Langmuir film balance technique

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. 

Lee et al. used the Langmuir film balance technique to determine the hydrolytic kinetics of stereo-complex monolayers formed from PLLA/PDLA mixtures spread at the air-water interface. The hydrolysis of the mixture monolayers under basic conditions is slower than that of individual PLLA or PDLA monolayers, depending on the composition or the degree of com-plexation. In the presence of proteinase K, the hydrolysis rate of mixture monolayers with >50 mol% PLLA is much slower than that of the singlecomponent PLLA monolayer. The monolayers formed from mixtures with <50 mol% l-PLA do not show any degradation. It is concluded that the slower hydrolysis of mixture monolayers is mainly due to the strong interaction between PLLA and PDLA chains, which prevents the penetration of water or enzyme into the bulk. In an in vivo study on the biocompatibility of PLLA and stereo-complexed nanofibres by subcutaneous implantation in rats, Ishii et al. also observed that stereo-complexed nanofibres exhibit slower degradation than PLLA. ... 

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. 

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). 

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. 

Geetha, B. Mandal, A. B. 2-Dimensional Surface Properties of w-Methoxy Poly(ethyleneglycol) Macromonomer in Absence and Presence of Stearic Acid and Its Interaction with SDS As a Fimction of Different Mole Compositions at Various Temperatures at Air-Water Interface Thermodynamic studies Using Langmuir Film Balance (Monolayer) Technique. Langmuir, 2000,16, 3957-3963. 

The Langmuir-Blodged (LB) technique allows one to form a monolayer at the water surface and to transfer it to the surface of supports. Formation of the BR monolayer at the air/water interface, however, is not a trivial task, for it exists in the form of membrane fragments. These fragments are rather hydrophilic and can easily penetrate the subphase volume. In order to decrease the solubility, the subphase usually contains a concentrated salt solution. The efficiency of the film deposition by this approach (Sukhorukov et al. 1992) was already shown. Nevertheless, it does not allow one to orient the membrane fragments. Because the hydrophilic properties of the membrane sides are practically the same, fragments are randomly oriented in opposite ways at the air/water interface. Such a film cannot be useful for this work, because the proton pumping in the transferred film will be automatically compensated i.e., the net proton flux from one side of the film to the other side is balanced by a statistically equal flux in the opposite direction. 

By means of this apparatus, it is possible to vary the area of a spread monolayer and measure the corresponding film pressure directly. Many different variations of the film balance are available, and a number of instrumentational techniques can be combined with the Langmuir balance to obtain information on the microstructure of the films and the properties of the films. Figure 7.4b illustrates, for example, a laser optics arrangement to monitor the molecular orientation of the hydrocarbon tails of the surfactant molecules. Below in this... 

Techniques for spreading monolayers of polar long chain compounds on mercury in a Langmuir type film balance, and for measuring their surface area-pressure properties, have been described by one of the present authors (3). Using these techniques, it has proved possible to measure continuously the change in contact angle of a water droplet superposed on the monolayer, as the film pressure is controllably varied. This has now been done for monolayers of the normal C12-C20 fatty acids and the normal primary Ci4-Ci8 alcohols on the mercury substrate. 

Only two years after Langmuir published the design of his surface film balance ), now known as the Langmuir trough, his co-worker Miss Katharine Blodgett developed a technique for transferring monolayers from the alr/water interface to... 

In a very recent development the pendent drop technique was used to study the static and dynamic behaviour of insoluble monolayers. Kwok et al. (1994a) were the first who performed measurements of surface pressure - area isotherms of octadecanol monolayer by using a pendent water drop and ADSA (cf Section 5.4) as a film balance. Consistent results with classical Langmuir-Wilhelmy film balance measurements reveal ADSA as a powerful tool also for monolayers. 

The Langmuir-balance technique was adapted for the study of Indian crudes by Singh and Pandey (69). They separated the crudes into anionic, cationic, and nonionic fractions and studied the effects of electrolytes and pH on their film properties. Maximum film pressure was observed for films made with the anionic fraction and minimum film pressure for the cationic fractions. Increased electrolyte concentrations caused increased viscosity and less resolution of emulsions. Film pressures were maximum at pH 12 and more stable emulsions resulted. The electrolyte also had an adverse effect on the demulsifier. 

Nordli et al. (146), using the Langmuir-balance technique, studied the monolayer properties of the interfacially active fractions extracted from six North Sea crude oils over a subphase of distilled water and simulated formation water. The pH and salinity were varied. They compared additives such as butanol, benzyl alcohol, and octylamine, added to the subphase, to note changes in film compressibilities. A typical phase-change pattern for Langmuir ciuves of siuface pressure versus area was observed for all cases. The smallest specific area attributed to the liquid ex-... 

The interaction with an external surface in any material may induce a discontinuity and anisotropy in the energetic balance of the system, imposing effects different from those observed in bulk. In ferroelectric materials, it has been observed that finite size effects may also appear. However, it was verified that ultrathin films of P (VDF-TrFE) copolymers prepared via the Langmuir-Blodgett (LB) technique exhibit a F-P transition with a Tc nearly equal to the bulk value, but, in addition, another transition appears at a lower temperature, associated with the surface layers only [41]. LB films are highly crystalline, therefore, interfacial layers in this particular case do not present a large number of defects. Nevertheless, dielectric experiments have reported the presence of a dielectric segmental relaxation in P (VDF-TrFE) LB films, attributed to the motion of amorphous chains [42]. 

Figure 6 shows polystyrene (PS) particles of an average diameter of 11.9 xm retained on a freshly excised piece of sheep trachea and on a surfactant film of dipalmitoylphosphatidylcholine (DPPC) in a modified Langmuir-Wilhelmy balance. The surface tension in both cases is approximately 30 mN/m, measured by a drop-spreading technique on the trachea and by a Wilhelmy plate in the surface balance. The aqueous substrate for the film in the balance was 0.9% NaCl with 55% sucrose. The density of the substrate was 1.26 g/mL, considerably higher than that of the particle (1.05 g/cm ). Most of the particles retained on the tracheal surface appear to be submerged in the substrate, and only a small segment of the spheres is exposed to air above the three-phase line. This is equivalent to the situation in the surface balance. 

High-resolution circuitry and active devices employing Langmuir-Blodgett film techniques or polymer-based transistors are being considered for the sophisticated electronics required in future vehicles. Temperature or energy balance in the vehicle could be controlled through conductive polymers or semiconductor deposits on electrochromic windows. Electroluminescent liquid crystals and fluorescent and electrochromic materials used for visual displays show promise for future development. 

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