bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Raman Spectra of Poly(vinylidene fluoride) Solution Under Drying Process
Authors: Yamada Noriyasu , Murasawa Go 
Published: February 2020

Poly(vinylidene fluoride) (PVDF) is a thermoplastic fluoropolymer used in tactile sensors and actuators because of its piezoelectricity, flexibility and other unique properties. PVDF shows four crystal structures based on the order of molecular chain: α-, β-, γ-, and δ-phase. The most stable phase of PVDF is the non-polar α-phase, and strong piezoelectricity appears in the β-phase. Thus, the phase transition from α-phase to β-phase are necessary so as to use PVDF as a piezoelectric material. It is generally realized by applying uniaxial stretch and polarization process to α-phase PVDF film. However, we recently found a novel method which converts PVDF crystal structure to β- or γ-phase without the above mechanical deformation processes. This method consists of only the PVDF solution dropping process and the drying process, and therefore, it enables us to print piezoelectric polymer film and create free-from 3D sensors and actuators.
In this study, we investigate the crystallization behavior of PVDF solution under the drying process. First, PVDF solutions are made with several solvents which have different vapor pressures. Second, a droplet is formed on a glass plate with a microsyringe. Third, the time series variations of Raman scattering intensity are measured with the in-house Raman spectrum spectroscopy. Finally, the temporal changes of the crystallization rate are calculated from the result of Raman spectrometry and the crystallization behavior is evaluated by Johnson and Mehl and Avrami equation.
Gel Transistor By Chemically Tunable Hydrogels
Authors: Shiblee MD Nahin Islam , Watanabe Yosuke , Ahmed Kumkum , Makino Masato , Khosla Ajit , Furukawa Hidemitsu 
Published: February 2020

The transport of liquid in the polymeric network of Hydrogels have been discussed for a decade because the gel membrane may use as chemical separator [1]. Here we demonstrate a system that control the flux of solvents by a combination of three types of gels of different swelling behavior as a gel transistor. Poly(dimethyl acrylamide-co-stearyl acrylate and/or Lauryl Acrylate) (PDMMAm-co-SA and/or LA)-based shape memory gels (SMGs) swelling behavior has been observed for different solvents and binary solvent mixtures. It was found that SMGs at all composition showed increased swelling when ethanol composition was increased. On the other hand, when an anionic copolymer was introduced in the DMAA network, swelling behavior was reversed in the presence of high ethanol composition. These oppositely responsive gels were tested for permeability of solvents through them and we successfully developed the gel diode [2]. The unidirectional solvent flow was achieved just like in diode. Information about the gel diode has been utilized to develop a system that simulate a transistor to more sophistically control the flow of liquid mixtures. This findings are expected to create positive impact to develop the gel membrane solvent separator, a hot topic for rectifier, calculator and separator in chemical systems.
References

Tanaka, Phys. Rev. Lett. 40, 820–823 (1978).

Arai, M., Gong, J., Makino, M., KABIR, M.,H., Furukawa, H. SPIE Proc. 9430, 94302A-1
(Invited) Micro-Manipulation of Hydrogel Sheet through Photoresponsive Polymer Dissolution
Authors: Sumaru Kimio , Takagi Toshiyuki , Morishita Kana , Satoh Taku , Kanamori Toshiyuki 
Published: February 2020

Various functional hydrogels have been developed, and their applications to the fields of bioengineering have been examined actively. In these situations, we developed novel technologies to manipulate hydrogel sheet and living cells through photoresponsive polymer dissolution.
Firstly, we proposed the fabrication of unique hydrogel microstructures through photolithography. As a photo-acid-generation (PAG) polymer, we synthesized a poly(methylmethacrylate) functionalized with visible- light-responsive PAG group (pPAGMMA), and spin-coated polystyrene surface with the polymer solution. Then we overcoated pregel solution containing hydrophilic polymer (hydroxypropyl cellulose) (HPC) and 1,3,4,6-Tetrakis(methoxymethyl)glycoluril, and carried out micro-patterned light projection. After post-bake and flushing, we obtained crosslinked hydrophilic polymer sheet only in the irradiated area. Due to another property of pPAGMMA getting dissolved in ethanol/water mixture by further irradiation, the cross-linked hydrophilic polymer sheet was lifted from the substrate surface and became swollen in the desired areas by the second micro-patterned projection in ethanol/water mixture. As a result, we obtained various microstructures which were composed of patterned swollen hydrogel sheet partially attached to the substrate in the patterned areas.
Secondly, we developed a novel photoresponsive polymer materials by functionalizing poly(N-isopropylacrylamide) with o-nitrobenzaldehyde (pNBANIPAAm) to implement in situ photocontrol in aqueous systems containing bio-compatible environment. We observed that the polymer exhibited sharp aqueous dissolution upon light irradiation in wide pH range including biological conditions. We prepared closs-linked HPC (cHPC) layer on pNBANIPAAm thin layer and carried out micropatterned light projection in PBS. As a result, we observed that the cHPC layer lifted off of the substrate and swelled while nothing happened in unirradiated areas. Also living cells were manipulated by light in a similar manner.
(Keynote) Preparation and Structural Investigation of Linear and 4-Arm Poly(ethylene glycol) (2 x 4 PEG) Gels
Authors: Shibayama Mitsuhiro , Tsuji Yui , Li Xiang 
Published: February 2020

Gel is a 3D polymer network holding solvent molecules inside its network. There are two major heterogeneities in gels. One is spatial heterogeneity, and the other is topological heterogeneity. The spatial heterogeneity is introduced by random cross-linking, so the network structure has both sparse and dense region. The spatial heterogeneity is observed as excess scattering in a light, X-ray, or neutron scattering experiment. On the other hand, the topological heterogeneity is related to the presence of dangling chains, loop structure, and entanglements inside the network, and is investigated by viscoelasticity and/or swelling experiments, or by other means, such as NMR. Because of these inhomogeneities, gels have seldom been applied to structural materials because of their poor mechanical properties. Hence, realization of ideal model networks free from heterogeneities has been strongly anticipated.
Sakai et al. succeeded in fabrication of near ideal polymer networks called “Tetra-PEG gel”.[1] A Tetra-PEG gel is synthesized from two complementary end-functionalized poly(ethylene glycol) (PEG) which is able to react each other. It is pointed out that the Tetra-PEG gel has insignificant small spatial homogeneity and negligible topological heterogeneity, respectively by small angle scattering[2] and mechanical test.[3]
Recently, we extended the above-mentioned method and succeeded in fabrication of multiple model network gels consisting of alternating tetra-functional poly(ethylene glycol)s (PEGs) and bis-functional linear PEGs (2 x 4 gels), where the molecular weight of linear PEG was varied from 200 Da to 20000 Da while that of tetra-functional PEG component was fixed to be 20000 Da.[4] The same level of homogeneities in the network structure as those of Tetra-PEG gels has been confirmed by dynamic light scattering (DLS) and dynamic viscoelastic measurements. Advantages of 2 x 4 gels are that one can independently tune the cross-link density (by the concentration of tetra-functional PEG) and the total polymer concentration. By using a series of 2 x 4 gels, we examined the concentration/cross-link density dependence of the correlation blob, the elastic blob, and geometric blob. We will discuss the scaling rules of these blob sizes as a function of polymer/cross-linker concentrations.

Sakai, T. et al, Macromolecules
2008, 41, 5379.

Matsunaga, T. et al, Macromolecules
2009, 42, 1344.

Akagi, Y. et al, Macromolecules
2010, 43, 488.

Tsuji, Y. et al., Gels
2018, 4, 50.
Multiscale Modeling of Carbon Black Aggregates Dispersion in Polyethylene Melt
Authors: Caputo Stefano , De Nicola Antonio , Milano Giuseppe 
Published: February 2020

Carbon black (CB) is a widely used filler in polymer composites materials, known to improve several properties of the medium in which it is dispersed, such as mechanical, electrical and optical ones1.
On the nanoscale level, CB is made essentially by aggregates ranging from ten to few hundreds of nanometers; these aggregates consist coalesced nanoparticles, called primary nanoparticles2. The nanoparticles are composed by many graphitic like stacks, arranged in a sphere.
To obtain materials with tailored properties, it is necessary to achieve a good dispersion of the CB aggregates into the polymer matrix, and this becomes more and more challenging when increasing the filler content.
In this work we address this task by performing simulations in a multiscale fashion, going from an atomistic scale to a granular-continuum scale, in order to gain informations on the process of aggregation and disaggregation of CB in polyethylene melts under shear.
At the first stage we have carried out all-atom molecular dynamics simulations of polyethylene chains in the melt state interacting with a semi-infinite graphite substrate, to get structural and dynamical properties.
In a second stage we have built up the the coarse-grained (CG) model, first by choosing an appropriate mapping scheme for the polymer and CB primary particles and then obtaining suitable potentials for bonded and nonbonded interactions among CG beads. At this scale potential of mean force calculation, through MD-SCF (molecular dynamics - self consistent field) simulations3, will be done to get the force of attraction/repulsion between two primary nanoparticles at various distances.
This force will be used as the input for the granular-continuum scale, in which aggregates of CB nanoparticles in a model fluid are simulated through a coupled CFD-DEM (complex fluid dynamics – discrete element method) method4, to observe in which conditions the disaggregation occurs and how this affects the dispersion of the filler.
Such work has the potential to provide predictive power and can allow for special resin design to ensure adequate filler dispersion/performance.

1 Carbon Black: Science and Technology, J. B. Donnet, 1993, CRC press

2 Encyclopedia of polymer science and technology, John Wiley & Sons, 2002

3 G.Milano, T. Kawakatsu, J. Chem. Phys., 2009, 130, 214106

4 https://www.cfdem.com/liggghts-open-source-discrete-element-method-particle-simulation-code
Control of Molecular Orientation in Naphthalene Diimides
Authors: Nakamura Tomoya , Shioya Nobutaka , Shimoaka Takafumi , Hasegawa Takeshi , Murata Yasujiro , Wakamiya Atsushi 
Published: February 2020

Lead halide perovskite solar cells represent attractive cost-effective and solution-processable photovoltaics. At present, the record-high performance perovskite solar cells are based on an n-i-p device configuration, in which metal oxides, such as TiO2, are generally utilized as electron transporting layer. Deposition of metal oxides usually requires high temperature sintering process, which prevents mass production and application to flexible devices on plastic substrates.
Here, we focused on the naphthalene diimide (NDI) skeleton as alternative transparent n-type materials. By introducing hydrogen atoms at the imide moiety (NDI-H), we envisioned the achievement of face-on orientation on the substrates, which is preferable for vertical charge transport, by the formation of intermolecular N–H···O hydrogen bondings. To realize both the solution-processability and the durability to the deposition of the upper layers, we designed NDI-Boc having tert-butoxycarbonyl (Boc) solubilizing groups at the imide moiety, which can be cleaved by simple thermal annealing. Infrared p-polarized multiple-angle incidence resolution spectroscopy (pMAIRS) not only confirmed the cleavage of the Boc group, but also revealed that the molecular orientation of NDI changed from edge-on to face-on during the cleavage process. Furthermore, NDI-H film works as electron transporting layer in n-i-p type planer perovskite solar cells with the power conversion efficiency of 10.7%.
Luminescent Properties of RE-Doped Mullite (Al6Si2O13) Phosphors for Energy Conversion from UV to Visible Rays
Authors: Takahashi Hirotaka , Matsushima Yuta 
Published: February 2020

Introduction

Leveraging of solar energy is a key issue in the world. The world’s energy consumption is increasing year by year due to rise in population and improvement of living quality. For the realization of sustainable development, utilizing alternative energy sources rather than fossil fuels is of critical importance.
Using solar cells, such as silicon (Si), is the most popular way for harvesting solar energy. However, light absorbing materials have their intrinsic band gaps, and therefore, the energy range that cells can harvest is limited, which brings power conversion loss. To overcome the problem, combining a solar cell and a phosphor, which is a wavelength conversion material, is important.
Here we report UV-excitable mullite (Al6Si2O13) phosphors doped with REs. Luminescence spectra can be tailored from 390 to 620 nm by changing doping rare-earth ions.

Experimental

Mullite samples were synthesized via a sol-gel process. Al(NO3)3•9H2O, tetraethylorthosilicate (TEOS) and a RE source (or sources) in a form of nitrate or oxide were dissolved in ethanol. Then the pH of the solution was increased to 10 by adding NH3 aq. The precipitate was filtered off by suction filtration and treated at 1400 °C for 6h. For Ce3+, Tb3+ and Eu2+ phosphors, the samples were heat-treated in 5% H2/Ar atmosphere for the reduction of the luminescent centres. For Eu3+ phosphor, the sample was treated in air.

Results
＆
discussions

Fig. 1 shows the emission spectra of the mullite phosphors doped with Ce3+, Eu2+, Ce3+-Tb3+ or Eu3+. Ce3+ and Eu2+ in mullite show relatively broad peaks around 380 and 410 nm, respectively. These peaks are typically assigned to the 5d-4f transitions in Ce3+ and Eu2+. The Ce3+-Tb3+ phosphor shows green emission with the sharp peaks attributed to the Tb3+ 4f-4f transitions. Absence of an emission peak of Ce3+ indicates the energy transfer from Ce3+ to Tb3+. Red luminescence with the sharp peaks in mullite are attributed to the 4f-4f transitions of Eu3+.
Fig. 2 shows the thermal quenching properties of the mullite phosphors compared with commercially available YAG:Ce3+ and SrSiO4:Eu2+ phosphors [2]. The mullite phosphors maintain more than 50% of the initial intensities even at 200 °C.

Conclusions

We have successfully synthesized red, green and blue phosphors with mullite doped with Ce3+, Eu2+, Ce3+-Tb3+ and Eu3+. They all show good thermal quenching properties, which are comparable with the commercially available phosphors of YAG:Ce3+ and SrSiO4:Eu2+.

Figure 1
Atomistic Simulations of Lithiation Induced Structural Changes in Layered-Spinel Nano-Architectured Li-Mn-O
Authors: Shibiri Beauty , Ledwaba Raesibe Sylvia , Ngoepe Phuti E 
Published: February 2020

Maximizing the potential of LIBs requires a firm and comprehensive understanding of the fundamental mechanisms during battery operation, including bulk phase transition of electrode materials, chemical variations at multiple interfaces between different battery components, changes in mechanical properties affecting the structural integrity, and so forth [1]. Atomistic modeling plays a vital role in advancement and understanding of microstructural evolution and mechanical properties of electrode materials. We present progress in the simulated synthesis of Li-Mn-O nanoporous electrode materials, from the atomic perspective using the amorphization and recrystallization technique [2]. The effect of lithiation on structural integrity and intercalation host capability of the LMO electrode are investigated under the NST ensemble. Evolution of a composite structured material is captured on the microstructures snapshots and XRD graphs, particularly co-existing formation of spinel and layered components. The nanoporous materials crystallize successfully although multiple grains are observed for Li1.75Mn2O4 (nanoporous with simulation lattice boxes of 67 Å and 75 Å) and subsequently yield a single crystals for Li2Mn2O4. However, this is not inherent on nanoporous 69 Å with the same concentration. Intercalation induced volume changes are observed during simulation of the discharge process, specifically when the lithium content in the system is increased above 75% (Li1.5Mn2O4). The nanoporous material contracts inwards and such accommodative nature may be attributed to flexing/relaxation into its pore/channel, unlike in the bulk structure, which suffers from drastic volume expansion.
References
[1] W. Li, B. Song and A. Manthiram, Chem. Soc. Rev., 46, 3006−3059, 2017.
[2] T.X.T. Sayle, R.R. Maphanga, P.E. Ngoepe and D.C. Sayle, J. Am. Chem. Soc., 131, 6161-6173, 2009.
(Invited) On the Active Sites in the Graphene-Catalyzed Oxygen Reduction Reaction
Authors: Radovic Ljubisa R 
Published: February 2020

A critical issue in the impressive worldwide fuel cell research efforts is the possibility of using graphene-based materials in the oxygen reduction reaction (ORR). In the overwhelming literature that has accumulated, much controversy (and even more confusion) exists regarding some of the essential aspects of the reaction mechanism. A consensus can emerge only if interpretations of the abundant experimental evidence are consistent with what is known about the behavior of graphene-based materials, both the novel and the traditional ones, as catalysts in the absence of an electric field, as well as with the well understood gas-phase behavior of sp2-hybridized carbon materials in the presence of dioxygen. From this standpoint, the key issue is whether a reasonable and instructive analogy exists between the mechanism of electron-transfer catalysis on the carbon surface,
e- + C(O2) = C(O2
-)
C(O2
-) + H2O(aq) = OH-(aq) + C(OOH)
C(OOH) = C=O + OH,
and the proposed mechanism of electrocatalysis:
Ar-C: + O2 → Ar-C(O2)
Ar-C(O2) + H+(aq) → Ar-C(OOH)
Ar-C(OOH) → Ar-C + HO2
-

A clarification can be sought by analyzing the results of the search for ever more effective (electro)catalysts. In this context, structural modifications of the graphene surface are particularly enlightening. Thus, for example, the superior electrocatalytic activity of nitrogen-doped graphene is attributed to the presence of either quaternary or pyridinic nitrogen. Boron is of interest as well, if for nothing else then for its contribution of one electron less than the carbon atoms to graphene’s pi-system. And the presence, or formation, of an embedded MN4 moiety – where M is most often a transition metal such as cobalt or iron – is also of great interest because of the obvious analogy with porphyrin or phthalocyanine structures. Using a heretofore unexplored approach to examine these widely varying graphene-based surfaces, and unifying the evidence based on density functional theory, a compelling case is presented here for the experimentally elusive identification of the active sites (AS) that are responsible for the technologically and economically crucial electron transfer at the fuel cell cathode: AS + O2 + 4e-(aq) + 4H+(aq) = AS + 2H2O. It is also argued, not unexpectedly, that these are essentially the same sites at which analogous oxygen transfer processes - carbon oxidation/combustion, graphene functionalization and oxygen spillover - also occur. Their thermodynamic driving force is shown to be crucially dependent on the details of the electron density distribution and spin pairing processes at the active sites and in their vicinity.
(Invited) Assembly of Electrochemically Reduced Graphene Oxide, at the Nano and Microscales, for the Preparation of Functional Coatings.
Authors: Chazaro Ruiz Luis Felipe , Quezada Renteria Javier Alan , Rangel-Mendez José René , Ania Conchi O. 
Published: February 2020

Graphene oxide (GO) presents the advantage of being easily dispersed in water, which facilitates the assembly of nano and microstructures by numerous methods, in order to form uniform and thickness-controlled functional coatings. For example, the electrophoretic deposition (EPD) is one of the most used techniques to produce anticorrosive coatings onto metals, including GO and reduced graphene oxide (rGO) coatings. We have used a variation of the EPD process of GO, which consisted in changing the GO’s charge to positive values allowing the electrophoretic deposition of GO onto the cathode (cEPD). The coating diminished by three times the corrosion rate of carbon steel. The preparation of these coatings also implies the understanding of the mechanism through which the electrochemical reduction of the GO is carried out.1 An electrochemical reduction mechanism of GO involving hydrogenation/hydrogenolysis reactions is suggested as the main reason to achieve an effective anticorrosive-coating by cEPD in comparison to the films produced by an anodic EPD. For this reason, we studied the electrochemical reduction of GO in aqueous and organic media containing H+ donor, to investigate the role of H+ in the reduction mechanism. In aqueous electrolyte, in both acid and basic pH, the H+ enhanced the removal of oxygenated groups by electrochemical reduction and promoted the loss of some sp2 domains due to hydrogenation reactions of the graphitic domains. The electrochemical reduction of GO in organic media, free of H+, resulted in the restoration, to some degree, of the sp2 domains. However, the removal of the oxygenated groups seemed hindered when compared to the same process in presence of H+ donor, in the organic solvent, at the same potential intervals.
Considering that through these studies it is possible to choose a route for the preparation of functional films, recently we proceeded to modify electrochemically the rGO through with 5-membered alkyne chains. The resulting rGO film presented lower conductivity, due to the loss of graphitic domains, and an increased hydrophobicity. The modified rGO film was evaluated as an anticorrosive coating for carbon steel, showing a better protection from corrosion in comparison to the protection granted by the regular rGO film.
[1] J.A. Quezada-Rentería, L.F. Chazaro-Ruiz, J.R. Rangel-Mendez, Synthesis of reduced graphene oxide (rGO) films onto carbon steel by cathodic electrophoretic deposition: Anticorrosive coating, Carbon 122 (2017) 266-275.