Phase crystalline structure

This treatment of melting in confined geometries is obviously oversimplified and the molecular nature of the phases and interactions between the adsorbent walls and the adsorbate should be taken into account by considering not only the surface energies but also the exact nature of the solid phase (structure, crystalline orientation, crystal defects, and so on). 

The content of the mesophase significantly decreases in fibres taken at other parameters. At certain conditions the mesophase completely disappears and inside fibres only two-phase structure, crystalline and amorphous, is formed. The high crystalline content was obtained in fibres extruded at low extrusion temperature and taken at high take-up velocities (Spruiell White, 1975 Bond Spruiell, 2001). 

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

Multiblock polyethylene-polydimethylsiloxane copolymers were obtained by the reaction of silane terminated PDMS and hydroxyl terminated polyethylene oligomers in the presence of stannous octoate as the catalyst 254). The reactions were conducted in refluxing xylene for 24 hours. PDMS block size was kept constant at 3,200 g/mole, whereas polyethylene segment molecular weights were varied between 1,200 and 6,500 g/mole. Thermal analysis and dynamic mechanical studies of the copolymers showed the formation of two-phase structures with crystalline polyethylene segments. 

A simple example of how molecular electronic structure can influence condensed phase liquid crystalline properties exists for molecules containing strongly dipolar units. These tend to exhibit dipolar associations in condensed phases which influence many thermodynamic properties [29]. Local structural correlations are usually measured using the Kirkwood factor g defined as... 

Kitamaru, R, Phase Structure of Polyethylene and Other Crystalline Polymers by Solid-State l3C/MNR.VoL 137, pp 41-102. 

NMR Self-Diffusion of Desmopressin. The NMR-diffusion technique (3,10) offers a convenient way to measure the translational self-diffusion coefficient of molecules in solution and in isotropic liquid crystalline phases. The technique is nonperturbing, in that it does not require the addition of foreign probe molecules or the creation of a concentration-gradient in the sample it is direct in that it does not involve any model dependent assumptions. Obstruction by objects much smaller than the molecular root-mean-square displacement during A (approx 1 pm), lead to a reduced apparent diffusion coefficient in equation (1) (10). Thus, the NMR-diffusion technique offers a fruitful way to study molecular interactions in liquids (11) and the phase structure of liquid crystalline phases (11,12). 

It has also been inferred that differences found between crystallinities measured by density and those from heat of fusion by DSC area determination, as given for polyethylenes in the example of Figure 4 [72], may be related to baseline uncertainties, or not accounting for the temperature correction of AHc. Given that similar differences in crystallinity from density and heat of fusion were reported for isotactic poly(propylene) [43] and polyfaryl ether ether ketone ketone), PEEKK [73], other features of phase structure that deviate from the two-phase model may be involved in the crystallinity discrepancy. 

The major components of the phase structure of semi-crystalline polymers and the most common techniques of characterization of the crystalline, amorphous... 

Copoly(ether ester)s consisting of short-chain crystalline segments of PBT and amorphous poly(ether ester) of poly(tetramethylene terephthalate) exhibit a two-phase structure and can be used for the production of high-impact-strength engineering plastics. These very interesting materials with their outstanding properties understandably require stabilization to heat and UV exposure [45],... 

Structural relations between quasicrystals and other intermetallic phases. As discussed in several sections of the review published by Kelton (1995) on quasicrystals and related structures, numerous studies and observations indicate structural similarities between non-periodic quasicrystal phases with crystalline phases and also, on the other hand, with amorphous, glassy and liquid phases. 

According to Tarascon and co-workers, the swelling of PVdF—HFP by liquid electrolytes was never complete due to the semicrystalline nature of the copolymer, which tends to microphase-separate after the activation by electrolyte. On the other hand, it is those crystalline domains in the gelled PVdF—HFP that provide mechanical integrity for the resultant GPE. Thus, a dual phase structure was proposed for the Bellcore GPE by some authors, wherein the amorphous domain swollen by a liquid electrolyte serves as the ion conduction phase, while tiny crystallites act as dimensional stabilizer. 

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