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Condensation two-dimensional

Evidence for two-dimensional condensation at the water-Hg interface is reviewed by de Levie [135]. Adsorption may also be studied via differential capacity data where the interface is modeled as parallel capacitors, one for the Hg-solvent interface and another for the Hg-adsorbate interface [136, 137]. [Pg.202]

It must be remembered that, in general, the constants a and b of the van der Waals equation depend on volume and on temperature. Thus a number of variants are possible, and some of these and the corresponding adsorption isotherms are given in Table XVII-2. All of them lead to rather complex adsorption equations, but the general appearance of the family of isotherms from any one of them is as illustrated in Fig. XVII-11. The dotted line in the figure represents the presumed actual course of that particular isotherm and corresponds to a two-dimensional condensation from gas to liquid. Notice the general similarity to the plots of the Langmuir plus the lateral interaction equation shown in Fig. XVII-4. [Pg.624]

Adsorption of a condensed 1-hydroxy-adamantane layer at the Hg elec-trode/(Na2S04 or NaF) solution interface has been studied as a function of temperature by Stenina et al. [174]. Later, Stenina etal. [175] have determined adsorption parameters and their temperature dependence for a two-dimensional condensation of adamantanol-1 at a mercury electrode in Na2S04 solutions. They have also studied coadsorption of halide (F , Cl , Br ) anions and 1-adamantanol molecules on Hg electrode [176]. More recently, Stenina etal. [177] have described a new type of an adsorption layer comprising organic molecules of a cage structure condensed at the electrode/solution interface. This phenomenon was discovered for adsorption of cubane derivatives at mercury electrode. [Pg.982]

At the surface of water, amphipathic molecules are oriented in such a way as to interact extensively, at least for ordinary surface concentrations. This results in the formation of the various two-dimensional condensed phases with the attendant effect on surface viscosity. In this section we consider some situations for which monolayers or the concepts involved in their discussion find application. [Pg.320]

Type I is represented by lines LONM in Figure 12, with two well-defined changes of slope occurring at O and N the precise form depends on the surface pressure. This behavior is found when the tt-A curve of the pure expanded component exhibits a two-dimensional condensation (Table I and Figures 2, 3, and 4). [Pg.146]

The results obtained at surface pressures of 5 and 10 dynes per cm. are complicated by the fact that the trilaurin has undergone a two-dimensional condensation at 5°C., and we will not attempt interpretation at this time. A complete understanding of the molecular interactions involved in such mixed films must await a deeper insight into the interactions involved in films of pure components. We are presently attempting to evaluate such interactions by a thermodynamic study of compression of single-component films (5), with the ultimate objective of obtaining a fuller understanding of mixed films on a molecular basis. [Pg.154]

A sigmoidal isotherm (type D) indicates cooperative effects. A molecule binds to the surface better if it can interact with a neighboring adsorbed molecule. As a consequence of this lateral interaction two-dimensional condensation occurs. In order to observe sigmoidal isotherms, flat and homogeneous adsorbents are required. [Pg.181]

Here, a is a material-dependent constant. Basic lectures on physical chemistry usually start by showing how the three-dimensional van der Waals equation of state explains condensation. Therefore the pressure is plotted versus the volume at constant temperature. By analogy, when plotting the film pressure 7r versus the molecular area a a at constant temperature, a two-dimensional condensation of monolayers is predicted, at least for temperatures below a certain critical temperature. [Pg.283]

Fang, Y. and Yang, J. (1997) Two-dimensional condensation of DNA molecules on cationic lipid membranes. J. Phys. Chem., B, 101,441 149. [Pg.188]

Step-wise adsorption results from two-dimensional condensation (Sec. VIII,4) on homogeneous surfaces. If, at the same time, multi-molecular adsorption takes place, steps may be found in the building up of every successive layer. These steps, however, do not coincide with the filling up of every successive layer 115). [Pg.62]

Argon on graphite, at higher 0 values, shows the same behavior as nitrogen on single-crystal copper, as has been described above 223). The mutual van der Waals attraction forces may, in this case, lead to two-dimensional condensation, as is also shown by the entropy data. We shall discuss two-dimensional condensation in Sec. VIII,4. [Pg.100]

The mutual van der Waals attraction of adsorbed molecules may lead to two-dimensional condensation phenomena. We shall not discuss these phenomena in detail but shall refer to some recent reviews and general treatments (238,239). A few remarks will, therefore, be sufficient here. [Pg.104]

Two-dimensional condensation may even be an endothermic process when the difference between the heats of adsorption of the molecules in their flat positions and in their positions perpendicular to the surface is larger than the contribution of the mutual attraction of the van der Waals forces during two-dimensional condensation (240). [Pg.105]

Hill (241) has discussed the two-dimensional condensation phenomena in localized adsorbed layers. Two-dimensional condensation from a dilute localized adsorbed layer to a relatively condensed localized layer may also occur in this case at temperatures lower than a two-dimensional critical temperature. [Pg.105]

Two-dimensional condensation—on homogeneous surfaces—leads to sudden jumps in the adsorption isotherm. These jumps may already be found at very low pressures of the gas which is in equilibrium with the adsorbed layer (242). Heterogeneous surfaces do not give rise to sudden jumps but to gradual slopes (Sec. V,12). There is sometimes a tendency to consider such jumps as indications of multimoleeular adsorption this is not correct. It is of course true that stepwise adsorption can also occur together with multimoleeular adsorption. (See also Sec. V,12.)... [Pg.105]

Another unique and specific feature of the interfacial reaction is the formation of aggregate of dye molecules, metal complexes, and other solvophobic molecules. As reported in many interfacial adsorption systems, the saturated interfacial concentration of usual molecules is of the order of 10 10mol/cm2, which can be attained even under an extremely low bulk phase concentration. This means that the liquid-liquid interface is ready to be saturated to form a two-dimensionally condensed state for the adsorbate. In solvent extraction process of metal ions, we used to find formation of some precipitate at the interface, which is called crud. The study of the interfacial aggregate is therefore important to know the real interfacial reaction as met in the industrial solvent extraction where rather concentrated solutes have to be treated. [Pg.301]

Merte, H., Jr. and Son, S., Further Consideration of Two-Dimensional Condensation Drop Profiles and Departure Sizes, Warmeund Stoffubertragung, Vol. 21, pp. 163-168. [Pg.603]

The occurrence of loops in the isotherms indicates the existence of two-dimensional condensation. This phenomenon sets in for a critical value C0 which is greater than that encountered by Bumble and Honig (2)—i.e., to achieve two-dimensional condensation the lateral interactions must be stronger than those required in (1). Again, this is believed to be primarily due to the difference in Z values for the two cases. [Pg.250]

Haly and Snaith (1968) measured the specific heat of the water-wool system from 0 to near 0.4 h, for temperatures from — 70 to 100°C. At high temperature (i.e., 80°C) the discontinuity between regions III and IV, defined above for the heat capacity isotherm and corresponding to the low-coverage two-dimensional condensation, may be absent, raising the possibility of a two-dimensional critical temperature. [Pg.50]

At the 0.07 h discontinuity, the heat capacity function shifts from generally downward-trending to strongly upward-trending. This is expected for a two-dimensional condensation process—here, the formation of mobile water clusters from dispersed water associated with ionizable protein surface groups. This transition in the surface water is seen also in the IR spectroscopic properties (Fig. 38) and other proper-... [Pg.132]

The interaction of CO with the solid surface produces several physical and chemical effects on the vibrational properties of the adsorbed species. The adsorption of CO can be envisaged as a two-dimensional condensation, leading to lateral coupling between adsorbed molecules. The vibrational properties of adsorbed CO can thus be used to monitor the effects of other interface properties, such as surface defects, two-dimensional phase transitions [45] and co-adsorption. Finally, CO is formed as an intermediate or poison during the oxidation of several organic molecules at electrodes, thus constituting one of the subjects of interest in electrocatalysis. [Pg.147]

Heterogeneity also has its consequences for the critical temperatures below which two-dimensional condensation may occur. For some models of monolayer adsorption with lateral attraction, the critical conditions have been established (in sec. I.3.8d for the FFG isotherm, in sec. I.3.8e for the quasi-chemical approximation and in sec. 1.5e for a two-dimensional Van der Waals gas). The value of Is a criterion for the validity of an isotherm model, but heterogeneity greatly detracts from it. Heterogeneity inhibits two-dimensional condensation or, in other words, is reduced by an extent that Is the greater, the more heterogeneous a surface. General experience confirms this for instance, for a two-dimensional Van der Waals gas = 0.5T (three-dimensional), but in practice always a factor below 0.5 is found ). [Pg.142]

Alemozafar AR, Madix RJ (2004) Two-dimensional condensation anisotropic crystallization H /Ni(110). Surf Sci 557 231... [Pg.248]

In the case of surfactants with more than 8 CH2 groups in the alkyl chain and for a particular equilibrium concentration C, , the filling of the surface abruptly increases from 0 0 up to 0 = 1. This vertical step corresponds to a two dimensional condensation for an undersaturation Afi with respect to the precipitate phase obtained at Csat, ... [Pg.322]


See other pages where Condensation two-dimensional is mentioned: [Pg.81]    [Pg.264]    [Pg.26]    [Pg.9]    [Pg.101]    [Pg.105]    [Pg.242]    [Pg.875]    [Pg.383]    [Pg.99]    [Pg.104]    [Pg.104]    [Pg.405]    [Pg.405]    [Pg.410]    [Pg.111]    [Pg.251]    [Pg.44]    [Pg.49]    [Pg.134]    [Pg.217]    [Pg.4]    [Pg.61]    [Pg.319]   
See also in sourсe #XX -- [ Pg.7 ]

See also in sourсe #XX -- [ Pg.311 ]




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