Surface-induced spinodal decomposition

Surface Induced Spinodal Decomposition Leading to Layered Coexisting Phases... 

The variation of the chemical composition of the substrate (not realized in a continuous tunable fashion) leads to drastic modifications of surface fields exerted by the polymer/substrate (i.e.,II) interface [94,97, 111, 114,119]. The substrate may, for instance, change contact angles with the blend phase from zero to a finite value. As a result the final morphology changes from a layered structure of Fig. 5b into a column structure of Fig. 5c [94,114]. On the other hand our very recent experiment [16] has shown that the surface fields are temperature dependent. Therefore, although it has been shown that surface-induced spinodal decomposition yields coexisting bilayer structure (Fig. 5b) at a singular temperature [114,115], that in principle may not be necessary true for other temperatures. This motivated our comparative studies [107] on coexistence compositions determined with two techniques described above interfacial relaxation and spinodal decomposition. 

Surface induced spinodal decomposition leads, for properly controlled surface fields, to a two layer structure characteristic for coexisting phases. Hence it may be used to determine the coexisting conditions in a more convenient way that with the interfacial relaxation method as the initial bilayer geometry may be avoided. In practical terms the overall composition of the whole thin film may be much better controlled in experiments involving spinodal decomposition. Therefore in experiments studying the equilibrium composition vs depth pro-... 

Coexistence conditions of high polymer mixtures may be determined directly with the advent of the novel approach [74,75] focused on two coexisting phases confined in a thin film geometry and forming a bilayer morphology. Such equilibrium situation is obtained in the course of relaxation of an interface between pure blend components or in late stages of surface induced spinodal decomposition. It is shown that both methods lead to equivalent results [107] (Sect. 2.2.1). 

The determination of the conformational and segregation properties of polymer brushes, created by diblock copolymers, has triggered their application to more complex problems. Diblock copolymers have been used to increase adhesion [277] or to eliminate the interfacial tension [256] between immiscible polymers. They may also modify the surface induced mode [116] and the bulk mode [278] of the spinodal decomposition observed in homopolymer blends. 

The same fact is true for surface effects on the dynamics of spinodal decomposition in polymer blends [374,375], dynamics of surface enrichment in blends [367, 375, 376], and, last but not least, for surface effects on block copolymers there one may have surface - induced ordering [377, 379] and interesting competition effects between the lamellar ordering (of wavelength X) and film thickness D in thin block copolymer films [380—388]. These phenomena are outside of our consideration here. 

We note that analogous condensation effects can take place in a liquid - for example, surface-induced phase transitions in self-assembly fluids (85, 86) - and it has also been speculated that the mechanism of the hydrophobic interaction involves a similar spinodal decomposition where vapour films on the hydrophobic surfaces grow and fuse (87). 

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