bluuebunny/crossref_metadata_2025 huggingface dataset:
(Keynote) All-Atomistic Molecular Dynamics Calculation of Impact Fracture of Glassy Polymers
Authors: Fujimoto Kazushi , Shinoda Wataru , Okazaki Susumu
Published: February 2020

Impact-resistance has been one of the target properties of polymer technology from a view point of their mechanical applications. A huge number of investigations have been done for this very important property. One of the key to understand the impact resistance is to investigate the difference in microscopic behavior between brittle and ductile fractures by comparing two extrema of industrial polymers such as PMMA and PC, respectively. However, in spite of an abundance of information about macroscopic behavior of the impact fracture, little has been known about its microscopic picture. This is from difficulty in experiment for the very rapid phenomena.

Molecular dynamics (MD) calculation has been one of the powerful tools for investigating microscopic behavior of molecular assemblies at an atomistic resolution. However, so far, poor performance of the supercomputers has prevented us from investigating polymers based on all-atomistic MD calculations since the systems are huge. Then, we have been obliged to depend upon coarse-grained models such as Kremer-Grest model and DPD model. But, they are not good at describing chemical character of polymers which is essential for the investigation of fracture.

However, recent very rapid progress of supercomputer technology is going to enable us to investigate polymers based on all-atomistic MD calculations free from phenomenological parameters. The all-atomistic model can describe chemical details of the polymers, which is essential for the investigation of the diversity of polymers. Fracture of the polymers depends much on their chemical details such as main-chain bond breaking and side-chain motions.

In particular, it is very important to include bond fracture in the simulation. Since most of the traditional MD calculations have not included bond breaking explicitly, the calculations couldn’t describe brittle fracture of polymers but always resulted in artificial ductile fracture. The bond fracture can be described using potential function such as Morse-type one. The function can be obtained by high quality quantum chemical calculations prior to the MD calculations.

In the present study, brittle fracture has been investigated for PMMA including bond fracture explicitly. Systems constructed for the simulation mimicked the real system. There, experimental molecular weight distribution, density, radius of gyration, and entanglement molecular weight were reproduced well in the initial configuration prepared for the impact fracture test calculations. The calculations clearly show characteristics of the brittle fracture at a molecular level such as void formation, chain reactions of main-chain bond breaking, and small Poisson ratio.
Fracture Behavior of Solid Polymer Electrolyte Membranes with Different Ion Exchange Capacity for Fuel Cell
Authors: Ito Hiroshi , Shoji Junya , Zhao Yunfeng , Kurose Takashi , Ishikawa Masaru , Watabe Hiroyuki
Published: February 2020

INTRODUCTION:

Fuel cells are known as one of power generation technologies with high efficiency, and are anticipated to be ecological and renewable energy. Polymer electrolyte membrane (PEM) fuel cells have excellent features including compact size and lightweight. Therefore, these are expected to be used in automotive and electric portable applications. PEMs are utilized as an ion conductive material between electrodes in the fuel cell. Perfluorosulfonic acid polymer is widely used as the electrolyte membrane because of its high proton conductivity. However, the major problem of PEMs is the mechanical degradation of the membrane. In this study, toughness properties were investigated to clarify the mechanical fracture behaviour of PEM.

EXPERIMENTIAL:

Flemion® CSH25 (Asahi Glass Co., Ltd) consisting of tetrafluoroethylene main chain and sulfonic acid group in the side chain was used. It exhibits good proton conductivity by dissociating protons from the side chain moiety. Three types of samples with different ion exchange capacity (IEC) were selected. The IEC is determined by the number of sulfonic acid groups which is one of the factors that greatly affect power generation efficiency of a fuel cell. These samples were prepared by casting method. Therefore, any residual strains were not observed in the optical strain gauge. Uniaxial tensile tests (Imoto Machinery Co., Ltd.) with dumbbell shape samples (JISK-6251-7) were performed at a stroke length of 15 mm, a temperature of 25.0 ± 1.0 °C, a test speed of 60 mm/ min, ambient conditions of 23 ± 1 °C, and 45 ± 5% RH. The essential work of fracture (EWF) was calculated from the load-displacement curve of the uniaxial tensile test result to evaluate fracture toughness. Double notches were applied to specimens at both ends of test pieces on parallel portions. A test speed of 5 mm/min and the ambient conditions were maintained the same as above tests.

RESULTS AND DISCUSSION:

Nominal stress-strain curves in uniaxial tensile tests were shown in Fig.1. With increasing the IEC, elastic modulus and yield stress of the samples were increased. Fig.2 show the results of EVF evaluation. The IEC 1.10 (the lowest IEC) showed the highest EWF (15.2 KJ / m2) compared with IEC 1.25 and IEC 1.43. In the uniaxial tensile test results without double notch, larger IEC showed higher mechanical properties, but it is opposite to the results of EWF.

Figure 1
Detailed Comparison Among Multi-Chain Simulations for Entangled Polymers
Authors: Masubuchi Yuichi
Published: February 2020

Although lots of coarse-grained models have been proposed to trace long time behavior of entangled polymers, compatibility among different models has not been frequently discussed. In this study, the multi-chain slip-link model (primitive chain network model) and multi-chain slip-spring model have been examined for some dynamical and static measures, such as diffusion, relaxation modulus, chain dimension, entanglement density and the results have been compared with those reported for the standard bead-spring model. For the diffusion, three models are compatible with scaling parameters for unit of length, time and molecular weight. The relaxation modulus is also compatible given that the model dependence is accommodated for the entanglement density and the unit modulus. The chain dimension is in reasonable coincidence with small deviations due to the weak non-Gaussianity for the bead-spring model. Apart from these plausible compatibility, significant discrepancy has been found for the inter-chain cross-correlations in the relaxation modulus.
Coarse-Grained Molecular Dynamics Simulation of Elongational Flow of Polymer Melts
Authors: Murashima Takahiro
Published: February 2020

Elongational flows in polymer melt are important for polymer processing. For fiber processes, uniaxial elongational flow stretches polymer chains and enhance the strength of the fibers. Biaxial elongational flow makes thin films during film extruding processes. Molecular dynamics (MD) simulation can be useful to understand the microscopic mechanics of polymer chains in elongational flow fields. However, it has been difficult to treat elongational flows in MD for a long time. Extending the Kraynik-Reinelt boundary condition [1] for planar elongational flow, uniaxial and biaxial elongational flow have been succeeded in MD and applied to Lenard-Jones fluid [2,3] and crystallization process of an n-eicosane melt [4]. We have investigated elongational flows of a weakly entangled polymer melt [5].

The highly entangled polymer melt in experiments shows extensional thinning [6] while our previous results show extensional thickening [5]. We investigate a mildly entangled polymer melt and discuss whether the non-linearity of elongational viscosity enhances or not. Moreover, we investigate the elongational viscosities of branched polymer melts.

[1] A. M. Kraynik and D. A. Reinelt, Int. J. Multiphase Flow 18, 1045 (1992).

[2] M. Dobson, J. Chem. Phys. 141, 184103 (2014).

[3] T. A. Hunt, Mol. Sim. 42, 347 (2016).

[4] D. A. Nicholson and G. C. Rutledge, J. Chem. Phys. 145, 244903 (2016).

[5] T. Murashima, K. Hagita, and T. Kawakatsu, arXiv: 1803.01517.

[6] A. Bach, K. Almdal, H. K. Rasmussen, and O. Hassager, Macromol. 36, 5174 (2003).
The Effect of Process Parameters on Impregnation Properties of Pultruded Carbon Fiber Reinforced Thermoplastic Epoxy Composites
Authors: Wongsriraksa Patcharat , Nakai Asami
Published: February 2020

During the pultrusion process, there are some parameters that effect the impregnation performance of pultruded composites. The pultruded carbon fiber reinforced thermoplastic epoxy composites processing parameter such as pulling speed, resin viscosity, molding temperature of the pultruded composites that have to be considered and pulling speed one of parameter is discussed in this research.

In our previous research, it has been clarified that the carbon fiber reinforced thermoplastic resin fiber composites had not been good impregnation and surface for pultrusion process. The main problem during the processing of carbon fiber reinforced thermoplastic resin composites is the impregnation of the fiber reinforcement with highly viscous resin. The objective of this research is to improve an impregnation performance by using the low viscosity of thermoplastic resin. To achieve this objective, thermoplastic epoxy resin were used instead of thermoplastic resin fiber.

In this research is to studies an effect of pulling speed on impregnation of carbon fiber reinforced thermoplastic epoxy resin composites by using pultrusion technology to produce the hollow shape composite. The effect of pulling speed were evaluated.
Optically Manipulated Bottom-up Growth of Nanopatterned Semiconductor Films
Authors: Carim Azhar I , Batara Nicolas A. , Atwater Harry A , Lewis Nathan S
Published: February 2020

Bottom-up growth of macroscale Se-Te alloy films displaying nanoscale patterning with significant periodic order was effected via photoelectrochemical deposition. The exact nature of the optical excitation was the determinant of the features sizes, periodicities, anisotropies, and orientations of the nanoscale pattern. Use of linearly polarized light resulted in highly-anisotropic lamellar morphologies with the long axes of the patterns aligned along the E-field vector and increasing the complexity of the polarization input resulted in a concomitant increase in pattern complexity. The pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the periodicity was found to be sensitive to all investigated tuning of such profiles. Structures with nonequal periodicities in the two orthogonal in-plane directions could also be generated and both periodicities could be independently controlled. Additionally, the anisotropies, subwavelength feature size and periodic nature of the deposits enables the fabrication of optical elements with significant wavelength and polarization discrimination.

The nanopatterning process occurred without the use of any type of physical or chemical templating agents: no photomask, patterned substrate nor surfactants/ligands were used to influence the morphology. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with probabalistic simulations of mass addition successfully reproduced the experimentally observed morphologies and indicated that morphology development was a consequence of the fundamental light-matter interactions during growth.
Processing and Physical Properties of Temperature-Sensitive-Gel / Polymer Film
Authors: Sakai Kohei , Gong Jin , Ito Hiroshi , Sato Kosei , Hamada Kazuhiro
Published: February 2020

The Temperature-Sensitive-Gel (TSG) is a stimulus-responsive gel whose volume and physical properties change responsive to a temperature. The purpose of this research is to develop a novel temperature-responsive microporous film by adding TSG particles into a polymer composite. The TSG particles were synthesized firstly, which have a melting point of around 60 ° C, a spherical shape with the diameter of from 50 to 300 μm. Then the synthesized TSG particles were blended with linear low density polyethylene/calcium carbonate (LLDPE/CaCO3) composite to prepare microporous TSG/LLDPE/CaCO3 film. In this paper, we discuss the processing and physical properties of TSG/LLDPE/CaCO3 composite film. Our findings confirmed the thermal expansion and shrinkage of TSG in the vicinity of its melting temperature. This behavior enables pores close/open, to provide the TSG/LLDPE/CaCO3 composite film temperature-responsive pore-size-adjustment function to control the gas permeability.
Dissipative Particle Dynamics Simulation for Clarifying Mechanism of Water Permeation in Polymeric Membranes
Authors: Araki Yusuke , Arai Noriyoshi , Kobayashi Yusei , Kawaguchi Touru , Kaneko Takashi
Published: February 2020

Polymeric membranes are widely used in engineering fields such as fuel cells and heat storage materials. The polymeric membrane has two properties, which are selective permeability and barrier. The selective permeation mean to let only certain substances pass through porimeric membrane. For example, it is used for fuel cells. The polymeric membrane used in fuel cells allow protons to pass through, but does not water and oxygen. Next, barrier is to not permeate anything. This is used for a microcapsule of a heat storage material and so on. The microcapsule is made of polymers and designed as substances in capsules are not discharged from it. In future, It will be used as CO2 separation technology or seawater desalination, which will be anticipated to solve global issues. However, the prediction and control of penetration into a membrane are still challenging subjects. In this research, we aimed to elucidate the mechanism of the water permeation. because water permeation is most basic. We performed molecular simulations of water transport through a polymeric membrane to clarify the key factors that dominate water permeation. We employed the dissipative particle dynamics (DPD) method. DPD method is a powerful mesoscopic simulation tool which enables the simulation of events occurring in millisecond timescales and on micrometre length scales. Since its introduction a decade ago, this method has been used to model various membrane cell systems, including the self-assembly of amphiphilic molecules interaction with rigid nanoparticles, and the effect of ligands and receptors in the membrane. Therefore, this method is suitable to simulate polymeric membrane system. we used model of actual molecules (COP (membrane polymer), sodium acetate (additive) and water). To determine the interaction parameters of the simulation models, we used the J-OCTA simulation software. We first computed the time-averaged mean square displacement (MSD) of water molecules to evaluate water permeability into a polymeric membrane. Then, MSD was also calculated for the additive system. Comparing of the systems, it was found that the water permeability decrease by adding additives (figure). The results were also reproduced in experiments and we get qualitatively same results. We found that additives enable the reduction of the water permeability into a polymeric membrane. In addition, we discussed polymer synthesis guideline decreasing water permeability.

Figure 1
Modeling of Spherical Objects Using 3D Printing of Soft and Bio-Compatible Materials
Authors: Yoshida Kazunari , Kawakami Masaru , Furukawa Hidemitsu
Published: February 2020

A fused deposition modeling (FDM) is widely used as a 3D printing method of plastics (polymeric materials). However, modeling of soft materials is conventionally quite difficult using such method although 3D printing of plastics and/or elastomers is required for medical application such as manufacturing of prosthetic arms.

In this study, we investigated the optimum 3D printing conditions for modeling of spherical objects made with FABRIALTM-R and -H (JSR corp.). First, we 3D printed spherical objects with various nozzle speeds. Then, we observed the surfaces of 3D printed objects using a stereoscopic microscope. In addition, the hardness of the objects was measured by using a durometer (type E, Japanese Industrial Standards). The results suggest that optimum nozzle speed is 2.0 mm/s. In addition, the hardness of FABRIALTM-R object was dependent on nozzle speed while that of FABRIALTM-H was constant. Furthermore, we investigated the dependency of object hardness on pushing direction, vertical to and along stacking plane during printing. The hardness in the case of vertical to stacking plane is lower than that in the case of along stacking plane. These findings are expected to be applied to modeling of parts of prosthetic arms and soft-matter robots.
(Keynote) 3D-Printed Biodegradable Implants for Orthopedic Applications
Authors: Liu Shih-Jung
Published: February 2020

This study developed a new biodegradable polymeric cage using 3D printing technique to convert corticocancellous bone chips into a structured strut graft for treating segmental bone defects. A biodegradable truncated-pyramid cage was designed and manufactured to serve as the bone graft. Commercially available PLA filaments with a diameter of 3.0 mm were used as the material for the bone cage 3D printing. The cage was fabricated using a fused-deposition-modeling (FDM) type 3D printer with a printing resolution of 200 mm. The experimental results show that higher leg length ratios and 3-point bending strengths demonstrated improved final bony ingrowths within the bone defects for rabbits implanted with the 3D printed cages. The present experimental results indicate that using 3D printing PLA can be remodeled into a cage of any geometric shape to fill the bone. With this 3D printed cage, the orthopedic surgeons will be able to convert small corticocancellous bone chips into a structured bone graft to avail both the osteoconductive and mechanical properties. Through this bone graft converting technique, the surgeons can merge different sources of bone graft to serve as an adequate strut bone graft for the treatment of large bone defects without experiencing donor site morbidity and graft resource limitations.
Electrochemical Deposition of Compact TiO2 Layer for Perovskite Solar Cells
Authors: Nonomura Kazuteru
Published: February 2020

This presentation is dedicated to the utilization of a compact TiO2 layer in n-i-p perovskite solar cells as blocking and electron transporting layer. The formation of a homogeneous compact TiO2 layer is a key step toward blocking the electron back-reaction between conductive substrate (F-doped tin oxide) and perovskite. In the present study, a compact TiO2 layer was prepared by electrochemical deposition. This method is an alternative to the frequently used alternative of spray pyrolysis commonly used to prepare a compact TiO2 layer.

The electrodeposited TiO2 films were characterized by a variety of methods, including UV-VIS spectroscopy, cyclic voltammetry, X-ray diffraction, and scanning electron microscopy. The electrodeposited TiO2 compact layer was introduced in perovskite solar cells, which were compared with cells prepared with sprayed TiO2 compact layers. The results confirmed that an electrochemically deposited compact TiO2 layer can work sufficiently as a blocking and electron transport layer in perovskite solar cells.
(Keynote) Electrochemical Reactions at Semiconductor Thin Films As Part of Solar Energy Conversion or Advanced Light Management
Authors: Schlettwein Derck
Published: February 2020

Semiconductor Electrodes play a key role not only in microprocessor technology but also in photovoltaics (PV) and in smart windows (SW). Devices based on classic semiconductors like silicon or tungsten oxide have been well established, matured and led to commercialization and widespread technical application. In this contribution I will focus on the development of alternative material systems offering relevant advantages in function or in the sustainability of energy technologies based on them. As can be expected, however, new challenges are posed by such alternative approaches which will also be tackled in the talk.

Dye-sensitized solar cells (DSSCs), typically based on porous TiO2 as photoanode material represent an alternative to established PV technologies with clear expected advantages in energy payback time and harvest factor because of significantly decreased energy input upon preparation of devices. This trend can be taken to the next level if ZnO crystallized from aqueous solution rather than annealed TiO2 is used. To reach such goal, however, cell efficiencies need to increase beyond the presently reached values. Chemical and photoelectrochemical surface reactions at ZnO, however, need to be overcome in order to realize such progress. Some strategies and recent results from the author´s laboratory will be discussed.

Electrochromic cells (ECs) are essential parts in well established self-dimming rear-view-mirrors for automobiles and in SW for vehicles and buildings. In particular the latter are thought to have a significant potential impact on the human energy consumption since they allow to adjust the amount of transmitted or reflected light and heat radiation into a room depending on the demand in the room and depending on the season and weather conditions to an increased extent compared even to modern multiple-coated window glass. In this context it is of uttermost importance to increase the long-term stability of EC devices which might be reached by use of solid rather than liquid electrolytes which, however, present a substantial hurdle to ion conductivity essential for the devices. Some recent progress will be presented. A different improvement is sought in the rate of switching the transparency. In this respect, organic semiconductor films may present attractive alternatives since thinner films already provide intense absorption and fast switching can be reached which will also be discussed in the talk.
(Invited) Proton-Conductive Ultra-Thin Nafion/Uhmwpe Nanocomposite Membranes for High-Power Density Low Temperature Fuel Cells and Redox Flow Batteries
Authors: Gao Ping , Li Jin , Li Runlai , Zeng Lin , Zhao Tianshou
Published: February 2020

Perfluorosulfonic acid (PFSA) ionomers have been used extensively in proton exchange membranes due to their high proton conductivity and strong electrochemical stability. However, their high-cost and poor ion selectivity have been the limiting factors in their applications for mixed liquid electrolyte systems as well as in fuel cells. We have developed a novel multilayer ionomer membrane consists of hydrophobic nanoporous ultra-high molecular weight polyethylene laminated with ultrathin PFSA membranes to address the high-cost and poor ion selectivity issues in conventional PFSA ionomer membranes. The new ultrathin membrane with overall thickness as low as 2 micron meter exhibits tensile yield strengths more than 10 times higher than that of Nafion membranes and exhibits high proton conductivity up to 100 mS/cm. In addition, the membrane also exhibits extremely high ion-selectivity by blocking all ions that do not form strong hydrogen bonding with water molecules. Application of the new membrane in all vanadium flow batteries has demonstrated that the membrane shows both strong ion selectivity and higher discharge capacity than Nafion membranes, particularly at large cycle numbers. The newly developed membranes are also applicable in low temperature hydrogen fuel cells as well as for use in anionic exchange membranes.
(Invited) Biomimetic Proton Conductive Polymer Electrolyte
Authors: Matsui Jun
Published: February 2020

Proton conductive polymer electrolyte is one of the key components to fabricate an efficient fuel cell. Perfluorosulfonic acid polymers, such as Nafion are widely used because of their high proton conductivity. It has been considered that a strong acid is important for high proton conductivity therefore many group synthesized acid contain polymer from the viewpoint of how much strong acid can be added with keeping the polymer mechanical strength. On the other hand, living cell, mitochondria also used proton to produce energy. The difference in proton concentration across a membrane produce electrochemical potential energy, which drives the synthesis of ATP. Mitochondria does not contain strong acid and the protons are transferred using weak acid and base, whereas efficient proton conduction occurred at the bilayer membranes. Although the detailed mechanism for the proton conduction at the membrane is still controversial, several groups suggested that protons efficiently conduct through the membrane surface [1].

In this paper, we present a polymer proton conductive membrane which mimic the proton conduction at the bilayer membrane [2]. The polymer membrane was prepared by deposition of poly(N-dodecylacrylamide-co-acrylic acid) monolayer formed at an air-water interface using the Langmuir-Blodgett technique. The membrane was formed by multilayer film of the monolayer, in which formed a clear lamellar structure composed of hydrophobic alkyl side chains and hydrophilic amide and carboxylic acid regions. The hydrophilic region created 2D proton conductive nanospace, which resembles to the bilayer membrane surface. The proton conductivity in the 2D proton nanospace of the biomimetic polymer membrane reached to 5.9×10-2 S/cm, which is comparable to strong acid polymer electrolyte. The achievement of high proton conductivity even using weak acid as a proton source clearly indicates an efficient proton conduction in 2D nanospace. Moreover, we found that acrylic acid groups should be located in a proper distance to achieve the high proton conductivity. The mechanism of proton conduction at the 2D nanospace will be discussed using reported works of theoretical calculation.

References: [1] G. Groenhof et al., Biophys. J.
2014, 107, 76. [2] J. Matsui et al., ACS Appl. Mater. Interfaces
2011, 3, 1394., Mol. Cryst. Liq. Cryst.
2013, 579, 17., Langmuir
2015, 31, 5174., Langmuir
2017, 33, 12897.

Figure 1
Synthesis of Novel Intramolecular Charge-Transfer Molecules Bearing Triphenylamine and Benzothiadiazole Moieties, and Application to Single-Absorber Organic Solar Cells
Authors: Okuda Yuki , Suenobu Tomoyoshi , Nakayama Kenichi
Published: February 2020

Organic solar cells (OSCs) have been extensively studied due to their potential for flexible, printable, and low-cost devices. Recently, power conversion efficiency (PCE) has reached around 10% by using bulkhetero junction (BHJ) system which possesses miscible interface between two kinds of materials, electron donor and acceptor. In the BHJ system, LUMO offset is required to promote charge separation at donor-acceptor interface, causing serious photovoltage loss.

In order to overcome this problem, we have pursued the possibility of single-absorber organic solar cells, whose active organic layer consists of one component. Generally, photogeneration efficiency in organic bulk film is quite low because of the large exciton binding energy (EBE). In previous work, we found that molecules with intramolecular charge transfer photoabsorption are suitable for the single-absorber OSC. A donor-acceptor (D-A) linked molecule DTDCPB (Fig. 1) was applied to the single absorber OSC, and comparatively good performance was obtained.

In this study, we synthesized novel donor-acceptor linked molecules bearing triphenylamine and benzothiadiazole moieties by derivatizing DTDCPB (Fig. 1). DTDCPB was extended by insertion of thienothiophene at the donor-acceptor linkage part to form DTDCPB-TT. DTERPB and DTRCNPB bear an acceptor moiety of 3-ethyl rhodanine and 2-(3-ethyl-4-oxothiazolidin-2-ylidene)malononitrile, respectively, instead of dicyanovinyl moiety. EBEs in the solid state were estimated with quantum chemical calculation to design a suitable molecule for lower EBE.

The D-A molecules were applied to a single absorber OSC composed of ITO/PEDOT:PSS/organic/Ca/Al. In the DTDCPB-TT device, FF and hole mobility increased compared with those in the DTDCPB device because the film crystallinity was improved due to thienothiophene. In the DTERPB and DTRCNPB devices, the photovoltage loss was only 0.60 V, that was less than that of the typical BHJ system. The ratio of the voltage loss to the absorbed energy was 33% for DTERPB and 35% for DTRCNPB, which were rather small in comparison with the typical BHJ system, e.g. 65% for P3HT:PC61BM and 56% for PTB7:PC71BM.

Figure 1
In Situ Structural Studies for Energy Conversion and Storage Using Surface X-Ray Scattering
Authors: Kondo Toshihiro
Published: February 2020

In order to quantitatively clarify the electrochemical reaction mechanism and to apply such electrochemical reaction to modern energy conversion and storage systems such as fuel cells and batteries, it is of great importance to observe the three-dimensional structures at the electrode/electrolyte interfaces with an atomic dimension in situ. Surface x-ray scattering (SXS) technique using synchrotron radiation as an x-ray source is one of the best methods to allow us to know the three-dimensional interfacial detailed structures in situ. Using this technique, we have clarified both static and dynamic interfacial structures in many electrochemical reactions. As examples, adsorbed structures of oxygen species on Pt(111) single-crystal electrode during oxygen reduction reaction (ORR), which is a cathode reaction of the polymer electrolyte fuel cell (PEFC), and formation/deformation of lithium-silicon alloy during charging and discharging, which is an anode reaction of the lithium-based batteries, will be introduced in this presentation.
Fabrication of Polymer Bonded Permanent Magnets
Authors: Khosla Ajit , Vaid Rakesh , Thundat Thomas , Nagahara Larry A. , Kawakami Masaru , Furukawa Hidemitsu
Published: February 2020

We present fabrication of polymer bonded magnets. These magnets were fabricated by mixing isotropic permanent magnetic Neodymium Iron Boron (NdFeB) fine powder in polydimethylsiloxne matrix (PDMS). The developed magnetic composite can be be micromolded on flexible PDMS substrate, via a novel hybrid soft lithographic technique previously reported by authors {1, 2, 3].

The developed PDMS based magnets find their application in microfluidics [4], Sensors and actuators [5], micromotors [6] and automotive industry [7]

References:

Khosla, A., and B. L. Gray. "New technologies for large-scale micropatterning of functional nanocomposite polymers." In Nanosensors, Biosensors, and Info-Tech Sensors and Systems 2012, vol. 8344, p. 83440W. International Society for Optics and Photonics, 2012. https://doi.org/10.1117/12.915178

Khosla, Ajit, Jasmine L. Korčok, Bonnie L. Gray, Daniel B. Leznoff, Jim Herchenroeder, David Miller, and Zhongmin Chen. "Fabrication of UV-micro-patternable permanent micro magnets for lab on a chip and MEMS." In Nanosensors, Biosensors, and Info-Tech Sensors and Systems 2010, vol. 7646, p. 76461L. International Society for Optics and Photonics, 2010. https://doi.org/10.1117/12.847288

Rahbar, Mona, Sam Seyfollahi, Ajit Khosla, Bonnie L. Gray, and Lesley Shannon. "Fabrication process for electromagnetic actuators compatible with polymer based microfluidic devices." ECS Transactions 41, no. 20 (2012): 7-17. doi: 10.1149/1.3687433

Khosla, A., J. L. Korčok, B. L. Gray, D. B. Leznoff, J. W. Herchenroeder, D. Miller, and Z. Chen. "Fabrication and testing of integrated permanent micromagnets for microfluidic systems." In Microfluidics, BioMEMS, and Medical Microsystems VIII, vol. 7593, p. 759316. International Society for Optics and Photonics, 2010. https://doi.org/10.1117/12.840942

Khosla, Ajit, and Sam Kassegne. "Fabrication of NdFeB-based permanent rare-earth micromagnets by novel hybrid micromolding process." Microsystem Technologies 21, no. 11 (2015): 2315-2320. https://doi.org/10.1007/s00542-014-2331-4

Khosla, Ajit. "Micropatternable multifunctional nanocomposite polymers for flexible soft MEMS applications." PhD diss., Applied Science: School of Engineering Science, 2011. http://summit.sfu.ca/item/12017

Gray, Bonnie, Daniel B. Leznoff, Jasmine L. Korcok, and Ajit Khosla. "Compositions Including Magnetic Materials." U.S. Patent Application 12/772,090, filed June 23, 2011.
Immobilizing Siderophores on Solid Surfaces for Bacterial Detection
Authors: Bhadra Priyanka , Shajahan Mohammad , Patel Paresh N , Bhattacharya Enakshi , Chadha Anju , Sekhar Praveen K.
Published: February 2020

The article reports a proof of concept validation of bacterial detection using Siderophores. Desferrioxamine B (DesfB) was used as the Siderophore to capture Escherichia coli on gold coated microcantilever surface. Self-assembled monolayer based gold thiol chemistry was used for surface functionalization of the Siderophore on top surface of the microcantilever. The bacterial attachment to the siderophore was observed through Fourier Transform Infrared Spectroscopy (FTIR) and Fluorescence Microscopy. The DesfB coated surface allows only the live bacterial cells to be attached and it is evident through the FTIR band formation. In a mixture of live and dead E. coli cells, the Fluorescence Microscope image indicates green emission from live cells and a core-shell structure formation upon progress of time. For a sample dilution of 10−1, the mass change of live E. coli bonded to Siderophores is four times higher than that of dead cells and 12 times higher to that of negative control on microcantilevers. Therefore this study should be considered as a foundation to build a miniaturized biosensing platform to distinguish between bacterial or viral infections in real time. The proposed platform could differentiate between bacterial and viral infections thus rendering it as Point of Care (PoC) diagnostic tool aiding Internet of Things (IoT) applications.
(Invited) Suitable Materials and Electrolytes for Li-Ion Battery Fast Charging Applications
Authors: Belharouak Ilias , Du Zhijia , Li Jianlin , Wood David L. , Nanda Jagjit
Published: February 2020

Extreme fast charging (XFC) and cost of Li-ion batteries are the major hurdle facing the wide acceptance of EVs. While thick electrodes are suited for high energy density and low cost, Li-ion mass transport limitation and concentration gradient lead to Li-ion depletion at higher C-rate, and charging the cells with reasonable energy density cannot be realized. In this work, we will examine the kind of materials and electrolytes that could be suitable for Li-Ion battery fast charging applications. On one hand, we coated LiNi0.5Mn1.5O4 with zirconia (ZrO2) nanosize particles. Unlike most coating processes, the method involved the use of a soft and scalable ball milling technique in which increasing amounts of ZrO2 (0.5-2 wt.%) were introduced to LiNi0.5Mn1.5O4 just before the final calcination. The obtained materials have been characterized by x-ray diffraction, scanning and transmission electron microscopies (SEM and TEM), and electrochemical charge and discharge. We also used the electrochemical impedance spectroscopy (EIS) to characterize the electrode/electrolyte interfaces before and after coatings. This process has resulted in significantly improving the life of LiNi0.5Mn1.5O4 under high-temperature (55oC) and rate performance (10-min charge) conditions. On the other hand, we improved Li-ion transference number and ionic conductivity in nonaqueous electrolyte system which will have significant impact on: (1) increasing accessible charge capacity (with thick electrodes) from 50% (industrial baseline electrolyte) to ≥80% and (2) reducing lithium metal plating to improve cell safety and cycle life.
High Performance Lithium Sulfur Batteries Via MoS2-Protected Lithium Metal Anode
Authors: Cha Eunho , Park Juhong , Choi Wonbong
Published: February 2020

It is no secret that lithium (Li) metal is considered an optimal anode material for the next-generation lithium (Li) metal-based batteries such lithium-sulfur (Li-S). However, challenges have hindered the progress in achieving practical rechargeable batteries based on the Li anode including: the formation of poor-quality interphases on the surface of Li when in contact with any electrolytes; high chemical reactivity of Li with other active species in the electrolyte (i.e. polysulfides); and the difficulty in controlling the morphology of Li electrodeposits (i.e. Li dendrites) during battery operation. In attempt to solve all those issues, we introduce an atomic layer two-dimensional MoS2 as a protective layer for Li metal anode. With the Li-intercalated atomic layer of MoS2 formed, stable Li electrodeposition is realized with the nucleation sites for dendrite growth inhibited. In addition to the prevention of Li dendrites, MoS2-protected Li anode has been demonstrated to prevent polysulfides from corroding the anode while facilitating reversibility of active materials without decomposing the electrolyte. Here, we report the mechanistic study of Li-ion transport in the atomic layer of MoS2 with varying microstructure of MoS2, and the performance of Li-S batteries utilizing MoS2-protected Li anodes. The full cell performance was characterized with different sulfur loading amounts from 4 to 7 mg cm-2 while tuning the electrolyte/sulfur (E/S) ratio from 10 to 6. The results have demonstrated the E/S ratio of 6 (42 µL electrolyte to 7 mg cm-2 sulfur) with reversible specific capacity of ~1068 mAh g-1 at 0.5C rate (~1.4mA cm-2) for up to 1000 cycles. The exceptional performance in Li-S battery that utilizes 2D MoS2 anode without reducing the sulfur amount opens a new pathway towards the realization of high energy density and safe Li-metal based batteries.
Operando Study of Lithium Dendrite Growth on Graphite Andoe By EC-AFM
Authors: Shen Cai
Published: February 2020

Lithium dendrite growth is one of the most challenging problems affecting safety performance of lithium ion batteries (LIBs). It causes low Columbic efficiency as well as safety hazards for LIBs. Understanding the evolution process of Li dendrite growth at nanoscale is critical for solving this problem.

Herein, we report an in-situ electrochemical atomic force microscopy (EC-AFM) investigation of the initial Li deposition in EC and FEC-based electrolytes on graphite electrodes. Our results showed solid electrolyte interphase (SEI) formed from FEC-based electrolyte can suppress Li dendrite growth. FEC-based electrolyte induced formation of LiF-rich SEI films which were harder and denser than that formed in EC-based electrolyte. Combining with its better mechanical property and larger resistance, the SEI layer formed from FEC-based electrolyte is sufficient to slow down Li+ ions intercalation, prevent reduction of Li+ ions and Li deposition get electrons to deposit on the graphite surface. Our results demonstrated that EC-AFM is a powerful in-situ technique for the study of lithium dendrite growth.
Conversion Reaction of Nanoporous ZnO Forstable Electrochemical Cycling of Binderless Simicroparticle Composite Anode
Authors: Kim Donghyuk , Park Minkyu , Kim Sang-Min , Shim Hyung Cheoul , Hyun Seungmin , Han Seung Min
Published: February 2020

Binderless, additive-less Si electrode design is developed where a nanoporous ZnO matrix is coated on a Si microparticle electrode to accommodate extreme Si volume expansion and facilitate stable electrochemical cycling. The conversion reaction of nanoporous ZnO forms an ionically and electrically conductive matrix of metallic Zn embedded in Li2O that surrounds the Si microparticles. Upon lithiation, the porous Li2O/Zn matrix expands with Si preventing extensive pulverization while Zn serves as active material to form LixZn to further enhance capacity. Electrodes with Si mass loading of 1.5 mg/cm2 was fabricated and high initial capacity of ~3,900 mAh/g was achieved with excellent reversible capacity of ~1,500 mAh/g (areal capacity ~1.7 mAh/cm2) beyond 200 cycles. A high first cycle coulombic efficiency was obtained owing to the conversion reaction of nanoporous ZnO, which is a notable feature in comparison to conventional Si anodes. Ex situ analyses confirmed that the nanoporous ZnO coating maintained the coalescence of SiMPs throughout extended cycling. Therefore, the Li2O/Zn matrix derived from conversion reacted nanoporous ZnO acted as an effective buffer to lithiation induced stresses from volume expansion and served as a binder-like matrix that contribute to the overall electrode capacity and stability.
Evaluation of Polymeric Binders in Aqueous Electrolyte Environment
Authors: Pace Gordon Taylor , Wu Wei
Published: February 2020

Energy storage systems utilizing aqueous electrolytes are ever increasing in importance, as they are inherently cheap and safe when compared to their traditional lithium ion battery counter parts. To date, however, no thorough study on binder characteristics in the aqueous environment has been published. This work characterizes an acrylic based polymer, LA133, LA133+Carboxymethyl cellulose (CMC), Styrene-butadiene rubber (SBR), SBR+CMC, and Polytetrafluoroethylene (PTFE) in an LiMn2O4 cathode. Data presented includes cyclic voltammetry (CV), resistivity, and porosity. Future work will focus on characterizing binders for anode materials then galvanostatic cycling of full cells.

Figure 1 shows half-cell (CV) data for LiMn2O4 cathodes cycled between 0-0.7 V at reference cycle rates of 3.33 mV/min and daily cycles rates of 30 mV/min. LA133 clearly degrades, while the other binders performed similarly. This is noteworthy, as it directly contradicts LA133’s behavior in organic electrolytes, as Wang, Rui et al. specifically selected it for its stability in the window of 0.1-3.0V [1]. Additionally, SBR appears to have poorer performance at faster scan rates, but the overall slow scan retention was on par with that of Acrylic and PTFE, indicating poor rate capability rather than electrode degradation. Overall slow scan retention is shown more clearly in Figure 2. This again contradicts findings from traditional Li-ion batteries, as Yingjin Wei et al. selected the SBR/CMC binder combination for its superior rate capability [2].

Figure 3 shows resistivity and porosity data for the LiMn2O4 cathodes. Measurements were taken at 10 MPa and 19 MPa of applied pressure, and the average values are presented here. The most noteworthy point is that the addition of CMC clearly reduces the resistivity in both LA133 and SBR. This motivates investigation into pairing CMC with the other binders, which is not traditionally done in Li-ion batteries.

References

Wang R, Feng L, Yang W, et al. Effect of Different Binders on the Electrochemical Performance of Metal Oxide Anode for Lithium-Ion Batteries. Nanoscale Res Lett. 2017;12(1):575. Published 2017 Oct 30. doi:10.1186/s11671-017-2348-6

Yan X, Zhang Y, Zhu K, Gao Y, Zhang D, Chen G, Wang C, Wei Y (2014) Enhanced electrochemical properties of TiO2(B) nanoribbons using the styrene butadiene rubber and sodium carboxyl methyl cellulose water binder. J. Power Sources

Figure 1
(Invited) A Review of Defects in 2D Metal Dichalcogenides: Doping, Alloys, Interfaces, Vacancies and Their Effects in Catalysis & Optical Emission
Authors: Terrones Maurcio
Published: February 2020

Two-dimensional transition metal dichalcogenides (TMDs) such as MoS2 and WS2 hold great promise for many novel applications. Recent years have therefore witnessed tremendous efforts on large scale manufacturing of these 2D crystals. A long-standing puzzle in the field is the effect of different types of defects in their electronic, magnetic, catalytic and optical properties. In this presentation an overview of different defects in transmission metal di-chalcogenides (TMDs) will be presented [1,2]. We will first focus on: 1) defining the dimensionalities and atomic structures of defects; 2) pathways to generating structural defects during and after synthesis and, 3) the effects of having defects on the physico-chemical properties and applications. We will also emphasize doping and allowing monolayers of MoS2 and WS2, and their implications in electronic and thermal transport. We will also describe the catalytic effects of edges, vacancies and local strain observed in MoxW(1-x)S2 monolayers by correlating the hydrogen evolution reaction (HER) with aberration corrected scanning transmission electron microscopy (AC-HRSTEM) [3]. Our findings demonstrates that it is now possible to use chalcogenide layers for the fabrication of more effective catalytic substrates, however, defect control is required to tailor their performance. By studying photoluminescence spectra, atomic structure imaging, and band structure calculations, we also demonstrate that the most dominating synthetic defect—sulfur monovacancies in TMDs, is responsible for a new low temperature excitonic transition peak in photoluminescence 300 meV away from the neutral exciton emission [4]. We further show that these neutral excitons bind to sulfur mono-vacancies at low temperature, and the recombination of bound excitons provides a unique spectroscopic signature of sulfur mono-vacancies [4]. However, at room temperature, this unique spectroscopic signature completely disappears due to thermal dissociation of bound excitons [4]. Finally, hetero-interfaces in TMDs, will be studied and discussed by AC-HRSTEM and optical emission.

References

[1] Z. Lin, M. Terrones, et al. “Defect engineering of two-dimensional transition metal dichalcogenides”. 2D Materials 3 (2016) 022002.

[2] R. Lv, M. Terrones, et al. "Two-dimensional transition metal dichalcogenides: Clusters, ribbons, sheets and more". Nano Today 10 (2015) 559-592.

[3] Y. Lei, M. Terrones, et al. "Low temperature synthesis of heterostructures of transition metal dichalcogenide alloys (WxMo1-xS2) and graphene with superior catalytic performance for hydrogen evolution". ACS Nano, 11 (2017), 5103-5112.

[4] V. Carozo, M. Terrones, et al. “Optical identification of sulfur vacancies: Bound excitons at the edges of monolayer tungsten disulfide”, Sci. Adv. 3 (2017), e1602813
(Invited) Cyclic Voltammetry of Gold Nanoparticles: Comparative Analysis of Redox, Electronic and Optical Properties
Authors: Figueroa-Gonzalez Aura , Cerro-Lopez Monica , Mendez-Rojas Miguel Angel
Published: February 2020

It has been reported that cyclic voltammetry (CV) can be a useful tool for the electrosynthesis of gold nanoparticles (AuNPs) from AuCl4
- solutions in the presence of different protective (surfactant) agents. However, the use of this electrochemical analytical tools for the characterization of electroactive nanomaterials has been scarcely explored. In this work, cyclic voltammetry has been used to characterize the redox properties of AuNPs with controlled sizes and almost monodisperse, previously synthesized by chemical reduction of AuCl4
-in aqueous solutions, in the presence of two different surface protective agents (citric acid and tartaric acid). For the CV characterization, the as prepared AuNPs colloidal solution were used without addition of any supporting electrolyte. A typical three electrode system was used, with a glassy carbon electrode as a working electrode, a platinum wire as the counter electrode and a Ag/AgCl (KCl sat) electrode as reference. The potential window was scanned from +0.4 V to +0.95 V and ended at 0.25 V, at a scan rate of 1.0 Vs-1. Nanoparticles size distribution and zeta potential (ζ) were previously characterized by dynamic light scattering (DLS) in aqueous suspensions, while precise size and morphology analyses were performed using high-resolution scanning electron microscopy (HR-SEM) in a MAIA Tescan FESEM. The UV-VIS surface plasmon resonance spectrum of the AuNPs was obtained by UV-Vis spectroscopy in water. The nanoparticles chosen for this electrochemical analysis, which were nearly monodispersed, had average sizes of 15 and 40 nm and an almost spherical morphology. Their electrochemical behavior showed an irreversible oxidation peak at +0.7 V and it was observed that the generated current and potential was dependent of nanoparticle size: the 40 nm AuNPs showed a higher oxidation potential than those AuNPs with an average diameter of 15 nm. The current evolved during cycling the AuNPs solution. A comparative analysis of redox properties and other physical properties (plasmon energy, size distribution) will be discussed in this work.