Surface tension reduction additive effect

For example, carbon atoms located on branch sites will contribute approximately two thirds as much to the character of a surfactant molecule as one located in the main chain (56). The above-mentioned surfactants [35a-h], [37a-h] follow this general trend. In addition, it has generally been found that the presence of alkyl groups attached to the nitrogen seems to have little effect on the surface tension reduction of a surfactant. This general trend also holds for the y values of the compounds [35a-h], [37a-h]. 

When discussing the performance of a surfactant in lowering the surface tension of a solution it is necessary to consider two aspects of the process (1) the concentration of surfactant in the bulk phase required to produce a given surface tension reduction and (2) the maximum reduction in surface tension that can be obtained, regardless of the concentration of surfactant present. The two effects may be somewhat arbitrarily defined as follows the surfactant efficiency is the bulk phase concentration necessary to reduce the surface tension by a predetermined amount, for example, 20 mN m. Its effectiveness is the maximum reduction in a that can be obtained by the addition of any quantity of surfactant. The typical shape of the surface tension-concentration curve for aqueous surfactants is shown in Figure 8.8. 

The addition of surfactant usually causes a reduction in and, if absorbed, a reduction in Both effects lead to better wetting. The change in is negligible in most cases so the dominating factor is the surface tension of the liquid phase. 

The sugars sucrose, fructose and glucose have also been found to affect bubble coalescence. On addition to water these sugars raise the surface tension and are desorbed from the air-water interface. Thus their effect on bubble coalescence equally cannot be described in terms of surfactant-like behaviour and certainly no charge effects are involved. Hence, even if an "explanation" could be found within the confines of the primitive model of electrolytes, that explanation could not accommodate this observation. The reduction in bubble coalescence achieved with increasing concentration is shown in Fig. 3.7. 

This effect of adsorption between hexane and the surface of zirconia may decrease the effective size of the pores and, consequently, lead to a decrease in the flow of hexane. Additionally, the surface of zirconia may be able to catalyze the isomerization of cyclohexane and decomposition reactions, which could also explain the reduction in permeate flux observed. These authors concluded then that the membranes of polyethersulfone submitted to pretreatment showed high flow with hexane, was stable over time, and increased linearly with pressure, following the usual behavior for pure solvents. The stability of these membranes pretreated to hexane allows a full potential of applications in edible oils. In ceramic membranes, however, the decline in the flow of hexane observed as a function of time indicated that the solvent interacted with the membrane, being adsorbed on its surface. As a result, the flow of hexane through ceramic membranes was much lower than those obtained with polyethersulfone membrane with similar values of molar weight cutoff The results are not explained by simple models used to predict conventional solvent flow, as the equation of Hagen-Poiseuille therefore, parameters other than viscosity must be taken into account, such as surface tension and hydrophilicity of the membrane. 

Generally, it is easier to obtain a fine domain size under conditions where the two melt viscosities are dose. Furthermore, the domain size reduction easily occurs when the interfacial tension (k) between each polymer particle is low, even if there exists a considerable melt viscosity difference. This means that both the addition of a compatibilizer and interfacial copolymerization reactions result in lower surface tension and, consequently, the domain size reduction is effectively accelerated. To develop and stabilize the optimum morphology of a polymer alloy, it is very important to utilize a particular interfacial reaction or a pre-designed compatibilizer to improve the surface tension or interaction between the domain and matrix polymeric components, as well as to select the optimum operational conditions for mixing. 

The addition of detergents to water results in the reduction of surface tension with the increase in the concentration of detergent. This effect is ascribed to the fact that the detergent molecules prefer to stay at the water/air interface instead of being in bulk. It can thus be said that the reduction in surface tension is due to the adsorption of detergent at the interface. 

The use of stearic acid as a modifier for silica and other fillers like CaCOs and Mg(OH)2 has been reported. The authors found that the presence of adsorbed stearic acid on the filler surface reduces the hydrophilicity of the silica surface and enhances the compatibility between filler and matrix, which may lead to an improvement in filler dispersion and the related mechanical performance of composites. Kosmalska et al also investigated the adsorption of DPG, ZnO and sulfur on the silica surface and reported that the bonding of DPG/ZnO and ZnO to silica causes a reduction in the surface energy of silica from 66 mN/m to 28.75 mN/m and 35.49 mN/m, respectively. A similar effect of ZnO on the surface tension of silica was also found by Laning et alP and Reuvekamp et al. The adsorption of that additive and its impact on the scorch time and reduction of the crosslink density in silica-filled rubber compounds have been frequently characterized. ... 

The effect of asphaltene and resin on the surface tension of solvents has also been described by Poindexter and coworkers [20]. Here crude oil was simulated by mixtures of toluene and mineral oil. Volume ratios of mineral oil to toluene were 50 50, 60 40, and 70 30. In all cases, 1-3 wt.% asphaltene decreased the surface tension of the solvent, but by no more than 2 mN m. The decrease was more pronounced on increasing the proportion of mineral oil from 50 to 60 vol.%. In the case of both these 50 and 60 vol.% mineral oil solvents, the addition of asphaltenes increased both foamability by sparging and foam stability. Increasing the asphaltene concentration in both of these cases also reduced the surface tension until it became constant at a supposed critical nanoaggregate concentration, which Mullins [21] argues is analogous to the CMC of ordinary surfactant solutions. However, further increasing the proportion of mineral oil to 70 vol.% precipitated the asphaltene out of solution so that only a modest reduction in surface tension was observed, consistent with the concomitant reduction in activity. Unfortunately, Poindexter and coworkers [20] did not indicate whether their surface tension measurements were equilibrium values. 

Foaming is sometimes unwelcomed in syrups, fruit concentrates, soft drinks, vegetable oHs, tea and coffee extracts and in many other commodities. Reduction of foaming in these cases can be achieved by adding certain substances to cause the coUapse of the foam. Their effect depends on their tendency to form a monomolecular film on the surface, which destabilises the foam. Often these substances reduce the surface tension of the Hquid phase to the threshold value at which the bubble walls are so thin that they burst. Commonly used additives are silicone oils in concentrations of 10-100 mg/kg and also primary fatty alcohols, fatty amides, fatty acids and their esters. 

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