Roseanna N. Zia is an Assistant Professor of Chemical Engineering at Stanford University. She received her Ph.D. from the California Institute of Technology in Mechanical Engineering in 2011 with Professor John F. Brady, for development of theory in colloidal hydrodynamics and microrheology. Zia subsequently conducted post-doctoral study of colloidal gels at Princeton University, in collaboration with Professor William B. Russel. Zia began her faculty career at Cornell in January 2013, then subsequently moved her research group to Stanford University in 2017.

Dr. Zia’s research includes developing micro-continuum theory for structure-property relationships of flowing suspensions, elucidating the mechanistic origins of the colloidal glass transition, and microscopic modeling of reversibly bonded colloidal gels, which resulted in discovery that gel aging is actually ongoing but very slow phase separation and the finding that mechanical yield of colloidal gels is actually a non-equilibrium phase transition, triggered by changes in osmotic pressure. More recently she is developing models of biological cells, examining biological processes orchestrated by colloidal-scale forces.

Dr. Zia’s work has been recognized by several awards, including the NSF PECASE Award, the NSF CAREER Award, NSF BRIGE Award, the Publication Award from the Society of Rheology, the Office of Naval Research (ONR) Young Investigator award, the ONR Director of Research Early Career Award, and the Engineering Sonny Yau (’72) Teaching Award. In addition, Zia serves as an Associate Editor for the Journal of Rheology, on the Advisory Boards of the journal Physics of Fluids and AIChE Journal.

Academic Appointments

Honors & Awards

  • PECASE Award, National Science Foundation (2019)
  • PECASE Award, Department of Defense (2019)
  • Director of Research Early Career Award, Office of Naval Research (2017)
  • Terman Faculty Fellow, Stanford University (2017)
  • Frontiers of Engineering, National Academy of Engineering (2015)
  • Sonny Yau ('72) Teaching Award, Cornell University College of Engineering (2015)
  • White House Workshop on the National Strategic Computing Initiative, Initiative held by Executive Order of President Barack Obama (2015)
  • Best Paper Award 01J Session, AIChE (2014)
  • Frontiers in Engineering Education, National Academy of Engineering (2014)
  • Young Investigator Award, Office of Naval Research (2014)
  • BRIGE Award, National Science Foundation (2013)
  • CAREER Award, National Science Foundation (2013)
  • Morgan Faculty Fellow, Cornell University (2013)
  • Publication of the Year, Journal of Rheology (2013)
  • Best Poster, Princeton University Symposium (2012)
  • Everhart Lecturer, California Institute of Technology (2011)
  • Graduate Dean's Award, California Institute of Technology (2011)
  • PEO Scholar Award, PEO (2010)
  • Best Overall Poster Award, California Institute of Technology Poster Symposium (2009)
  • Best Poster Award, Society of Rheology - International Congress on Rheology (2008)

Boards, Advisory Committees, Professional Organizations

  • Vice Chair, Media and Science Relations Committee, APS DFD (2018 - 2019)
  • Associate Editor, Journal of Rheology (2016 - Present)
  • Editorial Board Member, Physics of Fluids (2016 - Present)
  • Editorial Board Member, AIChE Journal (2019 - Present)
  • Guest Editor, PLOS One (2017 - Present)
  • Chair, Media & Science Relations Committee, American Physical Society Division of Fluid Dynamics (2019 - Present)
  • Fluids Programming Committee, AIChE (2015 - Present)
  • Program Comittee, American Physical Society DFD (2015 - 2018)
  • Liaison, AIP Publishing Partnerships Committee for Soc. Rheology (2016 - Present)
  • Chair, Electronic Publishing Committee (2013 - 2014)

Professional Education

  • PhD, California Institute of Technology, Mechanical Engineering (2011)

Current Research and Scholarly Interests

The Zia Group seeks answers to 3 Grand Challenge questions questions utilizing theory and computational analysis of complex fluids:
1. Understand the mechanical nature of the origin of life.
2. Elucidate the mechanics of the (colloidal) glass transition and kinetic arrest.
3. Develop generalized non-equilibrium fluctuation-dissipation theory for soft matter.

Though seemingly disparate avenues of inquiry, they are deeply and surprisingly connected by fundamental suspension mechanics, because they all involve complex fluids. Our generation of colloid scientists will connect multiple disciplines, from biology to physics, and create new areas of inquiry.

My group leads in this effort, by developing the unique tools of modern soft matter science: Strongly non-equilibrium statistical mechanics, low-Reynolds number hydrodynamics theory, and large-scale many-body Brownian/Stokesian dynamics computational models. A central hypothesis in our work is that answers to many of these questions are held in the vast separation between colloidal versus solvent-molecule relaxation time scales in complex fluids, where dynamic phenomena are set by an interplay between comparatively slow colloidal dynamics and the durable but temporary nature of physical interparticle bonds.

Exploration of these frontiers of science have immense potential to revolutionize the way we look at life on earth…how astro-biologists look for life elsewhere…and how to better understand path-dependent phase transitions that hold secrets to disease treatment and exotic new materials.

2019-20 Courses

Stanford Advisees

All Publications

  • Sticky, active microrheology: Part 1. Linear-response. Journal of colloid and interface science Huang, D. E., Zia, R. N. 2019; 554: 580–91


    Attractive colloidal-scale forces between macromolecules in biological fluids are suspected to play a role in important system dynamics, including association times, spatially heterogeneous viscosity, and anomalous diffusion. Passive and active microrheology provide a natural connection between observable particle motion and viscosity in such systems via generalized Stokes-Einstein and Stokes' drag law relations. While such models are robust for purely repulsive colloidal-scale interactions, no such theory exists to model the effects of attractive forces. Here we present such a model for the linear-response regime, where a Brownian probe particle is driven gently through a complex fluid by an external force that weakly augments thermal fluctuations. As the probe moves through the bath, hard-sphere repulsion results in an accumulation of particles on its upstream face and a trailing depletion zone, producing particle drag that slows the probe. Linear-response viscosity can be inferred constitutively from this speed reduction. One expects attractive forces to make the suspension more viscous, but surprisingly, weak attractions exerted by upstream particles actively pull the probe forward, giving it a "hypoviscous" environment through which it slides more easily. As attractions grow stronger, particles join to the probe in a long-lasting doublet, extracting particles from the upstream region and depositing them behind the probe. At a critical value of the second virial coefficient common to all potentials we studied, the distorted structure reverses direction, and continued growth of attraction strength causes the probe to drag a cluster of density along, dramatically increasing viscosity. But at this transition, the structure is neutral under the balance of attraction and repulsion, allowing the probe to "cloak" itself and move through the bath undetected and unhindered relative to hard-sphere dispersions. This poses an intriguing mechanism by which proteins or other macromolecules may change their surface chemistry in order to alter the viscosity of the surrounding medium to speed their own motion, or simply to pass undetected through a cell.

    View details for DOI 10.1016/j.jcis.2019.07.004

    View details for PubMedID 31326790

  • Toward a nonequilibrium Stokes-Einstein relation via active microrheology of hydrodynamically interacting colloidal dispersions. Journal of colloid and interface science Chu, H. C., Zia, R. N. 2018; 539: 388–99


    We derive a theoretical model for the nonequilibrium stress in a flowing colloidal suspension by tracking the motion of a single embedded probe. While Stokes-Einstein relations connect passive, observable diffusion of a colloidal particle to properties of the suspending medium, they are limited to linear response. Actively forcing a probe through a suspension produces nonequilibrium stress that at steady state can be related directly to observable probe motion utilizing an equation of motion rather than an equation of state, giving a nonequilibrium Stokes-Einstein relation [J. Rheol., 2012, 56, 1175-1208]. Here that freely-draining theory is expanded to account for hydrodynamic interactions. To do so, we construct an effective hydrodynamic resistance tensor, through which the particle flux is projected to give the advective and diffusive components of a Cauchy momentum balance. The resultant phenomenological relation between suspension stress, viscosity and diffusivity is a generalized nonequilibrium Stokes-Einstein relation. The phenomenological model is compared with the statistical mechanics theory for dilute suspensions as well as dynamic simulation at finite concentration which show good agreement, indicating that the suspension stress, viscosity, and force-induced diffusion in a flowing colloidal dispersion can be obtained simply by tracking the motion of a single Brownian probe.

    View details for PubMedID 30597285

  • Exploring the validity of time-concentration superposition in glassy colloids: Experiments and simulations PHYSICAL REVIEW E Peng, X., Wang, J., Li, Q., Chen, D., Zia, R. N., McKenna, G. B. 2018; 98 (6)
  • The Impact of Hydrodynamics on Viscosity Evolution in Colloidal Dispersions: Transient, Nonlinear Microrheology AICHE JOURNAL Mohanty, R. P., Zia, R. N. 2018; 64 (8): 3198–3214

    View details for DOI 10.1002/aic.16123

    View details for Web of Science ID 000441215000026

  • Physical biology of the cancer cell glycocalyx NATURE PHYSICS Kuo, J., Gandhi, J. G., Zia, R. N., Paszek, M. J. 2018; 14 (7): 658–69
  • Yield of reversible colloidal gels during flow start-up: release from kinetic arrest. Soft matter Johnson, L. C., Landrum, B. J., Zia, R. N. 2018


    Yield of colloidal gels during start-up of shear flow is characterized by an overshoot in shear stress that accompanies changes in network structure. Prior studies of yield of reversible colloidal gels undergoing strong flow model the overshoot as the point at which network rupture permits fluidization. However, yield under weak flow, which is of interest in many biological and industrial fluids shows no such disintegration. The mechanics of reversible gels are influenced by bond strength and durability, where ongoing rupture and re-formation impart aging that deepens kinetic arrest [Zia et al., J. Rheol., 2014, 58, 1121], suggesting that yield be viewed as release from kinetic arrest. To explore this idea, we study reversible colloidal gels during start-up of shear flow via dynamic simulation, connecting rheological yield to detailed measurements of structure, bond dynamics, and potential energy. We find that pre-yield stress grows temporally with the changing roles of microscopic transport processes: early time behavior is set by Brownian diffusion; later, advective displacements permit relative particle motion that stretches bonds and stores energy. Stress accumulates in stretched, oriented bonds until yield, which is a tipping point to energy release, and is passed with a fully intact network, where the loss of very few bonds enables relaxation of many, easing glassy arrest. This is immediately followed by a reversal to growth in potential energy during bulk plastic deformation and condensation into larger particle domains, supporting the view that yield is an activated release from kinetic arrest. The continued condensation of dense domains and shrinkage of network surfaces, along with a decrease in the potential energy, permit the gel to evolve toward more complete phase separation, supporting our view that yield of weakly sheared gels is a 'non-equilibrium phase transition'. Our findings may be particularly useful for industrial or other coatings, where weak, slow application via shear may lead to phase separation, inhibiting smooth distribution.

    View details for DOI 10.1039/c8sm00109j

    View details for PubMedID 29869670

  • Gravitational collapse of colloidal gels: non-equilibrium phase separation driven by osmotic pressure SOFT MATTER Padmanabhan, P., Zia, R. 2018; 14 (17): 3265–87


    Delayed gravitational collapse of colloidal gels is characterized by initially slow compaction that gives way to rapid bulk collapse, posing interesting questions about the underlying mechanistic origins. Here we study gel collapse utilizing large-scale dynamic simulation of a freely draining gel of physically bonded particles subjected to gravitational forcing. The hallmark regimes of collapse are recovered: slow compaction, transition to rapid collapse, and long-time densification. Microstructural changes are monitored by tracking particle positions, coordination number, and bond dynamics, along with volume fraction, osmotic pressure, and potential energy. Together these reveal the surprising result that collapse can occur with a fully intact network, where the tipping point arises when particle migration dissolves strands in a capillary-type instability. While it is possible for collapse to rupture a gel network into clusters that then sediment, and hydrodynamic interactions can make interesting contributions, neither is necessary. Rather, we find that the "delay" arises from gravity-enhanced coarsening, which triggers the re-emergence of phase separation. The mechanism of this transition is a leap toward lower potential energy of the gel, driven by bulk negative osmotic pressure that condenses the particle phase: the gel collapses in on itself under negative osmotic pressure allowing the gel, to tunnel through the equilibrium phase diagram to a higher volume fraction "state". Remarkably, collapse stops when condensation stops, when gravitational advection produces a positive osmotic pressure, re-arresting the gel.

    View details for DOI 10.1039/c8sm00002f

    View details for Web of Science ID 000431422500007

    View details for PubMedID 29637976

  • Y Non-equilibrium pair interactions in colloidaldispersions JOURNAL OF FLUID MECHANICS Dolata, B. E., Zia, R. N. 2018; 836: 694–739
  • Equilibrium structure and diffusion in concentrated hydrodynamically interacting suspensions confined by a spherical cavity JOURNAL OF FLUID MECHANICS Aponte-Rivera, C., Su, Y., Zia, R. N. 2018; 836: 413–50
  • Active and Passive Microrheology: Theory and Simulation ANNUAL REVIEW OF FLUID MECHANICS, VOL 50 Zia, R. N., Davis, S. H., Moin, P. 2018; 50: 371–405