Surface pressure-area relationships

Mixtures of N-(a-methylbenzyl) stearamides with both stearoyltyrosine and stearoyltryptophan methyl esters show no discrimination in their pressure-area relationships at 35°C, regardless of the surface pressure to which the films are compressed (Fig. 34). The Yl/A curves for homo- and hetero-chiral pairs are exactly coincident. 

These synthetic hydrophilic polymers hydrophobically modified can be good systems with which to try to establish relationships between chemical structure and interfacial characteristics. It was determined the surface pressure - area (tt - A) isotherms at the air - water interface for poly(4-vinylpyridine) quaternized as a function of the methylene group number of the alkyl lateral chains (n). The film formation of these polymers on aqueous subphase at constant pH and ionic strength... 

The surface pressure - area isotherms were collected at different temperatures and the energy relationship between rod and coil as a function of rod length was analized [134], The microstructures of these monolayers based on the energy relationship were also investigated using Atomic Force Microscopy (AFM). 

Figure 7.9 Surface pressure-area U-A relationships of monolayers showing the different phases. The molecular configurations for condensed and expanded monolayers are shown (right). Polar head groups are represented by circles and hydrocarbon chains by zig-zag lines.

When a monolayer at equilibrium, with surface pressure ir, is subjected to compression at a speed of v cm /sec, the surface pressure, it, is increased because of the reduction of surface area, A. The increase in surface pressure will change the free energy of the adsorbed molecules and lead to a desorption of whole molecules or segments of molecules if these are reversibly adsorbed. The relationship between surface pressure and surface area for a monolayer may be given by an equation of state ... 

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 ... 

Mixed Films. Isotherm data from two-component monolayers are frequently represented by plotting the mean molecular area as a function of film composition at constant surface pressure. A linear relationship is usually obtained when the two components are immiscible or when they form an ideal two-dimensional solution. For miscible components, deviations from ideality result in a nonlinearity in the plot. Positive deviations indicate an Increase in the area occupied by either one or both components, probably due to... 

Use of an organic monolayer can be either as prepared on the surface of a liquid or after being transferred to a solid substrate to make an LB monolayer. Use of such a molecular assembly as a stencil or a template has many advantages. Besides its relatively simple procedure for template preparation, the periodicity of the functional groups or particular ions can be regulated by appropriate additives and the surface area of the monolayer by using a known surface area-surface pressure relationship. 

Direct observations of sub-surface pressure allow a calibration to be made between the SGR and seal capacity. Ideally, an in situ measurement of the pore-pressure in the reservoir and that inside the fault zone would allow the capillary entry pressure of the fault to be calculated. However, fault-zone pressures are rarely available. Instead, the pressure difference between the two walls of the fault is a more general parameter that can be derived from pressure measurements in pairs of wells across the fault. Fig. 7a shows one such calibration, based on the Nun River dataset of Bouvier et al. (1989). From their strike projections of Fault K , values of SGR have been calculated on a dense grid across the fault surface. On the same grid, minimum across-fault pressure differences have also been derived, using the proven distribution of hydrocarbons in the footwall sands to calculate buoyancy pressures. Fig. 7a shows a cross-plot of these two parameters for the areas of sand-sand contact at the fault surface. The dashed line indicates the inferred relationship between SGR and seal capacity. At SGR < 20%, no fault-sealed hydrocarbons are observed the shale content of the slipped interval... 

Tnteractions at surfaces have long been at the center of interest in the study of surfactant monolayers and have been thought to influence both static and dynamic surface properties considerably (1,2). Although the theoretical interpretation and even the definition of surface interactions may be controversial, the experimental method has not been in doubt. Invariably, the equilibrium surface pressure vs. molar area relationship has been used as a criterion for assessing interactions in mono-layers since interactions, no matter what their precise definition, must appear in the measurable quantity of surface tension (y) or surface pressure (7r = y° — y) at a given surface concentration (r) or molar... 

For very large aggregates, a quite simple relationship can be proposed which provides a correction of F, with respect to the ratio of the molar areas of molecules existing in aggregates and as monomers, and to the surface pressure change [98]... 

Since the surface pressure of a spread film is the two-dimensional equivalent of pressure, attempts have been made to set down an equation of state for the spread film. All derivations make use of the basic thermodynamic relationship between the surface pressure and the surface area (A) ... 

Insoluble molecules spread on liquid surfaces. This behavior corresponds to that of an ideal gas if the coverage is small. Analogous to the ideal gas equation, the following is valid for the relationship between the surface pressure, given as 7o the difference between the surface tensions of the covering, and the covered surface, and the surface area per molecule of spreading material ... 

The relationships between surface pressure and surface or interfacial area can be used to gauge hydrophilicity. This method has been used, for example, to quantify the hydrophilicity of PDMS modified with ethylene oxide or propylene groups. ... 

The surface pressure (jr) and surface tension are related by the equation jt = 7t = y -y (y = surface tension of pure liquid, y = surface tension of liquid covered with a film). The relationship between surface pressure (jr) and surface area (A), which falls on one molecule of a substance is ir = k.T/A = k. TKA-a),... 

---