Binary polymer blend

In Chapter 8 the principles of phase segregation in polymer blends were considered. As would be expected surface segregation occurs and usually the lower surface energy component of the mixture will tend to appear at the surface. The surface energy can be directly related to the free energy. The techniques for the study of surfaces are discussed in Chapter 9. 

The surface composition gradient can be calculated from the theory, since 

Using experimentally determined binary interaction parameters, the statistical segment length and the surface energy difference between the blend components, the surface composition and the surface concentration profile can be calculated. The profiles obtained closely approximate to an exponential decay  

Equation (10.19) indicates that the surface decay length conveniently characterizes the concentration profile. For a strongly segregated system the decay length is small but becomes large, 10-20 nm, when the concentration fluctuations grow near the critical point. Experimental studies demonstrate that the surface composition scales directly with the surface energy difference between the constituents.  

In this chapter, we turn our attention to binary mixtures of different polymers. These are perhaps better termed pseudo-binary because here we do not consider molecular weight distribution effects of polymer chains of different molecular weights as independent species. Our hrst concern is with miscibility, as it was with polymer-solvent systems in Chapter 3 and with polymer-additive systems in Chapter 4. We consider which polymer structures are likely to lead to miscibility. This leads to a consideration of partially miscible systems and to mixtures involving copolymers. Finally, we consider immiscible polymer blends. Here we emphasize the role of interfacial tension between phases and the factors influencing phase morphology. 

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Figure B3.6.1. Illustration of the wide span of length seale in a binary polymer blend. (See the text for fiirther explanation.)...

The binary polymer blend exliibits a second-order unmixing transition. Close to the critical temperature the... 

Figure B3.6.2. Local mterface position in a binary polymer blend. After averaging the interfacial profile over small lateral patches, the interface can be described by a single-valued function u r. (Monge representation). Thennal fluctuations of the local interface position are clearly visible. From Wemer et al [49].

Esoobedo F A and de Pablo J J 1999 On the sealing of the oritioal solution temperature of binary polymer blends with ohain length Macromolecules 32 900... 

The wall-PRISM theory has also been implemented for binary polymer blends. For blends of stiff and flexible chains the theory predicts that the stiffer chains are found preferentially in the immediate vicinity of the surface [60]. This prediction is in agreement with computer simulations for the same system [59,60]. For blends of linear and star polymers [101] the theory predicts that the linear polymers are in excess in the immediate vicinity of the surface, but the star polymers are in excess at other distances. Therefore, if one looks at the integral of the difference between the density profiles of the two components, the star polymers segregate to the surface in an integrated sense, from purely entropic effects. 

Table 14. List of binary polymer blends which formed stable capsules...

Binary plutonium halides, 79 689 Binary plutonium oxide, 79 688 Binary polymer blends, 20 330-334, 343. See also Binary heterogeneous polymer blends... 

Phase structure development/evolution in binary polymer blends, 20 334 of polymer blends, 20 327-330 Phase-transfer catalysis, 5 220 ... 

Table 5.1. Binary polymer blends of industrial importance...

Apart from binary polymer blends, also blends consisting of three different polymers have foimd technical applications. Belonging to this group are mixtures of polypropylene, polyethylene, and ethylene/propylene elastomers. 

Binary composite membranes constitute the chief example of membranes classified under (b) in the introductory section. They include binary polymer blends or block or graft copolymers exhibiting a distinct domain structure, filled or semicrystalline polymers and the like. 

The feasibility of diffuse reflectance NIR, Fourier transform mid-IR and FT-Raman spectroscopy in combination with multivariate data analysis for in/ on-line compositional analysis of binary polymer blends found in household and industrial recyclates has been reported [121, 122]. In addition, a thorough chemometric analysis of the Raman spectral data was performed. 

SCFT today is one of the most commonly used tools in polymer science. SCFT is based on de Gennes-Edwards description of a polymer molecule as a flexible Gaussian chain combined with the Flory-Huggins "local" treatment of intermolecular interactions. Applications of SCFT include thermodynamics of block copolymers (Bates and Fredrickson, 1999 Matsen and Bates, 1996), adsorption of polymer chains on solid surfaces (Scheutjens and Fleer, 1979,1980), and calculation of interfacial tension in binary polymer blends compatibilized by block copolymers (Lyatskaya et al., 1996), among others. 

Consider a binary polymer blend (A and B components) of gaussian chains with degrees of polymerization NA, NB, volume fractions <(>A, 4>B, and monomeric volumes vA, vB, respectively. When the blend is a homogeneous phase mixture,... 

Consider a binary polymer blend [43] of deuterated polystyrene, PSD, (Mw = 1.95 x 10s g/mole, Mw/Mn = 1.02) and poly(vinyl methyl ether), PVME, (Mw = 1.59 x 10s g/mole, Mw/M = 1.3) with a composition of 48.4% PSD (volume fraction). SANS data were taken at various temperatures ranging from ambient to 160°C. De Gennes s RPA formula ... 

In some cases, one is interested in the structures of complex fluids only at the continuum level, and the detailed molecular structure is not important. For example, long polymer molecules, especially block copolymers, can form phases whose microstructure has length scales ranging from nanometers almost up to microns. Computer simulations of such structures at the level of atoms is not feasible. However, composition field equations can be written that account for the dynamics of some slow variable such as 0 (x), the concentration of one species in a binary polymer blend, or of one block of a diblock copolymer. If an expression for the free energy / of the mixture exists, then a Ginzburg-Landau type of equation can sometimes be written for the time evolution of the variable 0 with or without flow. An example of such an equation is (Ohta et al. 1990 Tanaka 1994 Kodama and Doi 1996)... 

For simplicity, assuming that the close-packed volume of a PS mer (vps) is equal to that of a PVME mer (vPVME), the binary polymer blend is miscible [20] when... 

Figure 14 exemplifies two computational methods to determine the probability distribution of composition for binary polymer blends described by the bond fluctuation model [67]. Phase coexistence can be extracted from these data via the equal-weight rule. For the specific example of a symmetric blend, the coexistence value of the exchange chemical potential, A/u, is dictated by the S3munetry. One can simply simulate at A oex = 0 and monitor the composition. Nevertheless, the probability distribution contains additional information, as discussed in Sect. 3.5. 

Fig. 22. (a) Snapshot of an interface between two coexisting phases in a binary polymer blend in the bond fluctuation model (invariant polymerization index // = 91, incompatibihty 17, linear box dimension L 7.5iJe, or number of effective segments N = 32, interaction e/ksT = 0.1, monomer number density po = 1/16.0). (b) Cartoon of the configuration illustrating loops of a chain into the domain of opposite type, fluctuations of the local interface position (capillary waves) and composition fluctuations in the bulk and the shrinking of the chains in the minority phase. Prom Miiller [109]... 

Section 3.1 considers the segregation from binary polymer blends towards external interface of a thin film described in a semi-infinite mixture approach. We relate the segregation with wetting phenomena. The role of a vapor and a gas in a classic formulation of this problem is played by two coexisting polymer phases. 

Fig. 1. Temperature T vs volume fraction phase diagram of a binary polymer blend. Solid line denotes the coexistence curve (binodal) while the me dashed line marks the spinodal line. Binodal connects with spinodal at the critical point (( )c> Tc)...

Figure 2.6 shows the extinction spectra of all possible binary polymer blends together with those of the individual polymers. The lack of additional features in any of the blends points to the absence of ground-state interactions between the different polymers. 

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