Welding dynamics in an atomistic model of an amorphous polymer blend with polymer–polymer interface

We consider an atomistic model of thermal welding at the polymer-polymer interface of a polyetherimide/polycarbonate blend, motivated by applications to 3D manufacturing in space. We follow diffusion of semiflexible chains at the interface and analyze strengthening of the samples as a function of the welding time t_w by simulating the strain–stress and shear viscosity curves. The time scales for initial wetting, and for fast and slow diffusion, are revealed. It is shown that each component of the polymer blend has its own characteristic time of slow diffusion at the interface. Analysis of strain–stress demonstrates saturation of the Young's modulus at t_w = 240 ns, while the tensile strength continues to increase. The shear viscosity is found to have a very weak dependence on the welding time for t_w > 60 ns. It is shown that both strain–stress and shear viscosity curves agree with experimental data.     

Intramolecular glycosylation as a regio- and stereocontrolled approach for the synthesis of 8-oxo-purine nucleosides

Intramolecular glycosylation of purine derivatives that are temporarily connected to the 5 position of ribofuranosyl donors at their 8 position through an ethereal linkage leads to 8-oxo-purine β-nucleosides in a stereoselective manner.     

A Semisynthetic Fusicoccane Stabilizes a Protein-Protein Interaction and Enhances the Expression of K+ Channels at the Cell Surface

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Self‐Healing Supramolecular Materials Constructed by Copolymerization via Molecular Recognition of Cavitand‐Based Coordination Capsules

The repeating guest units of poly‐(R)‐ 2 were selectively encapsulated by the self‐assembled capsule poly‐ 1 possessing eight polymer side chains to form the supramolecular graft polymer (poly‐ 1 )_n?poly‐(R)‐ 2 . The encapsulation of the guest units was confirmed by ¹H NMR spectroscopy and the DOSY technique. The hydrodynamic radius of the graft polymer structure was greatly increased upon the complexation of poly‐ 1 . The supramolecular graft polymer (poly‐ 1 )_n?poly‐(R)‐ 2 was stably formed in the 1:1 host–guest ratio, which increased the glass transition temperature by more than 10 °C compared to that of poly‐ 1 . AFM visualized that (poly‐ 1 )_n?poly‐(R)‐ 2 formed the networked structure on mica. The (poly‐ 1 )_n?poly‐(R)‐ 2 gelled in 1,1,2,2‐tetrachloroethane, which led to fabrication of distinct viscoelastic materials that demonstrated self‐healing behavior in a tensile test.     

Conformational studies on poly(ethacrylic acid) in aqueous salts by potentiometric,viscometric, optical and1H-NMR measurements

The conformation of poly(ethacrylic acid) was studied in aqueous salts by means of potentiometric, viscometric, optical and¹H-NMR measurements. The modified potentiometric titration curves in aqueous NaCl at ionic strengths 0.01–0.3 and 5–35 °C indicated the pH-induced conformational transition from the compact to extended coil. The standard free energy changes and the difference in molar heat capacity between the two conformers were estimated from the potentiometric data. The viscometric and optical behaviours did also show the existence of the compact form at acid pH's and the pH-induced conformational transition to the extended coil in aqueous NaCl and NaClO₄. From comparison with the data for poly(methacrylic acid), the results were concluded to be consistent with the existence of the compact form stabilized by hydrophobic interaction between ethyl groups. The methyl widths in 400 MHz¹H-NMR spectra indicated that the side chains in the polymer in the compact form are in a more restricted motional state than in the coil form. Intermolecular aggregations were found at very low degrees of ionization of carboxyl groups.     

Enhancement effect of organic solvents in inductively coupled plasma atomic emission spectrometry

Summary The enhancement factors of various organic solvents in inductively coupled plasma atomic emission spectrometry (ICP-AES) were measured for diethyldithiocarbamate-cadmium(II) or mercury(II)-solvent systems by comparing the maximum emission intensity of an extract with that of the corresponding aqueous solution. The correlation between the enhancement factors obtained and physical parameters of the solvents were investigated. Among them, the best inverse linear relationship existed between log dielectric constant and log enhancement factor. The plot of log (boiling point x viscosity) vs. log enhancement factor also resulted in a line with a negative slope except water. Carbon tetrachloride, chlorofom and xylene, which gave much larger enhancement factors, were recommended for the use in ICP-AES.

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Verstärkungseffekt durch organische Lösungsmittel in der ICP-AES

     

Spatial Resolution Enhancement in BOTDR by Spectrum Separation Method

BOTDR (Brillouin optical-fiber time domain reflectometry) is a promising technique for measuring the strain distribution along an optical fiber which can be used for diagnosing civil structures. However, there is a trade-off between the spatial and the frequency resolutions, and its practical spatial resolution is limited to about 1 m; to date the application scope has been restricted. In order to enhance the spatial resolution without decreasing the measurement accuracy, we intentionally introduce two kinds of strain within the spatial resolution length determined by the optical pulse width, which results in Brillouin gain spectrum separation. In this paper, we describe the theoretical analysis of the spectrum separation method together with experimental verification, where a spatial resolution of 0.5 m is demonstrated. We further propose a new parabolic data fitting method especially effective in the spectrum separation method.     

Conformational transition of copolymer of maleic acid and styrene in aqueous solution. III

Kinetic studies of the pH-induced conformational transition of the hydrophobic copolyelectrolyte of maleic acid and styrene in aqueous NaCl at ionic strength 0.09 were performed by an optical method at 25.0°C with a rapid reaction analyzer of high resolving power. A pH jump applied to a solution, in which the molecule is in the compact form, gives a kinetic trace from which, by appling the general kinetic theory of cooperative transitions, two mean relaxation times are determined. Plots of these relaxation times against the degree of ionization of the primary carboxyl groups of the maleic acid units agree well with theoretical predictions from the linear Ising model, where the molecule in the compact form is described as a random coil with hydrophobic “pockets.” The initiation parameter for a pocket obtained from the kinetic data is 0.036. On the other hand, the parameter calculated from the previous pH-titration results by applying Zimm–Rice theory is 0.015 at the ionic strength 0.09 and 25.0°C. Such values are compared with those determined from pH-titration data on other hydrophobic polyelectrolytes.