Water-air interface, effect

Adsorption Layers of /LCasein at the Air/Water Interface Effect of Guanidine Hydrochloride... 

Ruggles J.L., Holt S.A., Reynolds P.A., White J.W. Synthesis of silica films at the air/water interface Effect of template chain length and ionic strength. Langmuir 2000 16 4613 619 Ryan K.M., Erts D., Olin H., Morris M.A., Holmes J.D. Three dimensional architectures of ultra-high density semiconducting nanowires deposited on chip. J. Am. Chem. Soc. 2003 125 6284-6288... 

Shinkai [15] concluded that p-zert-butyl calix[n]ar-ene tetra esters form stable monolayers at the air-water interface and the metal responds, therein, quite differently from that in solution. They reported that examination of the metal template effect on the conformer distribution established that when the metal cation present in the base used serves as a template, the cone conformer results are predominant [16]. Hence, Na in... 

Fulda and Tieke [77] studied the effect of a bidisperse-size distribution of latex particles on the structure of the resulting LB monolayer. For this purpose, a mixed colloidal solution of particles la and lb was spread at the air-water interface. Particles la had a diameter of 434 nm, particles lb of 214 nm. The monolayer was compressed, transferred onto a solid substrate, and viewed in a scanning electron microscope (SEM). In Figure 10, SEM pictures of LB layers obtained from various bidisperse mixtures are shown. 

The interaction between the adsorbed molecules and a chemical species present in the opposite side of the interface is clearly seen in the effect of the counterion species on the HTMA adsorption. Electrocapillary curves in Fig. 6 show that the interfacial tension at a given potential in the presence of the HTMA ion adsorption depends on the anionic species in the aqueous side of the interface and decreases in the order, F, CP, and Br [40]. By changing the counterions from F to CP or Br, the adsorption free energy of HTMA increase by 1.2 or 4.6 kJmoP. This greater effect of Br ions is in harmony with the results obtained at the air-water interface [43]. We note that this effect of the counterion species from the opposite side of the interface does not necessarily mean the interfacial ion-pair formation, which seems to suppose the presence of salt formation at the boundary layer [44-46]. A thermodynamic criterion of the interfacial ion-pair formation has been discussed in detail [40]. 

These differences reflect the conformations of (+)- and meso-isomers as they sit at the air-water interface. What is much harder to elucidate is the effect of stereochemistry on intermolecular interactions. How does changing the stereochemistry at one chiral center affect interactions between diastereomers Ab initio molecular orbital calculations have been used to address the problem of separating stereochemically dependent inter- and intra-molecular interactions in diastereomeric compounds (Craig et al., 1971). For example, diastereomeric compounds such as 2,3-dicyanobutane exhibit significant energetic dependence on intramolecular configuration about their chiral centers. So far, however, little experimental attention has been focused on this problem. 

It has been shown by Harvey et al. (1989) that incorporation of palmitic acid into a monolayer spread from stearoylserine methyl ester (SSME) breaks up intermolecular SSME interactions. The palmitic acid acts as a two-dimensional diluent. Figures 52(A-C) give the Yl/A isotherms for mixtures of FE and SE C-15 6,6 -A with palmitic acid. Dilution of the monolayer cast from the second eluting isomer with 15 mol% palmitic acid separates the diacid molecules from one another on the water surface and perhaps allows for the expression of their stereochemically dependent conformations. The mixed film (15% palmitic acid/85% C-15 6,6 -A) expands at low II and behaves in much the same manner as the single-component monolayer (C-15 6,6 -A) behaves at 30°C. Addition of 15 mole% palmitic acid into a monolayer cast from the FE C-15 diacid has little effect on its energetics of compression, indicating a stronger intermolecular interaction afforded by its stereochemically dependent conformation at the air-water interface. 

This chapter has reported the only extensive and coordinated investigation of the effects of chirality on the properties of monolayer films spread at the air-water interface. Twenty compounds of varied headgroup and chain length have been examined carrying one and two chiral centers. In every case, all of the optical isomers—enantiomers and diastereomers—were made and their properties measured both as pure compounds and as mixed monolayers in order to compare phase changes in the films with mixed melting points of the crystals. 

Effect of lowering and raising speeds on the detachment of cadmium octadecanoate LB films from a QCM substrate at the air-water interface (20 °C)a... 

The effect of the time at the interface and the time in water on the detached amount was examined separately to clarify whether LB films peeled off mainly at the air-water interface or in the water phase, and the results are summarized in Table 5. Runs 1-8 show the flaking amount of cadmium octadecanoate LB films with the constant dipping speed the constant time at the interface) and the different time in water. The results indicate the detached amount was independent of the time in water. On the contrary, when the time at the interface was increased and the time in water was kept constant, the detached amount of the LB films increased about two times larger (Runs 9 - 15). From these findings, It can be concluded that the LB films peeled off at the air-water interface but not in the water phase when the substrate is lowered slowly with the long contact time at the interface. 

Figure 6 shows the effects of compression rate on the ji-A curve for the PhDA2-8 thin film at air/water interface. Accompanied with the increase in the compression rate, the hump becomes more significant and the maximum surface pressure of the hump shifts toward the larger surface area. It is to be noted that the region with zero surface pressure appears only with appropriate compression rates of 3 - 7.5 (A2/molecule)/min as in (d), (e), and (f). 

Figure 8. (A) Schematic representation of the shape of the function f(rt). The arrows represent the first order like phase transition effect. The two straight lines are f(tt) = 17.5tt + 20.0 and f(n) = O.Olrc, respectively. (B) Schematic representation of the relationship between the surface pressure (ji) and the effective concentration of surfactant at the air/water interface (T f). The solid and dashed lines represent the expected and ideal relationships, respectively.

Now we consider the relationship between the effective concentration(reff) and the surface pressure(tt) at the air/water interface. Ideally, the surface pressure is directly proportional to the concentration of surfactants. However, as the actual it-A isotherms show several specific effects, such as limiting area and points of inflexion, we shall assume the following relationships ... 

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