A HIGH-RESOLUTION SOLID-STATE NMR AND DSC STUDY OF MISCIBILITY AND CRYSTALLIZATION BEHAVIOR OF POLY(VINYL ALCOHOL)/POLY(N-VINYL-2-PYRROLIDONE) BLENDS

Blends of crystallizable poly(vinyl alcohol) (PVA) with poly(N-vinyl-2-pyrrolidone) (PVPy) were studied by C-13 cross-polarization/magic angle spinning (CP/MAS) n.m.r. and d.s.c. The C-13 CP/MAS spectra show that the blends were miscible on a molecular level over the whole composition range studied, and that the intramolecular hydrogen bonds of PVA were broken and intermolecular hydrogen bonds between PVA and PVPy formed when the two polymers were mixed. The results of a spin-lattice relaxation study indicate that blending of the two polymers reduced the average intermolecular distance and molecular motion of each component, even in the miscible amorphous phase, and that addition of PVPy into PVA has a definite effect on the crystallinity of PVA in the blends over the whole composition range, yet there is still detectable crystallinity even when the PVPy content is as high as 80 wt%. These results are consistent with those obtained from d.s.c. studies.

A HIGH-RESOLUTION SOLID-STATE NMR-STUDY OF THE MISCIBILITY, MORPHOLOGY, AND TOUGHENING MECHANISM OF POLYSTYRENE WITH POLY(2,6-DIMETHYL-1,4-PHENYLENE OXIDE) BLENDS

An extended Goldman-Shen pulse sequence was used to observe indirectly the proton spin diffusion in the blends of polystyrene (PS) with poly(2,6-dimethyl-1,4-phenylene oxides) (PPO). The results indicate that the average distance between PS and PPO is less than 5 angstrom in the intimately mixed phase, but there are heterogeneous domains on a 100-angstrom scale. The data of spin relaxation of carbons, T1(C), for homopolymers and their blends suggest that there is a strong pi-pi electron conjugation interaction between the aromatic rings of PS and those of PPO, while the aromatic rings of PPO drive the aromatic rings of PS to move cooperatively. It is the cooperative motion that markedly improves the impact strength of PS.

Response of coastal marine eco-environment to river fluxes into the sea: A case study of the Huanghe (Yellow) River mouth and adjacent waters

The impact of the Huanghe (Yellow) River outflows on its estuary was investigated with river gauging and shipboard hydrographic observations. The river flux has been decreasing dramatically; the discharges of water and sediment in the 1990s dropped to 27.4% and 31.9% of those in the 1950s, respectively, resulting in frequent and lengthy events of downstream channel dry-up since the 1970s. There were accumulatively 897 zero-flow days during the 1990s in the river course below the Lijin Hydrological Station, 100 km upstream from the river mouth, which is 82.4% of that in 1972. As freshwater input decreases, river-borne nutrients to the estuarine increased significantly. Concentration of dissolved inorganic nitrogen (DIN) in the 1990s was four times of that in 1950s. Changes in amount and content of the riverine inputs have greatly affected the estuarine ecosystem. Over the past several decades, sea surface temperature and salinity in the estuary and its adjacent waters increased and their distribution pattern altered in response to the reduction of freshwater inflow. The distribution of and seasonal succession in nutrient concentrations in the surface layer have also changed with a shift of river outlet and the decrease in riverine nutrient loads. Furthermore, deterioration of estuarine ecosystem by less river input has decreased primary productivity in the deltaic region waters, and in turn depressed the fishery. (C) 2008 Published by Elsevier Ltd.

Theoretical study on adsorption of Na+ and Na+(H2O)(n) (n=1-6) on a clean Si(111) surface

To model the adsorption of Na+ in aqueous solution on the semiconductor surface, the interactions of Na+ and Na+(H2O)(n) (n = 1-6) with a clean Si(111) surface were investigated by using hybrid density functional theory (B3LYP) and Moller-Plesset second-order perturbation (MP2) methods. The Si(111) surface was described with Si8H12, Si16H20, and Si22H21 Cluster models. The effect of the basis set superposition error (BSSE) was taken into account by applying the counterpoise (CP) correction. The calculated results indicated that the interactions between the Na+ cation and the dangling bonds of the Si(111) surface are primarily electrostatic with partial orbital interactions. The magnitude of the binding energies depends weakly on the adsorption sites and the size of the clusters. When water molecules are present, the interaction between the Nal and Si(I 11) surfaces weakens and the binding energy has the tendency to saturate. On a Si22H21 cluster described surface, the optimized Na+-surface distance for Na+(H2O)(5) adsorbed at on-top site is 4.16 angstrom and the CP-corrected binding energy (MP2) is -35.4 kJ/mol, implying a weakly adsorption of hydrated Na+ cation on clean Si(111) surface.

Kinetic study of the accelerating effect of coal-burning additives on the combustion of graphite

The catalytic and accelerating effects of three coal-burning additives (CBA) on the burning of graphite were studied with the help of thermogravimetric (TG) analysis. The kinetic study on the catalytic oxidation of the graphite doped with CBA was carried out and the results were presented. The results show that the CBA can change the carbon oxidation/combustion course by catalytic action and change the activation energy, thus improving the combustion efficiency.

The stability of nanosized HZSM-5 zeolite: a high-resolution solid-state NMR study

The thermal and hydrothermal stabilities of HZSM-5 zeolites with crystal sizes less than 100 nm have been studied by multinuclear solid-state NMR, combined with BET and XRD. As evidenced by Al-27 and Si-29 MAS as well as their corresponding cross-polarization/MAS NMR investigations, the thermal stability of nanosized HZSM-5 is not so good as that of microsized HZSM-5. This is due to two processes concerning dealumination and desilicification involved in the calcination of nanosized HZSM-5, while only the dealumination process is conducted in microsized HZSM-5 under the similar calcination process. The hydrothermal stability of nanosized HZSM-5 is, contrary to what was expected, not so bad as that of the microsized HZSM-5 in the course of steam treatment. The actual resistance of the hydrothermal stability to the crystal size of HZSM-5 can be ascribed to an active reconstruction of zeolitic framework through an effective filling of amorphous Si species into nanosized HZSM-5 during hydrothermal treatment. (C) 2001 Published by Elsevier Science B.V.