Semicrystalline domains

Formation of physical cross-links by the anchorage of chain ends in semicrystalline domains and production of permanent entanglements is shown in the HBIB block copolymers. No such arrangement exists for the inverted polymer HIBI. (No attempt has been made to show possible chain folding, or superstructure development of their... 

The hysteresis behavior of the diblock copolymer HBI-50 is not shown but is very similar to that of HIBI-49. In summary then, the difference in hysteresis behavior of the HBIB series to that of HIBI and HBI is related to the ability of the members of the first series to form permanent entanglements, by entrapment of the end blocks in the semicrystalline domains, whereas no such arrangment is possible for neither HIBI nor HBI series. The permanent entanglement serves as a physical crosslink which promotes recovery of the polymer after the deforming stress has been removed. At the same time, much less energy is lost as heat. 

Taddei, P., and Monti, P. (2005). Vibrational infrared conformational studies of model peptides representing the semicrystalline domains of Bombyx mori sik fibroin. Biopolymers 78, 249-258. 

PFCs have recently been shown to prevent formation of a liquid condensed (semicrystalline) phase upon compression of a phospholipid film (Fig. 15). PFCs can also help dissolve semicrystalline domains after they have already formed. This fluidization effect facilitates the respreading of dimyristoylphosphatidylcho-line (DMPC), the main component of the lung surfactant, on the surface of lung alveoli upon inspiration [59], Experimentation on premature rabbits demonstrated a significant increase in tidal lung volume, allowing survival of the treated animals, while controls were all dead within minutes. PFCs may thus prove... 

PE-PEP diblock were similar to each other at high PE content (50-90%). This was because the mechanical properties were determined predominantly by the behaviour of the more continuous PE phase. For lower PE contents (7-29%) there were major differences in the mechanical properties of polymers with different architectures, all of which formed a cubic-packed sphere phase. PE-PEP-PE triblocks were found to be thermoplastic elastomers, whereas PEP-PE-PEP triblocks behaved like particulate filled rubber.The difference was proposed to result from bridging of PE domains across spheres in PE-PEP-PE triblocks, which acted as physical cross-links due to anchorage of the PE blocks in the semicrystalline domains. No such arrangement is possible for the PEP-PE-PEP or PE-PEP copolymers (Mohajer et al. 1982). 

A good affinity between the polymer phase and fillers can lead to a rigidified polymer region around the nanoparticles (Case 3, Fig. 7.6). The rednced mobility of the polymeric chains and the possible formation of semicrystalline domains close to the inorganic phase determine a reduction in the permeation coefficient. In this condition, the efficiency of the nanoparticles can also be threatened becanse of the reduced flux at the interface. However, the permeability decrease typically corresponds to an... 

There has been some criticism of the study by Jang et a/., which address the importance of the equilibration procedure for polymeric systems. Elliott and Paddison have argued that the difference in density between the MD simulated system and the experimentally measured values are due to incomplete chain relaxation or an erratic force field. Since later MD simulations of Nafion using similar force field provided good agreement in density, the latter can probably be ruled out. Jang et al. used a rather complex equilibration process, were the MD boxes were heated, and expanded and compressed several times in the NPT ensemble. The resulting densities (1.60 and 1.67 g/cm ) are 5-10% lower than experimental values, which can partly be explained by the lack of semicrystalline domains in the MD box, which do exist in real membranes and contribute to a somewhat increased density. 

Mangipudi et al. [63,88] reported some initial measurements of adhesion strength between semicrystalline PE surfaces. These measurements were done using the SFA as a function of contact time. Interestingly, these data (see Fig. 22) show that the normalized pull-off energy, a measure of intrinsic adhesion strength is increased with time of contact. They suggested the amorphous domains in PE could interdiffuse across the interface and thereby increase the adhesion of the interface. Falsafi et al. [37] also used the JKR technique to study the effect of composition on the adhesion of elastomeric acrylic pressure-sensitive adhesives. The model PSA they used was a crosslinked network of random copolymers of acrylates and acrylic acid, with an acrylic acid content between 2 and 10%. 

For instance, crystalline lamellae in an amorphous matrix (semicrystalline polymer materials), hard domains in a soft matrix (thermoplastic elastomers)... 

How should such rigid domain coupling work In principle domains can only be rigidly coupled by a bridge of hard-phase material which has a different density. We know that the polyester hard-phase is semicrystalline. So the observation is indicative for a structure in which the hard domains are subdivided into crystalline and amorphous zones. 

SEM micrographs of two members of these polymers (HB and HBIB-50) are shown in Figure 7 to provide further evidence for superstructure on the micron level within the solution cast films. One can directly observe the surface of the spherulitic structure of the HB homopolymer as well as in that of the copolymer HBIB-50. Clearly, the level of structure (-5 pm) is well above that of the individual domains of either HB or HI and reflects the possible primary nucleation and subsequent growth behavior common to spherulitic semicrystalline polymers. The Hv patterns shown in... 

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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