Relation Between Solvent Quality and Phase Behavior of Ternary Mixtures of Polymers and Two Solvents that Exhibit Cononsolvency (original) (raw)
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Polymer, 1960
An experimental study is reported of phase equilibria in ternary systems comprising two polymers and one liquid. The measured distribution of the two polymers between two coexisting phases is used, in conjunction with the Flory-Huggins theory, to derive polymer-polymer interaction 'constants'. These can be used to predict the miscibility and heat of mixing of the same polymers in binary mixtures. Experimental studies on fluid polymers show that miscibility is less and heat of mixing larger than predicted. It is concluded that these studies on ternary systems do not afford a reliable guide to the behaviour of binary polymers mixtures. Possible reasons ]or the discrepancy are discussed.
Macromolecules, 1989
A renormalization group theory is used to devise a formula for the effective interaction parameter Xeff between different species of polymers, 1 and 2, in a common solvent. It describes the overall behavior as a function of the polymer volume fraction 4, the solvent quality, and the microscopic (bare) interaction parameter x12 The polymer-polymer phase transition is then examined by using a generalized pseudobinary approximation. Its critical line is shown to extend into a semidilute region, 4 > d-. Here 4is a minimum volume fraction of the order of the overlapping volume fraction $* in a 9 solvent and considerably larger than q5* in a good solvent. As 4-@-, deviations from the Flory-Huggins predictions on the phase transition become enhanced. Particularly Xeff saturates into a value proportional to a negative fractional power of the molecular weight and the critical value of xlz diverges as 4-&in. These are consistent with previous experiments and Monte Carlo simulations. However, as the solvent quality is decreased, the fluctuation effects of 4 become important and, as a result, the critical line will reach a tricritical point or a critical end point a t 4 larger than 4, h. Our theory is also used to explain spinodal decomposition processes in ternary systems.
Ind Eng Chem Res, 1995
The group contribution-Flory equation of state (GC-Flory EoS) is applied to the prediction of the phase behavior of monodisperse polymer/single solvent systems. The model is capable of predicting with satisfactory accuracy the most common types of phase diagrams typical of liquidliquid equilibria of polymer solutions (i.e., phase diagrams of the UCST, LCST, combined (UCST + LCST), and hourglass types). Combinatorial effects derived from differences in size, shape, and structure of the polymer and the solvent molecules strongly influence the phase behavior of the systems, but the type of a phase diagram of a specific polymerholvent system is primarily governed by the nature of the molecular energy interactions. The GC-Flory EoS predicts the significant effect of the free-volume contributions at high temperatures, which is in very good agreement with the nature of the liquid-phase separation at temperatures near the gas-liquid critical temperature of the solvent, where the highly expanded state of the solvent leads to LCST behavior.
A New Theory for Polymer/Solvent Mixtures Based on Hard-Sphere Limit
European Polymer Journal, 2003
Based on hard-sphere limit of binary mixtures with different molecular size of components a theory has been developed for calculating activities of solvents in polymer/solvent mixtures. The theory considers various chain configurations for polymer molecules, varying from extended chain to the coiled chain. According to this theory the activity of solvent can be calculated from molecular weights (MWs) and densities as the only input data. The only adjustable parameter in the calculations, is the hard-sphere diameter of polymer, which provides useful criteria for the judgement on the chain configuration of polymer. The activity calculations have been performed for seven binary mixtures of polymer/solvent and compared with experimental data at various temperatures and for a varying range of MWs of polymers. The solvents in the mixtures were both of polar and nonpolar natures. The activity calculations for the same systems were performed by the well-known Flory–Huggins theory. Comparing the results of calculations with those of Flory– Huggins theory indicates that, the proposed theory is able to predict the activities of the solvent with good accuracy. The radius of gyration, excluded volume and interaction parameter for polymer chain have been calculated using the parameter obtained in the new theory. The calculated interaction parameter in the new theory, is interpreted in terms of attraction, repulsion and interchange energy of polymer and solvent in the mixture.
Solvation of polymers as mutual association. II. Basic thermodynamic properties
The Journal of Chemical Physics, 2013
The theory of equilibrium solvation of polymers B by a relatively low molar mass solvent A, developed in the simplest form in Paper I, is used to explore some essential trends in basic thermodynamic properties of solvated polymer solutions, such as the equilibrium concentrations of solvated polymers A i B and free solvent molecules A, the mass distribution φ A i B (i) of solvated clusters, the extent of solvation of the polymer solv , the solvation transition lines T solv (φ o B), the specific heat C V , the osmotic second virial coefficient B 2 , phase stability boundaries, and the critical temperatures associated with closed loop phase diagrams. We discuss the differences between the basic thermodynamic properties of solvated polymers and those derived previously for hierarchical mutual association processes involving the association of two different species A and B into AB complexes and the subsequent polymerization of these AB complexes into linear polymeric structures. The properties of solvated polymer solutions are also compared to those for solutions of polymers in a self-associating solvent. Closed loop phase diagrams for solvated polymer solutions arise in the theory from the competition between the associative and van der Waals interactions, a behavior also typical for dispersed molecular and nanoparticle species that strongly associate with the host fluid. Our analysis of the temperature dependence of the second osmotic virial coefficient reveals that the theory must be generalized to describe the association of multiple solvent molecules with each chain monomer, and this complex extension of the present model will be developed in subsequent papers aimed at a quantitative rather than qualitative treatment of solvated polymer solutions.
Polymer collapse in miscible good solvents is a generic phenomenon driven by preferential adsorption
Nature communications, 2014
Water and alcohol, such as methanol or ethanol, are miscible and, individually, good solvents for poly(N-isopropylacrylamide) (PNIPAm), but this polymer precipitates in water-alcohol mixtures. The intriguing behaviour of solvent mixtures that cannot dissolve a given polymer or a given protein, while the same macromolecule dissolves well in each of the cosolvents, is called cononsolvency. It is a widespread phenomenon, relevant for many formulation steps in the physicochemical and pharmaceutical industry, that is usually explained by invoking specific chemical details of the mixtures: as such, it has so far eluded any generic explanation. Here, by using a combination of simulations and theory, we present a simple and universal treatment that requires only the preferential interaction of one of the cosolvents with the polymer. The results show striking quantitative agreement with experiments and chemically specific simulations, opening a new perspective towards an operational understa...
Concentration fluctuations in polymer-polymer-solvent systems
Macromolecules, 1987
We examine the dynamics of concentration fluctuations and spinodal decomposition in ternary systems composed of two polymers and a single solvent, assumed to be well-described by the Flory-Huggins model. The dynamic light-scattering spectrum in the one-phase region is calculated for systems in which one of the polymers is isorefractive with the solvent. It is shown that the spectrum in this case is well represented, in the limit qRG < 1, by a sum of two exponentials. Only in the limit where the probe species is infinitely dilute does single-exponential behavior occur. Recent experimental results showing nonsingle-exponential behavior and in some cases the existence of two distinct modes of decay are discussed in light of these predictions. The theory of spinodal decomposition as formulated for binary systems is extended to the ternary case. It is shown that the light-scattering spectrum will evolve as the sum of three exponentials after quenches into the spinodal region. Recent experimental results are in qualitative agreement with this finding.
Macromolecules, 2009
Experimentally obtained islands of immiscibility are reported for the systems PS/PVME/THF at 20°C and for PS/PVME/CH at 55°C (PS: polystyrene, PVME: poly(vinyl methyl ether), THF: tetrahydrofuran, CH: cyclohexane). THF is a good solvent and CH is a marginal solvent for both polymers. In the case of THF, information on the Flory-Huggins interaction parameters of the three binary subsystems suffices for a qualitative prediction of the phase behavior of the ternary system. Quantitative agreement can be achieved by means of composition-independent ternary interaction parameters. For the marginal solvent CH, the exclusive use of binary interaction parameters wrongly predicts complete miscibility of all three components. In this case, one ternary interaction parameter must be treated as a function of composition in order to match experiment and theory. On the basis of the present results, it can be concluded that the preparation of homogeneous mixtures with arbitrary composition from a pair of compatible polymers and a common solvent is only possible on rare occasions.
Ind Eng Chem Res, 1994
The group contribution-Flory equation of state (GC-Flory EoS) is applied to the prediction of the phase behavior of monodisperse polymer/single solvent systems. The model is capable of predicting with satisfactory accuracy the most common types of phase diagrams typical of liquidliquid equilibria of polymer solutions (i.e., phase diagrams of the UCST, LCST, combined (UCST + LCST), and hourglass types). Combinatorial effects derived from differences in size, shape, and structure of the polymer and the solvent molecules strongly influence the phase behavior of the systems, but the type of a phase diagram of a specific polymerholvent system is primarily governed by the nature of the molecular energy interactions. The GC-Flory EoS predicts the significant effect of the free-volume contributions at high temperatures, which is in very good agreement with the nature of the liquid-phase separation at temperatures near the gas-liquid critical temperature of the solvent, where the highly expanded state of the solvent leads to LCST behavior.