Correlation between the Soret coefficient and the static structure factor in a polymer blend

Mutual mass diffusion and thermal diffusion has been investigated in poly(dimethylsiloxane)/ poly(ethylmethylsiloxane) (PDMS/PEMS) polymer blends of equal weight fractions. Molar masses ranged from below 1 to over 20 kg/mol. Both the mutual mass (D) and the thermal diffusion (D_T) coefficient contain a thermally activated factor with an activation temperature of 1415 K. The molar mass dependence of D_T is due to an end-group effect of the local friction coefficient. The thermal diffusion coefficient in the limit of long chains and infinite temperature is D_T^0, = - 1.69×10^-7cm²(sK)^-1. The Soret coefficient S_T of blends far enough away from a critical point is proportional to the static structure factor S(q = 0).     

SYNTHESIS AND CHARACTERIZATION OF ORGANOMONTMORILLONITE AND POLYAMIDE 66/MONTMORILLONITE NANOCOMPOSITES

The montmorillonites (MMTs), layered, smectite-type silicates, were premodified by two different methods priorto the polymer melt intercalation. In one case MMTs were modified with cetyltrimethylammonium bromide (CTAB), andtermed as organomontmorillonites (OMMTs); in the other case MMTs were modified by nylon, and the products were calledmodified montmorillonites (MMMTs). The effects of CTAB and nylon on the MMTs were investigated by using TG andWAXD. The results show that interlayer spacings of CTAN and nylon modified MMTs are larger than that of sodium MMTs.Then, polyamide 66 (PA 66)/MMT nanocomposites were obtained through the method of melt intercalation of polymers. Thenanocomposites were characterized by WAXD, TEM and Molau experiments. The results indicate that the MMTs dispersehomogeneously in the PA 66 matrix. The mechanical properties of nanocomposites, such as tensile properties and flexuralproperties, were also measured and show a tendency to increase with increase of MMT content and reach the maximumvalues at 5phr MMT content. The heat distortion temperature (HDT) of the nanocomposites (7 phr) is about 32 K higher thanthat of pure PA 66.     

Proof of gridlock in a polymer model

It has been suggested that some lattice models of polymers, especially ones that incorporate more realistic excluded volume interactions extending to further neighbors, may be subject to gridlock. A model is defined to have the property of gridlock if it cannot melt at any temperature unless a density decrease is allowed. Classical theories of polymer melting are incompatible with the property of gridlock. This paper proves rigorously that a two-dimensional square-lattice model of polymer chains that have nearest-neighbor excluded volume interactions (called the X1S model) has the gridlock property. The proof uses elementary concepts from graph theory. Also, different interpretations of the X1S model are given in terms of real polymers. This leads to a discussion of a number of different classes of melting depending upon whether the intramolecular rotameric energies and the attractive intermolecular energies are antagonistic to or supportive of the melting transition.     

Continuous peeling extrusion of SEBS block copolymers

During continuous peeling, a central polymer rod free of visible defects was continuously extruded while being peeled at the die exit. Continuous peeling can occur at flow rates orders of magnitude higher than those at which initial surface cracking is observed. Thus, if continuous peeling can be controlled it may have potential industrial applications. The aim of this work was to study how different extrusion parameters (temperature, flow rate, die length and diameter) affect the presence of continuous peeling. The melt exiting the die has been filmed to link physical measurements and observations and to determine whether or not continuous peeling is present. Different criteria have been considered to represent the extrusion conditions under which continuous peeling may occur. Surface tension criteria can be used to try to predict the appearance and disappearance of continuous peeling. A correlation formula is also proposed for the rod diameter in terms of surface tension. Our results show that the ratio of the rod diameter to the die diameter is approximately 25% greater in the case of short-orifice dies (L/D ≈ 0) than for long capillaries (L/D ≈ 10). The correlations obtained allow analysis and discussion of flow regimes for possible applications.     

Quasielastic neutron scattering in soft matter

The general trend in soft matter is to study systems of increasing complexity which are more technologically and biologically relevant. This is facilitated by the capability of quasielastic neutron scattering (QENS) to selectively probe spatially resolved dynamical modes at a molecular level. The large number of recent publications using QENS for investigating complex and multi-component soft matter systems, serves as recognition of the suitability of this technique by the scientific community. Exploiting its complementarity with molecular dynamics (MD) simulations and other experimental techniques is the basis of a successful methodology for this scientific challenge. We illustrate the potential of QENS with three kinds of soft materials whose structural units increase in size/complexity: lipids, polymers and biomolecules.     

Three New Iron(II) Thiocyanato Coordination Polymers Based on 4,4′‐Bipyridine as Ligand and the Influence of Methanol on Their Structures

Reaction of iron(II) thiocyanate with 4,4‐bipyridine (bipy) in methanol leads to the formation of three new solvates of different composition depending on the reaction conditions: At room temperature two new ligand‐rich 1:2 (1:2 = ratio between metal and N‐donor ligand) polymorphic forms [Fe(NCS)₂(bipy)₂ · 2MeOH]_n ( 1I ) and [Fe(NCS)₂(bipy)(MeOH)₂ · (bipy)]_n ( 1II ) are obtained, whereas solvothermal conditions leads to the formation of the new ligand‐deficient 1:1 compound [{Fe(NCS)₂(bipy)(MeOH)}₂]_n ( 2 ). All crystal structures were determined by X‐ray single crystal structure analysis. In the crystal structure of modification 1I the metal atoms are coordinated by four bridging bipy ligands, which connect them into layers. The methanol molecules occupy voids in the structure. Compared to 1I in modification 1II the crystal structure contains of linear Fe–bipy–Fe chains, which are further connected by hydrogen bonds between coordinating MeOH and noncoordinated bipy ligands into layers. The ligand‐deficient 1:1 compound 2 shows a completely different coordination topology with linear Fe–bipy–Fe chains, which are connected by coordinating methanol molecules into double‐chains. In all compounds the thiocyanato anions are terminal N‐bonded to the metal atoms. Investigation of the thermal behavior of compound 1I shows a two‐step decomposition, in which ligand‐deficient intermediates are formed. Magnetic measurements on 1I reveal Curie–Weiss paramagnetism with increasing antiferromagnetic interactions on cooling.     

New Type of Nanocomposite CsH2PO4-UiO-66 Electrolyte with High Proton Conductivity

New (1−x)CsH₂PO₄–xUiO-66 electrolytes with high proton conductivity and thermal stability at 230–250 °C were developed. The phase composition and proton conductivity of nanocomposites (x = 0–0.15) were investigated in detail. As shown, the UiO-66 matrix is thermally and chemically suitable for creating composites based on CsH₂PO₄. The CsH₂PO₄ crystal structure remains, but the degree of salt crystallinity changes in nanocomposites. As a result of interface interaction, dispersion, and partial salt amorphization, the proton conductivity of the composite increases by two orders of magnitude in the low-temperature range (up to 200 °C), depending on the UiO-66 fraction, and goes through a maximum. At higher temperatures, up to 250 °C, the conductivity of nanocomposites is close to the superprotonic values of the original salt at low UiO-66 values; then, it decreases linearly within one order of magnitude and drops sharply at x > 0.07. The stability of CsH₂PO₄-UiO-66 composites with high proton conductivity was shown. This creates prospects for their use as proton membranes in electrochemical devices.     

Syntheses,crystal structures,and photoluminescence of two new coordination polymers derived from dicarboxylate and N-donor ligands

Two metal-organic coordination polymers, [Co(tda)(ip)(H₂O)₂] _n (1) and [Mn(tda)(ip)(H₂O)] _n (2) [H₂tda?=?thiophene-2,5-dicarboxylic acid, ip?=?1H-imidazo[4,5-f][1,10]-phenanthroline], have been synthesized and characterized by elemental analyses, IR, PXRD, and X-ray diffraction. Single-crystal X-ray analyses reveal that 2,5-tda is a bridging ligand, exhibiting two coordination modes to link metal ions: μ₁-η¹?:?η⁰/μ₁-η¹?:?η⁰ and μ₂-η¹?:?η¹/μ₁-η¹?:?η⁰. Compound 1 demonstrates a 1-D structure in which Co²⁺ centers are connected via tda anions into 1-D chains; the chains are further connected via hydrogen-bonding and π?···?π interactions. Compound 2 displays a 2-D structure in which tda connects two Mn ions forming a dinuclear molecule. In 2 the 3-D supramolecular structure arrays through hydrogen-bonding and π?···?π interactions. In addition, photoluminescence for 1 and 2 is also investigated in the solid state at room temperature.     

Thermal diffusion and bending kinetics in nematic elastomer cantilever

Vertically aligned monodomain nematic liquid-crystal elastomers contract when heated. If a temperature gradient is applied across the width of such a cantilever, inhomogeneous strain distribution leads to bending motion. We modelled the kinetics of thermally induced bending in the limit of a long thin strip and the predicted time variation of curvature agreed quantitatively with experimental data from samples with a range of critical indices and nematic-isotropic transition temperatures. We also deduced a value for the thermal diffusion coefficient of the elastomer.     

Dynamical study on the stimulated processes of an exciton and a biexciton in a polymer

By applying a femtosecond stimulating pulse, we theoretically study the stimulated processes of an exciton and a biexciton in a polymer within the framework of an extended Su–Schrieffer–Heeger tight-binding model. For an exciton, it is obtained that the stimulated emission and absorption between the intragap levels take place with the same probability, by which we will not get the light amplification. However, the light amplification can be realized by the stimulated emission between the intragap levels in a biexciton, which is found to have two different modes. Finally, effect of the stimulating energy and intensity on the stimulated processes is separately analyzed. These results might be of great importance for further improving the optical applications of polymers, especially for optimizing the polymer laser properties.