Dielectric Relaxation of Monodisperse Linear Polyisoprene: Contribution of Constraint Release

<i>cis</i>-Polyisoprene (PI) has the type A dipole parallel along the chain backbone so that the end-to-end fluctuation of PI chains results in slow dielectric relaxation. Comparison of dielectric and viscoelastic data of PI has revealed several interesting features related to the entanglement dynamics, for example, success and failure of the full dynamic tube dilation (DTD) picture for monodisperse linear and star PI, respectively [see a review: Watanabe, H. <i>Polym. J.</i><b>2009</b>, <i>41</i>, 929, for example]. For monodisperse <i>linear</i> PI, recent modeling [Glomann et al. <i>Macromolecules</i> <b>2011</b>, <i>44</i>, 7430] and single-chain slip-link simulation [Pilyugina et al. <i>Macromolecules</i> <b>2012</b>, <i>45</i>, 5728] suggest that the constraint release (CR) mechanism has negligible influence on the dielectric relaxation time τ_ε in the entangled regime, which appears to disagree with the previous data. Thus, we revisited the classical problem: CR contribution to the dielectric relaxation of PI. Specifically, we made dielectric and viscoelastic measurements for PI/PI blends in a wide range of the molecular weights of long and short components, <i>M</i>₂ = 1.1M and <i>M</i>₁ = 21K–179K, and with a small volume fraction of the short component, υ₁ = 0.1 and/or 0.2, to examine the CR contribution in the experimentally clearest way. It turned out that τ_ε of the short component was longer in the blends than in respective monodisperse bulk even for <i>M</i>₁ = 179K. Furthermore, the viscoelastic and dielectric data of the short components (<i>M</i>₁ ≤ 43K) in the blend exhibited identical mode distribution and relaxation time, which confirmed that the CR mechanism was fully suppressed for these components in the blends. These results demonstrate that the CR mechanism <i>does</i> contribute/accelerate the dielectric relaxation in monodisperse bulk PI systems even in the highly entangled regime (<i>M</i>₁/<i>M</i>_e = 36 for <i>M</i>₁ = 179K). This CR-induced acceleration was found to be consistent with the empirical equations for the terminal relaxation time and CR time of monodisperse PI available in the literature, as noted from a simple DTD analysis of the terminal relaxation process (reptation along a partially dilated tube that wriggles in a fully dilated tube)

Efficient Hydrogen Production by Direct Electrolysis of Waste Biomass at Intermediate Temperatures

Biomass has been considered as an alternative feedstock for energy and material supply. However, the lack of high-efficiency and low-cost processes for biomass utilization and conversion hinders its large-scale application. This report describes electrochemical hydrogen production from waste biomass that does not require large amounts of energy or high production costs. Hydrogen was produced by the electrolysis of bread residue, cypress sawdust, and rice chaff at an onset cell voltage of ca. 0.3 V, with high current efficiencies of approximately 100% for hydrogen production at the cathode and approximately 90% for carbon dioxide production at the anode. The hydrogen yields per 1 mg of the raw material were 0.1–0.2 mg for all tested fuels. Electrolysis proceeded continuously at plateau voltages that were proportional to the current. These characteristics were attributable to the high catalytic activity of the carbonyl-group functionalized mesoporous carbon for the anode reaction, and that the major components of biomass such as cellulose, starch, lignin, protein, and lipid were effectively utilized as fuels for hydrogen production

El Mercado Único. La Europa sin Fronteras Interiores: educación y formación para la CE. Universidad Politécnica de Madrid

Duración del vídeo: 1h 38min 05sCiclo de conferencias sobre el Mercado Único dentro de la Acción Institucional'93 celebrado en la Universidad Politécnica de Madrid y presidido por el Secretario de Estado para las CC.EE, D. Carlos Westendorp junto con el Rector de la Universidad Politécnica de Madrid D. Rafael Portaencasa

Additional file 1: Figure S1. of Re-evaluation of soluble APP-α and APP-β in cerebrospinal fluid as potential biomarkers for early diagnosis of dementia disorders

Standard curves for measurement of sAPPα and sAPPβ concentrations. Typical standard curves for sAPPα and sAPPβ obtained using the original method (A) and those obtained using our modified method (B) are shown. The modified method yielded apparent differences, including higher values of absorbance at 450 nm at lower concentrations and the requirement for a much shorter time for the TMB reaction than the original method. (TIFF 325 kb