No abstract

A general theory for microstructure in systems of copolymers with strongly interacting groups (SIGs) is proposed. The so-called superstrong segregation limit, corresponding to rather short blocks containing SIGs and strong attraction between them, is considered in detail. In particular, multiplet formation in melts and solutions of ionomers (block ionomers) is studied. It is shown that as the interaction parameter increases, the most stable shape of a multiplet continuously changes from spherical to disklike (oblate ellipsoid). A further increase of the interaction parameter induces another (first order) transition from disklike multiplets to lamellae. The same transitions could be induced by decreasing the average length of ionic blocks in block ionomer systems. The relevant experimental observations are discussed.

Equilibrium and dynamics of block-copolymer chains in a homopolymer layer (between the interface with another homopolymer and the free surface) are considered. An analytical mean-field theory for equilibrium copolymer segregation to the interface is presented, the results being in good agreement with those of another theoretical approach and with experimental data. The dynamics of an interface copolymer excess is also considered. The situation above the critical micelle concentration (cmc) is also analyzed. It is shown that (i) copolymer micelles usually strongly attract each other, tending to form a separate micellar macrophase; (ii) primings of the copolymer phase are attracted to the free surface and (somewhat weaker) to the interface; the superwetting of the free surface by the micellar phase is expected for copolymer molecular weights exceeding some critical value; (iii) the formation of micelles is an activation process usually with a high energy of activation; so, the apparent cmc might be appreciably greater than the equilibrium cmc; (iv) for high enough copolymer molecular weights the micellar geometry should be dynamically controlled; in that case the formation of spherical micelles dominates over other geometries in a wide range of copolymer compositions including symmetric copolymers (provided that the copolymer volume fraction is small); (v) the micellar contribution to the free surface and interface excesses is due to higher rate of the micelle's formation at the surfaces.

No abstract

The influence of polydispersity on the transitions occurring in the weak segregation regime and on the scattering functions of the disordered phase in diblock copolymers is studied for one-component and multicomponent systems including mixtures with homopolymers. Application of the fluctuation corrections given by Fredrickson and Helfand9 leads to the determination of the transition windows as a function of degree of polymerization N, polydispersity U, and composition /. The applicability of the fluctuation corrections appears to be extended to lower N and f with increasing U. The prediction of transitions is facilitated by the concept of a reduced phase diagram.Recently, Fredrickson and Helfand9 have extended Leibler's theory to include the effect of composition fluctuations using a method established by Brazovskii.10 They find that Leibler's theory is only valid in the limit N -* <=°a nd that direct transitions from the homogeneous melt