Core-shell gyroid structure

In the system of SIO triblock terpolymers detailed phase transition studies were carried out starting from a symmetric SI diblock copolymer with an increasing amount of PEO as the third block, with compositions between the lamellar diblock copolymer and the lamellar triblock terpolymer. Besides core-shell cylindrical and core-shell gyroid structures, pillared and perforated lamellar stmctures were found for compositions close to the lamellar diblock copolymer and lamellar triblock terpol)mer, respectively (Figure 23). To fine-tune the composition, blends of consecutive triblock terpolymers were used in various ratios and in these blends no significant differences from the thermodynamic properties of a block copolymer with the same net composition were found. As the molecular weight... 

The appearance and persistence of core-shell structures as well as the occurrence of phase separation are attributed to a small asymmetry in the X -parameters (xPS-pi = 0.06, xpi-pdms = 0.09 and xps-pdms = 0.20). Hence, a PDMS core surrounded by a PI shell embedded in a PS matrix results in a smaller inner diameter interfacial area, relative to that for the PS-PI case. In a blend of a PS-fo-PI-fc-PDMS triblock with PS and PDMS homopolymers, more PS homopolymer is expected to be found in the corona of the PS block than PDMS homopolymer in the corona of the PDMS block because the penalty for contact between the PI block and PDMS homopolymer is larger. In consequence, the distribution of homopolymers favours an expanded PS-PI interface, making the core-shell morphologies, gyroid and cylinder, more prevalent. 

Fig. 28 SEM images of about 60 nm thick films of SVT block terpolymers along with expected structural elements of the thin-film structure, (a) Core-shell cylinders (b) helices wound around a cylindrical core (c) (112) plane of an ideal double gyroid structure. Copyright (2002) Wiley. Used with permission from [18]...

Also block copolymers with more than three components have been studied. In principle, such systems can show more complex structures than the ones presented so far. A first systematic study has been published for tetrablock quaterpolymers, that are linear block copolymers with four chemically different blocks. In this case core-shell shell matrix morphologies analogous to the spheres, cylinders, and double gyroid known for diblock copolymers and lamellae (compare with Eigure 1) were found [170,171]. As a nice example, in Figure 13 core-shell shell cylinders are shown. 

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