Pressure-area isotherm

Neumann has adapted the pendant drop experiment (see Section II-7) to measure the surface pressure of insoluble monolayers [70]. By varying the droplet volume with a motor-driven syringe, they measure the surface pressure as a function of area in both expansion and compression. In tests with octadecanol monolayers, they found excellent agreement between axisymmetric drop shape analysis and a conventional film balance. Unlike the Wilhelmy plate and film balance, the pendant drop experiment can be readily adapted to studies in a pressure cell [70]. In studies of the rate dependence of the molecular area at collapse, Neumann and co-workers found more consistent and reproducible results with the actual area at collapse rather than that determined by conventional extrapolation to zero surface pressure [71]. The collapse pressure and shape of the pressure-area isotherm change with the compression rate [72]. 

The three general states of monolayers are illustrated in the pressure-area isotherm in Fig. IV-16. A low-pressure gas phase, G, condenses to a liquid phase termed the /i uid-expanded (LE or L ) phase by Adam [183] and Harkins [9]. One or more of several more dense, liquid-condensed phase (LC) exist at higher pressures and lower temperatures. A solid phase (S) exists at high pressures and densities. We briefly describe these phases and their characteristic features and transitions several useful articles provide a more detailed description [184-187]. 

Fig. IV-16. A schematic pressure area isotherm illustrating the general states of mono-layers.

Pressure-area isotherms for many polymer films lack the well-defined phase regions shown in Fig. IV-16 such films give the appearance of being rather amorphous and plastic in nature. At low pressures, non-ideal-gas behavior is approached as seen in Fig. XV-1 for polyfmethyl acrylate) (PMA). The limiting slope is given by a viiial equation... 

Fig. XV-3. Four types of pressure-area isotherms observed in end-functionalized PDMS monolayers. Up to six transitions (A-F) are observed and described in the text. (From Ref. 6.)...

Fig. XV-6. Pressure-area isotherms for a synthetic lecithin at the indicated temperatures in degrees Celsius. [From H. E. Ries, Jr., M. Matsumoto, N. Uyeda, and E. Suito, Adv. Chem. Ser, No. 144, ACS, 1975, p. 286 (Ref. 37). Copyright 1975, American Chemical Society.]...

Fig. XV-14. Surface pressure-area isotherms at 298 K for a DPPC monolayer on phos-photungstic acid (10 Af) at the pH values shown with 10 A/ NaCl added. (From Ref. 123.)...

FIG. 22 Side view snapshots of a simulation of a 16-carbon hydrogenated surfactant chain with a carboxylate-like head group on a water surface at 300 K. The view iu (a) (top) is au area of 0.21 um molecule (b) (bottom) is at 0.21 um molecule . These two areas roughly bracket a first-order trausitiou with some features of the LE-LC transition. See also Figure 23 for the correspoudiug pressure-area isotherm. (Reproduced with permission from Ref. 364. Copyright 1992 American Chemical Society.)... 

The important issue of size effects was addressed by Karaborni and Siepmann [368]. They used the same chain model and other details employed in the Karaborni et al. simulations described earlier [362-365] and the 20-carbon chain. System sizes of 16, 64, and 256 molecules were employed with areas of 0.23, 0.25 and 0.27 nm molecule simulations with 64 molecules were also performed for areas ranging from 0.185 to 0.40 nm molecule . The temperature used was 275 K, as opposed to 300 K used in the previously discussed work by Karaborni et al. with the 20-carbon chain. At the smaller areas no significant system size dependence was found. However, the simulation at 0.27 nm molecule showed substantial differences between N = 64 and N = 256 in ordering and tilt angle. The 64-molecule system showed more order than the 256-molecule system and a slightly lower tilt angle. The pressure-area isotherm data for these simulations are not... 

The performance of demulsifiers can be predicted by the relationship between the film pressure of the demulsifier and the normalized area and the solvent properties of the demulsifier [1632]. The surfactant activity of the demulsifier is dependent on the bulk phase behavior of the chemical when dispersed in the crude oil emulsions. This behavior can be monitored by determining the demulsifier pressure-area isotherms for adsorption at the crude oil-water interface. 

B. P. Singh. Performance of demulsifiers prediction based on film pressure-area isotherms and solvent properties. Energy Sources, 16(3) 377-385, July-September 1994. 

Ruckenstein and Li proposed a relatively simple surface pressure-area equation of state for phospholipid monolayers at a water-oil interface [39]. The equation accounted for the clustering of the surfactant molecules, and led to second-order phase transitions. The monolayer was described as a 2D regular solution with three components singly dispersed phospholipid molecules, clusters of these molecules, and sites occupied by water and oil molecules. The effect of clusterng on the theoretical surface pressure-area isotherm was found to be crucial for the prediction of phase transitions. The model calculations fitted surprisingly well to the data of Taylor et al. [19] in the whole range of surface areas and the temperatures (Fig. 3). The number of molecules in a cluster was taken to be 150 due to an excellent agreement with an isotherm of DSPC when this... 

We studied the surface pressure area isotherms of PS II core complex at different concentrations of NaCl in the subphase (Fig. 2). Addition of NaCl solution greatly enhanced the stability of monolayer of PS II core complex particles at the air-water interface. The n-A curves at subphases of 100 mM and 200 mM NaCl clearly demonstrated that PS II core complexes can be compressed to a relatively high surface pressure (40mN/m), before the monolayer collapses under our experimental conditions. Moreover, the average particle size calculated from tt-A curves using the total amount of protein complex is about 320 nm. This observation agrees well with the particle size directly observed using atomic force microscopy [8], and indicates that nearly all the protein complexes stay at the water surface and form a well-structured monolayer. 

FIG. 2 The surface pressure-area isotherms of PS II core complex with different concentrations of salt in the subphase. Subphase, lOmM tris-HCl, pH 8.0, 2mM sodium ascorbate and concentrations of 100, 200, and 500mM NaCl. Temperature, 23.0 0.5°C. 

Our studies on the surface pressure-area isotherms of MGDG and the mixture of PS II core complex and MGDG indicate the presence of both PS II core complex and MGDG in the monolayer. MGDG molecules diluted the PS II core complex concentration in the monolayer. MGDG lipid functions as a support for the protein complex and the resulting mixture forms higher-quality films than PS II core complex alone. 

Fig. 5 Surface pressure/area isotherm for the compression cycle of dipalmitoylphos-phatidyl choline (dashed line) and l-palmitoyl-2-(l2-hydroxystearoyl)phosphatidyl choline (solid line) on a pure water subphase at 25°C. Reprinted with permission from Arnett et al., 1989. Copyright 1989 American Chemical Society.

Fig. 17 Surface pressure/area isotherms for the compression and expansion cycles of racemic (dashed line) and enantiomeric (solid line) stearoylserine (A), stearoyl-alanine (B), stearoyltryptophan (C), and stearoyltyrosine methyl esters (D) on a pure water subphase at 25°C carried out at a compression rate of 7.1 A2/molecule per minute. Arrows indicate the direction of compression and expansion.

Fig. 22 Surface pressure/area isotherms for the compression cycles of stearoyltyrosine on a buffered pH 6.86 subphase carried out at a compression rate of 19.24 A2/molecule per minute at 16,19,22,25,28, 31, and 34°C. Reprinted with permission from Harvey et ah, 1990. Copyright 1990 American Chemical Society.

Fig. 24 Surface pressure/area isotherms for palmitic acid/stearoylserine methyl ester films at 25°C on a pure water subphase and compressed at 29.8 A2/molecules per minute. A, 16.7-33.3% B, 50% C, 66.6% D, 83.3% SSME.

Fig. 32 Surface pressure/area isotherms for the compression/expansion cycles of diastereomeric monolayers of (R or S)-iV-(a-methylbenzyl)stearamides mixed 1 1 with (R or S )-stearoylalanine methyl esters on a pure water subphase at 35°C. Dashed lines denote heterochiral pairs (R S or R S) and solid lines denote homochiral pairs (R R or S S ).

Fig. 38 Surface pressure/area isotherms for the compression/expansion cycles of meso- (dashed line) and ( )-(solid line) azobis-[6-(6-cyanododecanoic acid)] on a pH 3 subphase at 22°C. Compressed at a rate of 15.5 A2/molecule per minute. Reprinted with permission from Porter et al., 1986a. Copyright 1986 American Chemical Society.

Fig. 45 Surface pressure/area isotherms for the compression cycle of 12-ketooctadecanoic acid (A) and octadecanoic acid (B) on a buffered subphase (AR hydrochloric acid pH 4.0) at 30°C carried out at a compression rate of 2.0-3.0 A2/molecule per minute.

Figure 15. Pressure-area isotherms for spread diacetylene monolayer of cadmium...

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