The formation of gradient interfaces between PS-and PB-rich microphases in SBS block copolymers was investigated by means of solid-state NMR and solution NMR as well as TEM, AFM, and SAXS as a function of molecular architecture, comparing linear and star-shaped asymmetric block structures, and gradient as well as random incorporation of styrene comonomer into the PB-rich blocks. Although all studied SBS possess a very similar total styrene content, different morphologies and mechanical properties were found in the extruded SBS/PS blends, whose origin could be related to the formation of a compositional interface gradient. Employing the sensitivity of solid-state NMR for hard (glassy) and soft (rubbery) phases as well as their respective chemical compositions, we found that upon raising the temperature up to the PS glass transition different amounts of polystyrene from the hard PS phase "soften" and integrate into the soft PB-rich phase ("PS softening"). The degree of "PS softening" characterizes the interfacial gradients of SBS block copolymers at elevated temperatures up to the melt. The softened PS was found to partially mix into the soft phase and partially remain at the interface, thus forming different gradient interfaces, depending primarily on the amount of styrene randomly incorporated in the PB mobile blocks and much less on a compositional gradient at the block linkages in SBS chains. In SBS/PS blends, SBS with a substantial "PS softening" effect was found to preferentially form elongated PB lamellar morphologies, which lead to improved mechanical ductility. The purpose of this study was to apply different characterization methods and correlate their results in order to gain important compositional and morphological information as well as their effects on the SBS/PS blend mechanical properties. Rapid and robust low-cost pulsed solid-state NMR methods were established as versatile analytical tools for application in high-output polymer screening (HOPS) and quality control systems, enabling online monitoring of structure-property correlations as well as product quality of SBS-based materials.

We describe a three-dimensional imaging and analysis study of eight industrial cellular foam morphologies. The foam morphologies were generated by differing industrial processing methods. Tomograms are acquired on an X-ray micro-computed tomography facility at scales of approximately equal to ð5 mmÞ 3 at resolutions down to 7 mm. The image quality is sufficient in all cases to measure local structure and connectivity of the foamed material, and the field of view large enough to calculate a range of material properties. Phase separation into solid and porous components is straightforward.Three-dimensional structural characteristics are measured directly on the porous and solid phases of the images. A number of morphological parameters are obtained, including pore volume-to-surface-area ratio, connectivity, the pore and solid phase size distributions defined by maximal sphere openings and chord length measurements. We further calculate the pore size distribution associated with capillary pressure via simulating of mercury drainage on the digital images.The binarized microstructures are used as a basis for calculations of transport properties (fluid permeability, diffusivity and thermal conductivity) and elastic moduli. From the data, we generate property-porosity relationships for the range of foam morphologies imaged and quantitatively analyse the effects of porosity and microstructure on the resultant properties of the foams.We compare our numerical data to commonly used theoretical and empirical property-porosity relationships. For thermal conductivity, we find that the numerical results agree extremely well with an empirical expression based on experimental data of various foams. The upper Hashin-Shtrikman bound also provides an excellent prediction of the data across all densities. From simulation of the diffusivity, we can define the tortuosity of the pore space within the cellular solid. We find that different processing methods lead to strong variations in the tortuosity of the pore space of the foams. For elastic properties, our results show that for the Young modulus, E, both the differential effective medium theory and the classical correlation E=E s Z ðr=r s Þ 2 give a good Downloaded from correlation. Assuming a constant Poisson's ratio n leads to reasonable agreement. The best correlation for n is given by assuming a slight variation in n as a linear function of porosity. The permeability of the foams varies over three orders of magnitude. Correlations for permeability based on the classical Kozeny-Carman equation lead to reasonable agreement, except at the lowest porosities. Permeability estimations based on mercury porosimetry give excellent agreement for all foams.

Lithium manganese oxide spinel (LiMn 2 O 4 ) is gaining prominence as a positive electrode material for lithium-ion batteries. After an extensive research effort (see, for example, Ref. 1-3), LiMn 2 O 4 spinel with good cycling stability is now available. LiMn 2 O 4 is an attractive alternative to Co and Ni oxides currently used in lithiumion batteries. [4][5][6] For certain applications, such as in electric vehicles, lithium-ion batteries are required to have a high specific power in addition to a high specific energy. 7-10 Thus, electrode materials with high rate capability are of interest.The main strategies adopted so far to reach a high rate capability of the spinel electrode have been the preparation of spinel particles with small sizes, and an optimization of the electrode conductivity. 11-16 However, for industrial battery electrode coating processes, relatively large particles with a small Brunauer-Emmett-Teller (BET) surface area are advantageous. In the present report, we show that it is not necessary to use micrometer-or submicrometer-sized oxide particles when aiming at high rate capabilities. We adapted a high-temperature synthesis route for preparing a spinel consisting of agglomerates with an average size of 15 m. The agglomerates were composed of primary particles (ca. 0.5-3 m). We measured the discharge capability of electrodes containing this spinel up to a discharge rate of 20 C (3 min for full discharge) in an electrochemical test cell with a metallic lithium counter electrode and found a high rate capability for this spinel. ExperimentalSpinel synthesis.-The lithium manganese oxide spinel was synthesized using a proprietary ceramic process. A mixture of manganese oxide (Mn 3 O 4 ) with a specific surface area of about 10 Ϯ 5 m 2 /g and ground lithium carbonate with a particle size of less than about 40 m was heated for 1 h under N 2 to about 750ЊC. The resulting product, which did not yet have a spinel structure, was thoroughly ground. This spinel precursor material was suspended with about 1 wt % of polyvinyl alcohol in water and spray-dried to form a granular powder. This powder was oxidized in O 2 at a temperature of about 780ЊC to form the spinel. The spinel was finally coated with Li 2 CO 3 by spray-drying an aqueous slurry of the spinel and 1 wt % of the coating substance in a stream of hot air (200-300ЊC).Physical characterization.-The lattice constant of the spinel was determined at room temperature by powder X-ray diffraction (XRD) in a Siemens D5000 diffractometer. It was found to be 8.224 Å. The lithium content of the spinel was calculated to be Li 1.09 Mn 1.91 O 4 (by linear interpolation of the lattice constants, 8.248 Å for Li 1.00 Mn 2.00 O 4 and 8.16 Å for Li 1.333 Mn 1.667 O 4 ). 17The particle size distribution of the spinel was determined in an aqueous slurry of the spinel powder by laser scattering using a Helos instrument. The result is shown in Fig. 1. The average particle (agglomerate) size is 15 m.Scanning electron micrographs (SEMs) of the spinel were recorded with a...

No abstract

The physical properties of cellular solids are a direct consequence of their complex microstructure. Linking properties to structure will lead to an understanding of how cellular solids can be optimised and materials engineered for given applications. In this paper we illustrate a 3D imaging and analysis study of a number of industrial cellular foam morphologies; structural characteristics (porosity, pore size, interconnectivity and tortuosity) and physical properties (diffusivity, elasticity, permeability and conductivity) are calculated directly on the large three dimensional digitised images. Comparisons with common empirical estimates and theoretical formulae are encouraging.Manufactured cellular materials (e.g, polymer, ceramic or metallic foams) are an extremely attractive option as materials engineered for a range of applications ranging from light weight structures to packaging, insulation and crash protection. The useful properties of cellular solids are a direct consequence of their microstructure. Relevant aspects of the structure of cellular materials include porosity or apparent COMMUNICATIONS 238