Faculty


We are broadly interested in the interaction between complex fluids (polymers, colloids, nanoparticles, bacteria, protozoa, cells) and the surfaces that confine or support them. These interactions appear ubiquitously in applications in petroleum engineering (drilling media, microbial corrosion), environmental engineering (biofouling, bioremediation), materials engineering (rapid prototyping, direct-write assembly), and biodefense (diagnostics, biodetection). Moreover, this broad class of problems is scientifically fascinating: both the chemical and mechanical properties of surfaces can influence the adhesion, diffusion, motility, and phase behavior of complex fluids. Our current research thrusts include:
Flow and Transport of Complex Fluids in Confinement
Processes involving the flow of complex fluids in confined geometries appear prominently in technological, environmental, and physiological settings. Confinement effects strongly influence multiphase transport properties, and are thus relevant for technological applications involving porous media, such as gel electrophoresis and chromatography, and critical resource applications, such as water remediation and oil extraction from nonconventional sources. Despite their ubiquity, the science underlying these processes remains poorly understood. We use confocal and light microscopy to directly image the flow of complex fluids in microchannels. By quantifying the flow behavior in a variety of controlled microscale geometries using high-throughput tracking algorithms, we will identify the effects of confinement on the flow properties of complex fluids and inspire new designs for manipulating these materials on the microscale. Currently, we are investigating the effects of confinement on the structure, dynamics, and phase behavior of quiescent and flowing model colloid-polymer mixtures (in part with Jeremy Palmer), and the transport properties of nanoparticles in microfabricated post arrays and polymer solutions (with Ramanan Krishnamoorti).
Near-Surface Motility of Microorganisms
Over 99% of bacteria live in bacterial biofilms, which are surface-associated communities surrounded by a protective extracellular matrix that increases the resistance of bacteria to environmental and host stresses. These stress-resistant biofilms thus cause significant problems both in human health and in industrial processes. Preventing their formation requires understanding how bacteria adapt their motility mechanisms near surfaces. We directly image the motion of bacteria and other microorganisms near engineered surfaces with confocal and light microscopy. By translating microscopy images into a searchable database of trajectories, we will elucidate the effects of surface properties on microbial motility and inspire new strategies to create antifouling materials. Currently, we are quantifying the near-surface motility mechanisms of model bacteria on engineered surfaces, and applying insights gained from these studies to understand how bacteria respond to self-cleaning surfaces (with Megan Robertson) and identifying appendage-driven attachment mechanisms (in part with Patrick Cirino).
Biomedical Applications: Lateral Flow Assays and Protein Crystallization
We apply the fundamental scientific principles identified in other studies to address critical needs in public health. With Richard Willson, we are applying our insights into nanoparticle transport in porous media to design sensitive, specific, inexpensive, and portable diagnostics based on lateral flow immunoassays (the format used in the common pregnancy test). Our assays employ engineered viral nanoparticles, M13 bacteriophage, as reporters and exhibit sensitivities that are up to one-hundred times greater than conventional gold-nanoparticle-based assays. With Peter Vekilov, we apply our high-throughput imaging methods to study dense liquid protein clusters, which are precursors in which protein crystals subsequently nucleate. Understanding the mechanisms that lead to crystallization in biological settings can help to prevent or treat pathologies, including sickle-cell anemia, gout, and amyloid fibers, that are driven by protein crystallization.
- Graduate students: Narendra Dewangan, Tzu-Han Li, Deepak Mangal, Nayoung Park, Ryan Poling-Skutvik, Ryan Roberts, Mohammad Safari, Ali Slim, Maxwell Smith, Shiyu Zhu
- Undergraduate students: Esmeralda Umanzor
2018 University of Houston Alumni Association Outstanding Faculty Award
2017 – 2018 University of Houston Excellence in Research, Scholarship, or Creative Activity Award (Associate Professor level)
2017 – 2018 University of Houston Energy Fellow
2015 University of Houston WGRC Distinguished Faculty Scholar, Pre-Tenure
2014 Participant, Arab-American Frontiers of Science, Engineering and Medicine
2013 Participant, National Academies Keck Futures Initiative
2013 Junior Faculty Research Excellence Award, Cullen College of Engineering
2012 NSF CAREER
2010 University of Houston New Faculty Award
2005 – 2007 INEST Postdoctoral Fellowship
1999 – 2002 NSF Graduate Fellowship
2018 – 2020 Education Advisory Resource Group, AIP
2018 – 2020 Education Advisory Resource Group, AIP
2017 – 2019 Symposium Committee (COLL Division), ACS
2016 – 2021 Fluids Programming Committee (Area 1J), AIChE
2014 – 2017 Education Committee, Society of Rheology
Member: American Physical Society, American Chemical Society, American Institute of Chemical Engineers, and the Society of Rheology.
Journal reviewer: ACS Applied Materials and Interfaces, ACS Infectious Diseases, ACS Macro Letters, Advanced Materials, Biophysical Journal, European Journal of Physics E, Integrative Biology, Journal of Chemical Physics, Journal of Physical Chemistry C, Journal of Non-Newtonian Fluid Mechanics, Journal of Rheology, Langmuir, Macromolecules, Measurement Science and Technology, Nanoscale, Nanotechnology, Nature Communications, PLoS One, PNAS, Physical Review Letters, Physical Review Materials, Rheologica Acta, RSC Advances, Soft Matter.
Proposal reviewer: American Chemical Society Petroleum Research Fund, European Research Council, National Science Foundation (CBET, DMR, MPS), Leaders Opportunity Fund/Canada Foundation for Innovation, Wellcome Trust/DBT India Alliance, Center for Functional Nanomaterials (Brookhaven National Laboratory), Research Grant Council of Hong Kong, Swiss National Science Foundation.
Journal Papers / Refereed Journal Publications
- Chen, R. J., et al., "Influence of polymer flexibility on nanoparticle dynamics in semidilute solutions." Soft Matter 15(6): 1260-1268., 2019
- Conrad, J. C. and M. L. Robertson, "Towards mimicking biological function with responsive surface-grafted polymer brushes." Current Opinion in Solid State & Materials Science 23(1): 1-12., 2019
- J. C. Conrad and R. Poling-Skutvik, “Confined flow: Consequences and implications for bacteria and biofilms.” Annu. Rev. Chem. Biomol. Eng. 9, Review in Advance [DOI], 2018
- R. B. McLay, H. N. Nguyen, Y. A. Jaimes-Lizcano, N. K. Dewangan, S. Alexandrova, D. F. Rodrigues, P. C. Cirino, and J. C. Conrad, “Level of fimbriation alters the adhesion of Escherichia coli bacteria to interfaces.” Langmuir 34, 1133 – 1142 [DOI], 2018
Link to file - R. Chen*, R. Poling-Skutvik*, A. Nikoubashman, M. P. Howard, J. C. Conrad, and J. C. Palmer, “Coupling of nanoparticle dynamics to polymer center-of-mass motion in semidilute polymer solutions.” Macromolecules 51, 1865 –1872 [DOI], 2018
Link to file - R. Poling-Skutvik, J. Lee, S. Narayanan, R. Krishnamoorti, and J. C. Conrad, “Tunable assembly of gold nanorods in polymer solutions to generate controlled nanostructured materials.” ACS Appl. Nano Mater. 1, 877 – 885 [DOI], 2018
Link to file - J. D. C. Jacob, R. Krishnamoorti, and J. C. Conrad, “Particle dispersion in porous media: Differentiating effects of geometry and fluid rheology.” Phys. Rev. E 96, 022610 [DOI], 2017
Link to file - J. Kim, B. Vu, K. Kourentzi, R. C. Willson, and J. C. Conrad, “Increasing binding efficiency via reporter shape and flux in a viral nanoparticle lateral-flow assay.” ACS Appl. Mater. Interfaces 9, 6878–6884 [DOI], 2017
Link to file - J. Kim, R. Poling-Skutvik, J. R. C. Trabuco, K. Kourentzi, R. C. Willson, and J. C. Conrad, “Orientational binding modes of reporters in a viral-nanoparticle lateral-flow assay.” Analyst 142, 55–64 [DOI], 2017
Link to file - M. C. Byington, M. S. Safari, J. C. Conrad, and P. G. Vekilov, “Shear flow suppresses the volume of the nucleation precursor clusters in lysozyme solutions.” J. Cryst. Growth 468, 493–501 [DOI],, 2017
Link to file - M. S. Safari, M. C. Byington, J. C. Conrad, and P. G. Vekilov, Polymorphism of lysozyme condensates.” J. Phys. Chem. B, 121 9091–9101 [DOI], 2017
Link to file - M. S. Safari, R. Poling-Skutvik, P. G. Vekilov, and J. C. Conrad, “Differential dynamic microscopy of bidisperse colloidal suspensions.” npj Microgravity 3, 21 [DOI], 2017
Link to file - N. Park and J. C. Conrad, “Phase behavior of colloid-polymer depletion mixtures with unary or binary depletants.” Soft Matter 13, 2781–2792 [DOI], 2017
Link to file - R. Poling-Skutvik, K. N. Olafson, S. Narayanan, L. Stingaciu, A. Faraone, J. C. Conrad, and R. Krishnamoorti, “Confined dynamics of grafted polymer chains in solutions of linear polymer.” Macromolecules 50, 7372–7379 [DOI], 2017
Link to file - V. Yadav, Y. A. Jaimes-Lizcano, N. K. Dewangan, N. Park, T.-H. Li, M. L. Robertson, and J. C. Conrad, “Tuning bacterial attachment and detachment via the thickness and dispersity of a pH responsive polymer brush.” ACS Appl. Mater. Interfaces 9, 44900–44190 [DOI], 2017
Link to file - F. Babayekhorasani, D. E. Dunstan, R. Krishnamoorti, and J. C. Conrad, “Nanoparticle diffusion in crowded and confined media.” Soft Matter 12, 8407–8416 [DOI], 2016
Link to file - F. Babayekhorasani, D. E. Dunstan, R. Krishnamoorti, and J. C. Conrad, “Nanoparticle dispersion in disordered porous media with and without polymer additives.” Soft Matter 12, 5676–5683 [DOI], 2016
Link to file - H. Chen, A. E. V. Hagström, J. Kim, G. Garvey, A. Paterson, F. Ruiz-Ruiz, B. Raja, U. Strych, M. Rito-Palomares, K. Kourentzi, J. C. Conrad, R. L. Atmar, and R. C. Wilson, “Flotation immunoassay: masking the signal from free reporters in sandwich immunoassays.” Sci. Rep. 2, 24297 [DOI], 2016
Link to file - L. Ni, S. Yang, R. Zhang, Z. Jin, H. Chen, J. C. Conrad, and F. Jin, “Bacteria differently deploy type-IV pili on surfaces to adapt to nutrient availability.” npj Biofilms Microbiomes 2, 15029 [DOI], 2016
Link to file - M. C. Byington, M. S. Safari, J. C. Conrad, and P. G. Vekilov, “Protein conformational flexibility enables the formation of dense liquid clusters: tests using solution shear.” J. Phys. Chem. Lett. 7, 2339–2345 [DOI], 2016
Link to file - R. Pandey and J. C. Conrad, “Gelation in mixtures of polymers and bidisperse colloids.” Phys. Rev. E 93, 012610 [DOI], 2016
Link to file - R. Poling-Skutvik, K. I. S. Mongcopa, A. Faraone, S. Narayanan, J. C. Conrad, and R. Krishnamoorti, “Structure and dynamics of interacting nanoparticles in semidilute polymer solutions.” Macromolecules 49, 6568–6577. [DOI], 2016
Link to file - S. Sharma*, Y. A. Jaimes-Lizcano*, R. B. McLay, P. C. Cirino, and J. C. Conrad, “Sub-nanometric roughness affects deposition and mobile adhesion of Escherichia coli on silanized glass surfaces.” Langmuir 32, 5422–5433 [DOI], 2016
Link to file - V. Yadav, A. V. Harkin, M. L. Robertson, and J. C. Conrad, “Hysteretic memory in pH-response of water contact angle on poly(acrylic acid) brushes.” Soft Matter 12, 3589–3599 [DOI], 2016
Link to file - J. D. C. Jacob, K. He, S. T. Retterer, R. Krishnamoorti, and J. C. Conrad, “Diffusive dynamics of nanoparticles in ultra-confined media.” Soft Matter 11, 7515–7524 [DOI], 2015
Link to file - J. Kim, M. Adhikari, S. Dhamane, A. E. V. Hagström, K. Kourentzi, U. Strych, R. C. Willson, and J. C. Conrad, “Detection of viruses by counting single fluorescent genetically biotinylated reporter immunophage using a lateral flow assay.” ACS Appl. Mater. Interfaces 7, 2891–2898 [DOI], 2015
Link to file - M. Adhikari, U. Strych, J. Kim, H. Goux, S. Dhamane, M.-V. Poongavanam, A. E. V. Hagström, K. Kourentzi, J. C. Conrad, and R. C. Willson, “Aptamer-phage reporters for ultrasensitive lateral flow assays.” Anal. Chem. 87, 11660–11665 [DOI], 2015
Link to file - M. S. Safari, M. A. Vorontsova, R. Poling-Skutvik, P. G. Vekilov, and J. C. Conrad, “Differential dynamic microscopy of weakly scattering and polydisperse protein-rich clusters.” Phys. Rev. E 92, 042712 [DOI], 2015
Link to file - R. Poling-Skutvik, R. Krishnamoorti, and J. C. Conrad, “Size-dependent dynamics of nanoparticles in unentangled solutions of polyelectrolytes.” ACS Macro Lett. 4, 1169–1173 [DOI], 2015
Link to file - S. He, Y. Jiang, J. C. Conrad, and G. Qin, “Molecular simulation of natural gas transport and storage in shale rocks with heterogeneous nano-pore structures.” J. Petrol. Sci. Eng. 133, 401–409 [DOI], 2015
Link to file - F. Babaye Khorasani, R. Poling-Skutvik, R. Krishnamoorti, and J. C. Conrad, “Mobility of nanoparticles in semidilute polyelectrolyte solutions.” Macromolecules 47, 5328–5333 [DOI], 2014
Link to file - K. He, S. T. Retterer, B. R. Srijanto, J. C. Conrad, and R. Krishnamoorti, “Transport and dispersion of nanoparticles in periodic nanopost arrays.” ACS Nano 8, 4221–4227 [DOI], 2014
Link to file - R. Pandey, M. Spannuth, and J. C. Conrad, “Confocal imaging of confined quiescent and flowing colloid-polymer mixtures.” J. Vis. Exp. e51461 [DOI], 2014
Link to file - S. Sharma and J. C. Conrad, “Attachment from flow of Escherichia coli bacteria onto silanized glass substrates.” Langmuir 30, 11147–11155 [DOI], 2014
Link to file - K. He, F. Babaye Khorasani, S. T. Retterer, D. K. Thomas, J. C. Conrad, and R. Krishnamoorti, “Diffusive dynamics of nanoparticles in arrays of nanoposts.” ACS Nano 7, 5122–5130 [DOI], 2013
Link to file - R. Pandey and J. C. Conrad, “Dynamics of confined depletion mixtures of polymers and bidispersed colloids.” Soft Matter 9, 10617–10626 [DOI], 2013
Link to file - S. P. George, H. Chen, J. C. Conrad, and S. Khurana, “Regulation of directional cell migration by membrane-induced actin bundling.” J. Cell. Sci. 126, 312–326 [DOI], 2013
Link to file - J. C. Conrad, “Quantifying collective behavior in mammalian cells.” Proc. Natl. Acad. Sci. USA 109, 7591–7592 [DOI], 2012
Link to file - J. C. Conrad, “Physics of bacterial near-surface motility using flagella and type IV pili: implications for biofilm formation.” Res. Microbiol. 163, 619–629 [DOI], 2012
Link to file - K. He, M. Spannuth, J. C. Conrad, and R. Krishnamoorti, “Diffusive dynamics of nanoparticles in aqueous dispersions.” Soft Matter 8, 11933–11938 [DOI], 2012
Link to file - M. Spannuth and J. C. Conrad, “Confinement-induced solidification of colloid-polymer depletion mixtures.” Phys. Rev. Lett. 109, 028301 [DOI], 2012
Link to file - R. F. Shepherd, J. C. Conrad, T. Sabuwala, G. G. Gioia, and J. A. Lewis, “Structural evolution of cuboidal granular media.” Soft Matter 8, 4795–4801 [DOI], 2012
Link to file - R. Pandey and J. C. Conrad, “Effects of attraction strength on microchannel flow of colloid-polymer depletion mixtures.” Soft Matter 8, 10695-10703 [DOI], 2012
Link to file - F. Jin*, J. C. Conrad*, M. L. Gibiansky, and G. C. L. Wong (*Equal contribution), “Bacteria use type-IV pili to slingshot on surfaces.” Proc. Natl. Acad. Sci. USA 108, 12617–12622 [DOI], 2011
Link to file - J. C. Conrad*, M. L. Gibiansky*, F. Jin, V. D. Gordon, D. A. Motto, M. A. Mathewson, W. G. Stopka, D. C. Zelasko, J. D. Shrout, and G. C. L. Wong (*Equal contribution), “Flagella and pili-mediated near-surface single-cell motility mechanisms in P. aeruginosa.” Biophys. J.100, 1608–1616 [DOI], 2011
Link to file - J. C. Conrad, S. R. Ferreira, J. Yoshikawa, R. F. Shepherd, B. Y. Ahn, and J. A. Lewis, “Designing colloidal suspensions for directed materials assembly.” Curr. Opin. Colloid Interface Sci., 16, 71–79 [DOI], 2011
Link to file - J. C. Conrad and J. A. Lewis, “Structural evolution of colloidal gels during constricted microchannel flow.” Langmuir 26, 6102–6107 [DOI], 2010
Link to file - J. C. Conrad, H. M. Wyss, S. Manley, V. Trappe, K. Miyazaki, L. J. Kaufman, A. B. Schofield, D. R. Reichman, and D. A. Weitz, “Arrested fluid-fluid phase separation in depletion systems: implications of the characteristic length on gel formation and rheology.” J. Rheol. 54, 412–438 [DOI], 2010
Link to file - M. L. Gibiansky*, J. C. Conrad*, F. Jin, V. D. Gordon, D. A. Motto, M. A. Mathewson, W. G. Stopka, D. C. Zelasko, J. D. Shrout, and G. C. L. Wong (*Equal contribution), “Bacteria use type IV pili to walk upright and detach from surfaces.” Science 330, 197 [DOI], 2010
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Conference Proceedings Publications
- M. Spannuth and J. C. Conrad, “Dynamics of confined colloid-polymer mixtures.” AIP Conf. Proc. 1518, 351–356 [DOI], 2013
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JOURNAL PAPERS / REFEREED JOURNAL PUBLICATIONS
- D. J. Harris, J. C. Conrad, and J. A. Lewis, “Evaporative lithographic patterning of binary colloidal films.” Phil. Trans. R. Soc. A. 367, 5157–5165 [DOI], 2009
Link to file - J.C. Conrad and J.A. Lewis, “Structure of colloidal gels in microchannels.” Langmuir 24, 7628–7635 [DOI], 2008
Link to file - D.J. Harris, H. Hu, J.C. Conrad, and J.A. Lewis, “Patterning colloidal films via evaporative lithography.” Phys. Rev. Lett. 98, 148301 [DOI], 2007
Link to file - J.C. Conrad, P.P. Dhillon, E.R. Weeks, D.R. Reichman, and D.A. Weitz, “Contribution of slow clusters to the bulk elasticity near the colloidal glass transition.” Phys. Rev. Lett. 97, 265701 [DOI], 2006
Link to file - P.J. Lu, J.C. Conrad, H.M. Wyss, A.B. Schofield, and D.A. Weitz, “Fluid of clusters in attractive colloids.” Phys. Rev. Lett. 96, 028306 [DOI], 2006
Link to file - R.F. Shepherd, J.C. Conrad, S.K. Rhodes, D.R. Link, M. Marquez, D.A. Weitz, and J.A. Lewis, “Microfluidic assembly of homogeneous and Janus colloid-filled hydrogel granules.”Langmuir 22, 8618–8622 [DOI], 2006
Link to file - J.C. Conrad, F.W. Starr, and D.A. Weitz, “Weak correlations between local density and dynamics in liquids near the glass transition.” J. Phys. Chem. B 109, 21235–21240 [DOI], 2005
Link to file - S. Manley, H.M. Wyss, K. Miyazaki, J.C. Conrad, V. Trappe, L.J. Kaufman, D. R. Reichman, and D. A. Weitz, “Dynamic arrest in spinodal decomposition as a route to gelation.” Phys. Rev. Lett. 95, 238302 [DOI], 2005
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