Phase-Separating Polymer Mixtures

In the phase-separating system, there will be a most probable composition 

Figare 12.7 Scattered li t intendty (V, conditions) as a function of angle for different times for a phase-separating mixture of polystyrene and polyvinyl methyl ether. Times after start of i iase separation (seconds) 

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This document is organized into three sections. The first defines terms basic to the description of polymer mixtures. The second defines terms commonly encountered in descriptions of phase-domain behaviour of polymer mixtures. The third defines terms commonly encountered in the descriptions of the morphologies of phase-separated polymer mixtures. 

Fig. 37. Theoretical predictions for thin film morphology of a phase-separating polymer mixture. Case I yA where yA and yB are the surface tensions of components A and B, respectively, and yAB is the interfacial tension. Case II yA

Phase separated polymer mixtures are important in many practical applications, such as confectionery and low-fat foods. Values of the fraction (x) of a component can be replaced by those of the fraction of solvent (Sx) associated with polymer (Morris, 1998) so that Figure 6-22 may be used also to understand the role of solvent partitioning. A key assumption is that there is complete separation of the two polymers in to their respective phases, so that the relative phase volumes (hence, the polymer concentration in each phase) may be characterized by the p-factor, defined as ... 

Such phase-separated polymer mixtures serve as an excellent model system where molecular-level interactions between components are small. The system studied here is a film made of an immiscible binary mixture of atactic polystyrene and low-density polyethylene [2], The dynamic IR measurement was carried out as before by mechanically stimulating the system at room temperature with a 23-Hz dynamic tensile strain with an amplitude of 0.r/>. The time-dependent fluctuations of IR absorbance induced by the strain were recorded at a spectral resolution of 4 cm. ... 

Figure 4 shows that the orientation of the two chains follow similar paths. The similarity suggests that the local environment is very much the same for both blend constituents. In contrast, a phase-separated binary mixture of polymer segments will exhibit a different orientation for each component. For example, high-density polyethylene and isotactic polypropylene form multiphase systems when blended together (16). When the incompatible blends are deformed, the component which constitutes the continuous phase always orients to a higher degree than... 

In the case of polystyrene blends with poly(vinyl methyl ether) two phase behaviour was found for blends from various chlorinated solvents whereas single phase behaviour was found for blends from toluene The phase separation of mixtures of these polymers in various solvents has been studied and the interaction parameters of the two polymers with the solvents measured by inverse gas chromatography It was found that those solvents which induced phase separation were those for which a large difference existed between the two separate polymer-solvent interaction parameters. This has been called the A% effect (where A% = X 2 Xi 3)-A two phase region exists within the polymer/polymer/solvent three component phase diagram as shown in Fig. 2. When a dilute solution at composition A is evaporated, phase separation takes place at B and when the system leaves the two phase region, at overall... 

Phase separation in mixtures of polymers especially occurs at high concentrations and for large molar mass. The separation can be of two kinds. If the two polymers show mutual affinity, associative phase separation or complex coacervation occurs, i.e., a separation into a solution high in both polymers (a complex coacervate) and a very dilute solution. In most other cases, segregative phase separation or incompatibility is observed, i.e., separation in a phase rich in polymer A but poor in polymer B, and vice versa. 

Figure 20.22. Phase separation in mixtures of a polyelectrolyte and an oppositely charged surfactant changes from associative (a,b), to no phase separation (c) and finally to segregative (d,e) as electrolyte is added. This example shows mixtures of a cationic surfactant, tetradecyltrimethylammonium bromide (TTAB), and an anionic polysaccharide, sodium hyaluronate (NaHy). (Redrawn from B. Lindman and K. Thalberg, in Interactions of Surfactants with Polymers and Proteins E. D. Goddard and K. P. Ananthapadmanabhan (Eds), CRC Press, Boca Raton, FL, 1993, p. 254)...

AN2 Antonov, Y. and Friedrich, C., Aqueous phase-separated biopolymer mixture compatibihzed by physical interactions of the constituents, Polym. Bull, 58, 969, 2007. 

HAE Haegen, R. van der. Liquid-liquid phase separation in mixtures of statistical copolymers, in Integration of Polymer Science and Technology, Elsevier, London, New York, 1, 67, 1986. 

Recently, polymer-dispersed liquid-crystal materials have played an important role for many practical processes such as the electro-optical displays [1, 2]. Since the miscibility or phase separation of mixtures of polymers and liquid crystals controls the performance of the materials, the phase behavior and the phase separation kinetics have been of experimental and theoretical interest. One of the main problem is to examine the location of various phases, such as isotropic and nematic phases, depending on temperature and concentration. 

In the following two sections I will describe the dynamics and phase separation in mixtures of a flexible polymer and a liquid crystal, and the phase separation phenomenon in mixtures of a long rodlike polymer and a liquid crystal. 

I will introduce the phase separation of mixtures of rigid rodlike polymers and liquid crystal molecules in this section. Stiff, long liquid crystal polymers and carbon nanotubes are considered to be rodlike molecules. Because of the strong intermolecular van der Waals attraction, nanotubes aggregate and do not easily dissolve. However, they can be dispersed by modifications with surfactant-like molecules on the nanotube surface [51]. Such dispersed nanotubes can be aligned in a liquid crystal matrix. 

Niiyama S, Kikuchi H (2013) Optical microscopic observation of morphology in liquid crystal/ polymer composites and their electro-optical properties. Mol Cryst Liq Cryst 577 1-14 Nwabunma D, Chiu HW, Kyu T (2000) Morphology development and dynamics of photopolymerization induced phase separation in mixtures of a nematic liquid crystal and photocuratives. Macromolecules 33 1416-1424... 

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