Current Research Areas:

Synthesis of novel nanostructured materials
The use of colloidal systems to direct the synthesis of nanoporous solids is currently an area of tremendous interest and activity worldwide. These materials are expected to find application as molecular sieves, catalyst supports, sorbents, and biomimetic materials. Mesoporous silicas having pore diameters in the range 1 to 20 nm and some desired pore structure (e.g., hexagonal, lamellar, cubic) can be selectively synthesized in aqueous solutions containing cationic surfactant liquid crystalline mesophases. In some cases, this process can be viewed as a simple templating mechanism; however, surfactant self-assembly is strongly influenced by composition and so the actual mechanism is a much more complex, cooperative one, in which reactive silicate ions and silicate oligomers may affect the mesostructure of the surfactant aggregates.

 

 SEM images of mesoporous silica films having lamellar (left), cubic (center), and hexagonal (right) pore structure, synthesized by spreading a precursor silicate/surfactant gel at a water/benzene interface. Thin and thick films (thickness > 100 mm) with long-range structure can be prepared by this method.

Chemical reactions in micellar solutions and emulsions
Literature provides a wealth of evidence showing that reaction rates for many different types of reactions are enhanced in the presence of surfactant aggregates, including normal and reverse micelles. This phenomena results primarily from the localized concentration of reactants, due to micellar solubilization and counterion binding, within these microheterogeneous solutions instead of large reductions in activation energy. Our objective is to extend current knowledge in this area to make it possible to employ micellar catalysis in the industrial manufacture of chemicals, demonstrating the usefulness of aqueous surfactant solutions as replacements for volatile organic solvents. This effort requires analysis of systems at much different compositions than have been studied previously; in order to achieve sufficiently high yields, our reaction systems are emulsions, so that mass transport, interfacial, and product effects must be taken into consideration.

Molecular self-assembly at fluid/fluid interfaces
Collaborator: Professor Chihae Yang
The adsorption of soluble and insoluble surface-active molecules at liquid/gas and liquid/liquid interfaces is important in a huge number of natural phenomena and chemical processes. We have a number of experimental and theoretical projects in this area, including: modeling the equilibrium and dynamic "two-dimensional" phase behavior of insoluble monolayers; monolayer formation in systems containing mixtures of soluble and insoluble surfactants; chemical reactions in monolayers.

Brewster angle microscopy images of lipid monolayers at low surface pressure: DPPC on water (left); DPPC on cell buffer (center); monoolein on water (right)

Surfactants at biological interfaces
Collaborators: Professors Jeff Chalmers and Chihae Yang
Surface active compounds are ubiquitous in biological systems and play a key role in many natural processes. Indeed, cell membranes themselves are self-assembled structures composed largely of surfactant-like lipid molecules. Surfactant additives are also commonly used in industrial bioprocesses: for example, in air-sparged cell cultures surfactants are used to prevent adhesion of cells to gas bubbles or other surfaces. These surfactants may also have harmful effects, causing lysis or undesired fusion of cells. We are studying the effects of surfactants on Langmuir lipid monolayers, which can be used as idealized models of cell membranes. Other membrane components such as proteins and glycolipids are added to investigate progressively more complex and realistic systems. These studies are performed in parallel with cell growth experiments to evaluate the influence of surfactants and other compositional effects on the viability of Chinese hamster ovary (CHO) cells. Correlation of results from the fundamental and applied studies lead to a better understanding of surfactant effects on cell membranes.

Brewster angle microscopy images of DPPC monolayers on aqueous buffer (pH=7.3) at high surface pressure (25 mN/m) before (left) and after (right) insertion of dimethyldodecylamine oxide (DDAO) from the subphase. DDAO, a common surfactant, appears to induce a phase change in the lipid membrane. These studies provide insight into the effects of surfactants on cell membranes.

Instrumentation and Experimental Methods

• Langmuir film balances and troughs
• Ellipsometry and Brewster angle microscopy
• Scattering
• Interfacial tensiometry
• Surface probe microscopy, atomic force microscopy

Previous Research Topics

• Thermodynamics of micelle formation in surfactant mixtures
• Micellar autocatalysis
• Effects of lecithin on the biotransformation of cholesterol to ADD/AD
• Synthesis of alkylphenyl ethers in aqueous solutions by micellar phase-transfer catalysis
• Powder separations by foam flotation

Past Group Members

Visiting Scholar
Ik-Hwan Kim
Professor, Bioengineering Department
Korea University

Doctoral Students
Jared Archer (2005)
Turgut Battal (2000)
Paul Kust (1997)
Michael Triplett (2004)
Pei Sun (2005)

Masters Students
Yani Angsani
Janine Lawrence
Oron Schuss
Maggie Pee (co-advisor: Linda Weavers, Civil and Environmental Engineering)
Cincin Siswanto
Dede Surjadi
Zhifeng Wang
Angela Younger (co-advisor: Jeff Chalmers, Chemical Engineering)
Haiying Zhou
Liang Hiong Chia (co-advisor: Linda Weavers, Civil and Environmental Engineering)
 

Undergraduate Researchers
Pat Bennett
Shona Patel
Nick Brunelli
Erica Jones
Gary Koenig

Visiting Graduate Students
Tomohiro Imura (University of Science, Tokyo)
Hirobumi Shibata (University of Science, Tokyo)
Alvin Caparanga
Edwin Obra