Current Projects

My research interests fall into the general category of complex fluids. The systems that I have studied are colloids -- mixtures of small, undissolved particles suspended in other surrounding substances. I have conducted experiments, theoretical work, and computer simulations on the dynamic and electric properties of colloids in alternating electric fields. The system we are studying is a mixture of small silica particles in silicone oil. Non-aqueous silica gels, similar to the ones we have studied, are used widely as "fillers" for optical-fiber cables. Silica is also the most widely used reinforcement agent for silicone rubbers. The interaction between silicone oil and silica, however, is not well understood on a molecular level.

Students who have finished two semesters of introductory physics courses are encouraged to contact me to arrange for independent studies courses (PHYS 250/350) or for summer research opportunities related to the following research projects.

• Gels and fractals
  
  In the academic year 2003-04, Seila Selimovic ’04 wrote an honors thesis with me on the aging behavior of silica gels. We discovered that mixtures of silica particles in silicone oil, initially a viscous paste, become a free-flowing liquid in about 2 weeks of time. We also discovered that viscoelastic moduli of our samples -- those at different ages, with different silica concentrations, and with different kinds of silicone oil -- can be scaled onto a single set of master curves, showing similarity in the gel network of all of the samples. Our findings on this aging behavior have been published in the Journal of Rheology in 2007. More experiments are currently being carried out to systematically characterize how the viscoelastic properties of silica suspensions change with time, and how factors like temperature, silica concentration, and surfactants affect the aging behavior.
  
  In the academic year 2004-05, Paula Popescu ’07 found that the dielectric spectrum of these silica gels changed little over time, in contrast to the drastic change in the mechanical properties of the suspensions over time. This apparent decoupling between the mechanical properties and the electrical properties is quite intriguing. Experiments are currently being carried out to investigate a possible fractal behavior in the electrical properties of these gels.
  
  
• Electrorheology
  
  When small particles are suspended in an insulating fluid, the elastic properties of the suspension are very sensitive to an external electric field applied to the fluid. Without the field, the fluid flows like a normal liquid. When a strong field is applied, the fluid can become very viscous and almost solid-like. These fluids are called electrorheological (ER) fluids. In the academic year 2002-2003, Stella Offner ’03 completed an honors thesis with me on computer simulation of ER fluids. This work has been published in the journal Physical Review E. In Spring 2005, Mona Ali ’06 analyzed the polarization of particles in alternating electric fields under shear. We are currently continuing the simulation work and studying the flow of electrorheological fluids in alternating electric fields.