Research in The Barron Group


Overall Goals and Concepts
Why aluminum?
Why an interdisciplinary approach?
Research Areas - Highlights and Present Topics
Group 13 Organometallic and Coordination Compounds
Alumina nanoparticles: from sol-gel to composites to hybrid materials
Chemical control over materials formation
Undergraduate research
Collaborative research
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Overall Goals of the Research in the Barron Group

As highlighted by a joint appointment in the Department of Chemistry and Department of Mechanical Engineering and Materials Science, research in the Barron group focuses on the chemistry and materials science of aluminum and its related elements in the periodic table.
Research within the Barron Group is aimed at understanding the relationships between the structure and bonding within a compound or material with its physical and/or chemical properties. With such an understanding it is possible to control structure at the both the nanometer and Angstrom level. The control of nanometer structure is aimed at allowing for the design macroscopic structure and/or properties. Thus, it should be possible to design new materials (whether molecular or not) through an understanding of these relationships.

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Why Aluminum?

Or rather why aluminum, gallium, indium (and occasionally boron)? Since the focal point of the research within the Barron group is not a single topic or a specific technique, but a group of elements, some explanation is warranted: aluminum is the most abundant metal in the earth's crust, and is one of the most important elements in the modern world.
Aluminum oxides are an ubiquitous part of modern technology. Applications include: precursors for the production of aluminum metal, catalysts, and absorbents; structural ceramic materials; reinforcing agents for plastics and rubbers, antacids, and binders for the pharmaceutical industry; and as low dielectric loss insulators in the electronics industry. Although the applications for aluminum oxides themselves are extensive, doped and mixed metal systems and non-oxide materials are of increasing importance, e.g., the III/V (13/15) semiconductor materials.
Organoaluminum compounds are of industrial importance in processes for making a wide variety of chemical products and as highly selective reagents in organic synthesis. More recently organometallic compounds of aluminum, gallium and indium have become important as precursors to electronic materials and ceramics.
Each of the areas described above provides significant challenges for a multidisciplinary approach to scientific research, both at the level of basic science and that of direct technological application.

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Why an interdisciplinary approach?

Given the interdisciplinary nature of modern science, techniques traditional to chemistry can be used to solve real problems in materials science and, as is often overlooked, materials science can aid in the development of new areas or answer questions in chemistry. The diversity of research interests within the Barron Group enables members of the group to not only gain a broad range of knowledge, techniques, and views, but to leverage off of the expertise of other group members in creatively approaching scientific questions. Interdisciplinary collaborations are for the mutual benefit of both parties. Individual expertise, which separately cannot solve specific problems, jointly brings novel approaches to the fore.
It is important that researchers use a combination of appropriate characterization methods depending on the problem being tackled. Equally, it is important for researchers to bring techniques to an area where they have not been traditionally employed. In addition to the tools traditional to inorganic chemistry (Schlenk techniques, NMR and IR spectroscopy, TG/DTA, X-ray crystallography, computational methods, etc.) members of the Barron Group have the opportunity to become knowledgeable in the use of more unusual methods (e.g., gas phase photoelectron spectroscopy, BET, XAFS, etc. ) and those often associated with Material Science (SEM, TEM, AFM, XPS, etc.).

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Research Areas - Highlights and Present Topics

The research undertaken in the Barron Group may be described by three thrust areas, summarized below.
Where appropriate, links are provided to give more details of specific research areas. Sub-links are also provided for "Figures" (which would slow downloading of the main text). Abbreviated references to specific publications are provided (Journal, year, volume, page) in the links, however, complete citations are provided in the full publication list.
Group 13 Organometallic and Coordination Compounds
This area involves a study of relationships between the structure and bonding in Group 13 compounds. We have extensively studied several fundamental reactions of Group 13 organometallics (i.e., their oxidation and hydrolysis) as well as investigating the factors that control physical properties such as volatility.
The Lewis acidity of Group 13 compounds is well known. We have investigated the extent to which Group 13 Lewis acids activate small molecules and other metals upon coordination. Recent work in the Group is aimed at using the chemistry of the Lewis acid-base interactions as a route to solid state chemical switches.
An industrial important class of catalysts are the alkylalumoxanes, in particular methylalumoxane (MAO). We have discovered the structure of alkylalumoxanes, and demonstrated that their activity is dependent on their Latent Lewis acidity. Recent work in the group has been aimed at developing new routes to active catalyst compounds.
A recent project is the use of Group 13 compounds as ligands for transition and main group metals.

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Alumina Nanoparticles: from Sol-Gel to Composites to Hybrid Materials
The acid hydrolysis of aluminum compounds as a route to ceramics has been known since the 1950's, but the structure of the sol-gels was unknown. We have shown that alumina sol-gels (also called alumoxanes) have a structural core of the mineral boehmite. This allowed us to create a route to these alumoxanes directly from the mineral. Our investigations into the carboxylate-substituted alumoxanes (carboxylate-alumoxanes) have shown them to be alumina nanoparticles which are surface stabilized by carboxylate groups.
Having developed a large scale, environmentally benign, synthesis we have investigated the application of the carboxylate-alumoxanes as ceramic precursors. Their nanoparticle nature allows for superior processing of composites and coatings. In addition, the pore size of the resulting ceramic is controlled by the identity of the carboxylate group which has led to our fabrication of alumina ultra-filtration membranes.
Given the wide range of carboxylic acids available and their ease of chemical modification, we have investigated the application of chemically functionalized carboxylate-alumoxanes as catalysts and the key components in composites for automotive and aerospace applications.

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Chemical Control over Materials Formation
Several efforts have been directed towards the development of mild and/or highly controlled chemistry-based approaches to the formation of inorganic solid materials. These methods, loosely grouped under the name "chemie douce" (soft-chemistry), pay close attention to the structure, stability, and mechanisms of product formation.
We have demonstrated the principle of molecular control over the phase of a CVD film. Not only can meta-stable phases be grown, but a new cubic phase of GaS is only formed from a precursor with a cubic Ga4S4 core. The control exerted by the molecular core was demonstrated by a step-by-step analysis of the reaction pathway. This chemistry has been expanded to other Group 13 chalcogenides and led to the fabrication of a new class of GaAs transistor.
Other chemically controlled reactions we have explored include: the first formation of InP nanoparticles by Me3SiCl elimination; a room temperature metal exchange with alumina nanoparticles allowing a route to mixed metal oxides; and the microwave synthesis of semiconductors.
The formation of chemically (functionally) graded interfaces has been an area investigated by the group. In particular, we have been interested in the "reaction bonding" of dissimilar materials such as metal:ceramic or ceramic:carbon.
Two recent projects involve the control and inhibition of cement formation and the catalyzed aqueous synthesis of ceramic thin films under ambient conditions. These are part of a new research area aimed at developing bio-materials mimics.

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Undergraduate Research

The importance of research in an undergraduate degree cannot be quantified. It is often the experience that shapes a student's future interest in science. Undergraduates that undertake research within the Barron Group are given their own distinct projects that are closely allied with an ongoing project within the Group.
For a list of publications with undergraduate researchers in the Barron Group click here.


Collaborative Research

Since no scientist works in isolation, the development of meaningful collaborations are an important part of the research program in the Barron Group. Interactions are fostered within both academia and industry, either to bring new expertise to the research group, or, alternatively, in order to tackle problems of interest to the group in new ways. Collaborations are intended for the mutual benefit of both parties. Individual expertise, which separately cannot solve specific problems, jointly brings novel approaches to the fore.
For a list of publications that have resulted from outside collaborations click here.
For publications resulting from our on-going (and extensive) collaboration with Professor Simon G. Bott (U of Houston) for X-ray crystallography, see full publication list.


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