Rongjia Tao

Professor & Department Chair
Ph.D., Columbia University

APS Fellow

Office: BA212
Phone: 215-204-7651
Fax: 215-204-5652

Research Interests:

(1) Energy Science.
Presently, among all energy sources, liquid fuels, including crude oil, biodiesel, ethane, etc, are the leading source. The viscosity of liquid fuels plays an important role in energy production and energy conservation. For example, reducing viscosity of crude oil can speed up its transportation via pipelines and is the key to extract oil from oil sands and oil shale. Currently, the dominant method to reduce viscosity of complex fluid is to raise its temperature. This does not only require a large amount of energy, but also raises concerns of the green house effect in case of crude oil production and transportation. 
            Recently, based on the basic physics of viscosity, we developed a new technology, which utilizes an electric or magnetic field to change the rheology of complex fluid to reduce its viscosity, while keeping the temperature unchanged. The method is universal and applicable to all complex fluids with suspended particles in nano-meters, sub-micrometers, or micrometers. This technology is energy-efficient since it only requires small amount of energy to aggregate the suspended particles.
            When this method was applied to crude oil, the exciting results led the American Chemical Society to make a press release on August 23, 2006. Recently we applied this technology to refinery fuels for an efficient fuel injection. The exciting results led the American Chemical Society to make another press release on Sept. 25, 2008.
            Currently we are working on projects related to oil recovery from oil sands, off-shore oil transportation, heavy crude oil transportation, biodiesel production, and efficient fuel injection to improve the efficiency of internal combustion engines.

(2) Formation of high temperature superconducting balls

Self-aggregation into a ball is very rare in nature. Application of electric field further destroys space's isotropy. However, we have found that an electric field could drive high Tc superconducting (HTSC) particles into a ball. The experiment uses micrometer-size HTSC powders in liquid nitrogen. When a strong dc field is applied, the dispersed particles quickly form big balls, bouncing between the electrodes. If the temperature is above Tc, the balls disappear. Our current understanding relates this phenomenon to a new positive surface energy induced by surface charges on the HTSC particles. After an electric field is applied, HTSC particles pick up charges from the electrodes. These charges stay at the particles' surface, forming a thin charged layer. When the electric field within the layer is strong enough, it depletes Cooper pairs within the layer. This loss of superconducting condensation energy becomes a positive surface energy. Its minimization leads to the ball formation. As reported by Physics Today (p.9, Feb. 2000), Science News (VI 57, p2 1, Jan.8, 2000), and Physics News Update (Item 464, 1999), this discovery has received great attention. Our research explores the basic science and possible applications of this new property of superconductivity.

(3) Smart Fluids, electrorheological (ER) and magnetorheological (MR) fluids

In research on smart fluids, we have focused on the physical mechanisms, phase transitions, materials, microstructures, and dynamic process. As reported by Nature (V358, 373 (1992)), Scientific American (October, 58 (1993)), (German) Rheology journal (V.3, 284-285, Oct.-Dec. 1993), and New York Times (9/24/1996), our research in this area has received great attention and wide interest. On this project, we have extensive cooperation with industries, such as Ford Motor, Lord Corporation, Nippon Shokubai Co. Ltd. (Japan), Asahi Chemical (Japan), and Bridgestone/Firestone. Based on our understanding about the microstructure of MR and ER fluids, we recently invented a novel approach to change the microstructure of these fluids and produced super-strong MR and ER fluids. These fluids are about 10 times stronger than conventional MR and ER fluids. Their impact will be significant.

(4) Three-dimensional photonic crystals and communication

This research project is focused on 3-D photonic crystals and their application in communication. We have used irreversible ER and MR effect to produce 3-D photonic crystals, which have particles in micrometer size arranged in dielectrics periodically. The metallo-dielectric photonic crystals produced by this method have robust photonic band gaps. The analogy between the propagation of electromagnetic waves in photonic crystals and electron waves in atomic crystals has stimulated the excited research. We expect 3-D photonic crystals will have important applications in lasers, optical communications, quantum computers, etc.


(5) Nonlinear Optics

The goal of this project is to convert laser beams into coherent vacuum ultraviolet (VUV) or soft x-ray radiation by second-harmonic generation (SHG) of nonlinear optical crystals. Up to date, nonlinear optical crystals failed to produce SHG in VUV and x-ray region. The main cause is that these crystals are strongly absorptive in this region. To clarify the issue, we have developed a theory: absorptive nonlinear crystals can produce strong SHG signals under a double resonance condition; however, the conventional configuration does not work; we must use a new configuration, especially use a crystal film instead of bulk crystals. The preliminary experiment seems to support the theory. I am confident that a small VUV and X-ray laser suitable for conventional laboratories will become reality.

Selected Publications:

"Three-dimensional Structure of Induced Electrorheological Solid," R. Tao and J. M. Sun, Phys. Rev. Lett. V67, 398-401 (1991).

"Laser Diffraction Determination of the Crystalline Structure of an Electrorheological Fluid," T. J. Chen, R. N. Zitter, and R. Tao,  Phys. Rev. Lett. V68, 2555-2558 (1992).

"Simulation of Structure Formation in an Electrorheological Fluid," R. Tao and Q. Jiang, Phys. Rev. Lett. V73, 205-208 (1994).

"Second Harmonic Generation of Nonlinear Optical Crystals in Vacuum Ultraviolet and X-Ray Region," T. J. Chen, R. N. Zitter, and R. Tao, Phys. Rev. A V51 706-711 (1995).

"Formation of High Temperature Superconducting Balls," R. Tao, X. Zhang, X. Tang, and P. W. Anderson, Phys. Rev. Lett. V. 83, 5575-78 (1999).

"Path-integral approach to the statistical physics of random systems", R. Tao,J. of Statistical Physics, V103, N3/4, 575-588 (2001).

"Super-strong Magnetorheological Fluids", R. Tao, Journal of Physics:Condensed Matter Physics, V13, R979-R999 (2001).
"Three-dimensional dielectric photonic crystals of body-centered tetragonallattice structure", R. Tao, D. Xiao, Appl. Phys. Lett. 80, 4702-4704 (2002).
"Electric field induced formation of low temperature superconducting balls", R. Tao,X. Xu, Y.C. Lan, and Y. Shiroyanagi, Physica C, 377/ 3, 357-361 (2002).

"Structure and dynamics of dipole fluids under strong shear," R. Tao, Int. J. of Modern Physics B, V17, N16, 3057-3063 (2003).

"High temperature superconducting ball formation in low frequency ac fields," R. Tao, X. Xu, and E. Amr, Phys. Rev. B. V68, 144505-144511 (2003).

 “High temperature superconducting ball formation in low frequency ac fields,” R. Tao, X. Xu, and E. Amr, Phys. Rev. B. V68, 144505-144511 (2003).

 “MgB2 superconducting particles in a strong electric field,” R. Tao, X. Xu and E. Amr, Physica C, V398, N3-4, 78—84 (2003).

 “Interactions between a rotating polarized sphere and a stationary one in an electric field,” R. Tao and Y. C. Lan, Physical Review E 72 (4), 041508-1 to -7, (2005).

 “Structure and Dynamics of Dipolar Fluids under Strong Shear,” R. Tao, Chemical Engineering Science, V. 61/7, 2186-2190 (2006).

 “Electrostatic separation of superconducting particles from a mixture”, R. Tao, X. Xu, D. Khilnaney-Chhabria,  Applied Physics Letter, 88, 082503-1 to 082502-3 (2006).

“Reducing the viscosity of crude oil by pulsed electric or magnetic field,” R. Tao and X. Xu, Energy & Fuels, 20, 2046-2051 (2006).

 “The Physical Mechanism to Reduce Viscosity of Liquid Suspensions,” R. Tao, International J. of Modern Physics B, V. 21, N28&29, pp4767-4773 (2007).

“Structure of Polydisperse Inverse Ferrofluids: Theory and Computer Simulation,” Y. C. Jian, Y. Gao, J. P. Huang, and R. Tao, J. of Physical Chemistry B, 112, pp 715-721 (2008).

 “Electrorheology leads to efficient combustion,” R. Tao, K. Hunag, H. Tang, and D. Bell,  Energy & Fuels (to appear on Nov. 19, 2008).