Phase X

Phase transitions in binary systems, nomially measured at constant pressure and composition, usually do not take place entirely at a single temperature, but rather extend over a finite but nonzero temperature range. Figure A2.5.3 shows a temperature-mole fraction T, x) phase diagram for one of the simplest of such examples, vaporization of an ideal liquid mixture to an ideal gas mixture, all at a fixed pressure, (e.g. 1 atm). Because there is an additional composition variable, the sample path shown in tlie figure is not only at constant pressure, but also at a constant total mole fraction, here chosen to be v = 1/2. 

Drawing pseudo-binaryjy—x phase diagrams for the mixture to be separated is the easiest way to identify the distillate product component. A pseudo-binary phase diagram is one in which the VLE data for the azeotropic constituents (components 1 and 2) are plotted on a solvent-free basis. When no solvent is present, the pseudo-binaryjy—x diagram is the tme binaryjy—x diagram (Eig. 8a). At the azeotrope, where the VLE curve crosses the 45° line,... 

Fig. 8. Pseudo-binary (solvent-free)jy-x phase diagrams for determining which component is to be the distillate where (—) is the 45° line, (a) No solvent (b) and (c) sufficient solvent to eliminate the pseudo-a2eotiope where the distillate is component 1 and component 2, respectively (51) and (d) experimental VLE data for cyclohexane—ben2ene where A, B, C, and D represent 0, 30, 50, and 90 mol % aniline, respectively (52).

Legend O, transparent homogenous solution X, phase-separated p, translucent gel. 

Both compound I and a mixture of the two derivatives M70 (70% 1 30% II) display the usual monolayer smectic Aj phase on cooling down from the isotropic liquid. At lower temperatures the particular smectic phases (X and X ) showing polar behaviour have been observed [78]. The smectic X phase in... 

The IR dichroism measurements allowed a fairly precise determination of the preferential molecular conformations both in the smectic Ai and X phases (see Sect. 2.3). In the smectic Ai phase the biphenyl moiety is parallel on average to the layer normal, while the hydrocarbon and perfluorinated fragments are tilted at angles 18 and 32°, respectively. The phase transition to the smectic X phase is accompanied by a dramatic change in the main molecular conformation - now all the fragments are strongly tilted with respect to the layer normal (especially the biphenyl core which tilts at an angle of around 56°) (Fig. 12). 

The smectic X phase in the pure compound I shows additionally to the smectic C layering the two-dimensional (modulated) structure in which the smectic C layers are periodically shifted with a respect to one another by half a layer spacing. 

Fig. 13. X-ray intensity profile with diffi action vector along qx (in the plane of layers) in the smectic X phase for the mixture of polyphilic compounds M70. The solid line through the data points is the smn of three Lorentzian peaks which are shown hy broken curves (Blinov et al. [44])...

Compare the residence time for the X phase, Vi/L with the time constant ... 

Fractional extraction Concentration in X-phase Concentration in Y-phase... 

Figure 9 Timing diagram of the BIRD-HMBC pulse sequence for the detection of nJch correlations, including an additional two-step low-pass J filter. Thin and thick bars represent 90° and 180° pulses, respectively. 13C180° pulses are replaced by 90°y — 180°x — 90°y composite pulses. <5 is set to 0.5/(Vch) and A is set to 0.5/("JCH). Phases are cycled as follows fa = y, y, —y, —y 4>j = x, —x fa — 8(x), 8(—x) fa = 4(x), 4(— x) ( rec = 2 (x, — x), 4(—x, x), 2(x, —x). Phases not shown are along the x-axis. Gradient pulses are represented by filled half-ellipses denoted by Gi-G3. They should be applied in the ratio 50 30 40.1.

The complexes [PdCl2(133)2] catalyze the hydrogenolysis of 1-chloromethylnaphthalene with K[HCOO] or Na[HCOO]. Both the solid methanoates and their aqueous solutions could be used. Addition of [R4N]+X phase transfer agents significantly accelerated the hydrogenolysis of aryl halides with methanoates.347... 

The so-called HORROR experiment by Nielsen and coworkers [26] introduced continuous rf irradiation recoupling to homonuclear spin-pairs and initiated the later very widely used concept of /-encoded recoupling. Using a irreducible spherical approach as described above, the HORROR experiment (Fig. 2d) is readily described as starting out with the dipolar coupling Hamiltonian in (10) and x-phase rf irradiation in the form Hrf = ncor(Ix +SX), also here without initial constraint on n. The dipolar coupling Hamiltonian transforms into tilted frame (rotation n/2 around Iy + Sy)... 

At a given temperature and pressure eqs. (4.7) and (4.8) must be solved simultaneously to determine the compositions of the two phases a and P that correspond to coexistence. At isobaric conditions, a plot of the composition of the two phases in equilibrium versus temperature yields a part of the equilibrium T, x-phase diagram. 

The program includes a Pulse function, which has been added to the X phase. This is used to represent the effect of sudden addition of solute to this phase at TIME=Tswitch. 

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