Diffusion polymer chains

Since the possibility of direct melt intercalation was first demonstrated [11], melt intercalation has become a method of preparation of the intercalated polymer/ layered silicate nanocomposites (PLSNCs). This process involves annealing, statically or under shear, a mixture of the polymer and organically modified layered fillers (OMLFs) above the softening point of the polymer. During annealing, the polymer chains diffused from the bulk polymer melt into the nano-galleries between the layered fillers. 

Consolidation and development of interlaminar bond strength for thermoplastic matrix composites have been modeled by two mechanisms intimate contact and autohesion. Intimate contact describes the process by which two irregular ply surfaces become smooth (Fig. 13.10). In areas in which the ply surfaces are in contact, autohesion occurs, and the long thermoplastic polymer chains diffuse across the ply boundaries. Filament winding with thermoplastic matrix materials is considered an on-line consolidation process in that local... 

Nanocomposites of MMT polymer can be obtained by direct polymer melt intercalation where the polymer chains diffuse into the space between the clay galleries. This process can be carried out through a conventional meltcompounding process [6, 4]. 

Much literature involves extensions of the reptation/tube model of deGennes, Doi, cmd Edwards. The deGennes model [44] was originally proposed to describe a linear polymer chain diffusing in the presence of fixed obstacles, such as those presented by a covalently-crosslinked gel. In the original model, the chains of the gel are rigidly locked in plcice,... 

In other words, within the time period from Xe to Xf, the polymer chain diffuses along the tube with the Rouse mode. Owning to the tube confinement, the scaling exponent of the original Rouse chain has been reduced into half. Therefore, the... 

One criterion to distinguish the miscibility of blends is the glass transition temperature (Tg) that can be measured with different calorimetric methods [95]. Tg is the characteristic transition of the amorphous phase in polymers. Below Tg, polymer chains are fixed by intermolecular interactions, no diffusion is possible, and the polymer is rigid. At temperatures higher than Tg, kinetic forces are stronger than molecular interactions and polymer chain diffusion is likely. In binary or multi-component miscible one-phase systems, macromolecules are statistically distributed on a molecular level. Therefore, only one glass transition occurs, which normally lies between the glass transition temperatures of the pure components. 

Polymer diffusion reptation and interdigitation R P WOOL Mechanisms for polymer chain diffusion... 

Crystallization is the competition between two processes nucleation and crystal growth. Nucleation is the formation of small sites (nuclei) from which crystallites can grow. Primary nucleation creates the initial nuclei. Crystallites develop aroimd these nuclei. Then in secondary nucleation, the surfaces of the crystallites are nucleated. More polymer chains diffuse to the crystallite surfaces and growth continues. 

Therefore, the value of K is proportional to the decrease in entropy experienced as the polymer chains diffuse into the pores of the packing and 0 [Pg.3371]

Polymer chains find it almost impossible to move sideways by simple translation, for such motion is exceedingly slow for long, entangled chains. This is because the surrounding chains that block sideways diffusion are also long and entangled, and sideways diffusion can only occur by many cooperative motions. Thus polymer chain diffusion demands separate theoretical treatment. 

Two types of experiments have been carried out using FRES, segregation of various species at surfaces and interfaces, and polymer chain diffusion. In order to carry out depth profiling via FRES, the data are convoluted with an instrumental resolution function, typically Gaussian. 

Of course, rapid quenching substantially freezes in the morphology. At room temperature, both polymers are below Tg, and polymer chain diffusion is essentially zero within the time scale of the following experiments. 

Polymer melt intercalation (involving a polymer and a layered siUcale mixture heated under discontinuous or continuous shear above the softening point of the polymer thus, the polymer chains diffuse from the molten polymer into the silicate galleries and form intercalated or exfoliated sheets). 

Both polymer and the nanofiUer are introduced simultaneously into a melt mixing device (extruder, internal mixer, etc.). This process involves annealing a mixmre of polymer and nanofiller above the softening point the polymer, statically or under the shear. During annealing, the polymer chains diffuse from the bulk polymer melt into the galleries between the nanofrller layers (Liu et al. 2012 Sinha Ray and Okamoto 2003). 

It is interesting that the enzymes responsible for the synthesis of the main extracellular polysaccharides (i.e. hyaluronan and cellulose) are localized in the cytoplasmic ceU membrane. During the synthesis, a growing polymer chain diffuses through the manbrane directly into extracellular space. Such a synthesis route is apparently more ancient and differs from the synthesis of other extracellular polysaccharides that are synthesized inside the cell and transported into extracellular media by the exocytosis mechanism. 

The way that polymer chains diffuse at an interface is of high practical importance for example for coating applications. This question, however, turned out to be rather complex and measurements as well as theoretical considerations are challenging. The reason for this complexity are the numerous interactions and conformations that have to be considered at interfaces. A variatimi of FCS that is quite suitable to investigate surfaces is TIR-FCS where the sensitivity of FCS measurements at solid-liquid interfaces is significantly enhanced [76-78], However, so far most FCS studies at interfaces have been performed in the classical way. ... 

In this section, we discuss the effect of flow by considering the first and third terms of Equation 9.7. The situation is sketched in Figure 9.5. As in Section 9.2, the polymer chains diffuse and get absorbed by a spherical sink of radius R, except that now the diffusion takes place in the presence of a fluid flow with the velocity v(r). The fluid flow is assumed to be directed along the x-axis as... 

The BD simulation discussed in this section can also be used in simulating small polymer chain diffusion in heterogeneous solute. Extra constraints, such as orientation constraints, hydrodynamic interactions and finite boundaries, can be added into Equation [8.30] in order to represent a heterogeneous solute. The effective diffusion coefficient of a non-uniform system is calculated by comparing the trajectories of small polymer chains in heterogeneous solute to a hypothetical homogeneous medium with the same boundary conditions. 

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