
Technical Summary

Fundamental and applied Nano-Technology research to develop a new class of self-assembled organogels that spontaneously form when an anionic surfactant (AOT) dissolved in a nonpolar solvent is contacted with the suitable phenol. There has been significant recent research interest in designing small molecule gelators that form polymer-like networks in nonpolar solvents through non-covalent interactions. Such gels have tremendous potential as templates for materials synthesis in applications such as nanostructured membranes, as potential field responsive materials for sensor development, and in environmental applications related to containing organic spills.

The PI's earlier work has indicated that the AOT+phenol organogel system appears to be made up of three levels of self-assembly, from strands to fibers and thence to fiber assemblies. The proposed work seeks to understand the transition from inverse micelles of the anionic surfactant, to the gel state, upon doping with the phenolic component. This will be done through a full range of experimental techniques involving FTIR and NMR spectroscopy, neutron, x-ray and light scattering, differential scanning calorimetry, atomic force and electron microscopy, and rheology.

The PI's then propose to develop these organogels as templates for materials synthesis. By polymerizing the solvent phase, we will be able to generate nanostructured materials. They will be able to incorporate functional nanoparticles (luminescent and/or magnetic) into the gel strands to prepare new field responsive materials with possible erasable signatures. In all these applications, we will exploit the novel properties of the gel (1) its ability to spontaneously form by direct contact of the anionic surfactant and the phenol, and (2) the ability to very easily destroy the gel template by washing with water, thus breaking the AOT-phenol hydrogen bonding responsible for gelation, once the materials synthesis is done. The research may lead to new and simple methods for thin film membranes containing functional and field responsive materials.

Broader impacts
The project will provide excellent interdisciplinary training for both undergraduates and graduate students. The combination of spectroscopy, microscopy and scattering techniques that the students will be exposed to will be an invaluable research experience. Tulane operates a unique Coordinated Instrumentation Facility where centralized instrumentation and expertise allow excellent student training. The project investigators are fully committed to providing educational opportunities, and have a strong record of working towards such objectives with formalized programs such as the Louisiana Alliance for Minority Participation in Research (LAMP). The research is the continuation of collaboration at Tulane that has produced several Ph.D. graduates and has provided undergraduate research experience to over 10 students.

From a technical perspective, the proposed research results may have applications to the development of novel nanostructured membranes and sensors. Rather than focus on a specific short-term application, the proposal is written to develop concepts that have implications in long-range technology development.

0933734
John

Intellectual Merit:

The proposed research is directed towards the design of multifunctional particles that are effective in the remediation of chlorinated hydrocarbons such as trichloroethylene (TCE). These hydrocarbons form a class of dense non-aqueous phase liquid (DNAPL) contaminants in groundwater and soil that are difficult to remediate. They have a density greater than water and settle deep into the sediment from which they gradually leach out into aquifers causing long term environmental pollution.

Research will be conducted to understand the fundamental science and technology behind the development of composite particles based on attaching zerovalent iron nanoparticles (NZVI) to highly uniform carbon microspheres. The carbon serves as an adsorbent to sequester TCE and bring the contaminant to the site of reaction, while the NZVI is the reactive site. Colloidal stability is enhanced by adsorbing a corona of a biodegradable polyelectrolyte, carboxymethyl cellulose. The novelty of the research is the coupling of reaction, adsorption, transport and stability through the use of a simple and inexpensive system that is potentially environmentally benign. The work is distinct from earlier work in that all aspects of remediation are concurrently considered through the use of these systems. If successful, it would lead to a fundamental understanding of chlorinated hydrocarbon remediation, and would transform the field since the materials used can be tuned for optimal reactivity and transport.

Broader Impacts:
From a scientific and technical perspective, the broader impacts of the research clearly lie in the application to an environmental problem of significant importance. Chlorinated hydrocarbons are pervasive pollutants in groundwater and sediments and the fact that they migrate downwards in aquifers makes them extremely difficult to remediate through traditional pump and treat or sediment excavation techniques. The problem is intrinsic to the global grand challenge problem of providing adequate safe drinking water to the worlds population. The research has the potential to be truly transformative as it addresses a unique methodology to develop multifunctional nanoscale materials for environmental remediation.

From an educational and outreach perspective, the project will tie in to providing research opportunities for undergraduates from underrepresented minorities, through the Louisiana Alliance for Minority Participation in Research program. Additionally, we will tie in to a unique program connecting Tulane, Xavier and Nunez College whereby educational enhancement in the chemical sciences is brought about through collaboration, with the objective of addressing the recruitment and retention of a skilled workforce in the region.

1043163
John

The Macondo Oil Spill caused by the explosion of the Deepwater Horizon drilling rig operated by Transocean for British Petroleum, has the potential to rank amongst the most serious environmental catastrophes unless effective measures are taken to mitigate the consequences to the environment. Most importantly, it is necessary to disperse the oil over a wide range of the ocean water column and prevent the oil from reaching the shore where it can accumulate and create long term ecological hazards. The proposed research addresses the issues relating to creating oil droplets which can be effectively dispersed in the ocean water column. Requirements for dispersant efficacy include the following (1) The dispersant must be applied at the target oil at sufficient dosage to form droplets (2) It is important that the dispersant be applied early before the lighter components of the oil evaporate (3) The dispersant must be able to lower the oil-water interfacial tension sufficiently so that small oil droplets can be created which can be dispersed over the water column (4) It is preferable that the oil droplets remain dispersed long enough to be biodegraded by marine organisms. Alternatively, if the droplets are widely dispersed, it may be preferable to find a method to sediment the oil to the ocean floor where they can be biodegraded. The PIs propose to conduct research that will address the following aspects of dispersant design and efficacy evaluation (1) studies on the compositional variations of dispersants and their effects on droplet microstructure and stability (2) effects of compositional variations of oil characteristics to understand if droplet solidification can occur at the low temperatures and enhanced pressures relevant to deepwater injection of dispersants (3) introduction of methane into the system at high pressures and low temperatures to define the existence of gas hydrates in emulsion droplets (4) the implementation of highly biodegradable surfactants and biosurfactants to reduce toxicity potential significantly (5) the implementation of particle stabilized emulsions to gradually sediment the hydrocarbons and subject them to biodegradation.

The impact of this research would be broad, as several large constituencies are being affected by this deepwater oil spill. They include livelihoods for the fishermen in the Gulf area, the ecological impact on the wetlands which may cause unsustainable inland erosion around the Louisiana coastline and a threat to wildlife that may undermine the prevailing ecosystem. And, indeed the future of oil drilling at these extreme undersea environments may be at stake. The PIs plan to disseminate the results of our research through on line postings as quickly as we can confirm their scientific validity, so that the broader scientific community can take advantage of them rapidly. Over the longer term (but clearly of less consequence at this moment of crisis), this research, which has a strong scientific underpinning but is focused on rapidly solving a critical national problem represents an ideal learning experience for graduate students. They plan to present the results of this work, as well as the broader problem and potential solutions to the local community through evening lectures, to students in our colloidal phenomena classes, and to high school students and teachers so that they are well-educated on the different aspects of oil spills. Both Tulane and URI have strong, streamlined programs at the universities for pursuing these avenues.

1236089
PI: John

The research is based on the finding that an aerosol based process can be designed to prepare hollow submicron particles in a consistent and rapid manner. The novelty of the finding is that the shells of these particles can be designed to constitute two distinct layers, an outer hydrophilic silica layer and an inner hydrophobic carbon layer. Additionally, the particles contain iron based nanoparticles which makes them magnetically responsive. The concepts behind the research are all based on a simple hypothesis that specific salts form bridging complexes with surfactants that negate the templating effects of the surfactant in the synthesis of ordered mesoporous materials. Rather, a thin ceramic shell forms that locks in chemical constituents in the core of a hollow particle. This sealing of the particle can be exploited to design a variety of new particulate morphologies including silica-carbon and silica-titania bilayer systems and a system of protrusions leading to the generation of a nanohorn type particulate system. All these particle morphologies are new, and are consistently obtained at appropriate constituent levels. The research attempts to firmly understand the formation of the particulate morphologies and validate the hypothesis behind the shell formation and understand its generality. In addition to fundamental research to understand the process, new applications will be developed in stimuli induced delivery, in photocatalysis and in the development of novel classes of colloidosomes.

Hollow submicron particles are intrinsically of much relevance to a variety of technologies including encapsulation and controlled delivery. Titania based hollow particles have a host of applications in photocatalysis and solar cell technologies, and magnetic hollow particles can be used in imaging technologies. Additional applications of the research include the development of materials to stabilize oil droplets and is thus relevant to oil spill mitigation technologies. The research will be integrated strongly with graduate education, undergraduate research experiences, and outreach efforts at the community college level.