Interlamellar material

As can be seen from Table 4, two lower molecular weight samples actually comprise only the crystalline and noncrystalline interlamellar material, devoid of amorphous phase. On the other hand, the larger molecular weight samples comprise three phases the crystalline, amorphous, and crystalline-amorphous interphase in a similar fashion to the atmospheric-pressure crystallized samples. However, we note that the T2c s of the crystalline-amorphous interphase for two higher molecular weight samples is appreciably shorter than those of the atmospheric-pressure crystallized samples. This demonstrates that the molecular chain motion in the crystalline-amorphous interphase of these pressure-crystallized samples on a T2C time scale is more severely restricted. 

Cavitation is often a precursor to craze formation [20], an example of which is shown in Fig. 5 for bulk HDPE deformed at room temperature. It may be inferred from the micrograph that interlamellar cavitation occurs ahead of the craze tip, followed by simultaneous breakdown of the interlamellar material and separation and stretching of fibrils emanating from the dominant lamellae visible in the undeformed regions. The result is an interconnected network of cavities and craze fibrils with diameters of the order of 10 nm. This is at odds with the notion that craze fibrils in semicrystalline polymers deformed above Tg are coarser than in glassy polymers [20, 28], as well as with models for craze formation in which lamellar fragmentation constitutes an intermediate step [20, 29] but, as will be seen, it is difficult to generalise and a variety of mechanisms and structures is possible. 

Transmission electron mioro-graph of a sample crystallized at 523Kfor48h after etching at 453 K for 5.4 h with water to remove most of the amorphous interlamellar material. 

Figure 5.88 is an illustration of two-dimensional defects in the form of surfaces and grain boundaries. They either terminate a crystal or separate it from the three-dimensional defects. In polymer crystals, these surfaces and grain boundaries are rarely clean terminations of single-crystalline domains, as one would expect from the unit cell descriptions in Sect. 5.1. The surfaces may contain folds or chain ends and may be traversed by tie molecules to other crystals and cilia and loose loops that enter the amorphous areas, as is illustrated in Figs. 5.87 and 2.98. The properties of a polycrystalline sample are largely determined by the cohesion achieved across such surfaces and the mechanical properties of the interlamellar material, the amorphous defects. 

Since a substantial amount of material is contained in the interlamellar region, the properties of the latter give significant contributions to the overall material behavior. The properties of the interlamellar material he between those of the unconstrained amorphous melt and those of the crystalline phase [9-11], and the influence of the crystalline constraints can be addressed experimentally [12-14]. Furthermore, the properties of the crystal-melt interface have various ramifications that can be observed experimentally [15], e.g., interface stresses lead to distortion of the crystal lattice spacing [16-18], and they are possibly responsible for lamella twisting [19]. In addition, the surface tension enters in theoretical models for crystallization rates [20,21]. 

Reynolds [1967] has extended the MacEwan method to take account of the contribution to the structure factor of the interlamellar material. For the system glycol-montmorillonite-illite, this leads to a substantial change in the calculated intensities. 

Hydrophobic interactions and trapping of molecules in a molecular sieve formed by humic materials have been hypothesized as retention mechanisms for prometryn. It has been shown that fluridone, fluazifop, and bipyridyhum herbicides penetrate into interlamellar spaces of smectites and can become trapped. 

The formation of the microstructure involves the folding of linear segments of polymer chains in an orderly manner to form a crystalline lamellae, which tends to organize into a spherulite structure. The SCB hinder the formation of spherulite. However, the volume of spherulite/axialites increases if the branched segments participate in their formation [59]. Heterogeneity due to MW and SCB leads to segregation of PE molecules on solidification [59-65], The low MW species are accumulated in the peripheral parts of the spherulite/axialites [63]. The low-MW segregated material is brittle due to a low concentration of interlamellar tie chains [65] and... 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

Figure 9b, Real-space image of a new type of graphite intercalate (with FeCl2), There are two sheets of guest material accommodated in an expanded interlamellar space. Inset shows computed...

PCH materials offer new opportunities for the rational design of heterogeneous catalyst systems, because the pore size distributions are in the supermicropore to small mesopore range (14-25A) and chemical functionality (e.g., acidity) can be introduced by adjusting the composition of the layered silicate host. The approach to designing PCH materials is based on the use of intercalated quaternary ammonium cations and neutral amines as co-surfactants to direct the interlamellar hydrolysis and condensation polymerization of neutral inorganic precursor (for example, tetraethylorthosilicate, TEOS) within the galleries of an ionic lamellar solid. 

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