Jonathan K Whitmer
College of Engineering
Office: 122 Cushing
Ph.D, Physics, University of Illinois, Urbana-Champaign, 2011
M.S., Physics, University of Illinois, Urbana-Champaign, 2009
B.S., Math and Physics, Kansas State University, 2005
Assistant Professor, Department of Chemical and Biomolecular Engineering, University of Notre Dame, IN (2014-present)
Postdoctoral Research Scientist, Institute for Molecular Engineering at Argonne National Laboratories and the University of Chicago, de Pablo Lab, Chicago, IL (2013-2014)
Postdoctoral Researcher, Department of Chemical and Biomolecular Engineering, University of Wisconsin-Madison, Madison, WI (2011-2013)
Summary of Activities/Interests
- Equilibrium and Nonequilibrium Polyelectrolytes: Much in our world exists out of equilibrium. Weather patterns develop and disperse; cells grow and multiply; combustion engines turn molecular bonds into usable energy. Manufacturing processes utilize shear, compression, extrusion and flow to manipulate materials. At molecular scales exist glasses, comprising the solid-like phases of most synthetic polymers, and proteins, whose delicately-balanced folding is often irreversibly disrupted upon addition of salt or heat. In the particular case of soft materials, systematic study of nonequilibrium phenomena is daunting, with many length and timescales which must be simultaneously resolved. Strong electrostatic forces arising from Coulombic charge and hydrodynamic coupling due to motion in solvent exist alongside solvation and entropic interactions, competing and conspiring to yield intriguing, largely unexplained phenomena. Everything in these systems moves, and history of motion matters. This is particularly important for processing and presentation applications related to genomic analysis; it is also highly relevant for the charge and pH tunable assembly of polyelectrolyte complexes. My interests here are in understanding the equilibrium morphologies of charged biopolymers and polyelectrolyte complexes, and how these properties change under externally applied stresses. Elucidating these novel properties will lead to the design of new functional nanomaterials and devices.
- Liquid Crystalline Gels, Elastomers, and Sensors: Liquid crystals comprise phases of matter consisting of orientable molecules, referred to as mesogens, exhibiting properties intermediate between those of solids and liquids. They exhibit orientational ordering, and varying degrees of positional ordering that engender anisotropic mechanical, electric properties. Importantly, orientational ordering in these systems creates Schlieren textures that are not visible to the naked eye, but may be easily observed via polarized light microscopy. Distinct degrees of positional order are associated with different mesophases, referred to as isotropic, nematic, or smectic, to name a few. Through their interaction with surfaces or interfaces, these mesophases can include defects, regions of space where the orientation of the liquid crystal changes abruptly. The unique interactions between liquid crystal mesophases and polarized light form the basis for liquid-crystal display technology. Liquid crystal mesophases can be manipulated through the application of external fields, including surface fields, and they may incorporate defects that, owing to their topological charge and shape, have a unique signature in polarized microscopy. The ability of adsorbed impurities at an liquid crystal interface to alter these mesophases and any associated defects forms the basis of liquid-crystal based devices for detection of pathogens, including viruses and toxins. It is often desirable to combine the optical response of liquid crystals with the structural properties and enhanced stability of solids. Two methods that are able to solidify these materials include gelation of embedded colloids (which engenders soft solidity to the material) and polymeric crosslinking (which couples the mesogens to a rubber matrix. Colloids and nanoparticles within a liquid crystalline phase will create defects, and the system will seek minimization of its overall free energy by overlapping these defects. My interests in this area involves characterizing the elastic responses of liquid crystal dispersions and blends for use in novel technological applications, such as liquid crystalline biosensors, which leverage mechanical stability and elastic response.
- Colloidal Clustering and Assembly: Self-assembling structures are standard in nature; the delicate dance of functionally specific protein and nucleic acid macromolecules makes life possible. These are often only kinetically stabilized—if one perturbs the system through addition of salt or heat, the structure is denatured, transitioned to its thermodynamic ground state, and rendered useless. In the nascent discipline of molecular engineering, such structures are designed from the top down using molecular and macromolecular constituents. For instance, disordered colloidal solids have desirable properties as stable low-density solids that enhance (e.g.) food texture and shelf-life, while crystalline arrangements are desirable for photonic applications. The resulting structures may, as with proteins, be kinetically or thermodynamically stable. Simulation and theory has shown that kinetic trapping can often determine the final ordered structure into which the particles assemble. Proper prediction of these structures requires the understanding of both suspension thermodynamics and the effect of transient and processing flows on the particle assemblies. My interests are (1) the nucleation of colloidal clusters in equilibrium and nonequilibrium situations, (2) the cluster and crystal structures formed by patchy colloidal particles, and (3) the design of particulate systems which can be used to self-assemble into arbitrary structures.