Lamellar morphologies

The details of the lamellar morphology, such as crystalline layer thickness l and amorphous layer thickness /, are quantitatively evaluated using SAXS [18]. For example, they are conveniently derived from the one-dimensional correlation function, that is, Fourier transform of SAXS curves, assuming an ideal lamellar morphology without any distribution for and l [19]. More detailed information on the lamellar morphology can be obtained by fitting theoretical scattering curves (or theoretical one-dimensional correlation functions) calculated from some appropriate model to SAXS curves (or Fourier transform of SAXS curves) experimentally obtained. The Hosemann model in reciprocal space [20] and the Vonk model in real space [7,21] are often employed for such purposes. 

In the Hosemann model, which is based on a paracrystalline model, each crystalline region consists of N alternating stacks of crystalline and amorphous layers. The scattered intensity I(s) calculated from this model as a function of s is given by 

The parameters included in this model can be evaluated by fitting Equation 10.5 to I(s) experimentally obtained. 

The Vonk model is characterized by an infinite number of alternating units of crystalline and amorphous layers. The one-dimensional correlation function y(x) derived from this model is expressed as 

Four parameters, l, 1, and can be determined by curve-fitting procedures using the long period L (=lc + la) determined from the first maximum of experimental correlation functions. However, the parameters obtained do not have an equal accuracy. 

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Lamellar morphology variables in semicrystalline polymers can be estimated from the correlation and interface distribution fiinctions using a two-phase model. The analysis of a correlation function by the two-phase model has been demonstrated in detail before [30,11] The thicknesses of the two constituent phases (crystal and amorphous) can be extracted by several approaches described by Strobl and Schneider [32]. For example, one approach is based on the following relationship ... 

Figure Bl.9.13. Time-resolved SAXS profiles diirmg isothennal crystallization (230 °C) of PET (the first 48 scans were collected with 5 seconds scan time, the last 52 scans were collected with 30 seconds scan time) calculated correlation fiinctions j(r) (nonnalized by the invariant 0 and lamellar morphological variables...

Morphology of the anionically synthesized triblock copolymers of polyfp-methyl-styrene) and PDMS and their derivatives obtained by the selective chlorination of the hard segments were investigated by TEM 146). Samples with low PDMS content (12%) showed spherical domains of PDMS in a poly(p-methylstyrene) matrix. Samples with nearly equimolar composition showed a continuous lamellar morphology. In both cases the domain structure was very fine, indicating sharp interfaces. Domain sizes were estimated to be of the order of 50-300 A. 

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 %. 

SEES with oil leads to the transition from lamellar morphology to micellar morphology [15]. This transformation is reflected in the above images of pure SEES and its SEES/oil = 60 40 composition. The loading leads to an increase of the structural factor from 21 to 53 nm. Therefore, the incorporation of oil to ethylene-butylene blocks induced larger separation of micelles formed predominantly by styrene blocks. 

Tao C, Zheng S, Mohwald H, Li J (2003) CdS crystal growth of lamellar morphology within templates of poly electrolyte/surf actant complex. Langmuir 19(21) 9039-9042... 

A remarkable feature common to both iPP and sPP is that the lamellar morphological units of the mesophase obtained at ca. 0 °C evidenced by electron microscopy [38,39], hardly change in lateral size, thickness, or shape upon annealing and recrystallizing into the stable crystal form at about 80 °C. 

It has recently been shown (7) that a transformation from fibrillar to lamellar morphology is not required to replicate the force-temperature profile of stretched networks in the crystallization region. This latest work shows that a close duplication of the behavior of gutta percha (8) can be predicted with a model (7) of fibrillar crystallization that Incorporates several new features omitted in earlier theories, specifically ... 

The elastic free energy AFe causes difficulty because of its sensitivity to the crystallization model assumed. To estimate AFe for lamellar morphology, consider first an important property of a network, amorphous or crystalline. Network crosslinks are considerably restricted in their fluctuations. Fluctuations of crosslinks several chains removed from a particular chain are therefore inconsequential for that chain. A chain in the interior of a path traced through several sequentially connected chains behaves as if the path ends are securely anchored at fixed positions ( 7). If Gj chain vectors make up the path, then... 

A sketch of the perforated lamellar morphology is depicted in Fig. 2. Depending on the point of view, the 2D projection exhibits different patterns perpendicular to the layers of the perforated lamellar structure the projection appears like a hexagonal honeycomb mesh (Fig. 2a). By contrast, the parallel view (Fig. 2b) leads to rows of spots. 

Fig. 29 Cartoon demonstrating arrangement of dendrons in hexagonally dose-packed cylinder morphology (left) or in lamellar morphology (right). From [93]. Copyright 2002 American Chemical Society...

Homogeneous melt, Todt < Tc > Tg. In diblock copolymers exhibiting homogeneous melts, microphase separation is driven by crystallization if Tg of the amorphous block is lower than Tc of the crystallizable block. This generally results in a lamellar morphology where crystalline lamellae are sandwiched by the amorphous block layers and spherulite formation can be observed depending on the composition [6-10]. 

Ueda et al. [26] recently investigated a flow-oriented PE-fr-aPP diblock copolymer with Mw = 113 000 (Mn/Mw = 1.1) and a PE volume fraction of 0.48. This diblock copolymer is in the strong segregation regime (i.e., estimated xN = 10.5 and Todt = 290 °C) and has a lamellar morphology in the melt. They found a breakout phenomenon with the formation of spherulites in an intermediate crystallization temperature range 95 < Tc < 101 °C. At crystallization temperatures above 101 °C or below 95 °C spherulites were not formed and the crystallization was confined within the lamellar MD. Ueda et al. report that lamellar MD and spherulites do not co-exist when the material crystallizes from the melt which is separated in lamellar MDs. In other words, in this particular case, breakout or confined crystallization within lamellar MDs depends on the crystallization conditions. 

Analysis of S-SEBS by SAXS has revealed the presence of cylindrical morphologies for a degree of sulfonation of <34%. Interestingly, different morphologies can also be observed when membranes are cast from different solvents. Membranes (27 mol% degree of sulfonation) cast from THE form lamellar morphologies, as seen in Figure 3.27, while those cast from MeOH/ THE (tetrahydrofuran) (20/80 v/v) exhibit a diffusive phase boundary with disorderly interconnections between domains. This is due to the differences... 

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