Phase separation and crystallization

It was shown that adding low oxidation potential material to PFs can stabilize the emission color and increase the device efficiency [321]. However, using low-molecular-weight organic dopants causes several problems such as phase separation and crystallization. These problems can be partially solved by using polymer blends. Cimrova and Vyprachticky [334] reported... 

Landis, F A. and Moore, R. B. 2000. Blends of a perfluorosulfonate ionomer with poly(vinylidene fluoride) Effect of counterion type on phase separation and crystal morphology. Macromolecules 33 6031-6041. 

Post-heat treatment of glass induces phase separation and crystallization. A very precise secondary heat treatment is necessary to develop and control photochromic properties. Glass-ceramics receive a thermal ceramming process that induces crystallization. 

A more direct Interaction Is found In a W/O mlcroemulslon system In which an Inorganic polymer of SIO2 Is formed by hydrolysis of silicone tetraethoxlde. The competition for water molecules to dissolve the surfactant and to feed the hydrolysis of the silicone alcoxlde leads to phase separation and crystallization of the surfactant at low water content. 

Phase Field Approach to Thermodynamics and Dynamics of Phase Separation and Crystallization of Polypropylene Isomers and Ethylene-Propylene-Diene Terpolymer Blends... 

SUPERPOSITION OF LIQUID-LIQUID PHASE SEPARATION AND CRYSTALLIZATION... 

The polymer-based miscible systems can be either intermolecular mixtures, for instance polymer solutions and blends, or intramolecular mixtures, such as block copolymers, star-shape multi-arm copolymers, grafted copolymers, random copolymers, and gradient copolymers with a composition gradient from one chain end to the other. Polymer-based miscible systems can phase separate into segregated phases with stable interfaces, or crystallize into crystalline ordered phases. In other words, there are two types of phase transitions, phase separation and crystallization. Under proper thermodynamic conditions, two phase transitions may occur simultaneously. The interplay of these two transitions will dictate the final morphology of the system. In the following, we will choose polymer solutions as typical examples to introduce the polymer-based miscible systems. 

Polymer phase separation and crystallization, as introduced separately in the previous two chapters, have different molecular driving forces that can be simultaneously expressed by the use of the lattice model. Adjusting the corresponding driving forces, the mean-field theory can predict the phase diagrams, and at the meanwhile molecular simulations can demonstrate the complex phase transition behaviors of polymers in the multi-component miscible systems. 

Finally, gels may be also generated through a liquid-liquid (LL) phase separation, or a combination of LL phase separation and crystallization, as we shall see in Sect. 2.2 [17, 25]. 

Fig. 4 Schematic phase diagrams of a polymer solution showing LL phase separation with UCST behavior. Curve s is the spinodal, curve b is the binodal, and curve g is the glass transition temperature as a function of polymer concentration. BP indicates the Berghmans point, (a) LL phase separation is the only thermodynamic transformation of the system [17,25, 36]. (b) Curve c shows the crystallization temperature of a polymer fully miscible in a solvent as a function of concentration in the solution [17, 25], The LL phase coexistence curve (combined with vitrification) is a (classical) metastable process that lies beneath the crystallization curve c. In route 1, a polymer solution is supercooled at ALj, and the only active process is polymer crystallization. In route 2, the initially homogeneous solution is supercooled to a larger undercooling than namely AL2. Crystallization may compete either with LL phase separation when reaching point C, or LL phase separation coupled with vitrification when reaching point D. At C, crystallization may take place in the polymer-rich phase. At D, both LL phase separation and crystallization may become arrested by vitrification...

Fig. 3.41 Phase diagram of a binary polymer blend with miscibility gap (UCST) and intersecting crystal/melt coexistence curve. The curve is extrapolated into the miscibility gap. Quenching routes A to D are explained in the text. For routes B and C, the quenching-induced phase separation and crystallization...

The liquid-like situation results in thermodynamically induced density and concentration fluctuations, with a tendency toward phase separation and crystallization, which starts via a nucleation step. This can also be used as a technological route to produce unconventional, i. e. inhomogeneous, glasses. Some examples are... 

However, in the latter case, it was found that for the highly chlorinated, non-crystalline sample the gel setting and melting temperatures were the same, whereas the crystalline samples showed hysteresis. Again, the two processes of phase separation and crystallization were suggested, with the former apparently sufficient to form a gel. 

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