Penn Engineers’ Liquid Crystal Force Fields Enable New Kind of Microrobotics
Research published in Nature Communications led by graduate student Yimin Luo shows how fields generated by a liquid crystalline environment can be used to make a simple glass particle follow sophisticated trajectories.
Penn Engineers Develop Filters That Use Nanoparticles to Prevent Slime Build-up
Wednesday, November 1, 2017
Filtration membranes are, at their core, sponge-like materials that have micro- or nanoscopically small pores. Unwanted chemicals, bacteria and even viruses are physically blocked by the maze of mesh, but liquids like water can make it through. Researchers led by Martin F. Haase at the University of Pennsylvania have a new way of making membranes that could address this problem. Their method allows them to add in a host of new abilities via functional nanoparticles that adhere to the surface of the mesh.
Penn Researchers Demonstrate How to Control Liquid Crystal Patterns
Wednesday, November 1, 2017
Research led by graduate student Lisa Tran demonstrated that not only could patterns on liquid crystals be controlled at nanoscales, but the changes could be visible without microscopes. The work could potentially pave the way to new biosensors and energy-efficient harvesting devices. (Video)
Geometry Plays an Important Role in How Cells Behave, Penn Researchers Report
Tuesday, October 31, 2017
Inspired by how geometry influences physical systems such as soft matter, researchers led by graduate student Nathan Bade at the University of Pennsylvania have revealed surprising insights into how the physics of molecules within a cell affect how the cell behaves.
Langmuir "Curvature-Driven Migration of Colloids on Tense Lipid Bilayers"
Inspired by proteins that generate membrane curvature, sense the underlying membrane geometry, and migrate driven by curvature gradients, we explore the question: Can colloids, adhered to lipid bilayers, also sense and respond to membrane geometry? We report the migration of Janus microparticles adhered to giant unilamellar vesicles elongated to present spatially varying curvatures. In our experiments, colloids migrate only when the membranes are tense, suggesting that they migrate to minimize membrane area. By determining the energy dissipated along a trajectory, the energy field is inferred to depend on the local deviatoric curvature, like curvature driven capillary migration on interfaces between immiscible fluids. In this latter system, energy gradients are larger, so colloids move deterministically, whereas the paths traced by colloids on vesicles have significant fluctuations. By addressing the role of Brownian motion, we show that the observed migration is analogous to curvature driven capillary migration, with membrane tension playing the role of interfacial tension. Since this motion is mediated by membrane shape, it can be turned on and off by dynamically deforming the vesicle. While particle–particle interactions on lipid membranes have been considered in many contributions, we report here an exciting and previously unexplored modality to actively direct the migration of colloids to desired locations on lipid bilayers.
The Stebe Group, friends, and families gathered for a holiday party at Professor Stebe's house.
Nature Chemistry, News & Views runs an article "Nanomaterials: Two sides to every particle" to the publication
October 21, 2016
Janus particles are colloidal analogues of molecular amphiphiles that can self-assemble to form diverse suprastructures, exhibit motility under appropriate catalytic reactions and strongly adsorb to fluid-fluid interfaces to stabilize multiphasic fluid mixtures. To enable their widespread utilization, scalable methods that allow for the synthesis of Janus particles with diverse chemical compositions and shapes are highly desirable. We synthesize clickable Janus particles containing a click-active acetylene moiety that can be functionalized through thiol-yne click reactions with commercially available thiols. Our ability to design the structure and composition of diverse colloids will provide versatile new building blocks for self-assembly. link to article
Best Student Paper Award
July 18-22, 2016
Best student paper award: "Directed micro assembly of passive particles at fluid interface using magnetic robots" by D. Wong, I.B. Liu, E.B. Steager, K.J. Stebe, V. Kumar, International Conference on Manipulation, Automation and Robotics at Small Scale (MARSS), 18-22 July 2016, Paris, France.
Martin F. Haase Joins Rowan University
Dr. Martin F. Haase will join Rowan University to become an assistant professor in Chemical Engineering starting September 2016. Congratulations Martin!
Francesca Serra Joins Johns Hopkins University
Dr. Francesca Serra will join Johns Hopkins University to become an assistant professor in Physics & Astronomy starting November 2016. Congratulations Francesca!
June 28, 2016
Lassoing Saddle-Splay: Geomeotrical Control of Topological Defects" Lisa Tran, Maxim O. Lavrentovich, Daniel A. Beller, Ningwei L, Kathleen J. Stebe, Randall D. Kamien is featured on the cover of PNAS.
We combine strategies for particle assembly in soft matter with the robotics lab at Penn, Dr. Vijay Kumar's group, to develop means for controlled interaction.
March 14, 2016
Authors: D. Wong, I.B. Liu, E.B. Steager, K.J. Stebe, V. Kumar
We use a robot that serves as a programmable source of fluid curvature and allows the collection of passive particles. When settled on a fluid interface, the magnetic robot distorts the interface, which strongly influences curvature capillary migration. The shape of the robot dictates the interface shape, for example, by imposing high interface curvature near corners, create sites of preferred assembly. This freedom to manipulate interface curvature dynamically and to migrate laterally on the interface creates new possibilities for directed bottom-up particle assemblies and precise manipulation of these complex assembled structures. Since the passive particles can be functionalized to sense, report and interact with their surroundings, this work paves the way to new schemes for creation and control of functionalized micro robots.
Penn engineers and physicists find a new way to employ liquid crystal to create microlens arrays organized in a flower-like texture mimicking the compound eye in nature.
May 14, 2015
The collaborative endeavor is led by Francesca Serra and Mohamed Amine Gharbi, postdoctoral researchers in the Department of Physics & Astronomy in the School of Arts & Sciences, along with their advisers Kathleen Stebe (Chemical and Biomolecular Engineering), Randall Kamien (Physics and Astronomy) and Shu Yang (Material Science and Engineering and Chemical and Biomolecular Engineering).
Image chosen as "Best Artistic Award" in the NBIC NanoDay 2014 image contest.
Authors: Iris B. Liu, Yimin Luo, Francesca Serra, Mohamed A. Gharbi, Nathan D. Bade, Randall D. Kamien, Shu Yang, Kathleen J. Stebe
Description: A thin layer of smectic liquid crystal is spread out on a glass substrate. Liquid crystal molecules in contact with air prefer a perpendicular alignment, while in contact with the substrate, molecules prefer a planar alignment. To satisfy such alignment, smectic liquid crystal molecules can form two types of defect: focal conic domains and oily streaks. Smectics manifest extreme sensitivity to boundary conditions, in a small region both patterns emerge, interlacing each other, resembling ancient woven textiles. This image shows such a region under cross-polarizer, where focal conical domains emerge as four brushes, while oily streaks look like close-packed tiles.
Alumna Dr. Van Truskett Receives AIChE Industrial Research & Development Award
Dr. Mohamed Gharbi joins Prof. Mark Sutton and Prof. Linda Reven at McGill University as a Postdoctoral Research Fellow
Saturday, August 2, 2014
After his collaborative postdoctoral work with Prof. Kathleen J. Stebe, Prof. Randy Kamien and Prof. Shu Yang, Dr. Mohamed Gharbi has joined Prof. Mark Sutton and Prof. Linda Reven at McGill University as a Postdoctoral Research Fellow.
Dr. Lu Yao has successfully defended his PhD dissertation and has joined the Dow Chemical Company as Senior Engineer.
Paper featured in SPIE
March 11, 2014
"Controlling liquid crystal defects" Mohamed A. Gharbi, Daniel A. Beller, Apiradee Honglawan, Kathleen J. Stebe, Shu Yang and Randall D. Kamien: A novel approach to control the arrangement of the smectic layers to form flower texture on curved surfaces can potentially be used to create lenses.