About

Narayanan Menon is a Professor in the Department of Physics at the University of Massachusetts Amherst. He earned his Ph.D. from the University of Chicago in 1995. His research interests focus on experimental condensed matter physics, exploring fundamental interactions within this field. He is recognized for award-winning teaching and offers research opportunities and interdisciplinary programs within a diverse and inclusive community of excellence. His main office is located in the Department of Physics at 1126 Lederle Graduate Research Tower, University of Massachusetts Amherst.

Research topics

• Computer Science
• Chemistry
• Materials science
• Nanotechnology
• Composite material
• Physics
• Optics

Selected publications

• Hindered Stokesian Settling of Discs and Rods

  Physical Review Letters · 2025-04-22 · 3 citations

  articleSenior author

  We report measurements of the mean settling velocities for suspensions of discs and rods in the Stokes regime for a number of particle aspect ratios. All these shapes display "hindered settling," namely, a decrease in settling speed as the solid volume fraction is increased. A comparison of our data to spheres reveals that discs and rods show less hindering than spheres at the same relative interparticle separation. The data for all six of our particle shapes may be scaled to collapse on that of spheres, with a scaling factor that depends only on the volume of the particle relative to a sphere. Despite the orientational degrees of freedom available with nonspherical particles, it thus appears that the dominant contribution to the hindered settling emerges from terms that are simply proportional to the volume of the sedimenting particles, enabling prediction of hindered settling of other nonpolar axisymmetric shapes.

  PublisherDOI

• Editorial: Statistical and Nonlinear Physics Crosses a Threshold

  Physical review. E · 2025-08-13

  editorialOpen accessSenior author
  PublisherOA PDFDOI

• Dynamics and clustering of sedimenting disc lattices

  ArXiv.org · 2025-02-10

  preprintOpen access

  Uniform arrays of particles tend to cluster as they sediment in viscous fluids. Shape anisotropy of the particles enriches these dynamics by modifying the mode-structure and the resulting instabilities of the array. A one-dimensional lattice of sedimenting spheroids in the Stokesian regime displays either an exponential or an algebraic rate of clustering depending on the initial lattice spacing (Chajwa et al. 2020). This is caused by an interplay between the Crowley mechanism which promotes clumping, and a shape-induced drift mechanism which subdues it. We theoretically and experimentally investigate the sedimentation dynamics of one-dimensional lattices of oblate spheroids or discs and show a stark difference in clustering behaviour: the Crowley mechanism results in clumps comprised of several spheroids, whereas the drift mechanism results in pairs of spheroids whose asymptotic behavior is determined by pair-hydrodynamic interactions. We find that a Stokeslet, or point-particle, approximation is insufficient to accurately describe the instability and that the corrections provided by the first-reflection are necessary for obtaining some crucial dynamical features. As opposed to a sharp boundary between exponential growth and neutral eigenvalues under the Stokeslet approximation, the first-reflection correction leads to exponential growth for all initial perturbations, but far more rapid algebraic growth than exponential growth at large lattice spacing $d$. For discs with aspect ratio 0.125, corresponding to the experimental value, the instability growth rate is found to decrease with increasing lattice spacing $d$, approximately as $d^{-4.5}$, which is faster than the $d^{-2}$ for spheres (Crowley, 1971). Sedimenting pairs predominantly come together to form '$\perp$', which our theory accounts for through an analysis that builds on Koch & Shaqfeh (1989).

  PublisherOA PDFDOI

• Facilitating a 3D Granular Flow with an Obstruction

  Physical Review Letters · 2025-10-21 · 2 citations

  article

  Ensuring a smooth rate of efflux of particles from an outlet without unpredictable clogging events is crucial in processing powders and grains. We show by experiments and simulations that an obstacle placed near the outlet can greatly suppress clog formation in a 3-dimensional granular flow; this counterintuitive phenomenon had previously been demonstrated in 2-dimensional systems. Remarkably, clog suppression is very effective even when the obstacle cross section is comparable to that of a single grain and is only a small fraction of the outlet area. Data from two dissimilar obstacle shapes indicate that the underlying mechanism for clog suppression is geometric: while the magnitude of the effect can be affected by dynamical factors, the optimal location of the obstacle is not and follows a simple geometric rule. An optimally placed obstacle arranges for the most probable clogging arch to be at a perilous and unstable spot, where the flow geometry is at a point of local expansion and a slight perturbation leaves the arch without downstream support. This geometric principle does not rely on previously conjectured dynamical mechanisms and admits generalization to other agent-based and particulate systems.

  PublisherDOI

• Dynamics and clustering of sedimenting disc lattices

  Journal of Fluid Mechanics · 2025-08-08

  article

  Uniform arrays of particles tend to cluster as they sediment in viscous fluids. Shape anisotropy of the particles enriches this dynamics by modifying the mode structure and the resulting instabilities of the array. A one-dimensional lattice of sedimenting spheroids in the Stokesian regime displays either an exponential or an algebraic rate of clustering depending on the initial lattice spacing (Chajwa et al. 2020 Phys. Rev. X vol. 10, pp. 041016). This is caused by an interplay between the Crowley mechanism, which promotes clumping, and a shape-induced drift mechanism, which subdues it. We theoretically and experimentally investigate the sedimentation dynamics of one-dimensional lattices of oblate spheroids or discs and show a stark difference in clustering behaviour: the Crowley mechanism results in clumps comprising several spheroids, whereas the drift mechanism results in pairs of spheroids whose asymptotic behaviour is determined by pair–hydrodynamic interactions. We find that a Stokeslet, or point-particle, approximation is insufficient to accurately describe the instability and that the corrections provided by the first reflection are necessary for obtaining some crucial dynamical features. As opposed to a sharp boundary between exponential growth and neutral eigenvalues under the Stokeslet approximation, the first-reflection correction leads to exponential growth for all initial perturbations, but far more rapid algebraic growth than exponential growth at large dimensionless lattice spacing $\tilde {d}$ . For discs with aspect ratio $0.125$ , corresponding to the experimental value, the instability growth rate is found to decrease with increasing lattice spacing $\tilde {d}$ , approximately as $\tilde {d}^{ -4.5}$ , which is faster than the $\tilde {d}^{-2}$ for spheres (Crowley 1971 J. Fluid Mech. vol. 45, pp. 151–159). It is shown that the first-reflection correction has a stabilising effect for small lattice spacing and a destabilising effect for large lattice spacing. Sedimenting pairs predominantly come together to form an inverted ‘T’, or ‘ $\perp$ ’, which our theory accounts for through an analysis that builds on Koch & Shaqfeh (1989 J. Fluid Mech . vol. 209, pp. 521–542). This structure remains stable for a significant amount of time.

  PublisherDOI

• Hindered stokesian settling of discs and rods

  arXiv (Cornell University) · 2024-11-21

  preprintOpen accessSenior author

  We report measurements of the mean settling velocities for suspensions of discs and rods in the stokes regime for a number of particle aspect ratios. All these shapes display ''hindered settling'', namely, a decrease in settling speed as the solid volume fraction is increased. A comparison of our data to spheres reveals that discs and rods show less hindering than spheres at the same relative interparticle separation. The data for all six of our particle shapes may be scaled to collapse on that of spheres, with a scaling factor that depends only on the volume of the particle relative to a sphere. Despite the orientational degrees of freedom available with nonspherical particles, it thus appears that the dominant contribution to the hindered settling emerges from terms that are simply proportional to the volume of the sedimenting particles, enabling prediction of hindered settling of other nonpolar axisymmetric shapes.

  PublisherOA PDFDOI

• Facilitating a 3D granular flow with an obstruction

  arXiv (Cornell University) · 2024-11-18

  preprintOpen access

  Ensuring a smooth rate of efflux of particles from an outlet without unpredictable clogging events is crucial in processing powders and grains. We show by experiments and simulations that an obstacle placed near the outlet can greatly suppress clog formation in a 3-dimensional granular flow; this counterintuitive phenomenon had previously been demonstrated in 2-dimensional systems. Remarkably, clog suppression is very effective even when the obstacle cross-section is comparable to that of a single grain, and is only a small fraction of the outlet area. Data from two dissimilar obstacle shapes indicate that the underlying mechanism for clog suppression is geometric: while the magnitude of the effect can be affected by dynamical factors, the optimal location of the obstacle is determined entirely by a simple geometric rule. An optimally-placed obstacle arranges for the most-probable clogging arch to be at a perilous and unstable spot, where the local flow geometry is at a point of expansion and a slight perturbation leaves the arch without downstream support. This geometric principle does not rely on previously conjectured dynamical mechanisms and admits generalization to other agent-based and particulate systems.

  PublisherOA PDFDOI

• Stretching and Bending Moduli of Bilayer Films Inferred from Wrinkle Patterns

  Macromolecules · 2024-10-23 · 1 citations

  articleOpen access

  Wrinkling patterns were used to investigate the mechanical properties of thin poly(styrene) (PS)/poly(methyl methacrylate) (PMMA) and PS/gold (Au) bilayer films. Films were floated on water with a water drop on the surface to induce wrinkling. The thicknesses and thickness ratios of the films were varied over a broad range. The PS/PMMA bilayer was chosen to provide a contrast in wetting properties, with equilibrium contact angles of θPMMA = 68° and θPS = 88° with water. The PS/Au bilayer was chosen to provide a large contrast in Young’s moduli, EAu = 72 GPa and EPS = 3.4 GPa. The stretching (Y) and bending (B) moduli of the bilayer films were obtained from measurements of the length and number of wrinkles in the wrinkle patterns. The experimentally derived values of Y and B were in reasonable agreement with the values computed from the bulk Young’s moduli and the thicknesses of the two components in the bilayer. The values of Y and B did not depend on which face of the film was exposed to the water droplet or bath when the capillary stresses were considered. Thus, finite size effects from the film thicknesses were unimportant over the range of thicknesses studied, and no relative displacement of the films was found, with the films remaining well-bonded even with deformation associated with wrinkling.

  PublisherOA PDFDOI

• Peeling from a liquid

  arXiv (Cornell University) · 2023-03-08

  preprintOpen access

  We establish the existence of a cusp in the curvature of a solid sheet at its contact with a liquid subphase. We study two configurations in floating sheets where the solid-vapor-liquid contact line is a straight line and a circle, respectively. In the former case, a rectangular sheet is lifted at its edge, whereas in the latter a gas bubble is injected beneath a floating sheet. We show that in both geometries the derivative of the sheet's curvature is discontinuous. We demonstrate that the boundary condition at the contact is identical in these two geometries, even though the shape of the contact line and the stress distribution in the sheet are sharply different.

  PublisherOA PDFDOI

• Peeling from a liquid

  Soft Matter · 2023-01-01

  articleOpen access

  We establish the existence of a cusp in the curvature of a solid sheet at its contact with a liquid subphase. We study two configurations in floating sheets where the solid-vapor-liquid contact line is a straight line and a circle, respectively. In the former case, a rectangular sheet is lifted at its one edge, whereas in the latter a gas bubble is injected beneath a floating sheet. We show that in both geometries the derivative of the sheet's curvature is discontinuous. We demonstrate that the boundary condition at the contact is identical in these two geometries, even though the shape of the contact line and the stress distribution in the sheet are very different.

  PublisherOA PDFDOI

Recent grants

• Experiments on Granular Materials and Crumpled Sheets

  NSF · $345k · 2006–2010

• Structure and dynamics of flexible and active packings

  NSF · $420k · 2015–2019

• Mobility, interactions, and order in active granular systems

  NSF · $460k · 2019–2023

• Dynamics of elastic surfactants

  NSF · $500k · 2023–2027

• Geometry and Mechanics of Nonthermal Packings

  NSF · $360k · 2012–2016

Frequent coauthors

• Thomas P. Russell

  Lawrence Berkeley National Laboratory

  34 shared

• Sriraṁ Ramaswamy

  Indian Institute of Science Bangalore

  27 shared

• Joël Marthelot

  26 shared

• Benny Davidovitch

  University of Massachusetts Amherst

  21 shared

• Rama Govindarajan

  International Centre for Theoretical Sciences

  21 shared

• Jiangshui Huang

  Fuzhou University

  20 shared

• Vijay Narayan

  National Institute of Construction Management and Research

  18 shared

• S Ganga Prasath

  18 shared

Education

• Ph. D., Physics

  University of Chicago

  1995