Interfaces block copolymer phases

Highly branched polymers, polymer adsorption and the mesophases of block copolymers may seem weakly connected subjects. However, in this review we bring out some important common features related to the tethering experienced by the polymer chains in all of these structures. Tethered polymer chains, in our parlance, are chains attached to a point, a line, a surface or an interface by their ends. In this view, one may think of the arms of a star polymer as chains tethered to a point [1], or of polymerized macromonomers as chains tethered to a line [2-4]. Adsorption or grafting of end-functionalized polymers to a surface exemplifies a tethered surface layer [5] (a polymer brush ), whereas block copolymers straddling phase boundaries give rise to chains tethered to an interface [6],... 

PS and PB homopolymers are immiscible. Any added PB-PS block copolymer in a PS-PB blend will have one sequence miscible in PS and one sequence miscible in PB, hence they will localise at the interface. As a consequence, the interfacial energy will decrease, greatly helping dispersion and providing phase adhesion, thus a transfer of mechanical properties. 

Fig. 34 Illustration of A B miktoarm star-block copolymer, a AB4 diblock copolymer with A arm depicted by dashed line and B arms depicted by solid lines. b AB interfaces for A15 phase shown in Pm 3 n unit cell (extracted from SCFT results for n = 5 at yN = 40 and tfi = 0.349 [along Hex-Al5 phase boundary] vide infra). From [112]. Copyright 2004 American Chemical Society, c A B miktoarm-star block copolymer with n = 4. From [121]. Copyright 2003 American Chemical Society... 

Additionally, some properties unique to both systems may result. The majority of homopolymer blends are immiscible with one another and often experience poor interfacial adhesion between the separate phases. Since block copolymers are covalently linked together, macroscopic incompatibility at the interface is minimized. The macroscopic incompatibility of a two-polymer blend may be eliminated by the addition of a block copolymer derived from the two systems. Hence, copolymers can be used to strengthen blends of immiscible polymers by serving as emulsifiers (7-9). 

In addition to the previously mentioned driving forces that determine the bulk state phase behavior of block copolymers, two additional factors play a role in block copolymer thin films the surface/interface energies as well as the interplay between the film thickness t and the natural period, Lo, of the bulk microphase-separated structures [14,41,42], Due to these two additional factors, a very sophisticated picture has emerged from the various theoretical and experimental efforts that have been made in order to describe... 

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