Surface tension molecular mass

All aqueous solutions of anionic or cationic dyes have lower surface tension than pure water. Solutions of the free sulphonic acids give lower values than solutions of the sodium salts of anionic dyes. The decrease in surface tension depends more on the degree of sulphonation of the dye than on its relative molecular mass, although alkyl substituents may... 

Surface contaminants affect mass transfer via hydrodynamic and molecular effects, and it is convenient to consider these separately. Hydrodynamic effects include two phenomena which act in opposition. In the absence of mass transfer, contaminants decrease the mobility of the interface as discussed in Section ILD. In the presence of mass transfer, however, motion at the interface may be enhanced through the action of local surface tension gradients caused by small differences in concentration along the interface. This enhancement of surface... 

Surface tension can be explained on the basis of molecular theoiy. If the surface area of liquid is expanded, some of the molecules inside the liquid rise to the surface. Because a molecule inside a mass of liquid is under the forces of the surrounding molecules, while a molecule on the surface is only partly surrounded by other molecules, work is necessaiy to bring molecules from the inside to the surface. This indicates that force must be... 

Since the molecule is thermalized it does not possess sufficient energy to penetrate the surface of water. This requires energy on the order of the surface tension of the liquid. Therefore, the entry of the molecule into the liquid phase depends on collective phenomena wherein an opening sufficiently large to accommodate the molecule is created at the surface site of the gas molecule. Designating p as the rate at which sufficiently large holes are formed at the surface per unit area per unit time and Am as the area of the molecular site, then the mass accommodation coefficient can be written as... 

The surface tension is important for the calculation of mass transfer coefficients and the specific contact area (see Section 9.4.4). Depending on the availability of necessary parameters, the surface tension for a molecular species can be determined either with the simplest method of Hakim-Steinberg-Stiel or with a more complex DIPPR-method (see Ref. [52]). The mixture surface tension can be obtained via a mixing rule. A further extension to cover electrolyte mixtures is realized by the method of Onsager and Samaras (see Ref. [44]). The latter uses an additive term which can be estimated using the dielectric constant of the mixture and molar volumes of electrolytes. 

Studies on certain other physicochemical aspects of surfactant action have been reported or reviewed (9, 24, 30, 31, 40, 47). Entry of oils, some organic solvents, and aqueous sprays, with lowered surface tensions, into stomata is apparently a mass movement entry through cuticle is by diffusion, at least initially (12, 16, 25). Cuticular diffusion is conditioned by particle size, pH and buffers, molecular structures (of penetrant, solvent, additive, and plant surface), prevalence of water and other factors (reviewed in Refs. 12 and 47 cf. other references cited). The final influ-... 

Independence of the fundamental equations from the nature of molecular attraction. All the results of this chapter have been deduced from the existence of a constant free energy in the surface a constant amount of work must be done to form each fresh unit of area. The work comes from the inward pull exerted by the underlying molecules on the surface layer its constancy from the mobility of the molecules and the assumption that the molecular attractions do not extend with sensible intensity to distances comparable with the mass of liquid considered, so that some part of the liquid is free from surface influences. This assumption excludes the hypothesis that the molecular attractions are gravitational, which is still sometimes suggested if the attractions diminished as the inverse square of the distance, the surface tension of the oceans would be far greater than that of a cupful of water, because the distant parts would act with sensible effect. Any theory of molecular attraction, in which the forces practically vanish at small distances, will harmonize with the results of this chapter. 

Microscopic foam films have been used to study the steric interaction between two liquid/gas interfaces [130]. Two ABA triblock copolymers of the Synperonic PE series were employed P85 and F108. These commercial non-ionic surfactant were used as obtained from ICI Surfactants, Witton, UK. Blocks A are hydrophilic polyethylene oxide (PEO) chains, while block B is a hydrophobic polypropylene oxide (PPO) chain. The molecular masses and average EO contents are known from the manufacturer and yield approximate chemical formulae (Table 3.3). Data about the surface tension of electrolyte-free aqueous copolymer solutions can be seen in Fig. 3.31 [130]. It was additionally checked that NaCl (up to 510 2 mol dm 3) had no influence on these values. 

In many structured products, water management includes several mass transport mechanisms such as hydrodynamic flow, capillary flow and molecular self-diffusion depending on the length scale. Hydrodynamic flow is active in large and open structures and it is driven by external forces such as gravity or by differences in the chemical potential, that is, differences in concentrations at different locations in the structure. Capillary flow also depends on surface tension and occurs in channels and pores on shorter length scales than in hydrodynamic flow. A capillary gel structure will hold water, and external pressures equivalent to the capillary pressure will be needed to remove the water. 

Proteins and polysaccharides (PS) are present in many kinds of foods. The main role of proteins in foamed products is to stabilize the air-water interface through their capacity to lower the surface tension of water (Damodaran and Paraf, 1997). p-Lactoglobulin ((3-lg), the most abundant protein in whey, is a globular protein of molecular mass 18.3 kDa being stabilized by two internal disulfide cross-linkings, and exhibits good foaming properties. 

MeC adsorbs at the air water interface leading to a decrease in the surface tension. An equilibrium state is only reached at very long times, due to the high molecular mass of methylcellulose. The layer which is present at the interface at equilibrium is almost purely elastic with a large dilational elastic modulus. The value of the excluded volume critical exponent extracted from the E-n curve indicates that the air-water interface is not a good solvent for the polymer. 

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