My scientific interest involves extending the understanding of physics of complex fluids such as colloidal suspensions, emulsions and polymer composites to design new/multifunctional materials that are more energy efficient, environmentally friendly, clinically safe and cost effective. These studies are becoming particularly challenging when inherent material properties (e.g. opaqueness, thermal stability, photobleaching) limit utilization of conventional characterization techniques. Thus the nature of my research is based on simultaneous utilization of numerous characterization techniques, e.g. light scattering, optical microscopy, rheology, and microfluidics in conjunction with theoretical models. I attempt to answer fundamental questions such as how do materials’ pristine properties, the processing conditions and molecular/mesoscopic interactions affect the bulk properties? What are the mechanisms of structure formation under the influence of various parameters? What is the time scale of structural evolution under different processing conditions? How to control material bulk properties by manipulating the properties at smaller scales? To what extent do different forces contribute to transport of soft materials (such as vesicles, double emulsions, colloidal suspensions, etc.)?
Past Research Projects:
1) Microfluidic studies of emulsions and suspensions in wall-bounded shear flow (University of California, Berkeley)
• Investigated the individual dynamics and collective interactions of droplets and vesicles as drug delivery agents in microchannels.
• Analyzed flow behavior of complex fluids by experiments and simulations in micro-channels using micro-particle image velocimetrey (u-PIV).
• Investigated viscoelastic phenomena in microchannels with an abrupt contraction and the influence of channel geometry.
• Designed and fabricated microfluidic devices by thin film lamination and photolithography.
• Developed microfluidic devices for generation of monodisperse double emulsion droplets
• Khalkhal, Fatemeh, Kendrick Chaney and Susan Muller (2016), Optimization and application of dry film photoresist for rapid fabrication of high-aspect-ratio microfluidic devices, Microfluidics and Nanofluidics, 20 (11), 153.
• Khalkhal, Fatemeh and Susan Muller, (in preparation), Formation of inertio-elastic vortices of a shear thinning fluid in planar microfluidic abrupt contractions.
• Hidema, Ruri, Fatemeh Khalkhal and Susan Muller, Optimizing a microfluidic device to produce double emulsions, International Congress on Rheology (ICR), Kyoto, Japan, August 2016.
• Khalkhal, Fatemeh and Susan Muller, Dynamics of Double Emulsion Droplets in a Wall-Bounded Shear Flow, American Institute of Chemical Engineers Annual Meeting, Salt Lake City, UT, November 2015.
• Khalkhal, Fatemeh and Susan Muller, Microfluidic Studies of Emulsions and Suspensions in Wall-Bounded Shear Flow, American Institute of Chemical Engineers Annual Meeting, Salt Lake City, UT, November 2015.
2) A fundamental study to address carbon buildup in car engines by analyzing the efficacy of newly designed surfactants (Yale University)
• Proposed a set of bench experiments to simulate engine tests with high fidelity.
• Investigated the effect of temperature on dynamics of surfactant stabilized carbon black suspensions in lubricating oils.
• Developed robust adsorption isotherms to evaluate the performance of surfactants by FTIR spectroscopy.
• Elucidated basic structure-property relationships in the suspensions by combining rheology and adsorption isotherms.
• Khalkhal, Fatemeh, Ajay Singh Negi, James Harrison, Casey D. Stokes, David L. Morgan and Chinedum Osuji (2017), Evaluating dispersant stabilization of colloidal suspensions from the scaling behavior of gel rheology and adsorption measurements, Langmuir, 34 (3), 1092-1099.
• Khalkhal, Fatemeh and Chinedum Osuji, Scaling behavior of colloidal gel elasticity in the context of dispersant surface activity, Society of Engineering Science (SES) 50th Annual Technical Meeting, Brown University, Providence, RI, July 2013.
3) Characterization of flow-induced structures in carbon nanotube suspensions (Ecole Polytechnique de Montreal)
• Proposed a set of resolute experiments to characterize the flow-induced microstructural evolution of CNT suspensions quantitatively.
• Evaluated the kinetics of structure build-up under the influence of flow history, concentration and temperature.
• Investigated the mechanisms of structure formation during flow and in quiescent conditions.
• Investigated the nature of the suspensions network structure in the light of scaling and fractal theories.
• Analyzed the effect of flow history and temperature on fractal properties of the suspensions microstructure.
• Evaluated the performance of structural models in predicting the transient behavior of the suspensions.
• Analyzed the dynamics of the suspensions microstructure by coupling rheology and small angle light scattering (SALS).
• Khalkhal, Fatemeh and Pierre J. Carreau (2012) Critical shear rates and structure build-up at rest in MWCNT suspensions, J. Non-Newtonian Fluid Mechanics, 171-172, pages 56-66.
• Khalkhal, Fatemeh and Pierre J. Carreau (2011) Scaling behavior of the elastic properties of non-dilute MWCNT-epoxy suspensions, Rheologica Acta, 50(9), 717-728.
• Khalkhal, Fatemeh, Pierre J. Carreau and Gilles Ausias (2011) Effect of flow history on linear viscoelastic properties and the evolution of the structure of MWCNT suspensions in an epoxy, J. Rheology, 55(1),153-175.
• Khalkhal, Fatemeh, Characterization of flow-induced structures in carbon nanotube suspensions, Ph.D. thesis, Ecole Polytechnique de Montreal, Montreal, 2011.