Voids polymers

Casassa EF. Equilibrium distribution of flexible polymer chains between a macroscopic solution phase and small voids. Polymer Lett 1967 5 773. 

As ferroelectrets are a specific type of (voided) polymer material, they can show all the features of a glassy, brittle sohd or an elastic rabber depending on the... 

Following the Babinet principle, we cannot exclude the possibility that Rg is a size of void (polymer-poor region) instead of cluster (polymer-rich region), since the scattering intensity is proportional to the square of tte Ap whether Ap is positive or negative cannot be judged by the present scattering experiments. A similar calculation with the void model is also possible, and will be described elsewhere. 

Under compression or shear most polymers show qualitatively similar behaviour. However, under the application of tensile stress, two different defonnation processes after the yield point are known. Ductile polymers elongate in an irreversible process similar to flow, while brittle systems whiten due the fonnation of microvoids. These voids rapidly grow and lead to sample failure [50, 51]- The reason for these conspicuously different defonnation mechanisms are thought to be related to the local dynamics of the polymer chains and to the entanglement network density. 

A detailed examination of the correlation between Vj and M is discussed in references on analytical chemistry such as Ref. 6. We shall only outline the problem, with particular emphasis on those aspects which overlap other topics in this book. To consider the origin of the calibration curve, we begin by picturing a narrow band of polymer solution being introduced at the top of a solvent-filled column. The volume of this solvent can be subdivided into two categories the stagnant solvent in the pores (subscript i for internal) and the interstitial liquid in the voids (subscript v) between the packing particles ... 

The dissipation factor (the ratio of the energy dissipated to the energy stored per cycle) is affected by the frequency, temperature, crystallinity, and void content of the fabricated stmcture. At certain temperatures and frequencies, the crystalline and amorphous regions become resonant. Because of the molecular vibrations, appHed electrical energy is lost by internal friction within the polymer which results in an increase in the dissipation factor. The dissipation factor peaks for these resins correspond to well-defined transitions, but the magnitude of the variation is minor as compared to other polymers. The low temperature transition at —97° C causes the only meaningful dissipation factor peak. The dissipation factor has a maximum of 10 —10 Hz at RT at high crystallinity (93%) the peak at 10 —10 Hz is absent. 

The gas phase in a cellular polymer is distributed in voids, pores, or pockets called cells. If these cells are intercoimected in such a manner that gas can pass from one to another, the material is termed open-ceUed. If the cells are discrete and the gas phase of each is independent of that of the other cells, the material is termed closed-ceUed. 

Phase Separation. Microporous polymer systems consisting of essentially spherical, intercoimected voids, with a narrow range of pore and ceU-size distribution have been produced from a variety of thermoplastic resins by the phase-separation technique (127). If a polyolefin or polystyrene is insoluble in a solvent at low temperature but soluble at high temperatures, the solvent can be used to prepare a microporous polymer. When the solutions, containing 10—70% polymer, are cooled to ambient temperatures, the polymer separates as a second phase. The remaining nonsolvent can then be extracted from the solid material with common organic solvents. These microporous polymers may be useful in microfiltrations or as controlled-release carriers for a variety of chemicals. 

When monomers of drastically different solubiUty (39) or hydrophobicity are used or when staged polymerizations (40,41) are carried out, core—shell morphologies are possible. A wide variety of core—shell latices have found appHcation ia paints, impact modifiers, and as carriers for biomolecules. In staged polymerizations, spherical core—shell particles are made when polymer made from the first monomer is more hydrophobic than polymer made from the second monomer (42). When the first polymer made is less hydrophobic then the second, complex morphologies are possible including voids and half-moons (43), although spherical particles stiU occur (44). 

Nondestmctive testing (qv) can iaclude any test that does not damage the plastic piece beyond its iatended use, such as visual and, ia some cases, mechanical tests. However, the term is normally used to describe x-ray, auclear source, ultrasonics, atomic emission, as well as some optical and infrared techniques for polymers. Nondestmctive testing is used to determine cracks, voids, inclusions, delamination, contamination, lack of cure, anisotropy, residual stresses, and defective bonds or welds in materials. 

Density. Although the polymer unit cell dimensions imply a calculated density of 1.33 g/cm at 20°C, and extrapolation of melt density data indicates a density of 1.13 g/cm at 20°C for the amorphous phase, the density actually measured is 1.15—1.26 g/cm, which indicates the presence of numerous voids in the stmcture. 

Although the concept of polymer blends is sometimes a route for a voiding the development of new polymers, it often has been an integral part of the utiliza tion of new polymer chemistry, eg, the commercial success of PPO hinged on the advantages of its blends with PS. 

Most commercially available RO membranes fall into one of two categories asymmetric membranes containing one polymer, or thin-fHm composite membranes consisting of two or more polymer layers. Asymmetric RO membranes have a thin ( 100 nm) permselective skin layer supported on a more porous sublayer of the same polymer. The dense skin layer determines the fluxes and selectivities of these membranes whereas the porous sublayer serves only as a mechanical support for the skin layer and has Httle effect on the membrane separation properties. Asymmetric membranes are most commonly formed by a phase inversion (polymer precipitation) process (16). In this process, a polymer solution is precipitated into a polymer-rich soHd phase that forms the membrane and a polymer-poor Hquid phase that forms the membrane pores or void spaces. 

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