Lamellar phases domain morphology

The domain spacing and interfacial area per block were determined for blends of PS-PI diblocks in PS for a < 1 using SAXS by Hashimoto et al (1990). The domain spacing was found to increase with increasing homopolymer volume fraction, as depicted in Fig. 6.7 for blends of a diblock forming a lamellar phase in the melt. Addition of homopolymer leads to transitions to other morphologies... 

UsingTEM to identify blend morphology, two diblocks with/ps 0.8 that form cubic-packed spherical phases and cylindrical phases respectively in the pure copolymer were found not to macrophase separate in a blend with d = 2.2, but to form single domain structures (cylinders or spheres) in the blend (Koizumi et al. 1994c). Similarly, blending a diblock with fK = 0.26 with one with fK = 0.64 (d = 1.2) led to uniform microphase-separated structures, with a lamellar phase induced in the 50 50 blend. Vilesov et al. (1994) also observed that blending two PS-PB diblocks with approximately inverse compositions (i.e. 22wt% PS and 72 wt% PS) induces a lamellar phase in the 50 50 blend. These examples all correspond to case (i). 

Although no exact correlation between experiment and model was produced by this exercise, it has been shown that the two polymers studied exhibit phase-separated morphologies that are similar in nature to the extent that they are subject to nearly identical polarizations. The large polarizations measured can only be explained by high interfacial areas, congruent with semicrystalline lamellar morphologies. Finally, the divergence of the observed polarizations from those predicted by the two-phase model is quite likely due to the existence of finite-thickness, transition zones between dissimilar domains. 

The morphological feature is in accordance with that of binary blends of iPP and true diblock iPP-b-EPR copolymers (63). For the immiscible blends showing phase separation, the EP domains have no ability to affect the lamellar or crystalline morphology of iPP. It follows that the strength of iPP lamellae is essentially independent of the addition of EP copolymers although the magnitude of bulk stress is reduced by the addition of EP copolymers with a lower modulus. 

It was suggested [284] that the perforated lamellar phase may form via the growth of branched and multiconnected threadlike micelles. Interconnection of threadlike micelles reduces the overall curvature of the monolayer making up the micelles and thereby reflects a preference for microstructures of decreasing curvature [119]. The suggested morphological sequence for the system cetylpyridinium chloride-hexanol-brine is spheres, small disks, long capped cylinders, branched cylinders, perforated bilayers, smooth bilayers, loose network of connected bilayers (foamlike structure), and multiphasic domain [284]. 

Figure 2.3 Microphase separation in diblock copolymers. The shaded regions represent domains rich in A or B monomers, (a) /a = /b = 1/2, lamellar phase separation with flat domain interfaces, (b) /a > 1/2, spontaneous curvature of domains toward the minority phase in gyroidal, cylindrical, or spherical morphologies. The characteristic domain spacing A is typically in the range 10-100 nm.

Rod-coil diblock copolymers with a relatively short rod segment self-assembled into a wavy-lamellar morphology, while increasing the rod fraction resulted in the formation of a zigzag lamellar phase. At rod fractions/phic of 0-96 and 0.98, the PS coils were found to organize into arrowhead-shaped domains embedded in a PHIC matrix. Unlike the self-assembly of the PPP-17-PS and PPQ-b-PS diblock copolymers, the unconventional morphologies discovered for the PHIC-I7-PS rod-coils are related to their macromolecular architecture and are... 

Fig. 30 Schematic phase morphologies of binary cylindrical bottle brushes Janus cylinder (left), Janus dumbbell (middle) and lamellar-like (right) morphologies. The red and blue domains are filled by the A and B monomers interfacial regions are green. From [99]...

Figure 2 Schematic of morphologies for linear ABC triblock copolymer. A combination of block sequence (ABC, ACB, BAC), composition, and block molecular weights provides an enormous parameter space for the creation of new morphologies. Microdomains are colored as shown by the copol3mer strand at the top, with monomer types A, B, and C confined to regions colored blue, red, and green, respectively, (a) Lamellar phase, (b) coaxial cylinder phase, (c) lamella-cylinder phase, (d) lamella-sphere phase, (e) cylinder-ring phase, (f) cylindrical domains in a square lattice structure, (g) spherical domains in the CsCl type stmcture, (h) lamella-cylinder-II, (i) lamella-sphere-II, (j) cylinder-sphere, (k) cocentric spherical domain in the bcc structure. (Reproduced with permission from Ref. 33. American Chemical Society, 1995.)...

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