Langmuir monolayers molecular areas

Anotlier metliod applicable to interfaces is tlie detennination of tlie partial molecular area (7 of a biopolynier partitioning into a lipid monolayer at tlie water-air interface using tlie Langmuir trough [28]. The first step is to record a series of pressure 71-area (A) isotlienns witli different amounts of an amphiphilic biopolynier spread at tlie interface. 

This way it has been possible to observe the anticipated conformational transition by experiment. Cylindrical brushes of polybutylacrylate-graft polymethacrylate were adsorbed on the surface of water from a CHCI3 solution on a Langmuir trough and studied by recording the tt-A (surface pressure vs molecular area) isotherm. At different stages of compression, the monolayer was... 

Figure 3.3 shows as an example, the surface pressure-area per repeating unit (tt - A) isotherms of Langmuir monolayers obtaining by spreading of poly(N-vinyl-2-pyrrolidone) (PVP) on aqueous Na2SC>4 subphase, for both molecular weights and several temperatures [44],... 

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. 

Unwin and coworkers studied oxygen transfer across a monolayer dispersed at an air-water interface [74]. They have constructed an SECM measurement system in a Langmuir trough. A monolayer of 1-octadecanol was formed on the aqueous subphase containing potassium nitrate and the surface pressure of the mono-layer was controlled with a compression barrier. A U-shaped microelectrode probe was placed in the aqueous solution and moved up to the air-water interface. When the probe approaches an air-water interface in the absence of the monolayer, the reduction current for O2 is enhanced by positive feedback, due to fast translocation of O2 from the gas phase to the solution. They recorded a set of approach curves while controlling the monolayer compression. A plot of the oxygen transfer rate as a function of the molecular area has been shown. 

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