# Colloids and interfaces ## expand\_more Using digital holographic microscopy, we study how colloidal particles bind to oil-water interfaces. Small particles have a natural affinity for interfaces, and this affinity can be used to control their self-assembly and make some interesting materials. However, the dynamics of the particles before and after they breach the interface are not well-understood. We do experiments to observe these dynamics and find some surprising results. If you shake up a mixture of oil and vinegar, you will disperse droplets of one into the other only very briefly before the vinegar and oil separate into distinct layers. Colloidal particles can bind to the interface to reduce the total oil-water surface area (and energy). Once these particles bind to the interface it's virtually impossible for them to detach. This means the interface can be used as a scaffold for assembling the particles, or the particles can be used to coat the interface and stabilize it, forming what is called a "Pickering emulsion". The affinity of colloidal particles for liquid interfaces has been studied for more than a century. In 1903, W. Ramsden published a paper about solids accumulating at the interface between oil and water. Since then, there have been thousands of studies on micron-scale particles at immiscible fluid-fluid interfaces, but the dynamics of such systems are still quite poorly understood. We study the non-equilibrium behavior of these systems using [digital holographic microscopy](/holographic-microscopy), which can track the particles in three dimensions at high speed and with high spatial precision. [Dave Kaz](/people/david-m-kaz) and [Ryan McGorty](/people/ryan-mcgorty), the first students to work on this project, built a holographic microscope outfitted with an optical tweezer that could be used to exert a force on the particles. They pushed particles toward a planar water-oil interface and found something surprising happened when the particles started poking through the interface. Once the particles breach the interface, they relax *logarithmically in time* towards equilibrium. The velocity of the particles gets smaller and smaller the closer they get to equilibrium, despite the huge driving force. In fact, if we extrapolate our results, we find that a 1-micrometer particle could take months or even years to reach equilibrium. The explanation most consistent with this observation, proposed by [Madhav Mani](http://www.madhavmani.com/) (working with [Michael Brenner](/people/michael-p-brenner)), is that nanoscale surface features on the particles pin the three-phase contact line and hinder the progress of the particle toward equilibrium. We have since seen this behavior in a wide variety of different colloidal particles. Download 15 citations download- [BibTeX](/bibcite/export?pager_style=no_pager&number_of_items=30&sort_field=bibcite_year--desc&taxonomy_filters%5Bfield_hwp_c_researchareas%5D%5B0%5D%5Btarget_id%5D=14671&&&format=bibtex) - [EndNote X3 XML](/bibcite/export?pager_style=no_pager&number_of_items=30&sort_field=bibcite_year--desc&taxonomy_filters%5Bfield_hwp_c_researchareas%5D%5B0%5D%5Btarget_id%5D=14671&&&format=endnote8) - [EndNote 7 XML](/bibcite/export?pager_style=no_pager&number_of_items=30&sort_field=bibcite_year--desc&taxonomy_filters%5Bfield_hwp_c_researchareas%5D%5B0%5D%5Btarget_id%5D=14671&&&format=endnote7) - [Endnote tagged](/bibcite/export?pager_style=no_pager&number_of_items=30&sort_field=bibcite_year--desc&taxonomy_filters%5Bfield_hwp_c_researchareas%5D%5B0%5D%5Btarget_id%5D=14671&&&format=tagged) - [Marc](/bibcite/export?pager_style=no_pager&number_of_items=30&sort_field=bibcite_year--desc&taxonomy_filters%5Bfield_hwp_c_researchareas%5D%5B0%5D%5Btarget_id%5D=14671&&&format=marc) - [PubMedId](/bibcite/export?pager_style=no_pager&number_of_items=30&sort_field=bibcite_year--desc&taxonomy_filters%5Bfield_hwp_c_researchareas%5D%5B0%5D%5Btarget_id%5D=14671&&&format=pubmed_id) - [RIS](/bibcite/export?pager_style=no_pager&number_of_items=30&sort_field=bibcite_year--desc&taxonomy_filters%5Bfield_hwp_c_researchareas%5D%5B0%5D%5Btarget_id%5D=14671&&&format=ris) ### 2023 Sun, J. H.; Plummer, A.; Zhang, G. H.; Nelson, D.; Manoharan, V. N. [Geometric Frustration of Hard-Disk Packings on Cones](/publications/geometric-frustration-hard-disk-packings-cones). *Physical Review E* **2023**, *108* (5), 054608. Sun, J. H.; Plummer, A.; Zhang, G. H.; Nelson, D.; Manoharan, V. N. [Geometric Frustration of Hard-Disk Packings on Cones](/publications/geometric-frustration-hard-disk-packings-cones). *Physical Review E* **2023**, *108* (5), 054608. - [ descriptionPublisher's Version](https://journals.aps.org/pre/abstract/10.1103/PhysRevE.108.054608) - [ descriptionPublisher's Version](https://journals.aps.org/pre/abstract/10.1103/PhysRevE.108.054608) ### 2021 Tanjeem, N.; Wilkin, W. H.; Beller, D.; Rycroft, C. H.; Manoharan, V. N. [Geometrical Frustration and Defect Formation in Growth of Colloidal Nanoparticle Crystals on a Cylinder: Implications for Assembly of Chiral Nanomaterials](/publications/geometrical-frustration-and-defect-formation-growth-colloidal-nanoparticle). *ACS Applied Nano Materials* **2021**, *4* (10), 10682-10691. Tanjeem, N.; Wilkin, W. H.; Beller, D.; Rycroft, C. H.; Manoharan, V. N. [Geometrical Frustration and Defect Formation in Growth of Colloidal Nanoparticle Crystals on a Cylinder: Implications for Assembly of Chiral Nanomaterials](/publications/geometrical-frustration-and-defect-formation-growth-colloidal-nanoparticle). *ACS Applied Nano Materials* **2021**, *4* (10), 10682-10691. - [ descriptionPublisher's Version](https://pubs.acs.org/doi/abs/10.1021/acsanm.1c02126) - [ descriptionPublisher's Version](https://pubs.acs.org/doi/abs/10.1021/acsanm.1c02126) ### 2019 Memet, E.; Tanjeem, N.; Greboval, C.; Manoharan, V. N.; Mahadevan, L. [Random Sequential Adsorption of Spheres on a Cylinder](/publications/random-sequential-adsorption-spheres-cylinder). *Europhysics Letters* **2019**, *127* (3), 38004. Memet, E.; Tanjeem, N.; Greboval, C.; Manoharan, V. N.; Mahadevan, L. [Random Sequential Adsorption of Spheres on a Cylinder](/publications/random-sequential-adsorption-spheres-cylinder). *Europhysics Letters* **2019**, *127* (3), 38004. - [ descriptionPublisher's Version](https://iopscience.iop.org/article/10.1209/0295-5075/127/38004/meta) - [ descriptionPublisher's Version](https://iopscience.iop.org/article/10.1209/0295-5075/127/38004/meta) Wang, A.; Zwanikken, J. W.; Kaz, D. M.; McGorty, R.; Goldfain, A. M.; Rogers, W. B.; Manoharan, V. N. [Before the Breach: Interactions Between Colloidal Particles and Liquid Interfaces at Nanoscale Separations](/publications/breach-interactions-between-colloidal-particles-and-liquid-interfaces). *Physical Review E* **2019**, *100* (4), 042605. Wang, A.; Zwanikken, J. W.; Kaz, D. M.; McGorty, R.; Goldfain, A. M.; Rogers, W. B.; Manoharan, V. N. [Before the Breach: Interactions Between Colloidal Particles and Liquid Interfaces at Nanoscale Separations](/publications/breach-interactions-between-colloidal-particles-and-liquid-interfaces). *Physical Review E* **2019**, *100* (4), 042605. - [ descriptionPublisher's Version](https://journals.aps.org/pre/abstract/10.1103/PhysRevE.100.042605) - [ descriptionPublisher's Version](https://journals.aps.org/pre/abstract/10.1103/PhysRevE.100.042605) ### 2017 Wang, A.; Rogers, W. B.; Manoharan, V. N. [Effects of Contact-Line Pinning on the Adsorption of Nonspherical Colloids at Liquid Interfaces](/publications/effects-contact-line-pinning-adsorption-nonspherical-colloids-liquid). *Physical Review Letters* **2017**, *119* (10), 108004. Wang, A.; Rogers, W. B.; Manoharan, V. N. [Effects of Contact-Line Pinning on the Adsorption of Nonspherical Colloids at Liquid Interfaces](/publications/effects-contact-line-pinning-adsorption-nonspherical-colloids-liquid). *Physical Review Letters* **2017**, *119* (10), 108004. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1103/PhysRevLett.119.108004) - [ picture\_as\_pdfWang et al. - 2017 - Effe...](/sites/g/files/omnuum4256/files/manoharan/files/wang_et_al._-_2017_-_effects_of_contact-line_pinning_on_the_adsorption.pdf) The effects of contact-line pinning are well known in macroscopic systems but are only just beginning to be explored at the microscale in colloidal suspensions. We use digital holography to capture the fast three-dimensional dynamics of micrometer-sized... - [ descriptionPublisher's Version](http://dx.doi.org/10.1103/PhysRevLett.119.108004) - [ picture\_as\_pdfWang et al. - 2017 - Effe...](/sites/g/files/omnuum4256/files/manoharan/files/wang_et_al._-_2017_-_effects_of_contact-line_pinning_on_the_adsorption.pdf) ### 2016 Rahmani, A. M.; Wang, A.; Manoharan, V. N.; Colosqui, C. E. [Colloidal Particle Adsorption at Liquid Interfaces: Capillary Driven Dynamics and Thermally Activated Kinetics](/publications/colloidal-particle-adsorption-liquid-interfaces-capillary-driven-dynamics-and). *Soft Matter* **2016**, *12* (30), 6365-6372. Rahmani, A. M.; Wang, A.; Manoharan, V. N.; Colosqui, C. E. [Colloidal Particle Adsorption at Liquid Interfaces: Capillary Driven Dynamics and Thermally Activated Kinetics](/publications/colloidal-particle-adsorption-liquid-interfaces-capillary-driven-dynamics-and). *Soft Matter* **2016**, *12* (30), 6365-6372. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1039/C6SM00966B) - [ picture\_as\_pdfRahmani et al. - 2016 - C...](/sites/g/files/omnuum4256/files/manoharan/files/rahmani-2016-colloidal_particle_adsorption_at_liquid_interfaces.pdf) The adsorption of single colloidal microparticles (0.5–1 μm radius) at a water–oil interface has been recently studied experimentally using digital holographic microscopy [Kaz et al., Nat. Mater., 2012, 11, 138–142]. An initially fast adsorption dynamics... - [ descriptionPublisher's Version](http://dx.doi.org/10.1039/C6SM00966B) - [ picture\_as\_pdfRahmani et al. - 2016 - C...](/sites/g/files/omnuum4256/files/manoharan/files/rahmani-2016-colloidal_particle_adsorption_at_liquid_interfaces.pdf) Wang, A.; McGorty, R.; Kaz, D. M.; Manoharan, V. N. [Contact-Line Pinning Controls How Quickly Colloidal Particles Equilibrate With Liquid Interfaces](/publications/contact-line-pinning-controls-how-quickly-colloidal-particles-equilibrate). *Soft Matter* **2016**, *12* (43), 8958-8967. Wang, A.; McGorty, R.; Kaz, D. M.; Manoharan, V. N. [Contact-Line Pinning Controls How Quickly Colloidal Particles Equilibrate With Liquid Interfaces](/publications/contact-line-pinning-controls-how-quickly-colloidal-particles-equilibrate). *Soft Matter* **2016**, *12* (43), 8958-8967. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1039/C6SM01690A) - [ picture\_as\_pdfWang et al. - 2016 - Cont...](/sites/g/files/omnuum4256/files/manoharan/files/wang_et_al._-_2016_-_contact-line_pinning_controls_how_quickly.pdf) Previous experiments have shown that spherical colloidal particles relax to equilibrium slowly after they adsorb to a liquid-liquid interface, despite the large interfacial energy gradient driving the adsorption. The slow relaxation has been explained in... - [ descriptionPublisher's Version](http://dx.doi.org/10.1039/C6SM01690A) - [ picture\_as\_pdfWang et al. - 2016 - Cont...](/sites/g/files/omnuum4256/files/manoharan/files/wang_et_al._-_2016_-_contact-line_pinning_controls_how_quickly.pdf) ### 2015 Manoharan, V. N. [Colloids at Interfaces: Pinned Down](/publications/colloids-interfaces-pinned-down). *Nature Materials* **2015**, *14* (9), 869-870. Manoharan, V. N. [Colloids at Interfaces: Pinned Down](/publications/colloids-interfaces-pinned-down). *Nature Materials* **2015**, *14* (9), 869-870. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1038/nmat4400) - [ picture\_as\_pdfManoharan\_NatureMaterials...](/sites/g/files/omnuum4256/files/manoharan/files/manoharan-naturematerials-2015.pdf) (News and Views) A colloidal particle straddling an air/water interface experiences an unexpectedly large viscous drag. - [ descriptionPublisher's Version](http://dx.doi.org/10.1038/nmat4400) - [ picture\_as\_pdfManoharan\_NatureMaterials...](/sites/g/files/omnuum4256/files/manoharan/files/manoharan-naturematerials-2015.pdf) ### 2014 Meng, G.; Paulose, J.; Nelson, D.; Manoharan, V. [ Elastic Instability of a Crystal Growing on a Curved Surface ](/publications/elastic-instability-crystal-growing-curved-surface). *Science* **2014**, *343* (6171), 634-637. Meng, G.; Paulose, J.; Nelson, D.; Manoharan, V. [ Elastic Instability of a Crystal Growing on a Curved Surface ](/publications/elastic-instability-crystal-growing-curved-surface). *Science* **2014**, *343* (6171), 634-637. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1126/science.1244827) Although the effects of kinetics on crystal growth are well understood, the role of substrate curvature is not yet established. We studied rigid, two-dimensional colloidal crystals growing on spherical droplets to understand how the elastic stress induced... - [ descriptionPublisher's Version](http://dx.doi.org/10.1126/science.1244827) ### 2013 Wang, A.; Kaz, D.; McGorty, R.; Manoharan, V. [Relaxation Dynamics of Colloidal Particles at Liquid Interfaces](/publications/relaxation-dynamics-colloidal-particles-liquid-interfaces). *AIP Conference Proceedings*, 2013, *1518*, 336-343. Wang, A.; Kaz, D.; McGorty, R.; Manoharan, V. [Relaxation Dynamics of Colloidal Particles at Liquid Interfaces](/publications/relaxation-dynamics-colloidal-particles-liquid-interfaces). *AIP Conference Proceedings*, 2013, *1518*, 336-343. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1063/1.4794594) We study the dynamics of colloidal particles as they approach and breach a water-oil interface. We use a fast 3D imaging technique, digital holographic microscopy, to track particles with 2 nm precision and sub-millisecond time resolution. We find that... - [ descriptionPublisher's Version](http://dx.doi.org/10.1063/1.4794594) Small, A.; Fung, J.; Manoharan, V. [ Generalization of the Optical Theorem for Light Scattering from a Particle at a Planar Interface ](/publications/generalization-optical-theorem-light-scattering-particle-planar-interface). *Journal of the Optical Society of America A* **2013**, *30* (12), 2519-2525. Small, A.; Fung, J.; Manoharan, V. [ Generalization of the Optical Theorem for Light Scattering from a Particle at a Planar Interface ](/publications/generalization-optical-theorem-light-scattering-particle-planar-interface). *Journal of the Optical Society of America A* **2013**, *30* (12), 2519-2525. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1364/JOSAA.30.002519) The optical theorem provides a powerful tool for calculating the extinction cross section of a particle from a solution to Maxwell’s equations, relating the cross section to the scattering amplitude in the forward direction. The theorem has been... - [ descriptionPublisher's Version](http://dx.doi.org/10.1364/JOSAA.30.002519) ### 2012 Kaz, D.; McGorty, R.; Mani, M.; Brenner, M.; Manoharan, V. [ Physical Ageing of the Contact Line on Colloidal Particles at Liquid Interfaces ](/publications/physical-ageing-contact-line-colloidal-particles-liquid-interfaces). *Nature Materials* **2012**, *11* (2), 138-142. Kaz, D.; McGorty, R.; Mani, M.; Brenner, M.; Manoharan, V. [ Physical Ageing of the Contact Line on Colloidal Particles at Liquid Interfaces ](/publications/physical-ageing-contact-line-colloidal-particles-liquid-interfaces). *Nature Materials* **2012**, *11* (2), 138-142. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1038/nmat3190) Young’s law predicts that a colloidal sphere in equilibrium with a liquid interface will straddle the two fluids, its height above the interface defined by an equilibrium contact angle. This has been used to explain why colloids often bind to liquid... - [ descriptionPublisher's Version](http://dx.doi.org/10.1038/nmat3190) ### 2011 Kaz, D. [ Colloidal Particles and Liquid Interfaces: A Spectrum of Interactions ](/publications/colloidal-particles-and-liquid-interfaces-spectrum-interactions), 2011. Kaz, D. [ Colloidal Particles and Liquid Interfaces: A Spectrum of Interactions ](/publications/colloidal-particles-and-liquid-interfaces-spectrum-interactions), 2011. - add\_circle\_outline do\_not\_disturb\_on Abstract Young's law predicts that a colloidal sphere in equilibrium with a liquid interface will straddle the two fluids, its height above the interface defined by an equilibrium contact angle. This equilibrium analysis has been used to explain why colloids often... McGorty, R. [ Colloidal Particles at Fluid Interfaces and the Interface of Colloidal Fluids ](/publications/colloidal-particles-fluid-interfaces-and-interface-colloidal-fluids), 2011. McGorty, R. [ Colloidal Particles at Fluid Interfaces and the Interface of Colloidal Fluids ](/publications/colloidal-particles-fluid-interfaces-and-interface-colloidal-fluids), 2011. - add\_circle\_outline do\_not\_disturb\_on Abstract Holographic microscopy is a unifying theme in the different projects discussed in this thesis. The technique allows one to observe microscopic objects, like colloids and droplets, in a three-dimensional (3D) volume. Unlike scanning 3D optical techniques... ### 2010 McGorty, R.; Fung, J.; Kaz, D.; Manoharan, V. [Colloidal Self-Assembly at an Interface](/publications/colloidal-self-assembly-interface). *Materials Today* **2010**, *13* (6), 34-42. McGorty, R.; Fung, J.; Kaz, D.; Manoharan, V. [Colloidal Self-Assembly at an Interface](/publications/colloidal-self-assembly-interface). *Materials Today* **2010**, *13* (6), 34-42. - add\_circle\_outline do\_not\_disturb\_on Abstract - [ descriptionPublisher's Version](http://dx.doi.org/10.1016/S1369-7021(10)70107-3) Mix a drop of water into a vial of oil. With some surfactant and a vigorous shake, that one droplet has become thousands, and the total interfacial area has increased by an order of magnitude or more. Like the folded membranes in our mitochondria, the... - [ descriptionPublisher's Version](http://dx.doi.org/10.1016/S1369-7021(10)70107-3) ## Alumni [### Jerome Fung ](/people/jerome-fung)PhD Physics 2013 Jerome was a PhD student in Physics. His research involved characterizing and understanding the 3D dynamics of colloidal systems with holographic microscopy. He earned his PhD from Harvard in 2013. ![Jerome](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/jerome_1.jpg?itok=1MIbyP9Z) [### David M. Kaz ](/people/david-m-kaz)PhD Physics 2011 Dave was a PhD student in Physics who studied dynamic interactions between colloidal particles and liquid interfaces. He earned his PhD in 2011. ![Dave](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/dave.jpg?itok=9ZEA4wFN) [### Ryan McGorty ](/people/ryan-mcgorty)PhD Physics 2011 Ryan was a PhD student in Physics who studied colloidal particles at fluid interfaces with holographic microscopy. He earned his PhD from Harvard in 2011. ![Ryan](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/ryan.jpg?itok=00ssiRkS) [### Jennifer McGuire ](/people/jennifer-mcguire) PhD Applied Physics 2025 Jennifer was a PhD student in Applied Physics. She studied light transport through a variety of materials – including semiconductor nanowires, structurally colored colloidal assemblies, and grease films – using both computational and experimental... ![Jennifer McGuire](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/jennifer_headshot.jpg?itok=quIuTFB_) [### Jin-Gyu Park ](/people/jin-gyu-park)Former research associate Jin-Gyu was a research associate who studied structural colors made through self-assembly of colloidal particles. He received his BS (1995) and MS (1997) in the Department of Industrial Chemistry engineering from Hanyang University in 2002. He then worked... ![Jin-Gyu](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/img_1952.jpg?itok=imMLGZb5) [### W. Benjamin Rogers ](/people/w-benjamin-rogers)Former research associate Ben was a research associate in Applied Physics who studied a variety of problems in the area of soft and biologically-inspired materials, including colloidal self-assembly, light scattering and diffusion in nanoparticle films, and responsive photonic... ![Ben Rogers](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/ben-head.jpg?itok=x3FMVcdV) [### Jessica H. Sun ](/people/jessica-sun) PhD Engineering Sciences 2024 Jessica was a PhD student in Materials Science who studied self-assembly on curved surfaces. She earned her PhD in 2024. ![Jessica Sun](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/jessun.png?itok=3mDABuhB) [### Nabila Tanjeem ](/people/nabila-tanjeem) PhD Applied Physics 2020 Nabila was a PhD student in Applied Physics who studied self-assembly on cylinders and curved surfaces. She earned her PhD from Harvard in 2020. ![Nabila](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/nabila_crop.png?itok=2ZhNmQqK) [### Anna Wang ](/people/anna-wang) PhD Applied Physics 2016 Anna was a PhD student in Applied Physics. She studied particle-interface interactions and self-assembly of particles with holography. Her work included high-speed, precise measurements of particle movement in 3D, and applying the knowledge to making... ![Anna Wang](/sites/g/files/omnuum4256/files/styles/hwp_4_5__690x865/public/manoharan/files/img_20150427_180756.jpg?itok=J3KoZtnR) See also:- [ Current research areas ](/research-areas/current-research-areas) - [ Colloids and interfaces ](/research-areas/colloids-and-interfaces) - [ Project descriptions ](/page-categories/project-descriptions)