Phase separation temperature

Aniline point NF M 07-021 ISO 2977 ASTMD611 Phase separation temperature of a hydrocarbon/ aniline mixture... 

Fig. 3. Phase-separation temperatures for 50 50 PVC—a-MSAN blends, where (-------) represents the blend drying temperature, ( ) are experimentally...

Blends of poly(vinyl chloride) (PVC) and a-methylstyrene—acrylonitrile copolymers (a-MSAN) exhibit a miscibiUty window that stems from an LCST-type phase diagram. Figure 3 shows how the phase-separation temperature of 50% PVC blends varies with the AN content of the copolymer (96). This behavior can be described by an appropriate equation-of-state theory and interaction energy of the form given by equation 9. 

Equations (18) and (16) define a temperature where Gaussian behavior is observed (the phase separation temperature) where % — 1/2 and thermal energy is just sufficient to break apart PP and SS interactions to form PS interactions. Equation (12) using (17) for Vc is called the Flory-Krigbaum equation. This expression indicates that only three states are possible for a polymer coil at thermal equilibrium ... 

Figure 3 Radius of gyration, Rg, and hydrodynamic radius, Rh, versus temperature for polystyrene in cyclohexane. Vertical line indicates the phase separation temperature. 

Light scattering and electron microscopy studies of aqueous PVME solutions and PVME microgels were carried out by Arndt et al. [329,330]. They noted that the Mw of PVME in water was always higher (up to 20 times) than its value (Mw = 46 000gmoH) determined in organic solvent (butanone), even for dilute aqueous PVME solutions well below the phase-separation temperature [330]. Moreover the molar masses of the polymer in water depended on solution preparation conditions. The authors concluded that PVME does not exist as isolated chains in water, but forms loose aggregates (Rh = 200-220 nm) which decrease in size as the solution temperature passes... 

In gasoline-methanol mixtures containing 0.1% water i-propanol is added to the environment (medium) in order to decrease the phase separation temperature. Fuels containing different ratios of gasoline-methanol-i-propanol and water are also composed, which are proved to be stable in the climatic conditions. An increase in the aromatic character of the gasoline, a decrease in the water content of the mixtme, an increase in the amount of the additive used results in a decrease in the phase separation temperature of the mixture. In gasoline-ethanol mixtures the additive used is also i-propanol. In gasoline-alcohol mixtures various additives like i-propanol, n-butanol, i-butanol, and i-amylalcohol are used. 

Navard and Haudin studied the thermal behavior of HPC mesophases (87.88) as did Werbowyj and Gray (2), Seurin et al. (Sp and, as noted above, Conio et al. (43). In summary, HjPC in H2O exhibits a unique phase behavior characterized by reversible transitions at constant temperatures above 40 C and at constant compositions when the HPC concentration is above ca. 40%. A definitive paper has been recently published by Fortin and Charlet ( who studied the phase-separation temperatures for aqueous solutions of HPC using carefully fractionated HPC samples. They showed the polymer-solvent interaction differs in tiie cholesteric phase (ordered molecular arrangement) from that in the isotropic phase (random molecular arrangement). 

The phase separation temperature shift by photo-isomerization implies that in the temperature range between 19.4 and 26.0 °C, ultraviolet irradiation solubilizes the polymer or expands the polymer chain, while visible irradiation decreases the solubility, or shrinks the chain. Figure 3 shows the photo-stimulated phase separation at 19.5 °C accompanied by the conformation change of the polymer chain. Upon exposure to UV light (350 <%< 410 nm), the opaque solution became transparent, while visible irradiation (>. > 470 nm) again decreased the transmittance of the solution. The polymer chain conformation changed concomitantly with the phase separation. 

In the phase separation process, however, it needed some induction period for the polymer to start the phase separation. Almost complete isomerization of the azobenzene pendant groups from the cis to the trans form is required to decrease the phase separation temperature below 19.5 °C. The phase separation process exhibited a non-linear response to the irradiation time or the number of photons. When the number of absorbed photons reached a critical value, the system underwent the phase separation and the polymer chain was shrunk. The photo-stimulated phase separation/dissolution cycle was not observed below 19.4 and above 26.0 °C. 

Fig. 4. Phase separation temperature ( ) before and (O) after UV irradiation of the aqueous solutions of PNIPAM polymers containing leuconitrile (LN) groups...

When the pendant crown ether groups bind metal ions, the phase separation temperature is expected to rise because the hydrophilicity of the polymer increases. The concentration change of special metal ions in solution can be detected as the phase transition of the polymer solution, or the conformation change of the polymer chain. 

Fig. 5. Phase separation temperature changes of the aqueous solutions of PNIPAM containing pendant 11.6 mol % crown ether groups by the addition of potassium chloride (O), sodium chloride (3), lithium chloride (C), and cesium chloride ( ). Polymer concentration was 1 mass %...

The phase separation temperatures Tp were measured in two ways. Solutions of various concentrations in sealed glass tubes were placed in a water bath. In the previously roughly determined temperature range the temperature was lowered in steps about 0.1°C. Phases which separated out became clear within several hours. The highest phase-separation temperature was considered to be the cloud point. The second method is described below. 

Figures 1-3 show the observed reciprocal excess intensities of scattered light multiplied by sin 0 (to correct for the irradiated volume observed at each angle) plotted against sin2 (0/2) at constant polymer concentration for several temperatures above the phase-separation temperature. To give a clearer presentation the intensities are expressed in relation to intensities at the scattering angle 0 = 90°, as was also done by Eskin and Nesterow (11). In accord with the Debye theory, the plots give straight lines and can be represented by...

Figure 5. Dissymmetry ratio IiS/I1S5 vs. concentration of polystyrene in cyclohexane at different temperatures above the phase-separation temperature...

For the blend PMMA/SAN-31.5 (code 31.5 wt% of AN in SAN) a phase separation temperature of 184 C has been observed for the quiescent 60/40 blend which shifted by about 10 K at a shear rate of 2 s 1 [118]. All the parameters occurring in Eq. (63) are known for the system under discussion except the quantity AN,. Thus, AN, can be estimated. Employing the individual segmental interaction parameters submitted in Ref. [6] one easily arrives at... 

Figure 4, presented for illustrative purposes, shows the hydrogen purity achievable for the separation of a 65/35 hydrogen methane feedstock with a final phase separation temperature established by the back pressure of the fuel (methane) stream. 

The solutions of PDMS in MEK and CA in mixed solvents were prepared at 313 K during several days. The phase separation temperatures (Tph) for the solutions under shear field and in static conditions were determined by cloud-point method and viscometric. measurements using rotational reometer PVR-2. The spinodal was determined by the light scattering method according to [11. 

Saeki, S. Narita, Y. Tsubokawa, M. Yamaguchi, T., "Phase Separation Temperatures in the Polystyrene-Poly(alpha-methyl styrene)- Methylcyclohexane System," Polymer, 24, 1631 (1983). 

If cation and anion are preferentially solvated by the same solvent component (homo-selective solvation) the phase separation temperature of the solvent mixture is shifted to higher temperatures. On the other hand, with heteroselective solvation of an electrolyte, when one ion is preferentially solvated by one solvent component and the counterion by the second component, the upper critical solution temperature decreases by adding that electrolyte. 

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