Lower critical solution temperature Model

The phase diagram of some oil-solubilizer-water must be measured as a function of temperature in order to test the above approach. For this purpose decane (DEC) was chosen as a typical oil and 2-bu-toxyethanol (BE) as the solubilizer. We thought BE would be a good model solubilizer since the lower critical solution temperature for the BE-H2O system is 49 C this gives a good workable temperature range for our investigation. 

Liu H, Zhong C (2005) Modeling of the theta (lower critical solution temperature) in polymer solutions using molecular connectivity indices. Eur Polym J 41 139-147... 

Karlstrom, G 1985. A new model for upper and lower critical solution temperatures in polyethylene oxide) solutionsJ. Phys. Cherr89 4962—4964. 

Miscible blends of poly(vinyl methyl ether) and polystyrene exhibit phase separation at temperatures above 100 C as a result of a lower critical solution temperature and have a well defined phase diagram ( ). This system has become a model blend for studying thermodynamics of mixing, and phase separation kinetics and resultant morphologies obtained by nucleation and growth and spinodal decomposition mechanisms. As a result of its accessible lower critical solution temperature, the PVME/PS system was selected to examine the effects of phase separation and morphology on the damping behavior of the blends and IPNs. 

The phase behavior is similar to that of a lower critical solution temperature (LCST), hence it is different from the above systems. The HPC/water system is an interesting model system because of the rich variety of phase structure 01 the material. HPC is a semicrystalline polymer in the solid state (7), but exhibits thermotropic liquid crystalline character at elevated temperatures below the melting point (8). It shows isotropic phase in dilute solutions, but forms an ordered liquid crystalline phase with cholesteric structure in concentrated solutions (4). 

Polymer blends typically show a decrease in miscibility with increasing temperature. [27] McMaster has used a modified Flory equation of state thermodynamic model to show that the existence of a lower critical solution temperature (LCST) is caused mainly by differences in the pure component thermal expansion coefficients. 

In the phenomenological model of Kahlweit et al. [46], the behavior of a ternary oil-water-surfactant system can be described in terms of the miscibility gaps of the oil-surfactant and water-surfactant binary subsystems. Their locations are indicated by the upper critical solution temperature (UCST), of the oil-surfactant binary systems and the critical solution temperature of the water-surfactant binary systems. Nonionic surfactants in water normally have a lower critical solution temperature (LCST), Tp, for the temperature ranges encountered in surfactant phase studies. Ionic surfactants, on the other hand, have a UCST, T. Kahlweit and coworkers have shown that techniques for altering surfactant phase behavior can be described in terms of their ability to change the miscibility gaps. One may note an analogy between this analysis and the Winsor analysis in that both involve a comparison of oil - surfactant and water-surfactant interactions. 

KA Okada, Y., Tanaka, F., Kujawa, P., and Winnik, F.M., Unified model of association-induced lower critical solution temperature phase separation and its application to solutions of telechelic poly(ethylene oxide) and of telechelic poly(N-isopropylacrylamide) in water, J. Chem. Phys., 125, 244902, 2006. 

P10.7 Linear poly-N-isopropylacrj lamide (PNIPAM) dissolved in water shows a lower critical solution temperature (LCST). For the calculation of the liquid-liquid equilibrium with the help of the Koningsveld-Kleintjens model the parameter y the function (T) are required. The experimental critical temperature is Tc = 306.65 K and the experimental critical... 

Figure 1. Three-dimensional phase model for polyethylene + ethylene mixtures with constant temperature cuts at 120, 160 and 200 °C (showing upper critical solution pressures) and a constant pressure cut (showing lower critical solution temperature). [ Adapted from ref 6].

The thermodynamic properties of concentrated polymer solutions were studied by Floryi and independently by Huggins. The Flory-Huggins theory of polymer solutions still forms the basis for much discussion of these solutions in industry and even in academic research. Understanding this model is important for making coimections to much of the literature. Flory also substantially improved this model to include compressible fluids. The Flory-OrwoU theory of polymer solutions is still transparent and easily applicable, predicting both upper and lower critical solution temperatures. More-empirically adequate theories of concentrated solutions do not lend themselves to simple lecture presentation and often require detailed computer calculations to obtain any results. Concentrated solutions also introduce the phenomenon of viscoelasticity. An extensive treatment of the full distribution of relaxation times necessary to imderstand the dynamic properties of polymers in concentrated solution is presented. 

This is a simple model and cannot account for all the issues of mixture thermodynamics. Interaction parameters deduced from various phase behavior information are often believed to include other effects than purely enthalpic ones. This way, the LCST (lower critical solution temperature) behavior observed in polymer blends can be explained and accounted for quantitatively. These theories refine the binary interaction parameter by removing extraneous effects. EOS effects do not favor phase... 

Deshmukh, S., Mooney, D. A., Mcdermott, T, Kulkami, S., Macehoy, J. M. D. (2009). Molecnlar modeling of thermo-responsive hydrogels observation of lower critical solution temperature. Soft Matter, 5, 1514—1521. 

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