Condensed phase transferred monolayers

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... 

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. 

Prior to LB transfer, the surface pressure - molecular area (n-A) isotherms of dialkylsilane under various pH and temperature conditions were investigated. The pH condition of the subphase (water phase under the monolayer) is a crucial factor for the monolayer state. The condensed phase was formed directly without formation... 

By stud)dng the structure of LB monolayers as a function of transfer pressure different phases have been visualized, mostly on a mesoscopic scale ). Domain changes and phase transitions, e.g., as a function of temperature, have also been studied ). If the roughness of the underlying substrate precludes domain imaging by normal force measurements, domains might be imaged through lateral force measurements. The inner structure of condensed-phase domains czm be visual-... 

Monomolecular layers and LB-multilavers. Compound 21 exhibits amphiphilic properties. Spreading at the air-water interface leads to the formation of oriented monomolecular layers. The monolayer forms a solid condensed phase at 20 C with a collapse pressure near SOmN/m. It can easily be transferred onto various hydrophobic substrates such as CaF, ZnS, AgCl, Si, Ga or metal surfaces, and Langmuir-Blodgett-type multilayers (21> of variable thickness can be built up. These multilayers also exhibit a rapid reaction if exposed to UV- or y-irradiation. From an infrared spectroscopic study described recently (ll-JA) a 1,4-addition reaction is evident, as it also occurs in microcrystalline powders of 21- The solid state polymerization of 21 is schematically represented by Figure 14. 

At the air-water interface, water molecules are constantly evaporating and condensing in a closed container. In an open container, water molecules at the surface will desorb and diffuse into the gas phase. It is therefore important to determine the effect of a monomolecular film of amphiphiles at the interface. The measurement of the evaporation of water through monolayer films was found to be of considerable interest in the study of methods for controlling evaporation from great lakes. Many important atmospheric reactions involve interfacial interactions of gas molecules (oxygen and different pollutants) with aqueous droplets of clouds and fog as well as ocean surfaces. The presence of monolayer films would thus have an appreciable effect on such mass transfer reactions. 

The phase transition was induced by Ca and Mg in the case of dipalmitoyl-phosphatidylserine to form a condensed monolayer at the nitrobenzene-water interface, which was stable throughout the potential window. The capacitance in the presence of the condensed monolayer was as low as 1.5 pF cm [101]. The phase transitions from the expanded to the condensed monolayer accompanied the concomitant decrease in the rate of ion transfer but even the condensed monolayers were unable to block it completely [100, 101]. 

The lateral energy in the adsorbed layer calculated from Eq.(5) experimentally varies from 1.36+0.03 kT to 1.93+0.1 kT. It corresponds to an adsorbed layer in which the aliphatic chains are parallel and stretched towards the solvent. The free energy on transfer between CH2 is not constant. It is not the case for smooth or plane surface. In the present case the adsorbed phase is in a very condensed state. In this case the molecular area of the surfactants in the adsorbed layer is minimal 20.8[14]. Therefore the specific surface area of each solid precipitated at pH 6.5 and 7.5 may be calculated. At the monolayer the adsorbed amount Qq is ... 

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