Spherical domain morphology

Meier (9) has modeled the spherical domain morphology by a simple cubic lattice in which domains are arranged on the lattice sites. The tie molecules run between nearest-neighbor domains and are assumed to be confined by pairs of infinite, parallel walls. The extension ratio for the interdomain region is set equal to the macroscopic extension ratio divided by the volume fraction of the interdomain material. The ratio of the initial interdomain dimension to the domain dimension is set equal to the ratio of the volume fractions of the interdomain and domain material. Using this three-chain model, Meier calculates the stress-strain relation by differentiating his entropy expression with respect to the interdomain extension ratio. The Meier calculation has some difficulties the interdomain deformation fails to vanish in the absence of an applied macroscopic deformation the relation between the ratio of the domain dimension to the initial interdomain dimension and the ratio of volume fractions is incorrect and the differentiation should be carried out with respect to the macroscopic extension ratio. 

Gaylord and Lohse (10) have calculated the stress-strain relation for cilia and tie molecules in a spherical domain morphology using the same type of three-chain model as Meier. It is assumed that the overall sample deformation is affine while the domains are undeformable. It is predicted that the stress increases rapidly with increasing strain for both types of chains. The rate of stress rise is greatly accelerated as the ratio of the domain thickness to the initial interdomain separation increases. The results indicate that it is not correct to use the stress-strain equation obtained by Gaussian elasticity theory, even if it is multiplied by a filler effect correction term. No connection is made between the initial dimensions and the volume fractions of the domain and interdomain material in this theory. 

Partial Molar Elastic Free Energy of Swelling. Leonard (8) calculated the partial molar elastic free energy of swelling for an interdomain tie molecule in a spherical domain morphology. He included the entropy... 

Di-Block Copolymers with Spherical Domain Morphology. . . . 311... 

Di-block Copolymers with Spherical Domain Morphology... 

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. 

Two-phase domain morphology, of approximately spherical shape, comprising two polymers, each in separate phase domains, in which phase domains of one polymer completely encapsulate the phase domains of the other polymer. 

Figure 13 shows the TEM micrograph of a star block containing 22% PpClSt. The morphology shows phase-separated domains of PpClSt and PIB. The PpClSt formed spherical domains with diffused interphase and are irregularly dispersed in the PIB matrix. The formation of irregular domains with diffused interphase is attributed to the presence of diblock and PpClSt contaminants. 

The morphology of a polyethylene blend (a homopolymer prepared from ethylene is a blend of species with different molar mass) after crystallisation is dependent on the blend morphology of the molten system before crystallisation and on the relative tendencies for the different molecular species to crystallise at different temperatures. The latter may lead to phase separation (segregation) of low molar mass species at a relatively fine scale within spherulites this is typical of linear polyethylene. Highly branched polyethylene may show segregation on a larger scale, so-called cellulation. Phase separation in the melt results in spherical domain structures on a large scale. 

Fig. 23. Micrograph of a craze in a di-block with spherical morphology. Note the very narrow nature of the craze involving only about a layer of one spherical domain...

Figure 13.2 Illustration of the network morphology of a microphase-separated triblock copolymer with the glassy end blocks in hard spherical domains bridged by the rubbery center blocks.

The source of elasticity in block copolymers containing well-ordered spherical domains is analogous to that for simple three-dimensional erystalline solids. When a mechanical deformation displaces spherical domains from their equilibrium lattice positions, the domains are pulled back by the thermodynamic forces that are responsible for the existence of the macrocrystalline order in the static sample. Similar forces exist when the domains are cylindrical or lamellar, but these latter morphologies, if well-ordered and oriented appro-priately, can sustain shearing deformations without displacement of the domains from their equilibrium positions, since they are not ordered in all dimensions as spherical domains are. 

Figure 8.20 also shows the phase morphology of the cured material. The SEM micrograph was taken from a fractured and etched surface so that remaining material is cured epoxy. The connected-globule structure can be explained as a two-phase morphology of interconnected spherical domains of the epoxy-rich phase dispersed in a PES matrix. 

---