Langmuir film balance

Fig. 1 Schematic representation of the Langmuir film balance used for the measurement of pressure-area monolayer film properties. Reprinted with permission from Arnett et al., 1989. Copyright 1989 American Chemical Society.

The Langmuir film balance experiment as described above is generally considered to be thermodynamically determined by the relation between the independent variables temperature, surface pressure, and molecular area. 

Until very recently, there has been little or no experimental protocol for obtaining quantitative dynamic surface tension data on monolayer films. In most cases, the experimental set-up has consisted of a simple Langmuir film balance equipped with a variable-speed motor to drive the moving barrier. Hysteresis data were then obtained at a number of compression/expansion rates and compared qualitatively. This experimental set-up was improved considerably by Johnson (Arnett et al., 1988a), who modified a special... 

Figures 6 and 7 show a modem Langmuir film balance and its arrangement inside a Puffer-Hubbard temperature-controlled cabinet (63). Inside the cabinet, the film balance is protected further from circulating air currents by a Plexiglass case. At the bottom of the Teflon trough lies a serpentine glass coil through which water from a thermoregulator is circulated to help control subphase temperature.

A monomolecular layer of surfactants (or lipids) floating on an aqueous solution (the subphase), usually in a Langmuir film balance (the trough). 

EXPERIMENTAL MEASUREMENT OF FILM PRESSURE 7.3a LANGMUIR FILM BALANCE... 

Describe the Langmuir film balance and how it is used to measure surface tension. 

Fig. 6. Left Langmuir film balance, schematic right surface pressure/area isotherm of a monolayer at the gas/water interface (a-d, see text), n surface pressure A surface area33 ...

Using the surface of liquid water as the reflective substrate, infrared reflection-absorption spectra of phospholipid layers have been obtained (123-125). The infrared beam is taken external to the spectrometer with two CaF2 lenses and a flat mirror, with another flat mirror directing the reflected beam to the detector. A Langmuir film balance was designed (124) which allowed compression of the phospholipid layers to over 50 dyne/cm. 

Given the ubiquitous nature of interfacial thin films, and the current revival of interest in Langmuir film balance technology, we believe that the results and new techniques described in this chapter will find applications in analytical, physical, and biological chemistry. 

The interfacial properties of HM - PNIPAM, including the formation and the compression - expansion reversibility of the monolayers, at different subphase temperatures were more recently studied by using the Langmuir film balance technique [90], The stability and dynamic nature of the HM - PNIPAM monolayers were also further studied by the time - dependent surface pressure measurements. All results have suggested a compression - promoted temperature - and rate - dependent conformational rearrangement of the polymer on the water surface. Increasing the level of hydrophobic modifications progressively improved the monolayer compressibility and stability, and reduced the hysteresis. 

In the Langmuir film balance, a shallow trough is filled with a liquid, on top of which is placed material that can form a monolayer. The total surface area available can be adjusted by moveable barriers, and by means of a float. Any surface pressure thus created (jt) can be measured directly. See Figure 3.19. 

One of the most useful and more accessible experimental techniques allowing the behavior of molecules within membranes to be modeled is the study of monolayers. The easiest type of experiments to undertake in this field is the measurement of simple area/pressure isotherms using a Langmuir film balance. 

Neutron reflectometry has been applied to the study of a variety of surfaces, including solid polymeric films, ferromagnetic films, and pure liquid surfaces (Penfold and Thomas, 1990). The technique has also been used in conjunction with Langmuir film balance apparatus to study the adsorption of compounds at the air-water interface, e.g., alkyl trimethylammonium bromide surfactants (Lee et al., 1989), fatty acids (e.g., Grundy et al., 1988), and a variety of polymeric compounds (e.g., Henderson et al., 1991 Henderson, 1993). 

Blair et al. have also carried out Langmuir film balance measurements on monolayers of the photochromic polyamides mentioned above, namely the 3,3 - and 4,4 -poly-(azodibenzoyl-trans-2,5-monomer unit was observed and interpreted as resulting from azo trans to cis isomerization. The differences between the pressure-area curves of the meta(3,3 -) and para (4,4 -)polyamides were interpreted on the assumption that the meta compound has a helical structure and that the para compound is linear. 

To date, almost all attention has been paid to the nmacroscopic behavior at a centimeter level (film area and surface pressure) obtained with a Langmuir film balance. The photoinduced response at a molecular level, on the other hand, is obtainable by UV-visible absorption spearoscopy and surface-potential measurements. In these contexts, our attention recently has been paid to microscopic observations that cover the ranges between the previously cited scale levels using 6Azn-PVA monolayers. 

Fig. 8.18 Sketch of a Langmuir film balance. The trough (1) is completely filled with water or an aqueous solution the film is confined between a movable barrier (2) and a fixed floating barrier (3) which is attached to the posts of the pressure transducer system by gold foil barriers (4) surface pressure is detected by movement of mirror (5) attached between a torsion wire (6) and the floating barrier (3) the calibration arm (7) and torsion wire control (8) are used to relate mirror position to surface pressure.

From pressure-area isotherms on a Langmuir film balance, Smaby et al, (Smaby et al., 1997) reported the average area/molecule at 30 mN/m for a series of PCs decreased from... 

Abstract. Variations in the chemical composition of surfactants from natural sea slicks are compared to variations in surface elasticity using mass spectrometry, Langmuir film balance measurements, and multivariate statistical techniques. It is shown that the information on chemical class and molecular structure contained in the mass spectra is strongly correlated with measured static elasticity and can be used to estimate film elasticity at a given surface pressure. 

The mass spectral data selected for multivariate analysis represented a suite of 30 microlayer and bulk surface seawater surfactant samples (fraction FI Frew et al. (2006)) including seven from waters off Monterey and Santa Barbara, California and 23 collected along a transect from Delaware Bay on the U. S. east coast to the Sargasso Sea. Sample extracts were analysed in triplicate by desorption-electron ionisation (DEI) mass spectrometry (Boon 1992 Frew et al. 2006). Individual DEI mass scans were summed over the full desorption/pyrolysis interval, reduced to integer masses, and averaged for processing by multivariate analysis. Elasticities were estimated quasi-statically from surface pressure-area (El A) isotherm measurements in a KSV 2200 Langmuir film balance (Frew et al. 2006). The elasticity data were subsampled at fixed surface pressure intervals (0.5 mN m"1) for comparison with the results of the multivariate analysis. 

A Langmuir film balance can also be used to build up highly organized multilayers of surfactant films on solid substrates. This is accomplished by successively dipping a substrate... 

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