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Mixed-Film Formation

If two film components are structurally similar (e.g., two normal-chain carboxylic acids) the characteristics of the film produced by the mixture will lie between that formed by each separately (Fig. 8.19a). For example, if the two each form expanded films alone, the mixed film will also be of the expanded type. If, on the other hand, one is a condensed film and the other expanded, the mixture will be more condensed than the expanded film or more expanded than the condensed film. [Pg.170]

If dissimilar materials are mixed that can undergo specific interactions (e.g., alcohols with carboxylic acids), interesting effects can be observed (Fig. 8.19h). For example, if an alcohol is added to an acid layer of the same chain length. [Pg.170]

FIGURE 8.19. Mixed molecular films can have several possible structures, (a) An idel mixed film is one that has a homogeneous distribution of components throughout the film, but with no special interactions between components, (fe) A synergistic mixed film or complex involves specific interactions between component molecules that produce characteristics different from those expected for an ideal film, (c) Immiscible components may produce the expulsion of the more soluble component of the mixture at high surface pressure, (d) Heterogeneous mixed films may form islands (two-dimensional micelles ) of the components. [Pg.170]

A mixed-film phenomenon of particular interest in the biological and medical areas is that referred to as film penetration, in which a soluble surface-active material in the substrate enters into the surface film in sufficient quantity to alter its nature significantly, or to undergo some alternative physical or chemical process related to the surface (Fig. 8.20). Such penetration studies using films of biological materials have been used to mimic phenomena in biological systems (cell walls and membranes, for example) that cannot readily be studied directly. Of particular interest are such topics as cell surface reactions, catalysis, and transport across membranes. [Pg.171]

A typical penetration experiment might involve the formation of an insoluble monolayer at a surface pressure n, after which a soluble surface-active material is injected below the monolayer and changes in surface pressure (at constant area) due to penetration or inclusion of the new material in the monolayer are monitored. Alternatively, one can study changes in surface area at constant n, changes in surface potential, or a combination of any or all. [Pg.171]


Still another manifestation of mixed-film formation is the absorption of organic vapors by films. Stearic acid monolayers strongly absorb hexane up to a limiting ratio of 1 1 [272], and data reminiscent of adsorption isotherms for gases on solids are obtained, with the surface density of the monolayer constituting an added variable. [Pg.145]

In Chapter 4, Section III, attention was drawn to the Breuer-Robb (53) reactivity series of uncharged water-soluble polymers with anionic surfactants the reactivity followed the sequence PVA < PEO < MeC < PVAc < PPO PVP. Reactivity seemed to increase with increasing hydrophobic nature, and hence surface activity (19), of the polymer. An important implication is that those polymers that are reactive form mixed films at the surface of water when mixed with surfactants. Note that even though Jones (54), the pioneer of the surface tension method to assess interaction between polymer and surfactant in aqueous solution, utilized such measurements as an indicator of interaction in solution, he does not seem to have drawn any inferences of mixed film formation at the air/water interface—or its implications—at least in his early work. [Pg.212]

The energetics and kinetics of film formation appear to be especially important when two or more solutes are present, since now the matter of monolayer penetration or complex formation enters the picture (see Section IV-7). Schul-man and co-workers [77, 78], in particular, noted that especially stable emulsions result when the adsorbed film of surfactant material forms strong penetration complexes with a species present in the oil phase. The stabilizing effect of such mixed films may lie in their slow desorption or elevated viscosity. The dynamic effects of surfactant transport have been investigated by Shah and coworkers [22] who show the correlation between micellar lifetime and droplet size. More stable micelles are unable to rapidly transport surfactant from the bulk to the surface, and hence they support emulsions containing larger droplets. [Pg.505]

Figure 9-6T. (Top) Cascade Mini-Ring, (metal and plastic). Originally used by permission of Mass Transfer, Inc., now, Glitsch, Inc. (middle and bottom) Elevation and plan views of Ballast rings (right) and Cascade Mini-Rings (left). Note how high aspect ratio of former permits occlusion of interior surfaces. Low aspect ratio of Cascade Mini-Rings, on the other hand, favors orientation that exposes internal surfaces for excellent film formation, intimate mixing, and gas-liquid contact. Used by permission of Glitsch, Inc. Bull. 345. Figure 9-6T. (Top) Cascade Mini-Ring, (metal and plastic). Originally used by permission of Mass Transfer, Inc., now, Glitsch, Inc. (middle and bottom) Elevation and plan views of Ballast rings (right) and Cascade Mini-Rings (left). Note how high aspect ratio of former permits occlusion of interior surfaces. Low aspect ratio of Cascade Mini-Rings, on the other hand, favors orientation that exposes internal surfaces for excellent film formation, intimate mixing, and gas-liquid contact. Used by permission of Glitsch, Inc. Bull. 345.
Kinetic stability of lithium and the lithiated carbons results from film formation which yields protective layers on lithium or on the surfaces of carbonaceous materials, able to conduct lithium ions and to prevent the electrolyte from continuously being reduced film formation at the Li/PC interphase by the reductive decomposition of PC or EC/DMC yielding alkyl-carbonates passivates lithium, in contrast to the situation with DEC where lithium is dissolved to form lithium ethylcarbonate [149]. EMC is superior to DMC as a single solvent, due to better surface film properties at the carbon electrode [151]. However, the quality of films can be increased further by using the mixed solvent EMC/EC, in contrast to the recently proposed solvent methyl propyl carbonate (MPC) which may be used as a single sol-... [Pg.479]

A method resulting in improved encapsulation of aqueous phase by MLV is the so-called dehydration-rehydration procedure (Kirby and Gregoriadis, 1984 Shew and Deamer, 1985). The lipid (usually preformed liposomes) is dried (by either lyophilization or evaporation) in the presence of the aqueous solute to be entrapped, thus forming a mixed film with solute trapped between layers. Subsequent gradual rehydration with a minimum of aqueous phase leads to the formation of MLV with a high entrapment of the aqueous solutes added. [Pg.265]

The suppression of C60 crystallite formation in mixed LB films was attempted by mixing C60 and amphiphilic electron donor compounds [259]. Observation of the C60 LB film transferred horizontally by TEM clearly showed 10-40-nm-size crystallites. The diffraction pattern gave an fee lattice with unit cell length 1.410 nm. Examination of the mixed films with arachidic acid by TEM showed extensive crystallite formation. Mixed LB films of three different amphiphilic derivatives of electron donors with C60 were examined. One particular derivative showed very little formation of C60 crystallites when LB films were formed from monolayers of it mixed with C60 in a 1 2 ratio, while two others reduced C60 crystallite formation but did not eliminate it. [Pg.105]

Foam destabilization is also a factor in the packing and orientation of mixed films, which can be determined from monolayer studies. It is worth mentioning that foam formation from monolayers of amphiphiles constitutes the most fundamental process in everyday life. The other assemblies, such as vesicles and BLM, are somewhat more complicated systems, which are also found to be in equilibrium with monolayers. [Pg.165]

Bolhuis GK, Lerk CF, Zijlstra HT, De Boer AH. Film formation by magnesium stearate during mixing and its effect on tableting. Pharm Weekly 1975 110(16) 317—325. [Pg.107]

Sunflower Seed. Emulsion capacity of defatted sunflower meal was investigated by Huffman et al. (45) at three pH levels (5.2, 7.0, 10.8), blender speeds (4500, 6500, 9000 rpm), and oil addition rates (30, 45, 60 ml/min). With low mixing speeds and rapid rates of oil addition, optimum emulsion capacity occurred at pH 7.0. These authors related the observed emulsification properties to protein solubility, surface area and size of oil droplets, and rate of protein film formation. [Pg.229]

Discontinuities are seen in the relationship between increase in film pressure, An, and lipid composition following the injection of globulin under monolayers of lecithin-dihydro-ceramide lactoside and lecithin-cholesterol mixtures. The breaks occur at 80 mole % C 16-dihydrocaramide lactoside and 50 mole % cholesterol. Between 0 and 80 mole % lactoside and between 0 and 50 mole % cholesterol the mixed films behave as pure lecithin. Two possible explanations are the formation of complexes, having molar ratios of lecithin-lactoside 1 to 4 and lecithin-cholesterol 1 to 1 and/or the effect of monolayer configurations (surface micelles). In this model, lecithin is at the periphery of the surface micelle and shields the other lipid from interaction with globulin. [Pg.164]

Oxoalkoxocomplexes are oligomers of varying molecular complexity. The extent and conditions of distillation allow to control the nature of the species in solution, thus influencing the film-formation process [1368], This process of in situ modification ofmetal alkoxide solution by carboxylate ligand may have certain advantages with respect to the chemical uniformity as compared to the techniques based on simple mixing of a titanium alkoxide with alkaline-earth carboxylates. [Pg.135]

In order to facilitate optical quality film formation, the electroactive-diacid monomer was mixed with varying percentages of a saturated acid, with the electroactive acid incorporation varied from 5-50%. x was measured by DFWM on thin films (ca. 1 micron)... [Pg.664]

FIGURE 1.1. Schematic representation of a spin-coating experiment. Initially, the two polymers and the solvent are mixed. As the solvent evaporates during film formation, phase separation sets in resulting in a characteristic phase morphology in the final film (from [7]). [Pg.3]

Fluorescence Of Monolayers Containing Pyrene-Labeled Probes. A fluorescence probe method was also used as a complementary technique to study the thermodynamics of SA film formation. Mixed monolayers containing the fluorescence probe pyrene hexadecanoic acid, Py-C16, in host fatty acids of different lengths were prepared by adsoiption from solutions containing mostly the host fatty acid and a small fraction of Py-C16 (approximately 1 to 5 mol %). All monolayers were prepared under equilibrium adsoiption conditions. For fluorescence measurements only A1 substrate was used because when glass is used an impurity fluorescence from glass interferes with the pyrene fluorescence. [Pg.169]

A combination of ZDDP and hard-core RMs leads to a synergistic effect of metallic detergents on the degradation of ZDDP. These phenomena are observed in many tests and can be explained in terms of (a) the acid neutralization property of hard-core RMs that leads to the prevention of decomposition of ZDDP (in the valve train wear test and the thin film oxygen uptake test), (b) the competitive adsorption of detergents that reduce the effective concentration of ZDDP on the metal surface (in the four-ball test), (c) the formation of mixed films on the metal surface, formed through the decomposition of ZDDP in the presence of hard-core RM s (the coefficient of friction in the Falex wear test). [Pg.106]


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