Films film balance

The automated pendant drop technique has been used as a film balance to study the surface tension of insoluble monolayers [75] (see Chapter IV). A motor-driven syringe allows changes in drop volume to study surface tension as a function of surface areas as in conventional film balance measurements. This approach is useful for materials available in limited quantities and it can be extended to study monolayers at liquid-liquid interfaces [76],... 

A sketch of Langmuir s film balance is shown in Ref. 7 and a modem version of a film balance, in Fig. IV-5. 

The film pressure is defined as the difference between the surface tension of the pure fluid and that of the film-covered surface. While any method of surface tension measurement can be used, most of the methods of capillarity are, for one reason or another, ill-suited for work with film-covered surfaces with the principal exceptions of the Wilhelmy slide method (Section II-6) and the pendant drop experiment (Section II-7). Both approaches work very well with fluid films and are capable of measuring low values of pressure with similar precision of 0.01 dyn/cm. In addition, the film balance, considerably updated since Langmuir s design (see Section III-7) is a popular approach to measurement of V. 

This method suffers from two disadvantages. Since it measures 7 or changes in 7 rather than t directly, temperature drifts or adventitious impurities can alter 7 and be mistakenly attributed to changes in film pressure. Second, while ensuring that zero contact angle is seldom a problem in the case of pure liquids, it may be with film-covered surfaces as film material may adsorb on the slide. This problem can be a serious one roughening the plate may help, and some of the literature on techniques is summarized by Gaines [69]. On the other hand, the equipment for the Wilhelmy slide method is simple and inexpensive and can be just as accurate as the film balance described below. 

Neumann has adapted the pendant drop experiment (see Section II-7) to measure the surface pressure of insoluble monolayers [70]. By varying the droplet volume with a motor-driven syringe, they measure the surface pressure as a function of area in both expansion and compression. In tests with octadecanol monolayers, they found excellent agreement between axisymmetric drop shape analysis and a conventional film balance. Unlike the Wilhelmy plate and film balance, the pendant drop experiment can be readily adapted to studies in a pressure cell [70]. In studies of the rate dependence of the molecular area at collapse, Neumann and co-workers found more consistent and reproducible results with the actual area at collapse rather than that determined by conventional extrapolation to zero surface pressure [71]. The collapse pressure and shape of the pressure-area isotherm change with the compression rate [72]. 

Film pressure is often measured directly by means of a film balance. The principle of the method involves the direct measurement of the horizontal force on a float separating the film from clean solvent surface. The film balance has been considerably refined since the crude model used by Langmuir and in many... 

Some recommendations on reporting film balance r-a data have been made to the International Union of Pure and Applied Chemistry [82]. 

Polacolor films are balanced for daylight exposure and rated at ISO speed 80. Processing can be carried out satisfactorily at temperatures from 16—38°C, with slight exposure compensation recommended at the extremes. 

Kodak instant cameras included battery-operated motorized and lower cost hand-cranked models. The pictures began to develop as they were ejected from the camera, and development proceeded over several minutes under ambient conditions. The films were balanced for daylight exposure. 

Film balance techniques 49 Equilibrium thermodynamic properties 51 n/A curves and phase transitions 54 Dynamic methods 57... 

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. 

The film balance may be regarded as a two-dimensional piston, and the most commonly studied property is the surface pressure (n) versus area (A) isotherm. The analogy to a PV isotherm is so appropriate that in the gaseous monolayer regime the two-dimensional analogue of the ideal gas law pertains 114 = nRT. It is therefore reasonable to relate discontinuities in n/A isotherms as the monolayer film is compressed in two dimensions to... 

Fig. 6 Detail of the Verger film balance modified for measurement of surface shear viscosity. Reprinted with permission from Harvey et al, 1988. Copyright 1988 American Chemical Society.

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... 

Despite its attractive capabilities, the epifluorescence technique has some drawbacks. The fluorescent surfactant probe must not be miscible with the major phase of interest, and must not interact with the major phase in any way that changes the rheological flow or compression characteristics of the film. In addition, the probe itself must form a stable monolayer on the air-water interface. The area in which this work is to be performed must also be clean enough for accurate film balance work and must be free of vibration. 

We were interested in examining the corresponding monolayer photolysis products of the diazenes as a function of surface pressure. This goal was not reached due to our inability to collect enough material from the film balance experiment (typically, 1016 molecules per run) for HPLC analysis. However, the physical data acquired by interfacial techniques has given information about the nature of the aggregates and their diastereoselectivity. 

Because the adsorbed HM-HEC molecules exhibit such slow rates of chain reorientation, the effects of molecular weight, amount of hydrophobic substitution and chain lengths of the hydrophobes on the interfacial properties of HM-HEC monolayers can be investigated by two kinds of dynamic experiments hysteresis and stress-jump, using a Langmuir trough film balance. 

The dispersant used in these studies is Chevron Chemicals OLOA 1200, a polybutene of about 70 carbon atoms attached to a succinic acid group which is reacted with diethylene triamine to provide the basic anchoring group. Film balance studies showed that the adsorbed films have a film thickness of 50 X. This dispersant is supplied as a 50 w% solution in a mineral oil. It can be deoiled by adsorption from toluene onto silica with elution by acetone. In this paper the w% of dispersant refers to the deoiled material. 

Figure 2. Schematic of the Langmuir Blodgett film balance and monolayer deposition at the air-water interphase.

Pressure-area (jt-A) isotherms were obtained at various Tsps with a microprocessor-controlled film balance system. The static elasticity, Ks of the monolayer on the water surface was evaluated from the jr-A isotherm by using the following equation 1-3],... 

Figure 17 shows the chemical structures of anionic amphiphile sodium-1,2-bis (tetradecylcarbonyl)ethane-l-sulfonate (2Cj4SNa)[34] and poly(ethyleneimine)(PEI). A benzene/ethanol (9 1)(WV) solution of anionic amphiphile was spread on the pure water surface or the PEI-water solution (lxlO5 unit M in monomer unit, pH=3.2) surface at a subphase temperature, Tsp of 293 K. At this pH, ca. 70 % of nitrogen atom in PEI molecule was protonated[35]. Surface pressure-area(ji-A) isotherms were measured with a microprocessor controlled film balance system. 

Measurements of pressure-area (jc-A) isotherms and transfers of monolayers on a substrate were carried out by using a computer-controlled film balance system (San-Esu Keisoku, Co., Fukuoka, FSD-20). Maximum surface area on the trough was 475 X 150 mm2. The trough surface and the moving barrier were coated with Teflon, and the subphase was temperature-controlled with a thermostat (20 0.5 °C). The concentration of lipid solutions was 1 mg/ml and the spreading amount of lipid solutions was 50 - 150 pi. After solvent evaporation, the monolayer was compressed at the speed of 0.60 cm2 s-i. Measurements of n-A isotherms and transfers of monolayer on a QCM substrate were performed automatically with the usual manner [26,27]. 

Thin-film balance apparatus, 12 7 Thin-film composite membranes, 21 633 Thin-film deposition, laser ablation for, 24 740... 

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