Segregation of block copolymers

In a blend of immiscible homopolymers, macrophase separation is favoured on decreasing the temperature in a blend with an upper critical solution temperature (UCST) or on increasing the temperature in a blend with a lower critical solution temperature (LCST). Addition of a block copolymer leads to competition between this macrophase separation and microphase separation of the copolymer. From a practical viewpoint, addition of a block copolymer can be used to suppress phase separation or to compatibilize the homopolymers. Indeed, this is one of the main applications of block copolymers. The compatibilization results from the reduction of interfacial tension that accompanies the segregation of block copolymers to the interface. From a more fundamental viewpoint, the competing effects of macrophase and microphase separation lead to a rich critical phenomenology. In addition to the ordinary critical points of macrophase separation, tricritical points exist where critical lines for the ternary system meet. A Lifshitz point is defined along the line of critical transitions, at the crossover between regimes of macrophase separation and microphase separation. This critical behaviour is discussed in more depth in Chapter 6. 

Block copolymers, which combine polymer segments with different properties, are presumably the most widely examined system for the study of self-assembly to large-scale structures that have controlled structural and functional features on the nanometer length scale [80, 81]. Phase segregation of block copolymers, followed by selective degradation of one polymer block, leads to highly ordered porous 3D structures [82], The pore dimensions obtainable are in the micro- and mesoporous range (<50 nm), which do not meet the requirements for cellular infiltration. 

Nanostructured Interfaces by Surface Segregation of Block Copolymers... 

At the same time, based on the microphase separation occurring in block copolymers blends, including the latter may result in phase separated films exhibiting nano-domains. The formation of nanostructured domains at the interface induced by surface segregation of block copolymers is an interesting strategy to fabricate surfaces with controlled functionality and patterned in one single step. 

Yokoyama, H., Miyamae, T., Han, S., Ishizone, T., Tanaka, K., Takahara, A., et al. Spontaneously formed hydrophilic surfaces by segregation of block copolymers with water-soluble blocks. Macromolecules 38, 5180-5189 (2005)... 

Shull, K.R., Kramer, E.J., Hadziioannou, G., Tang, W. Segregation of block copolymers to interfaces between immiscible homopolymers. Macromolecules 23(22), 4780-4787 (1990)... 

K.R. Shull, E.J. Kramer, G. Hadziioannou, T. Wing, Segregation of Block Copolymers to Interfaces Between Immiscible Homopolymers, 1990, pp. 681-685. 

K.R. Shull, K.I. Winey, E.L. Thomas, E.J. Kramer, Segregation of block copolymer micelles to surfaces and interfaces. Macromolecules 24 (1991) 2748-2751. 

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