Lamellae thickness

The effect of different types of comonomers on varies. VDC—MA copolymers mote closely obey Flory s melting-point depression theory than do copolymers with VC or AN. Studies have shown that, for the copolymers of VDC with MA, Flory s theory needs modification to include both lamella thickness and surface free energy (69). The VDC—VC and VDC—AN copolymers typically have severe composition drift, therefore most of the comonomer units do not belong to crystallizing chains. Hence, they neither enter the crystal as defects nor cause lamellar thickness to decrease, so the depression of the melting temperature is less than expected. 

The order in PA can be studied by WAXS and SAXS. WAXS gives insights into the unit cell sttucture, the crystallinity, the crystallite size (if not too large), and the crystallite orientation. SAXS gives a more accurate measure of the lamella thickness. In a temperature sweep, the changes in structure with temperature can be followed. 

Similar types of lamellar morphologies were observed for triblock copolymers of diphenylsiloxane and dimethylsiloxane having 40 wt% polydiphenylsiloxane, using electron microscopy, 47-148>. The lamellae thickness was approximately equal to the chain length of the rigid polydiphenylsiloxane blocks. These copolymers showed elastomeric properties comparable to those of conventional silica-reinforced, chemically crosslinked silicone rubbers. Tensile tests yielded an initial modulus of 0.5-1 MPa, tensile strength of 6-7 MPa and ultimate elongation between 400 and 800 %. 

Figure 6. Evolution of the lamella thickness as it transports down the periodic pore for the conjoining/disjoining pressure isotherm of Figure 4. Three capillary pressures are considered in curves 1 through 3. These capillary-pressure values are also labelled in Figure 4. Curve 2 defines the critical or marginally...

Fig. 7 Lamella thickness 2.5 ns after quench to each crystallization temperature ( ), and that after annealing 6.4 ns (o). At 250 K and 300 K, the lamella is still thickening even after 6.4 ns by an appreciable rate...

The lamella thickening depends sensitively on the initial lamella thickness as well as on the annealing temperature. We first considered the thickening of very thin lamella of about 18-bonds thick this thickness nearly corresponds to that of the lamella crystallized at 0 K (Fig. 7). The temperature of annealing Ta was taken between 20 K and 150 K a quick jump to a higher temperature resulted in partial melting and re-crystallization and a continuous thickening process could not be observed. 

Fig. 15 Limiting thickness of the lamella plotted vs. crystallization temperature. The lamella thickness shows steep increases around the melting point...

Another shortcoming of the present model is that the MD cell size in the y-axis direction, the direction parallel to the crystalline chain axis, was rather small. There must be serious size effects along this direction, even if we adopt the periodic condition in this direction. Here again we need a much larger MD cell in order to reproduce the lamella thickness vs. temperature relation in crystallization from the melt. 

A value of 102 erg/cm2 for the ys of the end surfaces of the low-melting form of poly-trans-1,4-isoprene was derived80 in the same manner. The lamella thickness... 

The structure of crystalline polymers may be significantly modified by the introduction of fillers. All aspects of the structure change on filling, crystallite and spherulite size, as well as crystallinity, are altered as an effect of nucleation [9]. A typical example is the extremely strong nucleation effect of talc in polypropylene [10,11], which is demonstrated also in Fig. 2. Nucleating effect is characterized by the peak temperature of crystallization, which increases significantly on the addition of the filler. Elastomer modified PP blends are shown as a comparison crystallization temperature decreases in this case. Talc also nucleates polyamides. Increasing crystallization temperature leads to an increase in lamella thickness and crystallinity, while the size of the spherulites decreases on... 

The spectrum for samples with a very low molecular weight, ie., lower than about 1000, is fairly independent of the mode of crystallization, whether from the melt or from dilute solution. The spectrum is characterized by a very large broad component (wb 0.95) and a medium component with a large second moment, but no narrow component. In such samples the extended molecular chain length will be comparable to or slightly larger than the lamella thickness. The conformation of molecular chains to form the lamellar crystallites will be similar to that depicted schematically in Fig. 10 (B), independent of the crystallization mode. 

The lamella size - 100-500A A multiple of the lamella thickness, say 1 fi The crystal unit cell. 

M oreover, Figure 1.90 shows that not all lamellae have absolutely equal thickness, as opposed to the observations in Figure 1.89. The thickness decreases from the interior towards the exterior. An analysis of the lamellae thickness at various cross-sectional positions was derived by precise measurement of the respective high-... 

The depression of the orthorhombic/hexagonal transition temperature for lamellae thickness k follows from equating the differential surface and compensating volume contributions to the free energy according to the geometry of Fig. 4. Thus... 

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