Pressure area method

The subscript G specifies elasticity determined from isothermal equilibrium measurements, such as for the spreading pressure-area method, which is a thermodynamic property and is termed the Gibbs surface elasticity, EG. EG occurs in very thin films where the number of molecules is so low that the surfactant cannot restore the equilibrium surface concentration after deformation. 

The second-order steady drift force is derived directly from the first-order potential. Therefore, the steady drift force is computed by the pressure-area method within the linear diffraction/radiation program. The low or high frequency force calculations are much more complex in terms of a quadratic transfer function, which is extremely time-consuming. In order to reduce the computation effort for routine application in a design, simplified assumptions are often applied using fewer frequency pairs around the resonance frequency. This type of approximation is a common design practice. 

The catalytic activity of the pure /3-palladium hydride has been studied under the appropriate temperature and pressure conditions. The palladium sample was converted into the hydride in a manner which bypassed the area of coexistence of the phases. This was achieved by suitably saturating the metal with hydrogen at 35 atm above the critical temperature and then subsequently cooling the sample to the required temperature and reducing the hydrogen pressure. This method of sample prepare tion allowed one to avoid cracking the palladium crystallites, which would... 

The surface pressure-area (tc-A) isotherm measurements and LB film transfer were performed with the use of a KSV 5000 minitrough (KSV Instrument Co., Finland) operated at a continuous speed for two barriers of 10 cm2/min at 20°C. The buffer used in the present work was composed of 10 mM MES, 2 mM ascorbic acid sodium salt, and a given concentration of salt or polymers (pH =7.0). The accuracy of the surface pressure measurement was 0.01 mN/m. Monolayers of the PS I were transferred at 10 mN/m on hydrophobic substrate surface by horizontal lifting method. 

Two methods for applying blast loads will be used. The first is the Tributary Area Method which applies the roof panel pressure-time history to the loaded area of the purlin. The second method will use the dynamic reactions of the roof panel as the... 

For primary members (external walls, roof slabs, etc.), the load computation is performed in accordance with Chapter 3. Loads on supporting, or interior members, are determined either by I. the tributary area method or 2, from a computed dynamic reaction. In the tributary area method, external blast pressures are multiplied by the exterior surface area tributary to a support location. The resulting force is then applied to the next member. Dynamic reactions result from a numerical time history analysis (refer to Section 6.5.3) and provide a more accurate time-varying load on the supporting member. 

Influence of subphase temperature, pH, and molecular structure of the lipids on their phase behavior can easily be studied by means of this method. The effect of chain length and structure of polymerizable and natural lecithins is illustrated in Figure 5. At 30°C distearoyllecithin is still fully in the condensed state (33), whereas butadiene lecithin (4), which carries the same numEer of C-atoms per alkyl chain, is already completely in the expanded state (34). Although diacetylene lecithin (6) bears 26 C-atoms per chain, it forms both an expanded and a condensed phase at 30°C. The reason for these marked differences is the disturbance of the packing of the hydrophobic side chains by the double and triple bonds of the polymerizable lipids. At 2°C, however, all three lecithins are in the condensed state. Chapman (27) reports about the surface pressure area isotherms of two homologs of (6) containing 23 and 25 C-atoms per chain. These compounds exhibit expanded phases even at subphase temperatures as low as 7°C. 

When a surfactant is injected into the liquid beneath an insoluble monolayer, surfactant molecules may adsorb at the surface, penetrating between the monolayer molecules. However it is difficult to determine the extent of this penetration. In principle, equilibrium penetration is described by the Gibbs equation, but the practical application of this equation is complicated by the need to evaluate the dependence of the activity of monolayer substance on surface pressure. There have been several approaches to this problem. In this paper, previously published surface pressure-area Isotherms for cholesterol monolayers on solutions of hexadecy1-trimethyl-ammonium bromide have been analysed by three different methods and the results compared. For this system there is no significant difference between the adsorption calculated by the equation of Pethica and that from the procedure of Alexander and Barnes, but analysis by the method of Motomura, et al. gives results which differ considerably. These differences indicate that an independent experimental measurement of the adsorption should be capable of discriminating between the Motomura method and the other two. 

The measurement of surface pressure/area isotherms provides a method for studying the influence of parameters such as temperature, head group charge and size, alkyl chain length, and pH on membrane properties. The effect of head group bulkiness on surface pressure/area isotherms of polymerizable lysophospholipid analogs is illustrated in Fig. 7 36). 

Recording surface pressure/area isotherms is a relatively simple method for describing the miscibility behavior of a two component lipid mixture. The mean area per molecule of a binary mixture can be calculated using the following equation ... 

In the manufacture of MDIs, liquid filling procedures have been developed based on either a cold-filling method or a pressure-filling method. Both methods are suitable for either solution or suspension formulations and regardless of the process, it is important to maintain a low atmospheric relative humidity in the filling area to minimize condensation and possible absorption of water by the product. 

Methods. Using an Agla microsyringe, alkyl alcohol solution (0.025 ml) was spread on the subsolution of 0.01 M HC1. A time interval of 5 minutes was allowed for spreading solvents to evaporate or diffuse in the subsolution from the monolayers. The monolayer was compressed at a constant rate by an electrically operated motor. The surface pressure area curve for a monolayer was recorded automatically by x-y recorder. Three to five mono-layers of each mixture were studied and the results reported are average values. The reproducibility of data was + 0.15 8 /molecule. The detailed discussion of the apparatus is given elsewhere (17). 

There has been a continuous interest in monolayers since this pioneering work, motivated both by a desire to understand their nature and by the possible relation of monolayers to other structures, such as bilayers and micelles, which are built up from amphiphiles. This research has relied mainly on the methods that originated with the early workers in the field, chief among them measurements of surface pressure-area isotherms. These techniques are primarily thermodynamic in nature and therefore provide no direct information about the microscopic nature of the monolayer. Moreover, since the monolayer cannot be seen, the character of surface phases and the transitions between them can only be inferred. The experiments are difficult and subject to systematic errors, and their interpretation has often been ambiguous. 

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