Meeting Day Three: Wednesday, July 3, 2013
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Day three at the ICMAT 2013 meeting was filled with two more excellent Plenary Lectures by Yuan-Tseh Lee on matrix assisted laser desorption and C.N.R. Rao on inorganic analogues for graphene. A great Theme Lecture by Claes Granqvist on green technologies for buildings rounded out the special lectures nicely. Symposium Z4 had some particularly interesting talks on cellular targeting and therapeutics on the biomedical side of materials, and one presentation in Symposium V6.1 involved the controversial topic of cloaking devices, specifically for hiding fish and cats (read the summary in the Technical Program section below to understand the wit of this last phrase. Who says scientists don't have a sense of humor?). Of course, being at the halfway point in the meeting means that all the symposia were proceeding at full throttle. Three days in and there’s still so much more fascinating materials science to discuss!
Fourth Plenary Lecture
Introduction by Nordin Hasan, Director of the ICSU Regional Office for Asia and the Pacific
Nordin Hasan began the morning Plenary Lectures by introducing the audience to the International Council of Science, or ICSU (pronounced ee-sue). The Council is composed of 31 scientific unions (which is where the U in the acronym comes from; it’s a historical holdover) and 120 national members representing 140 countries. The vision of ICSU is to create a world where science is used for the value of all and scientific knowledge is effectively linked to policy making. The Council has three strategic themes: the universality of science, science for policy, and promoting scientific research. More information about ICSU and current news can be found at http://www.icsu.org.
Elementary Processes Involved in Matrix Assisted Laser Desorption
Yuan-Tseh Lee, Nobel Laureate in Chemistry, Academia Sinica, Tiawan, and President, International Council for Science (ICSU)
It’s always interesting to learn about the current research of a Nobel Prize laureate. Not surprisingly, Lee is working to change the current understanding of elementary processes in the field of Matrix Assisted Laser Desorption Ionization (MALDI). Currently there are two established mechanisms for creating ions of an analyte embedded in a matrix. The first involves exciton pooling, where a laser first creates excited states, then two excited analytes collide to emit an ion while the other analyte returns to the ground state. The other mechanism claims that ions are present in the matrix and are simply sublimated by the laser. Lee doesn’t agree with either of these mechanisms.
He says the key to ionization lies in weak bonding interactions, such as hydrogen bonding, between analyte pairs or between the analyte and the matrix. In this model, upon ionization, a proton is transferred to create a cation as well as an anion. Typically, only cations are measured by mass spectrometry, but if both cations and anions are measured, as a collaborator of his did, both positive and negative ions are found in nearly equal amounts. Additionally, isomers with different proton affinities produce variable amounts of ions—high proton affinity creates more ions, while low proton affinity creates less.
He has used this model to study carbohydrates, which typically degrade in MALDI systems because of the intense heat after sublimation. By adding water to the matrix and freezing the sample, ionization is encouraged by the extensive hydrogen bonding network, while lower plume temperatures keep the carbohydrate intact with little fragmentation or degradation. It may make you feel less alone in the struggle to publish to know that one of his graduate students is having trouble getting this new mechanism published, as it is radically different from the accepted mechanisms. However, as soon as the article finds a home, it will, surely, inspire new methods to broaden the scope of MALDI to increasingly sensitive biological samples.
Fifth Plenary Lecture
Graphene Analogues of Inorganic Materials
C.N.R. Rao, Jawaharlal Nehru Center for Advanced Scientific Research, India
“Graphene is the mother of all carbon—buckyballs, nanotubes, graphite, and more,” C.N.R. Rao said at the beginning of his talk. Given that inorganic fullerenes and nanotubes were fabricated shortly after the discovery of their carbon forms, why not investigate inorganic graphene?
So Rao has been doing just that, specifically focusing on MoS2 and WS2 analogues of graphene. He and his team have been using ultrasonication and chemical methods to make few-layer (defined as about 4 layers or less) analogues from these materials, although microwave synthesis and laser exfoliation of layered materials have also been successful in this effort.
They have discovered that all inorganic few-layer analogues of graphene are ferromagnetic, due to a zig-zag edge with unsatisfied valences and dangling bonds. Decorating a few-layer MoS2 material with gold nanoparticles makes it a good catalyst for hydrodesulfurization of hydrocarbon feedstocks. Rao has seen hysteresis in atomically-thin MoS2 FETs, with fairly good on/off ratios, but the mobilities are too low. In recent weeks he has been investigating H2 evolution using MoS2 and reduced graphene oxide MoS2 (RGO-MOS2); with nitrogenation, RGO-MoS2 is very good for H2 evolution. Few-layer WS2 has proven to be a good electrode material in Li-ion batteries.
“As chemists, we need to be investigating new materials that are unknown,” Rao said, emphasizing that continuing investigation of known materials, while valuable, is not enough. Toward this end, he has been experimenting with BxCyNz borocarbonitride analogues for graphene. BC1.6N and BC1.9 N occur in two structural morphologies: random orientation of B, C, and N atoms on the lattice, or separate domains of hexagonal BN and C . These borocarbonitrides have BET specific surface areas of 2,000 to 2,500 m2/g, with good adsorption properties for CO2 and CH4, making them candidates for catalysts. They also have shown promise as supercapacitor electrodes.
Third Theme Lecture
Green Nanotechnologies for Energy Efficient Buildings: Some Possibilities with New Technologies
Claes G. Granqvist, Uppsala University, Sweden
Buildings use approximately 40% of all energy consumed, and we spend 80 to 90% of our lives indoors, on average, according to Claes Granqvist. This is ample argument for improving the energy efficiency of buildings.
When talking about energy waste in buildings, windows are the weakest link. Heavily doped oxide semiconductor films, such as In2O3:Sn(ITO) and SnO2:F are good for low emittance in windows. Very thin metal films (if you can make them thin enough), carbon nanotubes, and Ag nanowires have also been considered for wavelength selectivity in window applications. Angular selectivity, which is needed for a car’s windshield, can be achieved with thin, Cr-Based films with columnar nanostructures.
Granqvist was most interested in electrochromic windows, which are essentially transparent, thin film batteries. A laminated window structure consisting of thin layers of PET/ITO, NiO as an anode, a rubber electrolyte, WO3 as a cathode, and another layer of PET/ITO, is the current state of the art. When sunlight strikes the window a current is generated in this thin film battery and darkens the window. But considering that 6 billion square meters of glass are produced every year, most of which goes into windows, any energy saving solution will have to be “cheap, cheap, cheap, and cheap,” Granqvist said. No such technology exists at the moment. Electrochromic foils might serve the purpose down the road.
Symposium B6: Device Design and Processing II
All-solution-processed Fabrication of Organic Field-effect Transistors with π-junction Au Nanoparticles
Takeo Minari, National Institute for Materials Science (NIMS), Japan
Minari and his colleagues are improving the resolution of organic field-effect transistors (OFETs) to 10 microns using surface patterning of hydrophilic and hydrophobic substances. Using a low temperature printing technique, they begin with a plastic substrate. They then apply Au–based ink to hydrophilic areas to form the source and drain, followed by printing of an organic semiconductor layer in the channel regions. A dielectric layer is placed on top of this, and Au ink is applied to form the top gate of the OFET. To date, their printed OFETs have shown an average mobility of 7.9 cm2/Vs, which they hope to improve upon with further research.
Symposium T6: Magnetic 8
Bottom-up Approaches to Fabrication of Nanocomposite Magnets
J. Ping Liu, University of Texas at Arlington
The size of magnets has shrunk dramatically over the past hundred years, which, in part, helped to fuel the technology explosion, as magnets are common in any electronic device. The newest application, however, involves electric vehicles and using strong magnets in traction motors to power cars. Liu and his group seek to find stronger but lighter magnets from new nanocomposite materials.
Nanocomposite magnets need a hard phase with an embedded soft phase that can phase-exchange couple to form a blend with high magnetization. The soft phase has a critical dimension, dependent on the material, usually around 3‒16 nm. The typical method to form nanocomposites is a top-down approach, where a melt of the two phases is rapidly cooled to create an amorphous mixture. Liu, instead, uses a bottom-up approach, in which he grows nanoparticles of each phase then mixes the two. Using this method, he can synthesize nanoparticles with specific shapes and sizes to control the morphology of the mixture.
Near the beginning of the talk, Liu, with a smile on his face, listed table after table after table, in rapid succession, of materials he has tested for magnetic properties—more than 40,000 in all (though he didn’t show quite that many). He has narrowed down his search to rare-earth materials and recently developed a method to synthesize non-aggregated nanoparticles through the use of a surfactant. Currently, he is optimizing the method for combining the two phases through either a gas gun approach or warm compaction.
Symposium V6.1: Fundamentals and Cloaking
Invisibility Fantasy and Reality
Baile Zhang, Nanyang Technological University
As Zhang says in his abstract, “There is hardly a research topic that could stir up as much enthusiasm and aversion simultaneously as did invisibility cloaking.” The topic has been met with excitement from the media, named one of the “Top 10 Breakthroughs of 2006” by Science, and has more than 15 publications in the Nature and Science families of journals. However, many serious scientists see the field as a joke and funding is hard to come by. Zhang says these misunderstandings come from the blurred boundary between fantasy and reality. In this talk, he explained the realities of cloaking.
The main principal of cloaking is to distort incoming light rays to control the propagation of light around an object; in other words, to bend the light around an object. But to actually have a working cloak, the bent light must travel at a faster rate around the object than the non-interacting light so that no background distortion is seen. However, Zhang found that in incoherent light, such as normal ambient lighting, an increase in velocity is not necessary.
He and his group have successfully constructed a free-standing cloak that hides an object so that a cohesive background is all that can be seen. In a first example, he showed a video of a “six-directional cloak for fish,” where a fish swimming inside the cloak was successfully hidden while the plants behind the cloak remained visible. He also concocted a cloaking box for a cat, which again successfully shielded a cat with an unbroken background video of a butterfly. The results of his work are certainly impressive and the comedy of his final bullet point—“we designed cloaks for hiding fish and cats”—was not lost on the audience.
Symposium X6: GRD Special Session – 1
Crystal Engineering Principles for the Design of Flexible Organic Materials
Malla Reddy Chilla, Indian Institute of Science Education and Research
Chilla is interested in creating organic crystals, which tend to be very brittle, that are elastic and can recover their shape after deformation. The co-crystal of caffeine and 4-chloro-3-nitrobenzoic acid has three structural forms, each with different mechanical properties. The first form is elastic and displays complete reversibility, as shown by examining the crystal structure before and after bending. To discover the mechanism for recovery, he looked at the crystal structure while the material was bent and found an elongated structure in the outer region, but a compressed structure in the inner region. The compression in the inner region forced the crystal to straighten out to its original shape once the stress was removed. The other two forms have similar crystal structures—both are 2D layered materials—but vastly different mechanical properties. The first is a shearing type material with abundant slip planes, while the second is brittle. Strong interlayer pi-pi interactions in the second material make the layers hard to slip past one another, which accounts for the brittleness.
Additionally, Chilla examined mechanochromic materials. These structures undergo a color change with applied pressure that can be reversed by heat. He found that the presence of slip planes, which allow for plastic deformation, make elastic crystals with better mechanochromic luminescence than their brittle counterparts.
Usefulness of Inorganic Chemistry in Preparing New Hybrid Structures
S. Natarajan, Indian Institute of Science
Natarajan uses the governing principles of inorganic chemistry in the design and synthesis of metal organic frameworks (MOFs) and coordination polymers. He found that by creating an MOF with an [Mn4Cl]7+ core linked by an analogue of benzene tricarboxcylic acid, he could form an octahedral cage complex that arranges into a cubic network with high surface area and almost 70% void space in the crystal. However, when he tried to use other metals, such as Fe, Co, Ni, and Cu, cages were not formed.
After much thought, he came upon the Irving-Williams series for the stability of 2+ states of first-row transition metal ions, which increase going across the periodic table. He soaked his Mn-MOFs in a solution of MCl2 and found complete exchange of the Mn ion for Fe, Co, and Ni after just 12 hours; Cu produced only a 66% exchange. The exchange was reversible for Co and Ni, but took a month to complete. Fe, surprisingly, was found not to be reversible, which was determined to be due to the presence of an Fe(III) oxidation state in the MOF rather than Fe(II); thus, the coordination geometry was altered in a way that was unfavorable for Mn replacement. It is important to note that there are currently only three entries in the Cambridge Structural Database for octa-carboxylates, and Natarajan has more than doubled that number by this study.
Symposium Z4: Cellular Targeting and Therapeutics
Biomimetic Technology to Capture Circulating Tumor Cells
Seungpyo Hong, University of Illinois at Chicago
The primary cancerous tumor is not the biggest concern for most patients, according to Seungpyo Hong. Rather, circulating tumor cells (CTCs) that flow through the blood stream can lead to metastasis, with potentially fatal results. Much research is going on to learn how to capture these highly elusive cells—only one in a billion cells in the blood stream is likely to be cancerous— for diagnosis and prognosis purposes. To date, only CellSearchTM from Veridex, LLC, has received FDA approval for CTC detection. Hong and his colleagues are trying a different approach based on cell rolling and adhesion using a technique called tumor cell extravasation. Extravasation occurs through concurrent rolling and firm adhesion of the circulating tumor cells on the endothelium.
Dynamic rolling can be successful in bringing fast flowing cells to the surface. When the surface is covered with E-Selectin /Anti-EpCAM, it serves as an effective region to statically bind these cancer cells. So the combination of rolling and static binding enhances the capture efficiency. Going a step further, the researchers are now using poly(amidoamine) dendrimers (PAMAM dendrimers) to improve CTC capture by a factor of 150,000. The high density branch structure of the dendrimer allows a high local density of multivalent ligands capable of binding the CTCs strongly.
Cellular and Subcellular Targeting by Folate-decorated Nanoparticles for Ocular Drug Delivery
Ying Chau, The Hong Kong University of Science and Technology
Delivering therapeutic agents to the back of the eye is difficult due to dynamic barriers and tissue complexity, according to Ying Chau. The current method is injection into the back of the eye every month, which is painful and could possibly cause retinal detachment. In her lab, Chau is using a three-pronged approach to improve this situation: (1) controlled release of the drug so injections can be done less frequently; (2) targeted release; and (3) non-invasive delivery.
Controlled release has been achieved by delivering the protein-based therapeutic agent in a hydrogel. The mesh of the hydrogel determines the rate of drug release. To date, Chau has achieved prolonged release of a drug called Avastin for over four months, which is a great improvement. Targeted release of therapeutics is aimed at the retinal pigmented epithelium (RPE), which serves as the blood-retinal barrier. The RPE has receptors for folate (vitamin B9), which is essential for healthy eyes, so Chau’s group is using folate as the targeting ligand. Attaching the folate ligands to polymer nanoparticles with diameters of 50 nm leads to high folate uptake in the RPE.
Scanning the Meeting
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This work was partially supported by the IMI Program of the National Science Foundation under Award No. DMR 08-43934. Specifically, the work of Apprentice Science Reporter Jenna Bilbrey was funded under this NSF award, which is managed by the International Center for Materials Research (ICMR), University of California, Santa Barbara, USA. MRS thanks the NSF and the ICMR for their continued support, without which the Meeting Scene would not be possible.
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