Morphology-shrinkage relationships in semi-crystalline polymers. Epitaxy,a way of eliminating amorphous contribution

A new approach for achieving a highly dimensionally stable film of semi-crystalline polymers via blending is demonstrated. To illustrate this approach, a model system, polyethylene-polypropylene is investigated using TEM, TMA, DSC, and DMA. It is shown that epitaxial growth in polymer blends and laminates can induce a cross-hatch morphology which eliminates or reduces the contribution of an oriented amorphous phase. This ultimately leads to greater dimensional stability and synergism in mechanical properties as well. The presence of an appropriate low-melting component can also be used to reduce shrinkage.     

Electron microscopic studies of SBS block copolymers I. A method to study the temperature dependence of phase separation

The potential applicability of a Film Formation Method of Crystal Growth to the study of morphological aspects of amorphous polymers was investigated using transmission electron microscopic techniques. A wide variety of morphologies of styrene-butadiene-styrene triblock copolymer can be achieved by varying the solvent power and film preparation temperatures. The effect of film preparation temperature indicates that below 100 °C (the glass transition temperature of polystyrene), there is very little change in the size of domains; above 100 °C a drastic change in morphology is observed. Not only is there rapid coarsening of both the constituent phases of the polymer above 100 °C, but also an intermixing of both phase components of the block copolymer. It was demonstrated that some monomeric materials are effective in maintaining the original morphology of the film; i. e. phase mixing is prevented.     

Binäre Mischkristalle in Polymeren: Das System Polypropylen-Polybuten-1

Ohne ZusammenfassungMit 3 Abbildungen und 1 Tabelle     

Annealing of polypropylene films crystallized from a highly extended melt

Thin films of isotactic polypropylene were drawn from the melt at a very high rate of extension. Transmission electron micrographs of this material reveal fibrous crystals lying along the draw direction. The chain axis and fiber axis are identical. Dark field micrographs show a dark/light modulation along the fiber axis. Annealing at temperatures below 110°C produces no qualitative change in the electron microscope observations. Annealing between 110 and 150°C produces gradual dominance of lamellar crystals, oriented normal to the draw direction. Small-angle x-ray scattering (SAXS) data exhibit a strong streaking normal to the fiber axis, in broad agreement with the observed fibrosity. A Bragg peak along the draw directions shows that the modulation observed microscopically is a density modulation. The absence of second-order maxima and the dependence of the SAXS peak on treatment temperature strongly suggest that the axial modulation is a spinodal decomposition of the material into crystalline and amorphous regions.     

Gallium alkoxides: Synthesis and properties

Compounds Ga(OR)₃ (R = Me, Et, Prⁱ, Buⁿ, C₂H₄OMe) were synthesized by exchange reactions between gallium chloride and alkali metal alkoxides, the reetherefication of Ga(OPrⁱ)₃ and Ga(OC₂H₄OMe)₃ by other ROH (R = Me, Et), and anodic dissolution of metallic gallium in the presence of a electroconductive additive (LiCl, Bu₄NBr). When solid GaCl₃ is introduced into an alcoholic solution of NaOEt, stable soluble gallium oxoalkoxyhalides are formed. The same reaction with a GaCl₃ solution in toluene or electrochemical synthesis produces nonvolatile Ga(OEt)₃ samples, which have the polymer zigzag configuration [Ga(OR)_4/2(OR)]_∞. Mass spectrometry shows that only Ga(OPrⁱ)₃ and freshly prepared X-ray amorphous Ga(OEt)₃ samples (produced by reetherefication) are transferred to the gas phase. The spectra of the latter contain ions generated by penta-and hexanuclear oxoalkoxide molecules, along with fragments of orthospecies [Ga(OEt)₃]_2?4. IR spectra are described for all compounds synthesized.     

The FT-IR study of the brain tissue of Labeo rohita due to arsenic intoxication

The brain is believed to be particularly vulnerable to arsenic due to its high oxygen consumption rate and high level of polyunsaturated fatty acids and relatively high rate of oxygen free radical generate without commensurable level of arsenic. Hence, in the present work an attempt is made to study the changes in the biochemical contents in the brain tissues of edible fish Labeo rohita due to arsenic intoxication using Fourier Transform Infrared (FT-IR) spectroscopy. FT-IR spectra reveal significant differences in absorbance intensities between the control and arsenic intoxicated brain tissues, reflecting an alteration on the major biochemical constituents, such as lipids, proteins and nucleic acids of the brain tissues of L. rohita due to arsenic intoxication. Further, the administration of antidote DMSA improves the protein and lipid contents significantly in the brain tissues when compared to arsenic intoxicated tissues. The decrease in α-helix structure due to arsenic intoxication might be responsible for the increase in β-sheet secondary structures, which is consistent with the mechanism of β-sheet formation.     

The Family of A6M2O6 Oxometalates: Synthesis and Crystal Structure Determination of Cs6Mn2O6, Magnetic Exchange within Dimeric Poly‐oxoanions,and Classification of Crystal Structures

The new compound Cs₆Mn₂O₆ was synthesized via the azide/nitrate route. According to single‐crystal X‐ray analysis (P1 ; a = 695.74(7), b = 733.24(7), c = 735.12(7) pm, α = 78.559(4), β = 62.685(3), γ = 88.788(4)°; 2705 independent data, R₁ = 0.041), the anionic part of the compound consists of dimeric Mn₂O₆ units, formed by edge sharing of two MnO₄ polyhedra of a shape intermediate between tetrahedral and square planar. The crystal structure is singular, however, can be related to several oxides of the same general formula by group‐subgroup symmetry descent. The magnetic properties of Cs₆Mn₂O₆ have been simulated by an antiferromagnetic dimer model of spin S = 2 entities, considering a small temperature dependence of the spin exchange parameters.     

Preparation and characterization of monovalent cation selective sulfonated poly(ether ether ketone) and poly(ether sulfone) composite membranes

Highly charged cation permeable composite membranes were prepared by blending of sulfonated poly(ether sulfone) (SPES) with sulfonated poly(ether ether ketone) (SPEEK) in 0 to 90% weight ratio, to adjust the hydrophobic properties and ion selective nature. Extent of sulfonation was confirmed by 1H NMR and ion exchange capacity and degree of sulfonation depending on blending composition. These membranes were characterized as a function of weight fraction of SPEEK by recording ion-exchange capacity, water uptake, thermogravimetric analysis, membrane conductivity and membrane potential in equilibration with different electrolytic solutions. Membrane permselectivity and solute flux were estimated using these data on the basis of non-equilibrium thermodynamic principles and for observing the selectivity of different membranes for mono- or bivalent counter-ions. It was observed that relative selectivity for monovalent in comparison to bivalent counter-ions were increased with the decrease in SPEEK content in the composite membrane matrix. The range of SPEEK content in the blend from 60 to 80% appears the most suitable for the selective separation of monovalent ions from bivalent ions. Furthermore, highly charged nature and stabilities of these membranes extend their applications for the electro-assisted separations of similarly charged ions as well as other electro-membrane processes.     

Microwave absorption studies of MgB2 superconductor

Microwave absorption studies have been carried out on MgB₂ superconductor using a standard X-band EPR spectrometer. The modulated low-field microwave absorption signals recorded for polycrystalline (grain size ∼ 10 μm) samples suggested the absence of weak-link character. The field dependent direct microwave absorption has been found to obey a ✓H dependence with two different slopes, which indicated a transition from strongly pinned lattice to flux flow regime.