About

Donald L. Koch is a full professor at the R.F. Smith School of Chemical and Biomolecular Engineering at Cornell University, located in Olin Hall, Room 167C. He received his B.S. in chemical engineering and B.A. in history from Case Western Reserve University in 1981, and his Ph.D. in chemical engineering from the Massachusetts Institute of Technology in 1986. After completing a postdoctoral fellowship at DAMTP in Cambridge University, he joined Cornell's School of Chemical Engineering. His research interests encompass rheology and transport processes in particle suspensions, porous media, and micro- and nano-structured materials, as well as particle-filled polymeric materials, solvent-free nanoparticle fluids, and aggregation processes in colloids and aerosols. He also investigates non-continuum gas flows, collective behavior of swimming micro-organisms, convective heat and mass transfer in particulate systems, and geologic sequestration of carbon dioxide, among other topics. Dr. Koch is a fellow of the American Physical Society, has coauthored over 100 scientific publications, and has supervised 18 Ph.D. students. His contributions include advancing understanding in fluid dynamics, complex fluids, and sustainable energy systems.

Research topics

• Physics
• Materials science
• Classical mechanics
• Composite material
• Mechanics

Selected publications

• Suppression of Electroconvection Due to Attractive Forces between Dissolved Polymers and A Metal Electrode

  Journal of The Electrochemical Society · 2026-04-03

  articleOpen accessSenior author

  Electroconvection in rechargeable batteries enhances the growth of non-planar deposits at the electrode surface and this can result in the formation of dendrites during the charging process. Experiments performed by Sharma et al. [ Langmuir 2023, 39, 1, 92–100] showed that the addition of low molecular weight polymers to the electrolyte can delay the onset of electroconvection because of the formation of a thin layer of higher polymer concentration adjacent to the electrode. In this study, we develop a model for the formation of such layers due to attractive potential forces such as van der Waals forces. Using linear stability analysis and nonlinear numerical simulations, we show that the van der Waals forces acting on the dissolved polymer result in a restoring body force on the electrolyte that opposes the growth of perturbations to the one-dimensional base state. This force opposes electroconvective flow, leading to increased critical voltages required for the onset of electroconvection, reduced growth rates of the combined electroconvective-morphological instability, time delays in the onset of electroconvection, and smaller overlimiting currents. The use of low-molecular weight polymers ensures that the properties of the bulk electrolyte are not significantly affected.

  PublisherDOI

• Linking the rheology of thermal amorphous materials to molecular-scale physics

  Journal of Fluid Mechanics · 2026-01-19

  articleOpen access

  Amorphous materials transition from solid-like to liquid-like behaviour (yield) under large stresses. Their constituent elements are caged in metastable configurations due to their neighbours. Microscale interactions between these elements lead to a large energy barrier to break the cages and trigger a plastic rearrangement. Thermal fluctuations can alter the yielding point as the elements hop to new configurations in anticipation. This work bridges the gap between molecular-scale physics and bulk rheology in thermal amorphous materials by connecting a classical density functional theory to a thermally activated elastoplastic model (EPM). We use a model system of solvent-free polymer-grafted nanoparticles which show rheological characteristics similar to those of soft glassy materials. We formulate the evolution of the free energy in a deforming array of polymer-grafted nanoparticles to obtain the energy landscape as an input to our EPM. We examine how the apparent yield stress depends on the shape of the energy landscape, thermal fluctuations and the rate of deformation. Our general scaling analyses reveal different regimes of structural relaxation governed by the applied shear rate and the inherent time scale for thermal hops. The complex interplay between mechanical loading and thermal fluctuations is further characterized by performing a variety of shear tests with different deformation history. The proposed framework provides an understanding of the yielding transition by integrating across a vast range of length and time scales.

  PublisherDOI

• Stress analysis of dilute particle suspensions in non-Newtonian fluids with efficient evaluation in the weakly non-Newtonian limit

  Journal of Rheology · 2026-01-08

  articleSenior author

  We present a semi-analytical framework to compute the suspension stress in dilute particle-laden non-Newtonian fluids, separating Newtonian and non-Newtonian contributions. The ensemble-averaged stress includes both the particle-induced non-Newtonian stress (PINNS) and an interaction stresslet arising from surface tractions due to the non-Newtonian stress and its induced Newtonian flow. Using a generalized reciprocal theorem, we express this interaction stresslet entirely in terms of the non-Newtonian stress, for a general constitutive model. For weakly non-Newtonian fluids, regular perturbation expansion combined with the method of characteristics yields all leading-order stress contributions from the Newtonian velocity field alone, avoiding the need to solve coupled partial differential equations. This generalizes the method of Koch et al. [Phys. Rev. Fluids 1, 013301 (2016)] beyond polymeric fluids to any weakly non-Newtonian medium driven by velocity and its gradients. We apply the method to two systems: (i) spheres suspended in a fluid of smaller spheroids, where the interaction stress becomes negative for sufficiently anisotropic shapes due to orientation misalignment of the spheroids; and (ii) suspensions in weakly anisotropic nematic liquid crystals. In the latter, assuming a uniform director field fixed by an external field, PINNS vanishes while interaction stresslets remain, either opposing or enhancing background anisotropic stress. These results demonstrate the utility of our framework in capturing first-order particle–microstructure interactions across a broad class of non-Newtonian fluids.

  PublisherDOI

• Simulating the swimming motion of a flagellated bacterium in a microstructured bio-fluid

  arXiv (Cornell University) · 2026-03-28

  preprintOpen accessSenior author

  We develop a numerical framework to simulate the locomotion of a flagellated bacterium with a spheroidal head (such as Escherichia coli) in biological fluids like mucus, which are entangled polymer solutions exhibiting elasto-viscoplastic (EVP) rheology and porous microstructure. To account for the scale disparity between the large bacterial head and the slender flagellar bundle, whose thickness is comparable to the pore size, we employ a two-fluid model in which the bundle directly drives the solvent and exchanges momentum with the polymer phase via drag proportional to their relative velocity. The numerical implementation combines a finite-difference discretization of the two-fluid equations with a slender-body theory (SBT) to model flagellar forcing. A key observation is that the coupled mass and momentum equations for these inertialess flows, together with SBT, are linear in the pressure and velocity fields and in the force distribution along the flagellar bundle. By treating the polymer stress as a body force, we decompose the flow field and hydrodynamic moments into three additive contributions: kinematic (motion), flagellar forcing, and polymer stress. This decomposition allows several components of the flow to be precomputed and enables the determination of swimming velocity via a resistivity formulation driven by polymer-induced forces, which greatly improves computational efficiency during transient calculations of the polymer stress and the resulting flow. We validate the method and use it to analyze how polymer microstructure and its interactions with the bacterial head and tail affect motility in complex biofluids.

  PublisherDOI

• Simulating the swimming motion of a flagellated bacterium in a microstructured bio-fluid

  arXiv (Cornell University) · 2026-03-28

  articleOpen accessSenior author

  We develop a numerical framework to simulate the locomotion of a flagellated bacterium with a spheroidal head (such as Escherichia coli) in biological fluids like mucus, which are entangled polymer solutions exhibiting elasto-viscoplastic (EVP) rheology and porous microstructure. To account for the scale disparity between the large bacterial head and the slender flagellar bundle, whose thickness is comparable to the pore size, we employ a two-fluid model in which the bundle directly drives the solvent and exchanges momentum with the polymer phase via drag proportional to their relative velocity. The numerical implementation combines a finite-difference discretization of the two-fluid equations with a slender-body theory (SBT) to model flagellar forcing. A key observation is that the coupled mass and momentum equations for these inertialess flows, together with SBT, are linear in the pressure and velocity fields and in the force distribution along the flagellar bundle. By treating the polymer stress as a body force, we decompose the flow field and hydrodynamic moments into three additive contributions: kinematic (motion), flagellar forcing, and polymer stress. This decomposition allows several components of the flow to be precomputed and enables the determination of swimming velocity via a resistivity formulation driven by polymer-induced forces, which greatly improves computational efficiency during transient calculations of the polymer stress and the resulting flow. We validate the method and use it to analyze how polymer microstructure and its interactions with the bacterial head and tail affect motility in complex biofluids.

  PublisherOA PDF

• Stress analysis of dilute particle suspensions in non-Newtonian fluids with efficient evaluation in the weakly non-Newtonian limit

  arXiv (Cornell University) · 2025-12-23

  preprintOpen accessSenior author

  We present a semi-analytical framework to compute the suspension stress in dilute particle-laden non-Newtonian fluids, separating Newtonian and non-Newtonian contributions. The ensemble-averaged stress includes both the particle-induced non-Newtonian stress (PINNS) and an interaction stresslet arising from surface tractions due to the non-Newtonian stress and its induced Newtonian flow. Using a generalized reciprocal theorem, we express this interaction stresslet entirely in terms of the non-Newtonian stress, for a general constitutive model. For weakly non-Newtonian fluids, a regular perturbation expansion combined with the method of characteristics yields all leading-order stress contributions from the Newtonian velocity field alone, avoiding the need to solve coupled partial differential equations. This generalizes the method of Koch et al. (Phys. Rev. Fluids 1, 013301 (2016)) beyond polymeric fluids to any weakly non-Newtonian medium driven by velocity and its gradients. We apply the method to two systems: (i) spheres suspended in a fluid of smaller spheroids, where the interaction stress becomes negative for sufficiently anisotropic shapes due to orientation misalignment of the spheroids; and (ii) suspensions in weakly anisotropic nematic liquid crystals. In the latter, assuming a uniform director field fixed by an external field, PINNS vanishes while interaction stresslets remain, either opposing or enhancing background anisotropic stress. These results demonstrate the utility of our framework in capturing first-order particle-microstructure interactions across a broad class of non-Newtonian fluids.

  PublisherDOI

• Extensional rheology of dilute suspensions of spheres in polymeric liquids

  Journal of Fluid Mechanics · 2025-09-05 · 2 citations

  articleOpen accessSenior authorCorresponding

  The extensional rheology of dilute suspensions of spheres in viscoelastic/polymeric liquids is studied computationally. At low polymer concentration $c$ and Deborah number $\textit{De}$ (imposed extension rate times polymer relaxation time), a wake of highly stretched polymers forms downstream of the particles due to larger local velocity gradients than the imposed flow, indicated by $\Delta \textit{De}_{\textit{local}}\gt 0$ . This increases the suspension’s extensional viscosity with time and $\textit{De}$ for $De \lt 0.5$ . When $\textit{De}$ exceeds 0.5, the coil-stretch transition value, the fully stretched polymers from the far-field collapse in regions with $\Delta \textit{De}_{\textit{local}} \lt 0$ (lower velocity gradient) around the particle’s stagnation points, reducing suspension viscosity relative to the particle-free liquid. The interaction between local flow and polymers intensifies with increasing $c$ . Highly stretched polymers impede local flow, reducing $\Delta \textit{De}_{\textit{local}}$ , while $\Delta \textit{De}_{\textit{local}}$ increases in regions with collapsed polymers. Initially, increasing $c$ aligns $\Delta \textit{De}_{\textit{local}}$ and local polymer stretch with far-field values, diminishing particle–polymer interaction effects. However, beyond a certain $c$ , a new mechanism emerges. At low $c$ , fluid three particle radii upstream exhibits $\Delta \textit{De}_{\textit{local}} \gt 0$ , stretching polymers beyond their undisturbed state. As $c$ increases, however, $\Delta \textit{De}_{\textit{local}}$ in this region becomes negative, collapsing polymers and resulting in increasingly negative stress from particle–polymer interactions at large $\textit{De}$ and time. At high $c$ , this negative interaction stress scales as $c^2$ , surpassing the linear increase of particle-free polymer stress, making dilute sphere concentrations more effective at reducing the viscosity of viscoelastic liquids at larger $\textit{De}$ and $c$ .

  PublisherDOI

• The effect of turbulence, gravity, and non-continuum hydrodynamic interactions on the drop size distribution in clouds

  arXiv (Cornell University) · 2025-01-02

  preprintOpen accessSenior author

  The evolution of micron-sized droplets in clouds is studied with focus on the 'size-gap' regime of 15-40 $μm$ radius, where condensation and differential sedimentation are least effective in promoting growth. This bottleneck leads to inaccurate growth models and turbulence can potentially rectify disagreement with in-situ cloud measurements. The role of turbulent collisions, mixing of droplets, and water vapour fluctuations in crossing the 'size-gap' has been analysed in detail. Collisions driven by the coupled effects of turbulent shear and differential sedimentation are shown to grow drizzle sized droplets. Growth is also promoted by turbulence-induced water vapour fluctuations, which maintain polydispersity during the initial condensation driven growth and facilitate subsequent growth by differential sedimentation driven coalescence. The collision rate of droplets is strongly influenced by non-continuum hydrodynamics and so the size evolution beyond the condensation regime is found to be very sensitive to the mean free path of air. Turbulence-induced inertial clustering leads to a moderate enhancement in the growth rate but the intermittency of the turbulent shear rate does not change the coalescence rate significantly. The coupled influence of all these phenomena is evaluated by evolving a large number of droplets within an adiabatically rising parcel of air using a Monte Carlo scheme that captures turbulent intermittency and mixing.

  PublisherOA PDFDOI

• The Effect of Turbulence, Gravity, and Noncontinuum Hydrodynamic Interactions on the Drop Size Distribution in Clouds

  Journal of the Atmospheric Sciences · 2025-06-16

  articleSenior author

  Abstract The evolution of micrometer-sized droplets in clouds is studied with focus on the “size-gap” regime of 15–40- μ m radii, where condensation and differential sedimentation are least effective in promoting growth. This bottleneck leads to inaccurate growth models, and turbulence can potentially rectify disagreement with in situ cloud measurements. The role of turbulent collisions, mixing of droplets, and water vapor fluctuations in crossing the size gap has been analyzed in detail. Collisions driven by the coupled effects of turbulent shear and differential sedimentation are shown to grow drizzle sized droplets. Growth is also promoted by turbulence-induced water vapor fluctuations, which maintain polydispersity during the initial-condensation-driven growth and facilitate subsequent growth by differential-sedimentation-driven coalescence. The collision rate of droplets is strongly influenced by noncontinuum hydrodynamics, and so the size evolution beyond the condensation regime is found to be very sensitive to the mean-free path of air. Turbulence-induced inertial clustering leads to a moderate enhancement in the growth rate, but the intermittency of the turbulent shear rate does not change the coalescence rate significantly. The coupled influence of all these phenomena is evaluated by evolving a large number of droplets within an adiabatically rising parcel of air using a Monte Carlo scheme that captures turbulent intermittency and mixing. Significance Statement This study is directed toward improving descriptions of the microphysical determinants of the time for rain formation in clouds. Existing models predict significantly longer times than the tens of minutes observed in warm clouds. There is a growing body of evidence that turbulence plays a key role in resolving this discrepancy. We incorporate accurate turbulent collision dynamics and assess the interplay of the various underlying physical factors facilitating growth to rain-sized droplets. Our study, in addition to providing important insight into cloud microphysics, will pave the path to the next generation of large-scale rain cloud evolution studies.

  PublisherDOI

• Stress analysis of dilute particle suspensions in non-Newtonian fluids with efficient evaluation in the weakly non-Newtonian limit

  ArXiv.org · 2025-12-23

  articleOpen accessSenior author

  We present a semi-analytical framework to compute the suspension stress in dilute particle-laden non-Newtonian fluids, separating Newtonian and non-Newtonian contributions. The ensemble-averaged stress includes both the particle-induced non-Newtonian stress (PINNS) and an interaction stresslet arising from surface tractions due to the non-Newtonian stress and its induced Newtonian flow. Using a generalized reciprocal theorem, we express this interaction stresslet entirely in terms of the non-Newtonian stress, for a general constitutive model. For weakly non-Newtonian fluids, a regular perturbation expansion combined with the method of characteristics yields all leading-order stress contributions from the Newtonian velocity field alone, avoiding the need to solve coupled partial differential equations. This generalizes the method of Koch et al. (Phys. Rev. Fluids 1, 013301 (2016)) beyond polymeric fluids to any weakly non-Newtonian medium driven by velocity and its gradients. We apply the method to two systems: (i) spheres suspended in a fluid of smaller spheroids, where the interaction stress becomes negative for sufficiently anisotropic shapes due to orientation misalignment of the spheroids; and (ii) suspensions in weakly anisotropic nematic liquid crystals. In the latter, assuming a uniform director field fixed by an external field, PINNS vanishes while interaction stresslets remain, either opposing or enhancing background anisotropic stress. These results demonstrate the utility of our framework in capturing first-order particle-microstructure interactions across a broad class of non-Newtonian fluids.

  PublisherOA PDF

Recent grants

• Collaborative Research: The role of microphysical processes and turbulence intermittency in droplet coalescence in warm cumulus clouds

  NSF · $247k · 2014–2017

• The Effect of Particle-polymer Interactions on the Rheology and Structure of Dilute Particle-filled Polymeric Liquids

  NSF · $317k · 2018–2021

• Hydrodynamically Assisted Bacterial Chemotaxis

  NSF · $328k · 2011–2014

• Slender body theory and finite difference computations to characterize particle-fluid interactions at moderate Reynolds numbers

  NSF · $371k · 2022–2025

• Using shape to control the orientations and positions of particles in processing flows

  NSF · $314k · 2014–2018

Frequent coauthors

• Ganesh Subramanian

  Jawaharlal Nehru Centre for Advanced Scientific Research

  32 shared

• Ashok S. Sangani

  Syracuse University

  24 shared

• Lynden A. Archer

  Cornell University

  21 shared

• Abraham D. Stroock

  17 shared

• Gaojin Li

  16 shared

• Anubhab Roy

  Indian Institute of Technology Madras

  15 shared

• Eric S. G. Shaqfeh

  Stanford University

  12 shared

• Claude Cohen

  12 shared

Labs

• Donald L. Koch Research GroupPI

Education

• PhD, Chemical Engineering

  Massachusetts Institute of Technology

  1985

• BS, Chemical Engineering

  Case Western Reserve University

  1981

Awards & honors

• Fellow, American Physical Society (1998)
• Fellow, National Science Foundation (1981)
• Presidential Young Investigator (1988)
• Frenkiel Award, Division of Fluid Dynamics (1988)
• Postdoctoral Fellow, North Atlantic Treaty Organization (NAT…