Polymer blends morphological changes

In block copolymers and in polymer blends interesting meso- and nano-morphologies of the dispersed phase are sometimes observed. Variations in structure of the polymers or in phase distribution can lead to changes in properties (Sects. 3.4.2.1 and 5.6 and Example 5-23). 

This article reviews the phase behavior of polymer blends with special emphasis on blends of random copolymers. Thermodynamic issues are considered and then experimental results on miscibility and phase separation are summarized. Section 3 deals with characteristic features of both the liquid-liquid phase separation process and the reverse phenomenon of phase dissolution in blends. This also involves morphology control by definite phase decomposition. In Sect. 4 attention will be focused on flow-induced phase changes in polymer blends. Experimental results and theoretical approaches are outlined. 

As previously mentioned, the quantity tc is governed by inner parameters of the system. When one considers morphology evolution in polymer blend solutions, tc has to be compared with the externally imposed pinning-down time tp after which no further phase changes occur. For blend solutions, the quantity tp is related to the rate of solvent evaporation. 

This book is concerned mainly with the study of the viscoelastic response of isotropic macromolecular systems to mechanical force fields. Owing to diverse influences on the viscoelastic behavior in multiphase systems (e.g., changes in morphology and interfaces by action of the force fields, interactions between phases, etc.), it is difficult to relate the measured rheological functions to the intrinsic physical properties of the systems and, as a result, the viscoelastic behavior of polymer blends and liquid crystals is not addressed in this book. 

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. 

The fourth measure of liquid elasticity, P, reflects the extenslonal properties rather than elasticity. For polymer blends it is difficult to determine P with a sufficient degree of accuracy. The data Indicate that this parameter Is most sensitive to morphological changes. For example, the degree of droplet coalescence In the Instrument reservoir drastically changes the values of P. ... 

Flow of emulsions provides the best model for polymer blends, where the viscosity of both polymers is comparable. The microrheology of emulsions provides the best, predictive approach to morphological changes that take place during flow of polymer blends. The effect of emulsifiers on the drop size and its stability in emulsions has direct equivalence in the compatibilization effects in polymer blends. 

Most models of the morphological changes in polymer blends assume that an average response e.g., an average size drop is being broken, or aver-... 

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