Foam control electrolytes

Highly efficient, stable, "reacted" silicone defoamers which virtually eliminate problems associated with free silicone oils common in most silicone defoamers. Excellent foam control plus strong lasting power minimizes the need for defoamer adds during processing. Stable to high electrolyte concentrations from salts, acids, alkali etc., present in processing baths. 

Poly(propylene oxide) is typically obtained by base catalyzed anionic polymerization of propylene oxide [12]. Both stereospecific and atactic forms are known. The polymer is used as a soft polyether unit in polyurethane elastomers and foams in polymer electrolytes as surfactants (lubricants, dispersants, antistatic agents, foam control agents) in printing inks, as solubilizers in hydraulic fluids, coolant compositions in various medical applications (protective bandages, drug delivery systems, organ preservation, dental compositions), etc. 

Features Exc. electrolyte stability reliable foam control In aq. media no silicone spotting... 

For some apphcations, eg, foam mbber, high soHds (>60%) latices are requited. In the direct process, the polymerization conditions are adjusted to favor the production of relatively large average particle-size latices by lowering the initial emulsifier and electrolyte concentration and the water level ia the recipe, and by controlling the initiation step to produce fewer particles. Emulsifier and electrolyte are added ia increments as the polymerization progresses to control latex stabiUty. A latex of wt% soHds is obtained and concentrated by evaporation to 60—65 wt % soHds. 

The question of the ( -potential value at the electrolyte solution/air interface in the absence of a surfactant in the solution is very important. It can be considered a priori that it is not possible to obtain a foam film without a surfactant. In the consideration of the kinetics of thinning of microscopic horizontal foam films (Section 3.2) a necessary condition, according to Reynolds relation, is the adsorption of a surfactant at both film surfaces. A unique experiment has been performed [186] in which an equilibrium microscopic horizontal foam film (r = 100 pm) was obtained under very special conditions. A quartz measuring cell was employed. The solutions were prepared in quartz vessels which were purified from surface impurities by a specially developed technique. The strong effect of the surfactant on the rate of thinning and the initial film thickness permitted to control the solution purity with respect to surfactant traces. Hence, an equilibrium thick film with initial thickness of about 120 nm was produced (in the ideal case such a film should be obtained right away). Due to the small film size it was possible to produce thick (100 - 80 nm) equilibrium films without a surfactant. In many cases it ruptured when both surfaces of the biconcave drop contacted. Only very precise procedure led to formation of an equilibrium film. 

These studies were performed at high surfactant concentrations (> 0.01 mol dm 3) where the appearance of -potential was hard to explain. Unclear remained the fact that f-potential did not depend on the electrolyte concentration (NaCl) up to a value of 3%. Anomalously high values of -potential ( 0.5 V) have been reported by Laniquielli and Galembeck [64] who studied electrokinetic phenomena occurring at gravitational foam drainage. They attribute this anomaly to the electrolyte accumulation in the electrode space. The analysis of these results indicates that reliable values of the -potential in foams can be derived with an especially developed theory of the electrokinetic phenomena in foams that accounts for the peculiarities of these systems. Furthermore, new apparatus is needed to allow the study of foams with controlled border sizes and precisely defined border profile. 

As listed in Table 5.20, the electrostatic charge on bubbles is controlled by charge of the frother ions and the concentration of electrolyte in solution. In addition, the hydration of the frother molecule is important for the stability of foam bubbles. Interaction between polar groups of the frothers and water molecules can increase the strength of the film between bubbles. 

In this context, nanoporous carbons are extremely interesting materials which can be used either as electrodes of supercapacitors or hydrogen reservoir. They are commercially available at a low cost and under various forms (powder, fibers, foams, fabrics, composites) [3]. They can be obtained with well-developed and controlled porosity [4,5] and with a rich surface functionality [6,7], As far as electrochemistry applications are concerned, very important advantages of carbons are a high electrical conductivity, a good chemical stability in various electrolytic media and the possibility to control wettability by the nature of the surface functionality. When they are not playing the role of active material for the storage process, carbons may be also useful as additive in a composite to improve its physical properties. Particularly carbon nanotubes are able to improve the electrical conductivity and mechanical properties of electrodes [8],... 

The main subject in this section is the quantitative analysis of the effect of humidity on foam film stability [161]. Three types of foam film were used by controlling the Marangoni effect, by changing the SDS and C12E7 concentration, and by disjoining pressure with the addition of electrolytes. In the low humidity conditions with regulating dry nitrogen gas, water evaporation from... 

Features Controlled foam stable in presence of caustic and electrolytes Properties Liq. sol. in water dens. 8.413 Ib/gal 85% act. 

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