Compression and expansion cycle

In addition, it should be noted that none of the compression and expansion cycles for these films are coincident. The considerable hysteresis exhibited during the compression/expansion cycle is evidenced at every compression/expansion rate investigated, and is indicative of a stereoselective kinetic process that must occur upon film compression. Table 3 gives the monolayer stability limits of the amino acid methyl ester films as defined by... 

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.

The Yl/A isotherms for ( + )- and meso-C-12 6,6 keto diacids were given in Fig. 46. As was discussed, there are differences between the compression and expansion cycles for films cast from these diastereomers, which reflect... 

Comparison of the compression and expansion cycles for C-15 6,6 diacids linked with a carbonyl group (Fig. 41) and those linked with an amide group (Fig. 51A) show that the C-15 amide diacids, 6-(6-pentadecanoiccarbamoyl)-pentadecanoic acids (C-15 6,6 -A), also form much more highly condensed monolayers than do their keto counterparts. Addition of three methylene... 

Figures 51(A-C) give the compression and expansion cycles for the two isomers of the C-15 6,6 -A diacids at 25, 30 and 35°C. At 30°C, the energetics of compression of the second eluting C-15 6,6 -A diacid are similar to those of the second eluting C-12 6,6 -A diacid at 25°C. Raising the temperature causes a weakening of the intermolecular interactions in the monolayer spread...

In the above subsection it was demonstrated that the inclusion of electrostatic interactions into the pressure-area-temperature equation of state provides a better fit to the observed equilibrium behavior than the model with two-dimensional neutral gas. Considering this fact, we would like to devote our attention now to the character of the lipid film under the dynamical, nonequilibrium conditions. In the following we shall describe the dynamical behavior of the phospholipid(l,2-dipalmitoyl-3-sn-phosphatidylethanolamines DPPE) thin films in the course of the compression and expansion cycles at air/water interface. 

Figure 1.33. Test for the pristine state of the water-decane interface. The Interfaclal tension is measured during compression and expansion cycles (a) meticulously purified decane, (b) commercial decane sample. (Redrawn from R. Miller, P. Joos and V.B. Falnerman, Adv. Colloid Interface Set 49 (1994) 249.)...

A remarkable hysteresis between the compression and expansion cycles is apparent for the cellulose derivatives, with E4M the cellulose that showed the highest area within the compression and expansion cycles. This behavior is associated with the rearrangement and reorganization of the polymer... 

Quantitative information on penetrated layers under dynamic and equilibrium conditions require much attention in respect to the experimental technique. There are a number of penetration experiments with different advantages and drawbacks. The classical experiment is the injection technique where a soluble component is injected into the subphase below a spread monolayer. Experiments can then be performed at constant monolayer coverage [212, 213, 214] or by compression and expansion cycles [215, 216]. Another possibility is to exchange the subphase below a spread monolayer using a laminar pumping system. Other experiments were performed by using the sweeping technique as described in [217, 218]. 

Figure 46. Representative successive compression and expansion cycles (hysteresis) with a monolayer of Lig.

Aside from cavitation, the enhanced mass transfer rates in acoustic fields can be attributed to plug flow of capillary liquid as well as to enhanced dispersion of the liquid and vapor moisture due to alternating compression and expansion cycles, which result in reduced viscosity of the liquid-vapor mixture. In fact, a substantial increase in the amount of liquid diffusing through porous solids has been noted in the presence of ultrasound (Fairbanks and Chen, 1969 Woodford and Morrison, 1969 Kuznetsov and Subbotina, 1965). The enhanced diffusion appears to be of the directional type since mass transfer was hindered when ultrasound irradiation was opposed to the direction of diffusive flow (Kuznetsov and Subbotina, 1965). 

In 1963, Mendenhall and Mendenhall described an Instrument which can carry out the compression and expansion cycles of surface films automatically upto a ratio of 70 1. This phenomenon of alternate compression and expansion is called hysteresis. Study of hysteresis loops, i.e., surface tension as a function of area, are of physiological Importance. It has been observed that a surfactant found in the alveoli, responsible for the pressure-volume hysteresis following contraction and relaxation of the whole lung, exhibits hysteretic behaviour and thus prevents the lung from collapsing after a contraction wave (see Box 6.2). 

Bosker et al. studied the interfacial behavior of polystyrene-block-maltodextrins at the air-water interface via Langmuir-Blodgett technique [124]. Owing to the slow adsorption/desorption of the polysaccharide chains and block copolymer aggregation, the systems show interfacial pressure hysteresis between consecutive compression and expansion cycles of a monolayer. 

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