Langmuir collapse pressure

Keywords Interface Langmuir monolayer Adsorption process Spreading solvent Surface tension Surface isotherm Langmuir-Blodgett film Collapse pressure Amphiphilic polymer... 

Different molecular areas of Langmuir monolayers can be determined. They can be defined in three ways Ao is the area per molecule extrapolated to zero differential surface tension, Ac is the minimum area per molecule at the collapse point, at the point in the tt - A isotherms where the pressure is the maximum reversible pressure (or collapse pressure ttc) and Am is the area at the midpoint pressure rrm = 0.5 TTC. 

The monomolecular area of the Langmuir films of DODA/HPA obtained at mN/m are 28.18 49.07iun mol. The monomolecular areas have been observed to decrease in the order of Cu>Mn>Ni>Co>Zn. The collapse pressures are 28,75-43.85 mN m, indicating that the monolayer and multilayer prepared have good stability. 

Langmuir films Cross section/(nm mol ) Collapse pressure/mN-m ... 

Monomolecular layers and LB-multilavers. Compound 21 exhibits amphiphilic properties. Spreading at the air-water interface leads to the formation of oriented monomolecular layers. The monolayer forms a solid condensed phase at 20 C with a collapse pressure near SOmN/m. It can easily be transferred onto various hydrophobic substrates such as CaF, ZnS, AgCl, Si, Ga or metal surfaces, and Langmuir-Blodgett-type multilayers (21> of variable thickness can be built up. These multilayers also exhibit a rapid reaction if exposed to UV- or y-irradiation. From an infrared spectroscopic study described recently (ll-JA) a 1,4-addition reaction is evident, as it also occurs in microcrystalline powders of 21- The solid state polymerization of 21 is schematically represented by Figure 14. 

Molecule 11 forms amphiphilic Pockels-Langmuir monolayers at the air-water interface, with a collapse pressure of 34 mN m and collapse areas of 50 A at 20 °C these monolayers transfer on the upstroke only, with transfer ratios around 100% onto hydrophilic glass, quartz, or aluminum,or onto fresh hydrophilic Au, but transfer poorly on the downstroke onto graphite, with a transfer ratio of only abont 50%. The LB monolayer thickness of 11 was 23-25 A by X-ray diffraction, spectroscopic ellip-sometry, surface plasmon resonance, and XPS. With... 

Collapse pressure (surface) The value of the surface pressure at which three-dimensional structures first emerge in a Langmuir monolayer upon compression. 

While the reviewer is prepared to admit the correspondence between the compressibility of a spread film of a protein and the chemical composition of the protein as expressed by the hydrophobic and hydrophilic character of the amino acid residues he feels that the correspondence is due to at least two causes First, a dehydration of the film as it is compressed and second, an orientation of the amino acid residue side chains. The relative importance of these two factors is a legitimate subject of controversy. Both factors should be very dependent on the hydrophobic and hydrophilic nature of the amino acid residues. There is, however, no evidence that at pressures below the collapse pressure any groups are forced out of the film in the sense of Langmuir and Waugh. 

Kwok DY, Tadros B, Deol H, VoUhardt D, Mfller R, Cabreiizo-Vilchez MA, Neumann AW (1996) Axisymmetiic drop shape analysis as a film balance rate dependence of the collapse pressure and molecular area at close packing of 1-octadecanol monolayers. Langmuir 12 1851-1859... 

Figure 8.20 Sequence of the preparation of a Langmuir-Btoggett film on water (a) before compression, (b) during compression, (c) at limiting pressure, (d) film collapse at higher pressure. Right Pres sure-surface diagram showing the phase changes L (gas-liquid) and S (liquid-solid). it, pressure and A surface area...

R. Aveyard, J. H. Clint, D. Nees, and N. Quirke, Structure and collapse of particle monolayers under lateral pressure at the octane/aqueous surfactant solution interface, Langmuir 16, 8820-8828 (2000). 

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