Condensation transition region

In Figure 7 a comparison is made of the frequency of the CHj antisymmetric stretching vibration as a function of molecular area for DPPC monolayer films at the A/W and A/Ge interfaces. As described above, the frequency of (his vibration is related to the overall macromolecular conformation of the lipid hydrocarbon chains. For the condensed phase monolayer (-40-45 A2 molecule 1), the measured frequency of the transferred monolayer film is virtually the same as that of the in-situ monolayer at the same molecular area, indicating a highly ordered acyl chain, predominately all-trans in character. For LE films as well as films transferred in the LE-LC phase transition region, however, the measured frequency appears independent (within experimental uncertainty) of the surface pressure, or molecular area, at which the film was transferred. The hydrocarbon chains of these films are more disordered than those of the condensed phase transferred films. However, no such easy comparison can be made to the in-situ monolayers at comparable molecular areas. For the LE monolayers (> ca. 70 A2 molecule 1), the transferred monolayers are more ordered than the in-situ film. In the LE-LC phase transition region ( 55-70 A2 molecule 1), the opposite behavior occurs. 

The results for the calculation of the orientation distribution for the hydrocarbon chains in the transferred monolayer films are presented in Figure 8. As is the case with the orientation distribution of the in-situ monolayers, the transferred films have a similar tilt angle in the expanded and phase transition regions. For the transferred monolayer, however, the tilt angle is in the range 35-40° from the surface normal, a much more oriented monolayer than the calculations indicate for the in-situ film (Figure 5). Figure 8 also shows that the condensed phase transferred monolayers are more oriented than those films transferred in the LE and LE-LC... 

Signs of elastic afterworking have been observed in a number of cases, though never so pronounced as in the above two. There seems to be a slight delay in reaching equilibrium in the films of myristic acid, especially in the transition region between the expanded and condensed states. A closer investigation of this phenomenon is needed. 

Nowadays the emphasis has switched to the study of phase transitions in condensed systems (left hand side of fig. 3.19). This is not surprising because it is a region to which modem optical techniques are often applied. As a systematic discussion is beyond the scope of FICS we make do with a few illustrations. 

In the transition region between laminar and turbulent condensation, the condensate film is wavy. In Fig. 4.12 this transition region is represented by the dotted lines, according to results from Henstock and Hanratti [4.16]. 

It should be noted that the local Nusselt numbers are plotted in Fig. 4.12. In a condenser, the Reynolds number formed with the film thickness changes from a value of zero, at the beginning of the condensation, to a final or end value. In between, within the transition region there may be states where the heat transfer is not particularly good, the mean heat transfer coefficient could be smaller than the local coefficient at the outlet cross section. Fig. 4.13 reproduces the mean heat transfer coefficients associated with Fig. 4.12, according to... 

In the calculation of heat transfer in the transition region between laminar and turbulent film condensation, empirical interpolation formulae are well established. One of these types of formulae is... 

Transition region between laminar and turbulent film condensation. 

In the transition region 256 Pr-0 44 < Petrans < 400 between laminar and turbulent Him condensation, the heat transfer coefficient according to (4.43) is obtained from... 

Fig. 15 Conceptual n - A isotherm for DPPC showing the different phases G for gas, LE for liquid expanded, LC-LE for the transition region where both liquid expanded and liquid condensed exist, and LC for the liquid condensed region...

To study the transition region, one must employ a hot fluid or a condensing vapor as the source of heat. Drew and Mueller (D3) obtained transition boiling data for six liquids boiling on a steam-heated copper... 

The LE one-phase region extends from the end of the first plateau to the start of the second. At this point, a phase transition takes place to another condensed phase, called the liquid-condensed (LC) phase. In the literature on phospholipids, the LE-LC transition region is called the main transition. 

Figure 1. Upper Schematic of it-A isotherms in the transition region F-F represents region where bulk of film material is in the condensed monolayer state G-G represents the region where virtually all of the film is in the gaseous monolayer state. Area per molecule is the total area occupied by the sum of all lipid molecules in the surface.

Chemical Activities by the Surface Vapor Pressure Method. Surface pressure measurements in the transition region between the condensed and gaseous monolayer states of a single lipid component spread as a monolayer on water yield a value of ir which is independent of the surface area. This value—the surface vapor pressure, irv—is analogous to the vapor pressure of a liquid in equilibrium with its vapor. When a second lipid component is in the surface, the limits of miscibility in the condensed phase may be determined on the basis of the surface vapor pressure dependence on the mole fraction in the condensed phase (8). 

Figure 1 represents the isotherms for two lipid components which are miscible in the condensed monolayer state. The major feature of the isotherms for the pure components (1 0, 0 1) is the transition region in which the surface pressure is independent of surface area here the limits of the transition region are at the low area end, Ac, and at the high area end, Ax. These areas are characteristic of each lipid and represent the area per molecule of the lipid in the condensed and vapor states (10). For an equimolar mixture of the two components (1 1), the surface pressure in the transition region depends on the surface area according to the phase rule (11, 12, 13, 14), two surface phases coexist here a condensed phase of lipids and the surface vapor phase. To obtain the activity coefficient of the ith component in the condensed phase the following relation may be used ... 

Measurement of the optical constants, that is, ideally, of the real and imaginary parts of the dielectric response of a medium, gives full information about the electronic and vibrational transitions in condensed media, at least those which are optically active through dipole interactions. Three regions of the spectrum can be distinguished, although they often overlap they more or less correspond to distinct physical phenomena. 

In our discussion of the inert adsorbent case in previous sections and in V (18) we implicitly chose, when gas was adsorbed, a dividing surface in the transition region between adsorbed film and gas (i.e., where the relatively high density of the film falls off rather suddenly to the gas density). This surface was not defined precisely. All molecules between the dividing surface and the surface of the adsorbent were considered as belonging to the condensed phase. Everywhere outside of the dividing surface the gas density was assumed to obtain. 

The formation and propagation of disturbance in an initially uniform gas bounded by its plane condensed phase in nonequilibrium with the gas are investigated in detail on the basis of the Boltzmann-Krook-Welander equation when evaporation takes place from the condensed phase. From the long time solution, the steady behavior of the gas (the transition region from the condensed phase to the uniform state at infinity, the relations among the variables at infinity and on the condensed phase) is clarified. Further the effect of different boundary conditions at the condensed phase on the steady evaporation is discussed. 

Most transitions in a supersaturated thymine solution leading from a non-condensed to a condensed film involve nucleation and growth, via a metastable intermediate surface state, as do some transitions between condensed films. The latter have unusually high Avrami slopes and, sometimes, involve multiple intermediate states. Of the three pit regions... 

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