Biomedical subjects

Yet-Ming Chiang

Publications and source records attributed to Yet-Ming Chiang.

5 recordsLinked to original sources

PubMed2006

Virus-enabled synthesis and assembly of nanowires for lithium ion battery electrodes.

The selection and assembly of materials are central issues in the development of smaller, more flexible batteries. Cobalt oxide has shown excellent electrochemical cycling properties and is thus under consideration as an electrode for advanced lithium batteries. We used viruses to synthesize and assemble nanowires of cobalt oxide at room temperature. By incorporating gold-binding peptides into the filament coat, we formed hybrid gold-cobalt oxide wires that improved battery capacity. Combining virus-templated synthesis at the peptide level and methods for controlling two-dimensional assembly of viruses on polyelectrolyte multilayers provides a systematic platform for integrating these nanomaterials to form thin, flexible lithium ion batteries.

Bacteriophage M13↗

PubMed2006

Ionic colloidal crystals: Ordered, multicomponent structures via controlled heterocoagulation.

We propose a new type of ordered colloid, the "ionic colloidal crystal" (ICC), which is stabilized by attractive electrostatic interactions analogous to those in atomic ionic materials. The rapid self-organization of colloids via this method should result in a diversity of orderings that are analogous to ionic compounds. Most of these complex structures would be difficult to produce by other methods. We use a Madelung summation approach to evaluate the conditions where ICC's are thermodynamically stable. Using this model, we compare the relative electrostatic energies of various structures showing that the regions of ICC stability are determined by two dimensionless parameters representing charge balance and the spatial extent of the electrostatic interactions. Parallels and distinctions between ICC's and classical ionic crystals are discussed. Monte Carlo simulations are utilized to examine the glass transition and melting temperatures, between which crystallization can occur, of a model system having the rocksalt structure. These tools allow us to make a first-order prediction of the experimentally accessible regions of surface charge, particle size, ionic strength, and temperature where ICC formation is probable.

Biophysics↗

PubMed2005

Nanometer-thick surficial films in oxides as a case of prewetting.

Stable, nanometer-thick films are observed to form at the {1120} facets of Bi(2)O(3)-doped ZnO in several bulk-phase stability fields. Electron microscopy shows these surficial films to exhibit some degree of partial order in quenched samples. The equilibrium film thickness, corresponding to the Gibbs excess solute, decreases monotonically with decreasing temperature until vanishing at a dewetting temperature, well below the eutectic. Assuming that perfect wetting occurs at some higher temperature above the eutectic, as is observed on polycrystal surfaces and at grain boundaries in the same system, the adsorption and wetting events in this system illustrate temperature- and composition-dependent prewetting. The observation of a second class of thicker films coexisting with nanodroplets and a numerical evaluation of thickness versus temperature elucidate the critical role of volumetric thermodynamic terms in determining film stability and thickness. Analogous temperature-dependent surface films involving adsorbed MoO(3) on Al(2)O(3) were also observed.

Journal Article↗

PubMed2003

Peptides with selective affinity for carbon nanotubes.

Because of their extraordinary electronic and mechanical properties, carbon nanotubes have great potential as materials for applications ranging from molecular electronics to ultrasensitive biosensors. Biological molecules interacting with carbon nanotubes provide them with specific chemical handles that would make several of these applications possible. Here we use phage display to identify peptides with selective affinity for carbon nanotubes. Binding specificity has been confirmed by demonstrating direct attachment of nanotubes to phage and free peptides immobilized on microspheres. Consensus binding sequences show a motif rich in histidine and tryptophan, at specific locations. Our analysis of peptide conformations shows that the binding sequence is flexible and folds into a structure matching the geometry of carbon nanotubes. The hydrophobic structure of the peptide chains suggests that they act as symmetric detergents.

Microspheres↗

PubMed2002

Electronically conductive phospho-olivines as lithium storage electrodes.

Lithium transition metal phosphates have become of great interest as storage cathodes for rechargeable lithium batteries because of their high energy density, low raw materials cost, environmental friendliness and safety. Their key limitation has been extremely low electronic conductivity, until now believed to be intrinsic to this family of compounds. Here we show that controlled cation non-stoichiometry combined with solid-solution doping by metals supervalent to Li+ increases the electronic conductivity of LiFePO4 by a factor of approximately 10(8). The resulting materials show near-theoretical energy density at low charge/discharge rates, and retain significant capacity with little polarization at rates as high as 6,000 mA x g(-1). In a conventional cell design, they may allow development of lithium batteries with the highest power density yet.

Electric Capacitance↗