Polymer blends phase diagrams

Figure B3.6.5. Phase diagram of a ternary polymer blend consisting of two homopolymers, A and B, and a synnnetric AB diblock copolymer as calculated by self-consistent field theory. All species have the same chain length A and the figure displays a cut tlirough the phase prism at%N= 11 (which corresponds to weak segregation). The phase diagram contains two homopolymer-rich phases A and B, a synnnetric lamellar phase L and asynnnetric lamellar phases, which are rich in the A component or rich in the B component ig, respectively. From Janert and Schick [68].

When the iateraction energy density is positive, equation 5 defines a critical temperature of the UCST type (Fig. la) that is a function of component molecular weights. The LCST-type phase diagram, quite common for polymer blends, is not predicted by this simple theory unless B is... 

The information available on aqueous polymer blends is qualitative in nature because of the lack of a suitable theory to interpret the experimental observations. Mixed gels can be comprised of an interpenetrating network, a coupled network (as discussed above), or a phase-separated network [2]. The latter is the most common as the blends have a tendency to form two phases during gelation. In such cases the miscibility and thermodynamic stability have to be empirically investigated and proper conditions for miscible blends identified. This involves a phase diagram study as is described in [3]. 

Fig. 14 Creation of a single specimen polymer blend phase diagram from orthogonal polymer composition and temperature gradients. The polymers are polystyrene and poly(vinyl methyl ether) (PVME) a composition library placed orthogonal to a temperature gradient b completed gradient library polymer blend phase diagram. White points are data derived from traditional measurement for comparison. See text for details, (b reproduced with permission from [3])...

Compared to bulk polymer mixtures, the interfacial behaviour of polymer blends is essentially different [341]. The demixing process in thin films is strongly affected by the thin film confinement and the interfacial interactions of the blend components with the confining phases (e.g., substrate and air). Even in the one-phase region of the phase diagram, preferential segregation of the components at one of the interfaces leads to a certain composition profile as a function of the distance from the free surfaces and the substrate plane [342,343]. In the... 

Many polymer blends or block polymer melts separate microscopically into complex meso-scale structures. It is a challenge to predict the multiscale structure of polymer systems including phase diagram, morphology evolution of micro-phase separation, density and composition profiles, and molecular conformations in the interfacial region between different phases. The formation mechanism of micro-phase structures for polymer blends or block copolymers essentially roots in a delicate balance between entropic and enthalpic contributions to the Helmholtz energy. Therefore, it is the key to establish a molecular thermodynamic model of the Helmholtz energy considered for those complex meso-scale structures. In this paper, we introduced a theoretical method based on a lattice model developed in this laboratory to study the multi-scale structure of polymer systems. First, a molecular thermodynamic model for uniform polymer system is presented. This model can... 

Paints, adhesives and lubricants are typically multicomponent polymer systems. The behavior of phase-separated blends in the bulk after quenching into the unstable region of the phase diagram is variable. In the bulk, the concentration fluctuations... 

Fig. 14. Schematic phase diagram of a blend solution of immiscible polymers Pi and P2. A - initial blend solution, B - stability limit, C - onset of phase separation, D - slowing down of phase separation owing to enhanced viscosity...

Fig. 7. Phase diagram for a binary blend mixture of a flexible (A component) and a rigid (B component) polymers with NA = 200, N = 800, vA = vB = 1, and W B/kBTxAB = 0.4 as predicted by the RPA...

Qian, C. Mumby, S.J. Eichinger, B.E., "Phase Diagrams of Binary Polymer Solutions and Blends," Macromolecules, 24, 1655 (1991). 

For a polymer blend, where both mA and mB may be 1000, the critical value of x will be very small, Keep in mind what this means. Any value of x that is larger than means that the system will phase-separate at some composition. This is perhaps more easily seen if you recall that x varies approximately as 1/T, and a phase diagram can therefore be plotted as 1/x versus composition, if we so choose (Figure 11-22). Note also that the shape of the binodal and spinodal curves will depend upon the relative size of the molecules and will be skewed to one side or the other if mA is not equal to mB. 

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... 

Fig. 2. A hypothetical phase diagram for two polymers with a common solvent showing a two phase region. When solvent is evaporated from a mixed solution at composition A it enters the two phase region at B. When it leaves at C the phase separated regions have grown to such a size that remixing does not easily occur and the resultant blend at D is inhomogeneous...

In situ polymerisation does not however guarantee homogeneous blends as two phase regions can exist within the polymer/polymer/monomer three component phase diagram. In the case of vinyl chloride polymerisation with solution chlorinated polyethylene, the vinyl chloride has limited solubility in both poly(vinyl chloride) and chlorinated polyethylene. The phase diagram has the form shown in Fig. 3 The limit of swelling of vinyl chloride in the chlorinated polyethylene is A and the highest concentration of PVC prepared by a one-shot polymerisation is B. 

In the case of vinyl chloride polymerisation in polyfbutyl acrylate) these materials are completely miscible but a two phase region exists within the phase diagram as shown in Fig. 4 Polymerisation from A to B produces a homogeneous blend whereas from E to F produces a two phase structure. Composition B can be reswollen to C with vinyl chloride which can then be polymerised to D to producea homogeneous blend. This route avoids the two phase region in the phase diagram and in principle all compositions of polymer blend can be prepared in a series of steps. 

I he diagram of Fig. 9-1 is typical of mixtures of two small molecules, or of two polymers of comparable molecular weight and comparable viscosity. Polymer solutions, or blends of two polymers with very different molecular weights, have asymmetric phase diagrams, reflecting the asymmetry of the molecular sizes (see Fig. 9-2). 

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