Phase separation INDEX

A useful guide when using the polarity index is that a change in its value of 2 units corresponds to an approximate tenfold change in a solute s capacity factor. Thus, if k is 22 for the reverse-phase separation of a solute when using a mobile phase of water (P = 10.2), then switching to a 60 40 water-methanol mobile phase (P = 8.2) will decrease k to approximately 2.2. Note that the capacity factor decreases because we are switching from a more polar to a less polar mobile phase in a reverse-phase separation. 

Two criteria for compatibility were used optical clarity and a single glass-transition temperature, Tg. Optical clarity indicates either that compatibility is present or that the domains involved in the phase separation are small compared with optical wavelengths. (The refractive indices must differ, of course. In these studies the refractive index between blend components varied from 0.02 for PS/S-MMA-80 blends to... 

Larger differentials in index and corresponding higher scattering efficiencies were observed with particular monomer systems, but the final materials underwent phase-separation degradation over a few weeks. 

Although styrene-diene diblock copolymers are used in some applications, particularly in the area of viscosity index improvement (VII) additives for motor oil, styrenic block copolymers are most often used as thermoplastic elastomers. In these applications the styrene blocks phase separate, crosslinking the rubber blocks in a thermally reversible fashion. The simplest structure capable of exhibiting this behavior is a linear styrene-diene-styrene triblock. The most obvious way to produce such a molecule is by sequential polymeriza-... 

The volume fraction at incipient separation of the nematic phase lies just beyond the volume fraction v at which exhibits critical behavior with respect to the disorder index y, according to the 1956 theory. The confusion of v calculated using Eq. (11) with Vp at incipience therefore has led to underestimation of the latter volume fraction according to that version of the theory. The improved theory leads to somewhat lower values of the volume fraction at incipient phase separation. Hence, the error attending misapplication of Eq. (11) is offset by inaccuracies of the original theory, with the fortuitous consequence that this equation offers a slightly better approximation for the threshold volume fraction than for vj, for which latter it was originally intended. The widespread misuse of Eq. (11) is therefore well justified. 

Several implications can be drawn directly from Eq. (2-39). First, A // is always positive. Thus, the rule like attracts like, inferred from Eq. (2-30) for molecular mixtures, should also hold at the continuum level. Second, when dispersion forces are dominant, the Hamaker constant is small when ha= b—that is when the dispersed phase (A) has an index of refraction close to that of the medium (B), These rules also apply to molecular mixtures. Nevertheless, small molecules with a significant difference in index of refraction often mix because of the large entropy thereby gained. But particles lose too little entropy on coagulation to resist doing so when there is an attractive van der Waals interaction, and so particle-particle clumping is the norm in suspensions, unless countermeasures are taken to stop it (see Section 7.1). Analogous considerations explain the prevalence of phase separation in polymer blends (see Section 2.3.1.2). 

Thus close to the critical point of phase separation the behavior is first nonmonotonic and then the scaling behavior of Ig e) becomes a two-index and then a one-index. Similar expressions can be derived for gas-liquid critical point behavior. 

Obviously a viscosity index recommended for characterization of bio-oil stability [2], using a viscometer type available in a participating laboratory , cannot be correctly applied due to tendency of bio-oils, non-Newtonian liquids, to phase separation into thin oil, thick tar and solid admixtures [1]. However, the ESR method allows to reveal considerable difference between the properties of the samples prior and after ageing It was shown (Table 3) that the concentrations of paramagnetic centers m samples taken after ageing from the top and the bottom of oil storage vessel differed significantly, e.g. m the cases of oils from IWC and Aston installations, by 10 and 800 times, respectively. 

In case of inhomogeneous oils, some analyses like kinematic viscosity and stability index caimot be applied due to possible phase-separation of oil during viscosity determination. 

The results for the TEA--water mixtures at atmospheric pressure are shown in Figure 6. These are for TEA mole fractions of x 0.05 and 0.59. The LOST is 18.2 at x - 0.09. We also obtained a very similar data set at the latter mole fraction, but we omitted it for clarity. For contrast and comparison, a data set for pure water is shown. These mixture results again show a sharp rise in heat transfer coefficient as condensate first appeared. In fact, the appearance was remarkably similar to the n-decane--C02 results for x - 0.973 discussed above, but the visibility of the phase separation was enhanced by the presence of a fine emulsion at the phase interface and the absence of strong refractive index gradients characteristic of the supercritical systems. This permitted the structure of the interface to be seen more clearly. In Figure 7 we show photographs that typify the appearance of the two phases. In all cases observed here, both in supercritical vapor--liquid and in liquid--liquid systems, the dense phase appears to wet the cylinder surface regardless of composition. 

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