Diblock Copolymers Block-Anchored to Homopolymer Interfaces

Diblock Copolymers Block-Anchored to Homopolymer Interfaces 

Diblock copolymers A-N immersed in a homopolymer P matrix segregate to its interfaces. One of the copolymer blocks ( anchor moiety A) selectively attaches to the interface while the other ( buoy block N) dangles out to form a brush like layer, providing a simple means for the realization of polymer brushes (see Fig. 33). 

a Schematic illustration of N-mer brush layer created by diblock copolymers A-N attached selectively to the interface by their anchor moiety A. Copolymers in the brush layer are in equilibrium with free diblocks incorporated in the bulk region of the sample abundant in homopolymer P. b The form of the diblock volume fraction vs depth ( )(z) profile used in theoretical model, c Potential U(z) affecting the anchor moiety A and driving the diblock segregation 

This name covers all polymer chains (diblocks and others) attached by one end (or end-block) at ( external ) solid/liquid, liquid/air or ( internal ) liquid/liq-uid interfaces [226-228]. Usually this is achieved by the modified chain end, which adsorbs to the surface or is chemically bound to it. Double brushes may be also formed, e.g., by the copolymers A-N, when the joints of two blocks are located at a liquid/liquid interface and each of the blocks is immersed in different liquid. A number of theoretical models have dealt specifically with the case of brush layers immersed in polymer melts (and in solutions of homopolymers). These models include scaling approaches [229, 230], simple Flory-type mean field models [230-233], theories solving self-consistent mean field (SCMF) equations analytically [234,235] or numerically [236-238]. Also first computer simulations have recently been reported for brushes immersed in a melt [239]. 

Here we outline a mean field Flory-type model introduced by de Gennes [230] and developed by Leibler [231] and Aubouy and Raphael [232]. This approach is less detailed than SCMF models but it captures the main features of the physics of segregated copolymers. Even though it makes a number of assumptions, which are a simplification in comparison with the SCMF models, its predictions of the main features (such as, e.g., variation of mean brush height L vs size and surface density o of the diblocks) agree [226] well with those of more detailed SCMF calculations [236-238]. Because of clearness and simplicity it has been used as a basic framework for many experimental papers on brush conformation [240-245] and segregation properties of end-adsorbing polymers [246-255]. 

---