My current research interests are in the area of interfacial rheology of multiphase systems at reduced length scales and sample volumes. Multiphase systems can be found everywhere in nature and industry: foods, pharmaceutics, cosmetics, paints, oil recovery, etc. The morphology and stability of these systems depend on dynamic interfacial properties and dynamics that are not yet fully understood.
Microfluidic measurement methods (e.g. droplet flows) are employed to probe the dynamics of interfacial surfactant properties and mass transfer rates. The microfluidic approach facilitates measurement of such interfacial properties at length scales typical of applications (<100 um, e.g. detergents). Furthermore, the geometry of microfluidic flow devices is easily adjustable, allowing for the measurement of dynamics under more realistic, complex flow conditions.
A microfluidic device is used to create a two-phase flow (small, isolated drops) through constriction / expansions. The interfacial tension is determined by the transient deformation of the droplet entering the constriction, and particle tracers are added to the droplet phase to track the internal velocity field. A detailed shape analysis is also performed on the drop, yielding the position of the droplet interface to less than one tenth of a pixel.
The internal velocity field is coupled with the detailed shape of the droplet and the interfacial tension to probe dynamic surfactant effects (i.e. Marangoni effects, gradients in interfacial tension along the interface). Specifically, measurements of the internal circulation velocity at only two points within the droplet are sufficient to determine the magnitudes of shear and dilatational interfacial rheological properties.
Awards and Honors:
National Research Council Postdoctoral Research Fellowship, 2008-Present.
NIST Sigma Xi Postdoctoral Poster Presentation, 1st place, Engineering Category, 2010.
Pennsylvania Space Grant Consortium Fellowship, 2004.
Deans’ Scholarship, Youngstown State University, 1999 – 2003.
Professional Promise Award, AIChE Pittsburgh Chapter, 2003.
NSF Green Processing REU, North Carolina State University, 2002.
J. Martin, S. Hudson, "Mass transfer and interfacial properties in two-phase microchannel flows," New Journal of Physics, 11, 115005, 2009.
J. Martin, J. Marhefkaa, K. Migler, S. Hudson, "Interfacial rheology through microfluidics," Advanced Materials, In Press, 2010.
J. Martin, S. Velankar, “Effects of compatibilizer on immiscible polymer blends near phase inversion”, Journal of Rheology, 51, 669-692, 2007.
J. Martin, S. Velankar, “Varying the blending protocol to control the morphology of compatibilized polymer blends”, AIChE Journal, 54, (3), 791-801, 2008.
J. Martin, S. Velankar, “Interfacial tension errors from the Cohen and Carriere analysis of imbedded fiber retraction”, Macromolecules, 38, 10614-10618, 2005.
J. Martin, S. Velankar, “Unusual behavior of PEG/PPG/Pluronic interfaces studied by a spinning drop tensiometer”, Journal of Colloid and Interface Science, 322, (2), 669-674, 2008.
D. Freytes, J. Martin, S. Velankar, A. Lee, S. Badylak, “Preparation and characterization of an injectable form of the porcine urinary bladder matrix”, Biomaterials, 29, 1630-1637, 2008.
J. Martin, S. Velankar, “Preparation and Rheology of High-dispersed Phase Morphologies in Compatibilized Immiscible Polymer Blends”, Submitted to AIChE Journal.
NRC Postdoctoral Fellow
Complex Fluids Group
University of Pittsburgh: Ph.D. Candidate, 2003 – 2007
NIST Polymers Division: NRC Postdoctoral Associate, 2008 – Present
B.A. Chemical Engineering, Youngstown State University, 2003
Ph.D. Chemical Engineering, University of Pittsburgh, 2007 Under Dr. Sachin Velankar. Dissertation title “Effects of surface-active block copolymers on two-phase flow”