Polymer solution thermodynamics phase diagrams

For most polymer blends, the phase diagram is characterized by the presence of the lower critical solution temperamre, LCST. Thus, as the temperature increases, the miscible polymer blends may phase-separate. Theoretically, the miscibility region extends up to the binodal. However, as the system approaches the binodal, there is strong mutual interaction between the rheology and thermodynamics [Rangel-Nafaile et al., 1984 Larson, 1992]. 

Using an interparticle potential, the characterization of the equilibrium state is possible by thermodynamic analysis. Van Megen and Snook [10,11] have adopted the statistical approach to predict the disorder—order phase transitions in concentrated dispersions that are stabilized electrostatically. Using the perturbation theory for the disordered phase and the cell model for the ordered phase, they have estimated the particle concentrations in the two coexisting phases when an electrostatically stabilized dispersion undergoes phase separation. Recently, Cast et al. [12] have used a similar approach to construct phase diagrams for colloidal dispersions that have free polymer molecules in solution. Using the interaction potential of Asakura... 

The most basic question when considering a polymer blend concerns the thermodynamic miscibility. Many polymer pairs are now known to be miscible or partially miscible, and many have become commercially Important. Considerable attention has been focussed on the origins of miscibility and binary polymer/polymer phase diagrams. In the latter case, it has usually been observed that high molar mass polymer pairs showing partial miscibility usually exhibit phase diagrams with lower critical solution temperatures (LCST). 

From a thermodynamic point of view, phase diagrams may be constructed by changing the temperature (ii), pressure (12). or composition of a material. The present experiments are concerned with changes in composition at constant temperature and pressure, leading to a ternary phase diagram with polymer network I at one corner, monomer II at the second corner, and polymer network II at the third corner. According to classical concepts, at first there should be a mutual solution of monomer II in network I, followed by the binodal (nucleation and growth kinetics) and finally the spinodal (spinodal decomposition kinetics). 

Phase diagrams and thermodynamics of demixing of polymer/solvent solutions in... 

Fig. 11.2 (a) Theoretical phase diagrams of melting point versus polymer volume fraction curves of polymer solutions with the chain length 32 monomers, (b) Molecular simulation results under parallel thermodynamic conditions. The reduced interaction parameter sets are labeled near the liquid-solid coexistence curve (EpIEc, B/E ) (Hu et al. 2003a) (Reprinted with permission)... 

Liquid interfaces are prevailing within the immiscible polymer blends and solutions. The effect of interfaces to polymer crystallization cannot be overlooked, not only because the practical system accumulates impurities at interfaces for heterogeneous crystal nucleation, but also because the thermodynamic conditions for crystal nucleation at interfaces are different from that in the bulk phase. The latter effect can be revealed by the theoretical phase diagrams for immiscible polymer blends, as... 

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...

Sophiea et al. published the first classical composition-temperature phase diagram, working with the semi-IPN Mct-polyurethane-jMtcr-poly(vinyl chloride) (Sophiea et al. 1994). They found a lower critical solution temperature, LCST S 120 °C below this temperature the system was one phased and above two phased. Such behavior is now known to be characteristic of most polymer blends (see Chap. 2, Thermodynamics of Polymer Blends ). 

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