Skip over navigation

events

Seminar 9/24/2014 - Tadanori Koga, Stony Brook University: New Paradigm for the Design of Polymer-Solid Interfaces

Sep 24, 2014  ·  12:00 p.m. 1:00 p.m.  ·  Bowen Hall Auditorium

Abstract: Polymer thin films on top of impenetrable solids is of vital importance in many traditional technologies as well as new emerging nanotechnologies such as organic photovoltaics and biosensors. In this talk, I will focus on polymer-solid interfaces where irreversible polymer adsorption occurs regardless of the magnitude of solid-segment attractive interactions. In order to unveil the equilibrium conformations of adsorbed polymer chains, spin-cast homopolymer films prepared on Si substrates were used as models. The films were annealed at a high temperature to promote adsorption and ensure equilibrium and subsequently rinsed with a good solvent to remove non-adsorbed chains. A suite of surface sensitive techniques including grazing-incident x-ray/neutron scattering and atomic force microscopy were utilized. Firstly, I will present the unique nano-architectures and dynamics of the adsorbed chains and highlight the resultant long-range effects on the local structures and properties of the film. Secondly, I will discuss the unique adhesive property of the adsorbed chains that controls the thermodynamic stability of spin-cast films. Thirdly, I will also demonstrate the formation of the adsorbed layers in monolayer films of block copolymers, which would be a crucial parameter to control the orientation of the microdomain structures. Lastly, I will focus on geometric effects of solids on the nano-architectures by comparing with the adsorbed layers on nanoparticle surfaces.

Bio: Tad Koga is an associate professor in Chemical and Molecular Engineering Program at Stony Brook University. He received his Ph.D from Kyushu University, Japan in 1998 under the guidance of Prof. Takeji Hashimoto (Kyoto University, Japan). He is currently the spokesperson of the Advanced Polymers Beamline (X27C) at National Synchrotron Light Source and the research member of the Advanced Soft Material Beamline Consortium, Synchrotron Radiation Research Institute, SPring-8 (Japan). He received the NSF CAREER award for his work on green polymer surface processing using supercritical carbon dioxide in 2009.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.

Seminar 10/15/2014 - Enrique Gomez, Pennsylvania State University: Fully Conjugated Block Copolymers for Organic Photovoltaics

Oct 15, 2014  ·  12:00 p.m. 1:00 p.m.  ·  Bowen Hall Auditorium

Abstract: Organic electronic materials have the potential to impact almost every aspect of modern life including how we access information, light our homes, and power personal electronic devices. Unfortunately, weak intermolecular interactions and disorder at junctions of different organic materials limit the performance and stability of organic interfaces and hence the applicability of organic semiconductors to electronic devices. Our approach has focused on utilizing block copolymer architectures –where critical interfaces are controlled and stabilized by covalent bonds– to provide the hierarchical structure needed for high-performance organic electronics from self-assembled soft materials. For example, we have demonstrated control of donor-acceptor heterojunctions through microphase-separated conjugated block copolymers to achieve 3% power conversion efficiencies in non-fullerene photovoltaics. Characterization through X-ray scattering and electron microscopy reveals that the efficient performance of block copolymer solar cells is due to self-assembly into mesoscale lamellar morphologies with primarily face-on crystallite orientations. Although inferior in performance to inorganic and champion polymer/fullerene solar cells, the significant photovoltaic response of block copolymer devices provides the initial results needed to accelerate the development of next-generation materials.  Incorporating the donor-acceptor interface within the molecular structure facilitates computational design efforts, such that we can utilize quantum calculations to predict charge transfer state energies near 1.8 eV for P3HT-based block copolymers and explain the unusually high open-circuit voltages of 1.2 V.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.

Seminar 10/22/2014 - Dean DeLongchamp, NIST: Structure Measurements for Organic Photovoltaics and Manufacturing

Oct 22, 2014  ·  12:00 p.m. 1:00 p.m.  ·  Bowen Hall Auditorium

Abstract: Organic photovoltaics (OPV) is a promising candidate technology for the low-cost fabrication of modules to harvest solar energy.  Although OPV technology has significantly matured over the past few years, there remain significant challenges in addressing the gap between lab-scale devices and real manufacturing. Structure-property-performance relationships for OPV devices are still underdeveloped, and relationships based on one system are not necessarily transferrable to new, higher-performance systems. This talk will describe our efforts to develop measurements that support OPV manufacturing. Using a blade coating process as a prototype for slot-die coating, we have developed several techniques to observe the structure of OPV films in-situ as they dry. Our measurements include synchrotron-based X-ray scattering and a variety of optical methods. We use these techniques to identify the mechanisms by which formulation and processing choices influence the nanoscale structure of the films. Several OPV systems will be described including polymer/fullerene, small-molecule/fullerene, and polymer/polymer. Throughout solidification, we can follow the number of phases, their composition, and the extent of order within them. In-situ techniques provide far more information about the solidification process than can be obtained by measuring already-dried films, providing a valuable tool to guide the selection of formulation and processing parameters.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.

Seminar 11/5/2014 - Georg Steinhauser, Colorado State University: Radionuclide Analysis in Environmental Research after the Fukushima Nuclear Accident

Nov 5, 2014  ·  12:00 p.m. 1:00 p.m.  ·  Bowen Hall Auditorium

Abstract: The Fukushima nuclear accident will remain in public memory as one of the worst environmental disasters of the 21st century. In my presentation, I will focus on radionuclide monitoring after the accident and its challenges. Radionuclide monitoring is essential to understanding radioecological consequences and effects on food safety. In this context I will also discuss legal implications such as the regulatory limits of radionuclides in food.  Monitoring also is central to forensic work that may help understand the accident and its chronology. To date most of radionuclide monitoring has focused on volatile and ?-emitting radionuclides such as 137Cs, 131I, and 132Te. Relatively little work has been done on the monitoring of “difficult” radionuclides such as 90Sr or plutonium that are highly health relevant but much more laborious to measure compared with ?-emitters. We succeeded in obtaining unique sample material from inside the “exclusion zone” around the Fukushima power plant that was analyzed for 90Sr and plutonium. Our analyses revealed relatively high concentrations of 90Sr; however, these activity concentrations were exceeded by 137Cs by usually 3 to 4 orders of magnitude. In two spots within the exclusion zone we could also prove environmental presence of plutonium from Fukushima. Our studies show that, although the damaged Fukushima reactors emitted primarily volatile radionuclides, small but detectable amounts of less volatile radionuclides such as radiostrontium and plutonium have been emitted from the reactors, which was not expected for this accident scenario. The mechanisms of release of these radionuclides are not yet fully understood.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.

Seminar 11/12/2014 - Daeyeon Lee, University of Pennsylvania: Janus Particles as Solid Surfactants

Nov 12, 2014  ·  12:00 p.m. 1:00 p.m.  ·  Bowen Hall Auditorium

Abstract: Janus particles are asymmetric colloids with polar and apolar sides. Their amphiphilicity makes this new class of colloids exhibit behaviors that are similar to those of surfactant molecules.  The major goal of our work is to address the following intellectual questions: are Janus particles efficient “solid surfactants” for the stabilization of multiphasic fluid mixtures such as emulsions and foams? And how do their geometry and surface wettability influence their behaviors at fluid interfaces and, in turn, their properties as solid surfactants? In particular, we are inspired by how the chemical composition and shape of molecules influence the surfactant properties of molecular amphiphiles. In this talk, I will discuss our recent work on (1) understanding the effect of particle shape on the configuration and assembly of non-spherical Janus particles at fluid interfaces, (2) the thermodynamics of emulsion stabilization using Janus particles and (3) the emulsion stabilization and phase inversion emulsification using shape-changing/amphiphilicity-reversing Janus particles. I will first show that the configurations of nonspherical Janus particles such as ellipsoids and dumbbells at an oil-water interface strongly depends on the particle characteristics, such as their size, shape, aspect ratio, surface wettability, and the location of the Janus boundary. In the second part of my talk, I will discuss the thermodynamic aspect of emulsion formation using Janus particles.  Because the attachment energy of Janus particles to fluid-fluid interfaces is significantly larger than that of homogenous particles, it is possible to generate Pickering emulsions that are thermodynamically stable when Janus particles are used as emulsifiers. In the last part, I will discuss recently developed Janus particles that undergo significant changes in their shape and amphiphilicity in response to changes in the solution pH. We show that it is possible to stabilize different types of emulsions and also induce the phase inversion of emulsions using these stimuli-responsive Janus particles.

Bio: Daeyeon Lee is Associate Professor of Chemical and Biomolecular Engineering at the University of Pennsylvania. Daeyeon received his B.S. in Chemical Engineering from Seoul National University in 2001 and received his Ph.D. in Chemical Engineering/Program in Polymer Science and Technology at MIT in 2007 co-supervised by Robert E. Cohen and Michael F. Rubner.  After his Ph.D., Daeyeon was a postdoctoral fellow in the School of Engineering and Applied Sciences at Harvard University where he worked with David A. Weitz.  Daeyeon joined the Department of Chemical and Biomolecular Engineering at the University of Pennsylvania in 2009.  Daeyeon has won numerous awards and recognitions including the 2010 Victor K. LaMer Award from ACS Colloid and Surface Chemistry Division, the NSF CAREER Award (2011), the 2011 Korean-American Scientists and Engineers Association Young Investigator Award, the 2012 KIChE President Young Investigator Award, the 2013 3M Nontenured Faculty Award, the 2013 AIChE NSEF Young Investigator Award and the 2014 Unilever Young Investigator Award for Outstanding Young Investigator in Colloid and Surfactant Science.
 
All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.

Seminar 11/19/2014 - Ertugrul Cubukcu, University of Pennsylvania

Nov 19, 2014  ·  12:00 p.m. 1:00 p.m.  ·  Bowen Hall Auditorium

Title and abstract will be posted as we get closer to the event.
 
All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.

Seminar 12/10/2014 - Stephane Stebban, Laboratoire d' ’Optique Appliquée,– CNRS: Toward Compact and Ultrafast Soft X-Ray Lasers Sources

Dec 10, 2014  ·  12:00 p.m. 1:00 p.m.  ·  Bowen Hall Auditorium

Abstract: Emerging applications of coherent soft x-ray sources, notably in biology, require high energy and ultrashort pulse duration in the femtosecond-scale to probe the ultra-fast dynamics of matter in the nanometer scale. Alongside current efforts to provide high brilliance x-ray coherent sources with X-ray free electron lasers, significant potential lays in the realization of compact and relatively cheap ultra-intense x-ray coherent sources. Plasma-based soft x-ray lasers turn out to be good candidates since they can emit a large number of photon (up to 1015 per pulse) within a narrow linewidth and exhibit high-quality optical properties once seeded with high-harmonic sources. However, the duration of these sources has been limited so far to the picosecond range consequently restricting the field of possible applications.

In this presentation, we report on an original method able to generate intense femtosecond soft x-ray lasers pulse based on ultrafast ionization gain gating in a high-density plasma. By focusing a few 1018 W.cm-2 laser driving pulse into a high-density optically pre-formed krypton plasma waveguide, we observed a strong amplified spontaneous emission at 32.8 nm. For electronic density as high as about 2x1020cm-3, the measurement of the gain life time provides evidence of generating about 100 fs soft soft x-ray lasers pulses containing a few µJ. Overcoming previous bottlenecks in terms of pulse duration and peak brightness, this scheme may be paving the way for prospective laboratory-scale ultra intense soft x-ray lasers beams.

Bio: Stéphane Sebban, is “”Directeur de Recherche” at the National Center for Scientific Research (CNRS-LOA- Palaiseau, France) since 1998. He is an experimental physicist who is experienced in the conception, development and characterization of femtosecond laser driven soft x-ray laser.

Stéphane Sebban obtained his PhD from the University of Paris XII in 1997 on the “optimization and applications on a neon-like soft-x-ray lasers”. He spent one year as a postdoc at the Institute of Laser Engineering (ILE) at Osaka in Japan before joining the CNRS in September 1998. He initiated and directed the development of soft x-ray laser techniques using femtosecond laser drivers at LOA, leading to the realization of a practical approach of high repetition rate seeded amplification geometry. From 2005 to 2011, Stéphane Sebban has been in charge of the “Femtosecond Laser for EUV to X-ray sources” (FLEX) group composed by 5 senior scientists, 1 engineer, 3 post-docs and 3 PhD students. The activities of his group has covered a large variety of laser-plasma sources including high order harmonic generation, X-ray lasers and hard X-ray radiation from relativistic electron beams. From 2011 he is also leading the Research Activity 2 of the ELI-Beamline facility in Prague (Czech Republic) in charge of the development and the implementation of laser-driven x-ray sources.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.