Search results for "FINE"

Anomalous scaling of the critical temperature of unmixing with chain length for two-dimensional polymer blends

2003

The thermodynamics, structure and the chain configurations of symmetrical polymer mixtures confined into ultrathin films are studied by Monte Carlo simulations of the bond fluctuation model. It is shown that the Flory-Huggins–type scaling of the critical temperature (Tc ~ N) with chain length N in the bulk is replaced by a weaker increase, Tc ~ N1/2, in an ultrathin film, and this is interpreted in terms of geometric arguments. The pair-correlation function g(r) of monomers from different chains exhibits a pronounced correlation hole, and the density of intermolecular contacts zc decreases with N as zc ~ N−1/2.

Monte Carlo simulation studies of the interfaces between polymeric and other solids as models for fiber-matrix interactions in advanced composite mat…

1996

As a coarse-grained model for dense amorphous polymer systems interacting with solid walls (i.e., the fiber surface in a composite), the bond fluctuation model of flexible polymer chains confined between two repulsive surfaces is studied by extensive Monte Carlo simulations. Choosing a potential for the length of an effective bond that favors rather long bonds, the full temperature region from ordinary polymer melts down to the glass transition is accessible. It is shown that in the supercooled state near the glass transition an “interphase” forms near the walls, where the structure of the melt is influenced by the surface. This “interphase” already shows up in static properties, but also h…

Polymer-Polymer Interaction: Consistent Modeling in Terms of Chain Connectivity and Conformational Response

2006

An approach developed for the modeling of polymer solutions is extended to polymer blends. It accounts explicitly for the fact that the segments of a given macromolecule cannot spread out over the entire volume of the system (chain connectivity) and that the space a polymer molecule occupies may change after contact formation between the components of a mixture (conformational response ζ). The validity of the equation obtained for the Flory-Huggins interaction parameter between polymers is tested by means of critical data published for the system PVME/PS. The measured phase diagrams can be modeled equally well by two limiting assumptions concerning the temperature dependence of the conforma…

No-Flow Temperature in Injection Molding Simulation

2010

Most injection molding simulation packages use the no-flow temperature (NFT) as a means of determining whether the polymer flows or is solid. The NFT is not well defined, and a standard method for measuring it does not exist. A sensitivity analysis of the filling stage has been carried out with two different packages [VISI Flow (Vero Software Limited, Gloucestershire, UK) and Moldflow (Autodesk, Inc., San Rafael, CA)] to estimate the influence of the NFT on the main processing parameters. The NFT has a large influence on the thickness of the frozen layer, but it does not appreciably affect the filling pressure. Because the NFT affects the frozen layer, an effect on the estimation of shrinka…

On the reaction of [Ph2(OH)Si]2O with t-Bu2SnCl2: Synthesis and characterization of the first well defined polystannasiloxane [(t-Bu2SnO)(Ph2SiO)2]n

1997

Abstract The high yield synthesis of [(t-Bu2SnO)(Ph2SiO)2], 1 is reported. Compound 1 is a linear polymer in the solid state but a six-membered ring in solution.

Local Environment of Co2+ Ions in β″-Alumina Crystals

1992

Structural characterization of U(VI) surface complexes on kaolinite in the presence of humic acid using EXAFS spectroscopy.

2007

To determine the influence of humic acid (HA), pH, and presence of atmospheric CO2 on the sorption of U(VI) onto kaolinite, the structure of the surface complexes was studied by U L III-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The best fits to the experimental EXAFS data were obtained by including two uranium coordination shells with two axial (O ax) and five equatorial (O eq) oxygen atoms at 1.77+/-0.02 and 2.34+/-0.02 A, respectively, and two coordination shells with one Al/Si atom each at 3.1 and 3.3 A. As in the case of the binary system U(VI)-kaolinite, uranium forms inner-sphere surface complexes by edge sharing with aluminum octahedra and/or silicon tetrahe…

Temperature and pH Dependence of Gd-DOTA and Gd-DTPA Complexes Dissociation Studied by EXAFS

1997

The Gd L3-edge of Gd(DTPA) 2- and Gd(DOTA) - complexes, in crystalline state and aqueous solutions presenting various pH (0.15-8) at different temperatures (25-90 °C), are investigated by XAFS experiments. For the Gd(DTPA) 2- . complexes we observe a strong pH (0.15-1.5) dependence of XAFS signals. On the other hand, the XAFS signals of Gd(DOTA) - complexes exhibit a light pH (1-1.5) dependence and for pH<1 we observe a ligand decomposition. Conceming both complexes, we note just a light temperature dependence. To obtain information about the short and medium range order (up to 5 A), multiple scattering calculation is performed. For the first coordination shell, we apply multi-shell fitting…

Metal-organic frameworks-based catalysts for biomass valorization

2020

Abstract The objective of this chapter is to review the most promising metal-organic framework (MOF) catalysts in biomass valorization processes in the bulk and fine chemical industries. Either bulk metal-organic frameworks, encapsulated catalytic species in MOFs, or MOF-derived catalysts are revised in terms of activity, selectivity, and stability for biomass valorization applications. The work revised here is focused on the transformation of lignocellulose biomass through purely chemical pathways. In the first part of the chapter, the few studies of cellulose hydrolysis into monosaccharides reported are commented, since this crucial first step in the valorization of hemicellulose is expec…

Experimental study of the long range interactions between a Na (3S) and a Rb (5S) atom

2005

Transitions to near asymptotic levels of the a3Σ+ and the X1Σ+ electronic states in NaRb were recorded by high resolution Fourier transform spectroscopy technique. The hyperfine splitting of the a3Σ+ state levels was analysed. The application of coupled channels calculations is discussed for determination of accurate potential energy curves of the a3Σ+ and the X1Σ+ states capable for reliable description of cold collisions between a Na and a Rb atoms in their ground states.