Surface pressure-area diagrams

The polymer forms a stable monolayer on the surface of water. The surface pressure-area diagram of the monolayer is shown in Figure 7.1, where the surface area S is calculated per ionic side group. The collapse pressure ofthe monolayer is equal to 54 mN/m. 

The pol3mierization behaviour of these membrane systems can be characterized in monolayers and liposomes using surface pressure-area diagrams or DSC investigations respectively. Decreased membrane permeability and improved stability towards the addition of detergents of pol3nnerized vesicles can be verified by leakage measurements of entrapped 6-carboxyfluorescein. 

Amphiphilic compounds such as lipids are able to form monomolecular films when applied to a gas-water interface. These two-dimensional systems can be characterized recording phase diagrams in variation of surface-pressure, area, or temperature. These surface pressure-area diagrams are usually measured on a Langmuir film balance schematically illustrated in fig. 3. 

Fig. 3 Left Langmuir film balance, schematic right surface pressure-area diagram of a monolayer at the gas water interface (a-d, see text). p=pressure, A=area...

Besides studying the influence of parameters such as temperature, headgroup size and charge, alkyl chain length, and pH, surface pressure-area diagrams also allow the observation of polyreactions in such systems as shown in fig. 4. 

The orientation of the monomer units during pol3nneri-zation of the monolayer remains unchanged the reaction results in a highly oriented stable film. UV-initiated monolayer pol mierization has been intensively studied in recent years (12-15), Normally, the reactions involve contraction of the film the surface pressure-area diagrams of the polymers exhibit a smaller occupied area, a steeper slope, and a higher collapse pressure (13). Hence, the polyreaction can be followed by measuring the film contraction V9. time at constant surface pressure as shown in fig, 5 for the diacetylene lipid (12),... 

In the present study various surface measurements were made on interfacial lipid films to analyze in more detail the nature of interactions of lipids, Ca2+, ATP, and the glycolate esters. Surface pressure-area and surface potential-area diagrams were obtained on surface films of stearic acid, lecithin, and a mixture of brain lipids with Ca2+, ATP, and the drugs present in the subsolution, individually or in combination. Using radioactive Ca2+, ATP, and drug, quantitative measurements were made on the surface adsorption of these substances to lipid films. In addition, electron microscopy was performed on brain lipid films formed in the presence or absence of Ca2+ and ATP. Our objective was to establish the existence of surface complexes involving these substances with the hope... 

Figure 1 shows the surface pressure—area curve of stearyl alcohol monolayer at pH 2.0 and 25 °C, where Ae is the area/molecule in the expanded state at zero surface pressure, Ac is the area/molecule in the condensed state at zero surface pressure, and A2o is the area/molecule at surface pressure of 20dynes/cm. Figure 2 shows the values of Ae, Ac, and A2o for various alkyl alcohols. From this diagram the average area per molecule in mixed monolayers was calculated using simple additivity rule. Figure 3 shows the excess molecular area when Ci6 alkyl alcohol... 

Monolayers of adsorbed molecules at the air-water interface display phase transitions. Monolayers of octadecylamine salts of perfluoroalkanoates on 4.4M NaCl solution exhibit two or three types of phase transitions in their tt-A (surface pressure-area) isotherms [43]. The phases were classified and phase diagrams drawn from the phase-transition pressures and surface potentials. 

Fig. 13 shows the curves of surface pressure against area for the fatty acids with from 11 to 15 carbon atoms in the hydrocarbon chains.1 The main diagram has the surface pressure as ordinates and the area as abscissae inset are the FA-F curves. With the shorter chain acids, below about 0 1 dyne, the product FA is of the same order as, but somewhat below, the value for a perfect and unassociated gaseous film Moss and... 

The relation between film stability, spreading coefficient on a substrate and surface pressure can be found using the method proposed by Frumkin [20] and Derjaguin [538]. A diagram is drawn of the dependence film tension versus area of a mole of the substance in the film (Ao = I/O, T being the number of moles of the substance in a unit area. At small substance concentrations (pressures) in the gas phase, its adsorption is close to Gibbs adsorption. 

Figure 4.3. To maintain a constant surface pressure during the deposition process, the area enclosed by the barrier is reduced systematically. This schematic Y-type dipping sequence for a diagram shows a staircase structure of 4, 8, 12, and 16 monolayers. Courtesy of Joyce-Loebl Company, Gateshead, England.)...

Figure 1. Schematic diagram of a Langmuir trough. The monolayer is deposited to the right of the barrier, and the barrier can be moved across the surface to change the area accessible to the monolayer. The surface pressure can be measured either by determining the force on a float that separates the monolayer from a clean water surface, or from the difference in the force exerted on the Wilhelmy plate when the plate is suspended in pure water and in water covered by the monolayer.

A number of methods have recently been applied to determining the properties of polymer membranes. These include the spreading of mono-layers at an air-water interface and also the production of vesicles or liposomes. The former method allows for the compression of the two-dimensional film between movable barriers. At the same time a film balance registers the change in surface pressure as a function of molecular area, thereby producing a pressure-area isotherm. Various states of molecular orientation can be determined from the shapes of the plot, typified by the diagram in Fig. 5.20. Such states are analogous to those in three-dimensional systems, i.e. solid, liquid, gas. 

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