Head-tail ordering phase diagram

The analogy between three- and two-dimensional phase diagrams can be carried much further. Monomolecular amphiphilic films show ordered phases similar to three-dimensional systems [579], The phases of an amphiphilic monolayer can be detected most conveniently in pressure-area (7r-versus-OA) isotherms. These may look different for different substances. The behavior of simple amphiphilic molecules, like long-chain alcohols, amines, or acids, was extensively investigated (reviews Refs. [580,581]). In monolayers so-called mesophases can occur. In a mesophase the tail groups are ordered over relatively large areas, while the order in the hydrophilic head groups is only over a much smaller distances. 

Figure 49. Phase diagram of CO physisorbed on graphite with the following phases commensurate orientationally disordered (>/3 x -s/3)/J30° solid phase (CD), commensurate orientationally ordered herringbone phase (HB), head-tail (dipolar) ordered commensurate herringbone phase (DHB), fluid (F), reentrant fluid (RF), incommensurate orientationally disordered solid (ID), incommensurate orientationally ordered pinwheel phase (PW), second-layer orientationally disordered solid (2SD), second-layer liquid (2L), second-layer vapor (2V), second-layer fluid (2F), bilayer orientationally ordered solid (BO) the parentheses are included for clarity only. The solid lines are based on experimental results, whereas the dashed lines are speculative. Note that the phase boundary (ID + CD) RF and the orientational disordering temperamre of the BO phase are unknown. Coverage unity corresponds to a coverage of CO forming a complete ( /3 x Vs) commensurate monolayer. (The phase diagram is based on Fig. 1 of Ref. 112, Fig. 2 of Ref. 113, and Refs. 380 and 381.

In order to investigate the effects of curvature in these systems further, a Gibbs binary phase diagram for mixtures of N,N-bis D-mannitolyl)-dodecylamide (two heads one tail, eolumnar). A, with octadecanoyl D-galactocerebroside, B, (two tails one head, columnar) was investigated, see Fig. 20. It was found that as the phase diagram was traversed as a... 

Amphiphiles are intriguing materials that self-assemble in various forms when mixed with oil and water. In disordered phases they take a structure of spherical droplets of water-in-oil (or oil-in-water) or a bicontinuous structure, in which both water and oil are separated from each other by intertwined interfacial films. In ordered phases they take a rather regular structure of hexagonal arrays of cylindrical tubules made of oil (or water) in surrounding water (or oil) or parallel arrays of alternative oil and water sheets. In these mixtures amphiphile molecules are mostly located at the interface of oil and water with their polar heads directed into water media and with apolar acyl tails into oil media, thus forming interfacial monolayers. The phase diagram of these structures depends strongly on temperature, pressure, kinds and concentrations of the... 

In the basic hydrodynamic equilibrium system (left), the slow rotation of the coil distributes the two phases evenly from the head of the coil (top). In order to obtain retention of the stationary phase in the coil under this hydrodynamic condition, the mobile phase, regardless of whether it is the heavier or lighter phase, should be introduced from the head of the coil. This operation results in a low level of stationary phase retention, usually much less than 50% of the total column capacity, as shown in the diagram. Elution of either phase from the tail of the coil would result in a total loss of the stationary phase from the coil. 

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