Immobilized amorphous phase

From the simultaneous SWD-experiments the following attempt to relate structure and dynamics can be made. For times shorter than a characteristic one t 90 min) the decrease of (Ae), Fig. 21.9a, indicates a significant reduction of the mobile material which follows the increase of crystalUnity (Fig. 21.9e). However, the reduction of (Ae), is stronger than the increment in crystallized material as determined by the increase of Xc- This effect, observed in different polymers [13,17], can be attributed to the formation of an immobilized amorphous phase frequently referred to as rigid amorphous phase (RAP) [40]. 

When samples are immersed in water a significant decrease of the contact angle of water is observed. The change from the solid line with open circles to the dotted line with closed circles indicates the extent of contact angle change. The extent of decrease was inversely proportional to the crystallinity of the sample, which indicates that the surface configuration change occurs mainly in the amorphous phase in the surface state, i.e., F atoms attached to the crystalline surface are immobile. 

Low-pressure cascade arc torch polymerization or coating could be considered more or less the same as the plasma polymerization or coating by other conventional plasma processes. The ultrathin layers prepared by LPCAT polymerization have the general characteristics of plasma polymers, i.e., amorphous (noncrystalline), high concentration of the dangling bonds (free radicals trapped in immobile solid phase), and the high degree of the internal stress in the layer. 

During polymerization with Cr /silica in the solution process, the polymer is formed, and remains, in hydrocarbon solution. In this situation, the macromer insertion mechanism of Scheme 24A seems intuitive and plausible, because the terminated chain is free and mobile in solution and can be considered to be just another (albeit large) reactive comonomer. However, in the slurry and fluidized-bed processes, the polymer chains are not in solution, but instead they are "frozen out" or immobilized in a solid-phase immediately as they are formed. Therefore, this conventional mechanism of macromer incorporation is intuitively less likely, because it is not clear how the vinyl end-groups have access to the active sites. This issue is seldom considered in the literature. One possible explanation is that the active sites are embedded in the amorphous phase of the polymer, and that chain ends, being excluded from crystallites, are therefore concentrated into this same phase, where they do have some degree of limited motion (Scheme 24B). 

The chain immobilization term indirectly reflects the amount of increase in activation energy of diffusion that is observed in the amorphous phase upon crystallization. 

The films crystalline volume fraction does not change after anneaiing at 120 °C, and so the amorphous phase volume fraction is constant during the dielectric measurements at the annealing temperature employed. In subsequent analyses, we make the usual assumption that crystalline units are immobile relative to amorphous units and do not contribute to relaxations. 

Moreover, most researchers agree that protection by compounds such as lactose and trehalose depends on the formation of an amorphous phase with the protein [15], The proteins are mechanically immobilized in the glassy, solid matrix during dehydration. The restriction of translational and relaxation processes is thought to prevent protein unfolding, and spatial separation between the protein molecules (i.e dilution of protein molecules within the glassy matrix) is proposed to prevent aggregation [12],... 

In Eq. (46), the subscript p refers to values in the primary particles. Equation (47) has been suggested to estimate the effective diffusivity of monomer in the primary particle, where Do is the diffusivity of monomer in amorphous polymer and / and i are correction factors to account for the decrease in diffusivity due to chain crystallinity and immobilization of the polymer amorphous phase due to the crystallites. As can be very well imagined, these parameters are also hard to determine and Dp is generally used as an adjustable parameter in the model. 

Based on the rigidification concept, Mahajan [25] has developed an approach in which the Maxwell model is used twice. The polymer region in the vicinity of the CMS particle is assumed to have reduced permeabihty due to the immobilization effect. This is an extension of the concept given for the semi-crystalline polymer. When crystallites are present within an amorphous phase the chain mobility of the amorphous phase appears to be reduced leading to high activation energy of diffusion. Michaels et al. introduced chain irmnobilization factor p by which the overall diffusion coefficient ) is given by... 

In Figure 7-26 are shown CP-MAS NMR spectra of PG-12 as a function of temperature. Below -20° C, both of peaks for the side chains and the main chain are broad, and the mobility for them is in region A. At 0° C, the NMR chemical shift of the int-CHj carbons moves upfield and the intensity of the OCHj carbon becomes very weak. The side chains are in region B at this temperature. The NMR chemical shift of the int-CH2 carbons of PG-12 moves upfield by about 3 ppm as the temperature is raised from -20° C to 0° C. Above 0° C, the chemical shift value of ca. 30 ppm indicates that the side chains are in the amorphous phase. Below 0°C, the NMR chemical shift is about 32.9 ppm. Therefore, it shows that the int-CH2 carbons take the all-trans zigzag conformation in the immobile state. Therefore, the drastic change in the side chains between -20 and 0° C shows the melting of the side-chain crystallite. 

Crystallization, whereby the polymer chains are immobilized due to the formation of an ordered crystalline phase. Many of the polymers are semi-erystalline, whieh eonsist of both an unordered amorphous phase and an ordered crystalline phase. 

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