OUR RESEARCH FOCUSES ON DYNAMICS at scales that are small macroscopically (μm to mm), but are large compared to molecular sizes. The research combines statistical mechanics and fluid dynamics with advanced computing to elucidate the key physical processes that underlie laboratory observations and measurements. Current applications include:

REACTIVE TRANSPORT IN POROUS MEDIA Flow and transport in porous media are usually modeled at the Darcy scale, where the system is described locally by average properties, such as porosity, permeability, dispersion coefficients, and reactive surface area. Although this allows large volumes to be simulated efficiently, there are serious difficulties in developing suitable models for the properties of the individual elements. Pore-scale modeling overcomes many of the limitations of Darcy-scale models, replacing unknown functions with well-defined parameters. Nevertheless, it is not yet clear that a single set of parameters – fluid viscosity, ion diffusion coefficients, and surface reaction rates – can consistently describe the dissolution of samples with different pore structures. The goal of our DOE sponsored project is to investigate the dissolution of idealized samples both numerically and experimentally to prove (or disprove) the correctness of the underlying equations.

MIGRATION OF DNA IN COMBINED FLOW AND ELECTRIC FIELDS This project (in collaboration with Dr. Jason Butler) aims to investigate both the fundamental physics and potential biotechnological applications of the effect of a combination of hydrodynamic shear and electric field. From a fundamental point of view, the interest is to better understand the novel mechanism by which a charged polymer (like DNA) can be manipulated in directions perpendicular to the field lines. In a simple microfluidic device this can cause a rapid accumulation and trapping of the DNA, with implications for both biosensing and DNA extraction applications.

Education

Ph.D., 1978, University of Cambridge, Cambridge, England

Research Areas

Complex Fluids
Soft Matter
Transport phenomena

Awards & Distinctions

• American Institute of Chemical Engineers Thomas Baron Award
• American Physical Society Fellow
• Humboldt Research Award

Publications

• A. J. C. Ladd and P. Szymczak. /Comment on “Validity of using large-density asymptotics for studying reaction-infiltration instability in fluid-saturated rocks”./ J. Hydrol., 564:414-415, 2018. <http://dx.doi.org/doi:10.1016/j.jhydrol.2018.07.029>
• A. J. C. Ladd. /Electrophoresis of sheared polyelectrolytes./ Mol. Phys., In Press, 2018. <http://dx.doi.org/doi:10.1080/00268976.2018.1460498>
• V. Starchenko and A. J. C. Ladd. /The development of wormholes in laboratory scale fractures: perspectives from three-dimensional simulations./ Water Resources Res., In Press, 2018. <http://dx.doi.org/doi:10.1029/2018WR022948>
• P. Kondratiuk, H. Tredak, V. Upadhyay, A. J. C. Ladd, P. Szymczak./Instabilities and finger formation in replacement fronts driven by an oversaturated solution./ J. Geophys. Res., 122:5972-5991, 2017. <http://dx.doi.org/doi:10.1002/2017jb014169>
• A. J. C. Ladd and P. Szymczak. /Use and misuse of large-density asymptotics in the reaction-infiltration instability./ Water Resources Res., 53:2419-2430, 2017.<http://dx.doi.org/doi:10.1002/2016WR019263>
• V. Starchenko, C. J. Marra and A. J. C. Ladd. /Three-dimensional simulations of fracture dissolution./ J. Geophys. Res. Solid Earth, 121:6421-6444, 2016. <http://dx.doi.org/doi:10.1002/2016JB013321>
• I. A. Kent, P. S. Rane, R. B. Dickinson, A. J. C. Ladd, and T. P. Lele. /Transient Pinning and Pulling: A Mechanism for Bending Microtubules./ PLOS ONE, 11:e0151322, 2016. <http://dx.doi.org/doi:10.1371/journal.pone.0151322>
• M. Arca, A. J. C. Ladd, and J. E. Butler. /Electro-hydrodynamic concentration of genomic length DNA./ Soft Matter, 12:6975-6984, 2016. <http://dx.doi.org/doi:10.1039/c6sm01022a>