Shotaro Nishitsuji

Fabrication of Two‐Dimensional Polymer Arrays: Template Synthesis of Polypyrrole between Redox‐Active Coordination Nanoslits

1 / 1 Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University Title: Fabrication of Two-Dimensional Polymer Arrays: Template Synthesis of Polypyrrole between Redox-Active Coordination Nanoslits Author: N. Yanai, T. Uemura, M. Ohba, Y. Kadowaki, M. Maesato, M. Takenaka, S. Nishitsuji, H. Hasegawa, and S. Kitagawa Journal: Angew. Chem. Int. Ed., Vol. 47, No. 51, 9883-9886 (2008) Abstract: Oxidative and intercalative polymerization of pyrrole was conducted within the nanoslits of a layered coordination open framework containing redox-active sites. Isolation of polypyrrole from the host framework led to stacked sheet polymer objects whose orientation and morphology are directly related to the original coordination polymer template.

Collective Structural Changes in Vermiculite Clay Suspensions Induced by Cesium Ions

Following the Fukushima Daiichi nuclear disaster in 2011, Cs radioisotopes have been dispersed over a wide area. Most of the Cs has remained on the surface of the soil because Cs+ is strongly adsorbed in the interlayer spaces of soil clays, particularly vermiculite. We have investigated the microscopic structure of an aqueous suspension of vermiculite clay over a wide length scale (1–1000 Å) by small-angle X-ray scattering. We determined the effect of the adsorption behavior of Cs+ on the structural changes in the clay. It was found that the abruption of the clay sheets was induced by the localization of Cs+ at the interlayer. This work provides important information for predicting the environmental fate of radioactive Cs in polluted areas, and for developing methods to extract Cs from the soil and reduce radioactivity.

Comparative Molecular Dynamics Study on Tri-n-butyl Phosphate in Organic and Aqueous Environments and Its Relevance to Nuclear Extraction Processes.

A refined model for tri-n-butyl phosphate (TBP), which uses a new set of partial charges generated from our ab initio density functional theory calculations, has been proposed in this study. Molecular dynamics simulations are conducted to determine the thermodynamic properties, transport properties, and the microscopic structures of liquid TBP, TBP/water mixtures, and TBP/n-alkane mixtures. These results are compared with those obtained from four other TBP models, previously described in the literature. We conclude that our refined TBP model appears to be the only TBP model from this set that, with reasonable accuracy, can simultaneously predict the properties of TBP in bulk TBP, in organic diluents, and in aqueous solution. The other models only work well for two of the three systems mentioned above. This new TBP model is thus appropriate for the simulation of liquid-liquid extraction systems in the nuclear extraction process, where one needs to simultaneously model TBP in both aqueous and organic phases. It is also promising for the investigation of the microscopic structure of the organic phase in these processes and for the characterization of third-phase formation, where TBP again interacts simultaneously with both polar and nonpolar molecules. Because the proposed TBP model uses OPLS-2005 Lennard-Jones parameters, it may be used with confidence to model mixtures of TBP with other species whose parameters are given by the OPLS-2005 force field.

Two-Dimensional Phase Separation of a Poly(methyl methacrylate)/Poly(l-lactide) Mixed Langmuir Monolayer via a Spinodal Decomposition Mechanism

We have found the first evidence that a polymer blend Langmuir monolayer can phase-separate via spinodal decomposition (SD) mechanism. The system was a poly(methyl methacrylate)/poly(L-lactide) mixture. It phase-separated immediately after compression on a water surface and formed a spinodal-like morphology, as observed by atomic force microscopy (AFM). The fast Fourier transform of the AFM images showed a clear spinodal ring with a maximum intensity at a wavenumber of q(m). At the small quench depth at a surface pressure of 2 mN/m, q(m) did not change, but the concentration difference between the domains (ΔΦ) grew with time, corresponding to the early-stage SD. At larger quench depths at 4 and 5 mN/m, q(m) significantly decreased, but ΔΦ was constant with time; this behavior corresponded well to the late-stage SD. Thus, the 2D phase separation in the Langmuir monolayer was basically explained by the SD mechanism well-known in 3D systems. In the late stage SD of the monolayer, q(m) scaled with time much faster than that expected by theories for the 2D state. Phase separation via a SD mechanism is a promising new way to control the lateral morphology of Langmuir monolayers, one of the main issues in nanotechnology that remains difficult to attain even today.

Ultra small angle X-ray scattering studies on density heterogeneity of linear low density polyethylene

We have investigated density heterogeneity of linear low density polyethylene (LLDPE) in the order of submicron scale with 2 dimensional ultra small angle X-ray scattering (2D USAXS). We found that power-law behaviour in small q- region of isotropic scattering patterns of LLDPE studied here, indicating that the density heterogeneity obeys mass fractal. Under stretching, isotropic 2D USAXS patterns of some LLDPE samples were transformed into butterfly patterns caused by heterogeneous deformation.

A Novel Micro-Emulsion Phase Transition: Towards the Elucidation of Third Phase Formation in Spent Nuclear Fuel Reprocessing

We present evidence that the transition between organic and third phases, which can be observed in the plutonium uranium reduction extraction (PUREX) process at high metal loading, is an unusual transition between two isotropic bicontinuous microemulsion phases. As this system contains so many components, however, we have been seeking first to investigate the properties of a simpler system, namely, the related metal-free, quaternary water/n-dodecane/nitric acid/tributyl phosphate (TBP) system. This quaternary system has been shown to exhibit, under appropriate conditions, three coexisting phases: a light organic phase, an aqueous phase, and the so-called third phase. In the current work, we focused on the coexistence of the light organic phase with the third phase. Using Gibbs ensemble Monte Carlo (GEMC) simulations, we found coexistence of a phase rich in nitric acid and dilute in n-dodecane (the third phase) with a phase more dilute in nitric acid but rich in n-dodecane (the light organic phase). The compositions and densities of these two coexisting phases determined using the simulations were in good agreement with those determined experimentally. Because such systems are generally dense and the molecules involved are not simple, the particle exchange rate in their GEMC simulations can be rather low. To test whether a system having a composition between those of the observed third and organic phases is indeed unstable with respect to phase separation, we used the Bennett acceptance ratio method to calculate the Gibbs energies of the homogeneous phase and the weighted average of the two coexisting phases, where the compositions of these phases were taken both from experimental results and from the results of the GEMC simulations. Both demixed states were determined to have statistically significant lower Gibbs energies than the uniform, mixed phase, providing confirmation that the GEMC simulations correctly predicted the phase separation. Snapshots from the simulations and a cluster analysis of the organic and third phases revealed structures akin to bicontinuous microemulsion phases, with the polar species residing within a mesh and with the surface of the mesh formed by amphiphilic TBP molecules. The nonpolar n-dodecane molecules were observed in these snapshots to be outside this mesh. The only large-scale structural differences observed between the two phases were the dimensions of the mesh. Evidence for the correctness of these structures was provided by the results of small-angle X-ray scattering (SAXS) studies, where the profiles obtained for both the organic and third phases agreed well with those calculated from simulations. Finally, we looked at the microscopic structures of the two phases. In the organic phase, the basic motif was observed to be one nitric acid molecule hydrogen-bonded to a TBP molecule. In the third phase, the most common structure was that of the hydrogen-bonded TBP-HNO3-HNO3 chain. A cluster analysis provided evidence for TBP forming an extended, connected network in both phases. Studies of the effects of metal ions on these systems will be presented elsewhere.

Quantitative comparison between dynamic structure factors obtained experimentally and those calculated with Doi-Onuki theory

This paper reports results of quantitative comparison between dynamic structure factors obtained experimentally and those calculated by using the Doi and Onuki (DO) theory for semidilute polymer solutions. The authors obtained the dynamic structure factors with dynamic light scattering (DLS) experiment while the dynamic structure factors were calculated by using DO theory with osmotic compressibility, viscoelastic relaxation function, and friction coefficient which are obtained independently of DLS experiment. Calculated dynamic structure factors agree with experimental ones well and can express the q-dependent fast modes and the q-insensitive slow mode which experimental ones show. The authors estimated the characteristic parameters, interdiffusion coefficient and cooperative diffusion coefficient, from experimental and calculated results by using the procedure proposed by Einaga and Fujita [Polymer 40, 565 (1999)]. The estimated parameters for the DLS experiment agree with those for the calculation. These agreements in dynamic structure factors and the parameters indicate that DO theory can describe well the relaxation processes of semidilute polymer solutions.

Temperature Fall and Rise of Plastics During Uniaxial Stretching

Dumbbell specimens of common plastics—polyethylene, polypropylene, and polyamide—were uniaxially stretched and the surface temperature was measured by thermography. The surface temperature decreased at small strain below the yield point and then increased at larger strain. The endothermic deformation in the elastic regime was unexpected. It might be a characteristic of polymer material, which is possessed of free volume. The endotherm is interpreted by the volume increment with stretching as represented by Poissons ratio. The temperature rise at larger strain is not surprising for plastic deformation over the yield point. The exotherm is interpreted in terms of the melting of crystallites and re-crystallization induced by large deformation.

Structure analyses of rubber-filler systems by contrast variation SANS

The network structures in rubber containing silica particles have investigated with contrast variation small-angle neutron scattering (SANS) method. The contrast variation SANS for the rubber specimens swollen by the solvents having various scattering length densities yielded partial scattering functions: the scattering function for polymer-polymer correlation Spp (q), the scattering function for silica-silica correlation Sss(q), and the scattering function for polymer-silica correlation SPS(q). The analyses of the partial scattering functions explored the following features:(1) Silica particles form aggregates consisting of several silica particles, and (2) there are relatively dense polymer layers around silica aggregates. Several characteristic parameters are estimated from the analyses, such as the size of aggregates, the thickness of layers, the volume fractions of polymer of layers and matrix, and the correlation length of the matrix network. This result suggests that the contrast variation SANS is a powerful tool of the analyses of the structures of the rubber-filler systems.

Concentration fluctuations induced by orientation fluctuations in polybutadiene–4-cyano-4'-n-octylbiphenyl mixtures

The changes in concentration fluctuations of polymer–liquid crystal (LC) binary mixtures with temperature were investigated by small-angle X-ray scattering in their one-phase region and in the isotropic state of the LC. The concentration fluctuations consist of two modes: an OZD mode expressed by the Ornstein–Zernike–Debye equation with a correlation length ξ and a DB mode expressed by the Debye–Buche equation with a correlation length l. The temperature dependence of the OZD mode exhibits critical phenomena similar to common binary mixtures. Under the condition where the LC molecules are oriented by an electric field, the OZD mode is insensitive to the orientation while the DB mode is enhanced perpendicular to the orientation direction. These results indicate that the DB mode is induced by the orientation of the LC molecules.