Surface-active solute

Both the hquid and cured 2-cyanoacryhc esters support combustion. These adhesives should not be used near sparks, heat, or open flame, or ia areas of acute fire ha2ard. Highly exothermic polymerization can occur from direct addition of catalytic substances such as water, alcohols, and bases such as amines, ammonia, or caustics, or from contamination with any of the available surface activator solutions. 

Foam Fractionation. An interesting experimental method that has been performed for wastewater treatment of disperse dyes is foam fractionation (88). This method is based on the phenomenon that surface-active solutes collect at gas—Hquid iaterfaces. The results were 86—96% color removal from a brown disperse dye solution and 75% color removal from a textile mill wastewater. Unfortunately, the necessary chemical costs make this method relatively expensive (see Foams). 

Ashokkumar M, Hodnett M, Zeqiri B, Grieser F, Price G (2007) Acoustic emission spectra from 515 kHz cavitation in aqueous solutions containing surface-active solutes. J Am Chem Soc 129 2250-2258... 

Lee J, Tuziuti T, Yasui K, Kentish S, Grieser F, Ashokkumar M, Iida Y (2007) Influence of surface-active solutes on the coalescence, clustering, and fragmentation of acoustic bubbles confined in a microspace. J Phys Chem C 111 19015-19023... 

Tuziuti T, Yasui K, Lee J, Kozuka T, Towata A, Iida Y (2009) Influence of surface active solute on ultrasonic waveform distortion in liquid containing air bubbles. J Phys Chem A... 

Grieser F, Ashokkumar M (2001) The effect of surface active solutes on bubbles exposed to ultrasound. Adv Colloid Interface Sci 89-90 423 138... 

During the transfer of a surface-active solute across the surface, unstable surface-tension gradients may occur in the plane of the surface. A good example is furnished by Langmuir s experiment (10) on the evaporation of ether from a saturated (5.6%) solution in water talc... 

Surface-active solutes accumulate in the interface between two phases in accordance with their concentration and their ability to re-... 

As in Basic Protocol 1, the steps below describe determination of interfacial tension for a liguid/gas interface (i.e., a sample consisting of a single surface-active solution). Although it is very difficult, the ring method can also be used to determine the interfacial tension between two liquid phases (for modifications see Alternate Protocol 1). 

Finally, we can estimate the comparative influence of plasma and serum proteins with molecular weights > 20,000 on the cell-serum and cell-plasma interfaces, as opposed to surface-active solutes such as ethylene glycol or dimethylsulfoxide (6). The latter will adsorb at the interfaces to an extent that is comparable with their adsorption at the liquid-... 

A comprehensive study on the sonochemical synthesis of colloidal solutions of noble metals was conducted by Grieser and coworkers [32-34]. The 515 kHz ultrasound-initiated reduction of AuCl4 to Au (0) was examined as a function of the concentration of various surface-active solutes [32]. The amount of AuCU reduced in the presence of ethanol, 1-propanol, and 1-butanol was found to be dependent on the surface excess of the alcohol at the gas/solution interface, i.e., the relative concentration of the alcohol at the gas/solution interface compared to the bulk solution concentration. The efficiency of reduction of AuCl4 in the presence of the surfactants sodium dodecyl sulfate or octaethylene glycol monodecyl ether was found to be related to the monomer concentration of the surfactant in solution. 

Bubble fractionation is similar to foam fractionation except that there is no foam produced in the system thus, it is applied to dilute surface-active solutions that do not foam while foam fractionation is applied to surface-active solutes at high concentration (76,77). Technically speaking, bubble fractionation represents an operation in which gas is bubbled up through a vertical bubble reactor containing the surface-active solute(s)... 

For an ideal two-component solution consisting of a solvent and a single surface-active solute at equilibrium condition, and with concentration assumed to be equivalent to activity (i.e., dilute solution), Eq. (1) may be written as... 

In water solution containing small particles (i.e., suspended solids or turbidity) and non-surface-active solutes, when air is bubbled through it, little or no particles will be removed by any adsorptive bubble separation process. This is because the particles have virtually no natural affinity for air bubbles and hence there is no adhesion when contact is made. This particular phenomena may be explained by the contact angle between a particle and an air bubble. Consider the case of the three-phase fine of contact between a smooth, rigid, solid phase, a liquid phase and a gas phase. The equilibrium contact angle can be expressed in terms of the average surface tensions (i.e., interfacial tensions, dyne/cm) of the liquid-gas solid-liquid (r j ), and solid-gas (r ) interfaces, by the well-known Young s equation ... 

Increasing surfactant concentrations in the aeration cell has been found to decrease bubble diameter, bubble velocity, axial diffusion coefficient, but increase bubble s surface-to-volume ratio, and total bubble surface area in the system. The effect of a surface-active agent on the total surface area of the bubbles is also a function of its operating conditions. The surfactant s effect is pronounced in the case of a coarse gas diffuser where the chances of coalescence are great and the effectiveness of a surface-active solute in preventing coalescence increases with the length of its carbon chain. 

In the batch adsorptive bubble separation processes, a feed solution was introduced to a bubble separation column (or chamber) containing an aqueous solution of surface-active materials. Surface-active solutes or complexes that are hydrophobic and readily attachable to the air bubbles are carried up to the surface of the water by the bubbles. The enriched material at the top (whether collapsed foam from a foam separation column or overflow liquid from a nonfoaming bubble separation column) and the clarified drain solution at the bottom are withdrawn from the system. The overall material balance for the process is as follows ... 

Non-reacting surface-active solutes may tend to keep reactants, which are less surface-active, out of the interface and so slow down the reaction rate. They may also retard mass transfer and hence reactions, by impeding the surface renewal. But surface-active solutes, which enter into reactions, may speed up surface renewal and accelerate reactions by causing turbulence in the vital interfacial region. Examples of all the three effects have been discussed and their relative importance considered by Richardson (1982). It would appear that the interfacial blocking may retard rates up to one-hundred fold, whereas retardation or enhancement of surface renewal in stirred systems is only likely to decrease or increase rates by a factor of five or ten. Interfacial phenomena may also... 

In the case of a dilute, ideal solution of a non-surface-active solute, y = 1 and tJ2V2 Expanding the last term on the right-hand side of (9.25) and keeping... 

The adsorption isotherm of nonionic surfactants are in many cases Langmuirian, much like those of most other highly surface active solutes adsorbing from dilute solutions, and the adsorption is generally reversible. However, several other adsorption types are produced [29], and these are illustrated in Figure 5.7. The steps... 

Stemling and Scriven wrote the interfacial boundary conditions on nonsteady flows with free boundary and they analyzed the conditions for hydrodynamic instability when some surface-active solute transfer occurs across the interface. In particular, they predicted that oscillatory instability demands suitable conditions cmcially dependent on the ratio of viscous and other (heat or mass) transport coefficients at adjacent phases. This was the starting point of numerous theoretical and experimental studies on interfacial hydrodynamics (see Reference 4, and references therein). Instability of the interfacial motion is decided by the value of the Marangoni number, Ma, defined as the ratio of the interfacial convective mass flux and the total mass flux from the bulk phases evaluated at the interface. When diffusion is the limiting step to the solute interfacial transfer, it is given by... 

There are a number of mechanisms by which surface-active solutes may adsorb onto solid substrates from aqueous solution. In general, adsorption of surfactants involves single ions (Kolbel, 1959 Griffith, 1967) rather than micelles (Chapter 3). 

For dilute solutions of surfactants then, the number of moles of surface-active solute adsorbed per unit mass of the solid substrate can be calculated from the concentrations of the solute in the liquid phase before and after the solution is mixed with the finely divided solid adsorbent and the mixture is shaken until equilibrium has been reached. Then n is plotted against C to yield the adsorption isotherm. A variety of analytical techniques are available for determining the change in concentration of the surfactant (Rosen, 1972). 

For solutions consisting of the solvent and only one solute, dy = —RT(Todln ao + Ty/ln a ), where subscripts 0 and 1 refer to the solvent and the solute, respectively. For dilute solutions (10-2 M or less) containing only one nondissociating surface-active solute, the activity of the solvent and the activity coefficient of the solute can both be considered to be constant and the mole fraction of the solute xi may be replaced by its molar concentration C. Thus... 

For surface-active solutes the surface excess concentration, p can be considered to be equal to the actual surface concentration without significant error. The concentration of surfactant at the interface may therefore be calculated from surface or interfacial tension data by use of the appropriate Gibbs equation. Thus, for dilute solutions of a nonionic surfactant, or for a 1 1 ionic surfactant in the presence of a... 

The Gibbs adsorption equation (2.17) for two surface-active solutes in dilute... 

A nonionic surface-active solute in aqueous solution at 30°C gives the following y-log C data (C in moles dm-3) ... 

Absolutely pure liquids do not foam. Foam is also not pronounced in mixtures of similar types of materials (e.g., aqueous solutions of hydrophilic substances). Bubbles of gas introduced beneath the surface of an absolutely pure liquid rupture immediately on contacting each other or escape from the liquid as fast as the liquid can drain away from them. For true foaming to occur, the presence of a solute capable of being adsorbed at the L/G interface is required. The presence of this surface-active solute produces lamellae between the gas cells of the foam that have... 

Theories concerning the mechanisms of operation of this film elasticity depend on two observations concerning the surface tension of aqueous solutions of surface-active solutes (1) its increase in value with decrease in concentration of the surface-active solute, at concentrations of the latter below the CMC, and (2) the time required for it to obtain its equilibrium value (the fact that the initial value of these surface tension at a new surface is always greater than the equilibrium... 

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