Days 4,5: Friday, Saturday, December 12-13

DAYS 4,5
Friday, Saturday, December 12-13, 2008

CONTENTS

• Plenary Lecture - Baixin Liu
• Plenary Lecture - Samuel I. Stupp
• Technical Talks
• Young Researcher Award Winners

The IUMRS-ICA 2008 concluded on Saturday, December 13, in Nagoya, Japan, after a successful run during the week. The last two plenary sessions were held on Friday and Saturday, with talks by Prof. Baixin Liu and Prof. Samuel Stupp, respectively. The plenary session on Saturday afternoon was the final event of the conference. Following this a brief concluding ceremony was held to mark the end of ICA 2008. Prof. B.V.R. Choudhari (National University of Singapore) took this opportunity to invite everyone to the IUMRS-ICA 2009 conference which will be held in conjunction with ICMAT 2009 organized by MRS-Singapore from June 28-July 3, 2009 in Singapore.

Finally, conference Chair Prof. Osamu Takai announced the winners of the Young Researchers award. He concluded by thanking all attendees, symposium organizers, staff and other volunteers for making the conference a resounding success.

We hope you have enjoyed this coverage of the ICA 2008 conference courtesy of the Materials Research Society (MRS). We welcome your feedback and comments.

Some of the Young Researcher Award winners

PLENARY LECTURE: BAIXIN LIU

Multi-Scale Modeling of Metallic Glass Formation in Equilibrium Miscible and Immiscible Binary/Ternary Metal Systems

Prof. Baixin Liu (Tsinghua University, Beijing, China) gave the plenary lecture on Friday in the afternoon, presenting a summary of up-to-date experimental studies on the formation of amorphous alloys/metallic glasses by ion beam mixing of multiple metal layers in equilibrium miscible and immiscible binary metal systems. He started with a quick introduction to metallic glasses. He then introduced ion beam mixing as a powerful metallic glass producing technique and gave some brief historical background. He described the physical processes involved in ion beam mixing under far-from-equilibrium conditions. Ion beam mixing is capable of producing metallic glasses in both miscible and immiscible binary metal systems. The favored composition range in the phase diagram could be from the central portion to extend to about the edges of the solid solution systems. Next, based on the framework of Miedema’s theory, thermodynamic modeling of metallic glass formation was briefly described with consideration of the additional interfacial free energy in metal-metal mutilayers. Through proper design of metal-metal multilayers, ion beam mixing is able to produce amorphous alloys with adjustable compositions in immiscible systems at equilibrium.

For atomistic modeling, an important method, ab initio-assisted construction of interatomic potentials, was introduced. This is necessary for an immiscible system, since there is no equilibrium compound providing the necessary physical property data for fitting the cross potentials. Realistic potentials were constructed in representative binary metal systems, including miscible and immiscible ones characterized by very negative to very positive heats of formation as well as possible combinations of three major structures (bcc, fcc and hcp). Applying the constructed potentials, molecular dynamics simulations indicated that the physical origin of the crystal-to-amorphous transition, which results in metallic glass formation, is the collapse of crystalline lattice, while the solute atoms exceed the critical value, thus determining the two critical solid solubilities for each system. In other words, in a binary metal system, the composition range bounded by the two calculated critical solid solubilities could be considered to be the intrinsic glass-forming ability of the system quantitatively, within which metallic glasses are energetically favored. Finally, he described similar atomistic modeling for some ternary metal systems.

Prof. Masao Doyama, Prof. Baixin Liu and Prof.
Osamu Takai at the plenary session on Friday.

PLENARY LECTURE: SAMUEL I. STUPP

Self-Assembly of Supramolecular and Hybrid Materials

There is tremendous current interest in regenerative medicine for obvious reasons. Prof. Samuel Stupp (Northwestern University) gave a fascinating talk on self-assembly of supramolecular materials for applications in regenerative materials. Stupp and his co-workers are exploring various areas including spinal cord and retina regeneration, heart regeneration after infarcs, neuron repair, cell therapies for diabetes, cartilage repair, and growth and universal repair of bone fractures. Stupp presented a few examples to illustrate the techniques used by his group. Essentially, self-assembling systems are are molecularly programmed to form nanostructures, macroscopic hierarchical materials, and hybrids with both soft and hard matter. The systems have the capacity to integrate multiple biological functions of importance in regenerative medicine technologies. The basic idea is that cylindrical nanofibers that mimic collagen architecture invade extracellular space for cell signalling, targeting, and delivery. The self-assembly can occur in situ or using pre-assembled nanofibers. He showed how peptide amphiphiles self assemble in water to form cylindrical 1-D nanostructures. Macroscopic gels are formed from the nanofiber networks, and this gelation process can be reversed. Also, cells can be encapsulated in 3D in the gels.

This self assembly platform can be used in various ways to yield biomaterials. In one example presented by Stupp, in traumatic injuries to the spinal cord, it is cut and a scar is formed preventing the axons of the cord from reconnecting. Using the self assembled nanofibers injected into the injury area in rats allowed them to regain most of the movement in their hind legs, which normally would be paralyzed for life. Another example discussed by Stupp was the design of an angiogenic system wherein nanofibers were nucleated by heparin. This was used to grow blood vessels in a cornea within 7 to 10 days. In another study, diabetic mice were cured by using transplanted islets in the omentum with angiogenic nanostructures present. Stupp also described repair of mineralized tissue (bone) by using supramolecular nanofibers as matrices to trigger mineralization and stem cell differentiation. Clearly, the self-assembled supramolecular and hybrid materials have a bright future in tissue regeneration as demonstrated by this large body of work.

TECHNICAL TALKS

Symposium M: Innovative Material Technologies Utilizing Ion Beams

Processing Of Patterned Nanostructures By Energetic Particle Beams: Implantation vs Irradiation Effects

Lumin Wang (University of Michigan, USA) described forming patterned nanostructures using ion beams in symposium M. Traditionally, ion beams have been used to implant specific ion species for modifying materials. However, energetic ions also cause irradiation effects due to electronic excitation (as opposed to nuclear collisions) and Wang's work takes advantage of irradiation effects of energetic ions. Wang's presentation focused on recent progress in his group on the processing of patterned arrays of nanostructures with ion beam technology. Resulting structures included one dimensional periodical surface ripples, two dimensional patterned surface nanodots and three dimensional nanocavity supperlattices. He presented several examples. For instance, he showed micro-patterns containing self-organized nano-fibers obtained by a focused ion beam (FIB) on a (100) Ge surface - the word nano as well as the University of Michigan logo could be patterned in this way. Another interesting example was 1 MeV Au implantation of GaSb, which formed a porous structure within the material but left an intact surface shell. The fundamental mechanism for these results can be explained with recent results of computer simulations based on a single phase field model that considers the balance of defect production, annihilation, migration as well as surface sputtering and redeposition.

High Energy Ion Beams as a Tool for Fabricating Nanostructures

In the second talk in this session, Wolfgang Ensinger (Darmstadt University of Technology, Darmstadt, Germany) also described the use of very high energy heavy ion beams to fabricate nanostructures. When polymers, such as polycarbonate and polyimide, are irradiated with such energetic heavy ions, the ions completely penetrate the polymer generating ion tracks. These latent ion tracks can be etched preferentially yielding channels through the polymer. Ensinger uses high atomic mass species such as Ti, Kr, Mo, Sm, Au and U. The diameters of these channels can range from tens of nanometers to micrometers, and their aspect (length-to-diameter) ratios l/d can be very high with pore densities up to 1 Gigapores/cm². He described several applications for these nanoporous membranes, including filtering uranium aerosols in a nuclear reactor fuel processing facility. The U particles were found to be collected within the walls of the pores, while larger dust particles accumulated on the membrane surface. The overall alpha-activity due to the U significantly decreased to very safe levels.

In a twist to this technique for forming pores, conical nanopores can also be formed. Ensinger described forming a single conical nanopore in a polymer. One application of such a single conical nanopore could be as a single molecule sensor when used in an electrochemical cell. The electric current through the pore is measured and is steady. However, when a molecule such as DNA passes through the pore, the electrical current through the pore is disrupted or modified and this signals the passing of a molecule. Another interesting possibility is if a biorecognition element is attached to the pore wall. An analyte protein for example will bind to the wall which will block the pore and this effect can be used for biomolecular sensing. Ensinger also described current rectification using the nanopore and this effect could also be used for nanoscale sensing. Finally, he described using nanoporous membranes as a template for forming metallic nanowires, such as copper, bismuth, gold or platinum. This method was used to form the smallest ever platinum microreactor with nanowires within. By changing the irradiation angle, a nano-net could also be formed. Clearly, energetic ion beams represents a versatile tool for forming unique nanostructures.

Symposium Y: Frontiers of Polymeric Nano-Soft Materials

Graft Polyrotaxane: Synthesis, Characterization, and Properties

Toshikazu Takata (Tokyo Institute of Technology) described the synthesis of a new novel class of polymers, graft polyrotaxane, in his talk in symposium I. Graft polyrotaxane is a special class of graft polymers or polyrotaxanes, in which the incorporated rotaxane moiety plays a specific role in the mobility of the chains. From the viewpoint of the mobility of the graft chain, two types of graft polyrotaxane can be considered. While graft chains in graft polyrotaxane (A) can freely rotate and slide along the axle polymer, graft chains as axle components in graft polyrotaxane (B) can move across the cavity of the main chain polymer. Graft polyrotaxanes could generate characteristic properties depending on the mobility of the graft chains as well as their density and length. Thus, graft polyrotaxane can be regard as a novel category of polymers possessing properties between the polymer blend and covalent graft polymer. Tabata described the detailed synthesis of one such polymer. Polyrotaxane with its monofunctional wheel components was prepared according to the threading-end capping protocol from a mixture of polytetrahydrofuran (PTHF) and monohydroxy permethylated á- cyclodextrin in solid state. This was then modified to form either the A or the B variations. Takata described some preliminary physical and mechanical properties of these materials as well.

Polymer Nanotechnology Applied to Polymeric Nano- Soft-Materials

In a keynote lecture in symposium Y, Toshio Nishi (Tohoku University) presented an overview of polymer nanotechnology that his research group has been involved with as part of a major project. He classified polymer nanotechnology into nanoscale three dimensional (3D) measurements, nanoscale physical property evaluation systems, and nanoscale spectroscopy for material identification. He then showed several interesting applications of polymer nanotechnology especially for polymeric nano-soft-materials. The first was the development of a polymer-oriented 3D transmission electron microscopy (TEMT). This was used to image micro-phase separated block copolymers, injection-molded plastic/thermoplastic elastomer polymer alloys, carbon black/silica filled elastomers, polymer clay nanocomposites, and elastomers under elongation. The researchers were able to obtain important information unobtainable by conventional TEM and were able to quantitatively analyze their spatial structures. Nishi also described the development of physical property measurement based on a modified atomic force microscope. A nanomechanical mapping system was developed with which they are able to reconstruct the true surface topography, Young’s modulus mapping, and perform adhesive energy mapping at the same position. He concluded by describing a technique called static nanofishing to measure the elasticity of a single polymer chain using an AFM tip.

YOUNG RESEARCHER AWARD WINNERS

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