Crystalline Filled

Fig. 4.28 First cycle work input W on loading to e = 3, plotted versus degree of crystallinity. Filled symbols = MDl-based polymers open symbols = DBDl-based polymers. Lines are only to guide the eye they link materials differing only in diisocyanate (full lines) or in chain extender (dashed lines) [135]...

Figure 4A.20. Electrochemical three-electrode impedance complex-plane plots for the real (R) and the imaginary (X) parts of the impedance of crystalline (filled squares) and disordered (filled circles) WO3 recorded at 2.9 V vs. Li (StrOmme Mattsson [2000]). This equilibrium potential corresponds to -0.004Li/W unit for the aystalline film and 0.03 LiAV for the amorphous one (Strpmme Mattsson [2000]). Included in the figure are also fits (open squares for crystalline and open circles for disordered WO3) to the Randles circuit in Figure 4.3.17. Explicit frequency readings are shown at a few selected data points.

The field ion microscope (FIM) has been used to monitor surface self-diflfiision in real time. In the FIM, a sharp, crystalline tip is placed in a large electric field in a chamber filled with Fie gas [14]. At the tip. Fie ions are fonned, and then accelerated away from the tip. The angular distribution of the Fie ions provides a picture of the atoms at the tip with atomic resolution. In these images, it has been possible to monitor the diflfiision of a single adatom on a surface in real time [15]. The limitations of FIM, however, include its applicability only to metals, and the fact that the surfaces are limited to those that exist on a sharp tip, i.e. difhision along a large... 

The reason for the constancy and sharpness of the melting j)oint of a pure crystalline solid can be appreciated upon reference to Fig. 7,10, 1, in which (a) is the vapour pressure curve of the solid and (6) that of the liquid form of the substance. Let us imagine a vessel, maintained at constant temperature, completely filled with a mixture of the above liquid and solid. The molecules of the solid can only pass into the liquid and the molecules of the liquid only into the solid. We may visualise two competitive processes taking place (i) the solid attempting to evaporate but it can only pass into the liquid, and (ii) the liquid attempting to distil but it can only pass into the solid. If process (i) is faster, the solid will melt, whereas if process (ii) proceeds with greater speed the... 

In order for a plasticizer to enter a polymer stmcture the polymer should be highly amorphous. Crystalline nylon retains only a small quantity of plasticizer if it retains its crystallinity. Once it has penetrated the polymer the plasticizer fills free volume and provides polymer chain lubrication, increa sing rotation and movement. 

Highest thermal performance with PPS compounds requires that parts be molded under conditions leading to a high level of crystallinity. Glass-filled PPS compounds can be molded so that crystalline or amorphous parts are obtained. Mold temperature influences the crystallinity of PPS parts. Mold temperatures below approximately 93°C produce parts with low crystallinity and those above approximately 135°C produce highly crystalline parts. Mold temperatures between 93 and 135°C yield parts with an intermediate level of crystallinity. Part thickness may also influence the level of crystallinity. Thinner parts are more responsive to mold temperature. Thicker parts may have skin-core effects. When thick parts are molded in a cold mold the skin may not develop much crystallinity. The interior of the part, which remains hot for a longer period of time, may develop higher levels of crystallinity. 

These phenomena are most rapid and easiest to observe in fairly concentrated aqueous detergent solutions, that is, minimally 2—5% detergent solutions. In a practical quaHtative way, this is a familiar effect, and there are many examples of the extraordinary solvency and cleaning power of concentrated detergent solutions, for example, in the case of fabric pretreatment with neat heavy-duty Hquid detergents. Penetration can also be demonstrated at low detergent concentrations. As observed microscopically, the penetration occurs in a characteristic manner with the formation of a sheathlike stmcture, termed myelin they are filled with isotropic Hquid but have a Hquid crystalline birefringent skin. 

Amorphous nylons are transparent. Heat-deflection temperatures are lower than those of filled crystalline nylon resins, and melt flow is stiffer hence, they are more difficult to process. Mold shrinkage is lower and they absorb less water. Warpage is reduced and dimensional stabiUty less of a problem than with crystalline products. Chemical and hydrolytic stabiUty are excellent. Amorphous nylons can be made by using monomer combinations that result in highly asymmetric stmctures which crystalline with difficulty or by adding crystallization inhibitors to crystalline resins such as nylon-6 (61). 

ABS, polycarbonate and polysulphone) but large effects on crystalline polymers. It is particularly interesting, as well as being technically important, that for many crystalline polymers the unfilled polymer has a heat deflection temperature (at 1.82MPa stress) similar to the Tg, whereas the filled polymers have values close to the T (Table 9.2). 

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