Lehigh professor garners NSF grant to study macro-ionic 'blackberries'

May 16, 2006

Tianbo Liu, assistant professor of chemistry at Lehigh University, was recently named the recipient of the National Science Foundation CAREER Award. Liu was awarded $450,000 to fund research for a five-year period.

The Faculty Early Career Development grant, one of NSF's most highly competitive awards, supports researchers who integrate research and education.

Liu's research will focus on what he describes as "a new type of fascinating solution system," known as hydrophilic macro-ionic solutions. His work is expected to provide insight into catalytic, electronic, magnetic and biomedical materials.

"It is our common sense that soluble ions distribute homogeneously in dilute solution, and that anions are attracted to cations while repelling other anions," says Liu, who created a Lehigh course titled "Complex Solutions and Self-Assembly" to introduce students to progressions in hydrophilic macro-ionic solutions.

"But such well-accepted ideas seem invalid when the ions become larger, that is, macro-ions. In macro-ionic solutions, anions strongly attract other anions. They have much different behaviors from well-known conventional solution systems such as small ions, surfactants and colloidal suspensions, and they represent a transitional stage between simple ions and complex biomacromolecules."

Liu wants to study the phenomena of macro-ionic solutions, in which, he says, soluble macro-ions amazingly come together and form a type of new structure: single-layer, hollow, spherical structures which Liu calls "blackberries," or "strange aggregates formed by different types of polyoxometalate macro-ions (POMs).

"What are the detailed structures and properties of these 'blackberries,' their size, charge density, inter-macro-ion distance, mechanical strength and permeability to small ions?" he asks. "How do we effectively characterize the new structure by using various physical and chemical techniques? How do these blackberries form? How do changes in internal and external conditions affect their formation and structures? And, more importantly, why do large anions like each other? Can we use 'blackberries' as model systems to explore the properties of polyelectrolyte solutions that remain poorly understood?

"The unique inorganic 'blackberry' structure has a biomembrane-like nature - soft, robust and permeable to cationic species. It may also find applications in controlled drug carriers, nanocontainers or biomimetric materials," Liu says.

Liu received his Ph.D. in 1999 from the State University of New York at Stony Brook, where he specialized in polymer physical chemistry. After a two-year post-doctoral fellowship at Stony Brook, Liu went to Brookhaven National Laboratory as a physicist before joining the Lehigh faculty.

During his graduate work with complex fluids, particularly block copolymer solutions and colloids, Liu used such major techniques as laser light scattering (LLS) and small-angle X-ray scattering (SAXS) techniques. LLS is suitable for studying solutes and suspensions ranging in size from 1 to 1,000 nm. When Liu started to work at Brookhaven, he used LLS to characterize the solutions of giant inorganic ions.

"Traditionally," Liu says, "inorganic chemists do not care about LLS because inorganic molecules/ions are so small. I realized the size of the giant POM and decided to use LLS to characterize these solutions, and I obtained promising results."

What Liu found was the answer to a question that had puzzled chemists for several hundred years - the nature of the particles in solutions of molybdenum blue, or the so-called "blue water" mystery. LLS showed that various nanometer-sized, highly soluble inorganic anions were self-assembling into Liu's blackberries - 100-nm, single-layer, hollow spherical structures containing more than 1,000 single ions in diluted solution.
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Results of Liu's work were published in Nature and The Journal of the American Chemical Society, and described in New Scientist, Scientific American, Materials Today and Popular Mechanics.

Liu is now working with the Journal of Chemical Education to incorporate his recent research into textbooks.

Lehigh University

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