Water surface tension, surfactant concentration effect

Acetone, IPA, and methanol were purchased on lab or from local chemical vendors and were used, as received. All chemicals were of high grade purity (>99.5% pure). Standard distilled water was used for the pure water and diluted water/methanol tests. To reduce uncertainty in the data due to a reduction in water surface tension due to the presence of impurities, the water bottles were subjected to the shake test to ensure minimum surfactant concentration. The shake test uses the property that foam fraction is an effective separation process for surfactants in aqueous solutions. Simply shake a sample of the water in a clean volumetric flask. Any bubbles will immediately break if the surfactant concentration due to contamination is ignorable. 

Surfactants lower the surface tension of water, typically from 72 to ca 30—35 mN/m (= dyn/cm), and many surfactants have a strong effect on the contact angle when used at low concentrations. Both changes help dewatering. Too much surfactant, near or above the critical micelle concentration... 

Modem oil spill-dispersant formulations are concentrated blends of surface-active agents (surfactants) in a solvent carrier system. Surfactants are effective for lowering the interfacial tension of the oil slick and promoting and stabilizing oil-in-water dispersions. The solvent system has two key functions (1) to reduce the viscosity of the surfactant blend to allow efficient dispersant application and (2) to promote mixing and diffusion of the surfactant blend into the oil film [601]. 

In water the surfactant molecules orient themselves with their hydrophobes at the centre of the cluster. The CMC is typically quite low, perhaps 0.5-0.2 g/l. At concentrations lower than this the molecules orient themselves only at the interfaces of the solution, and it is this effect which brings about the lowering of surface tension. Once the CMC is reached the... 

The influence of surfactants is predominantly of importance in waste water ozonation studies where often comparatively high concentrations of such compounds occur. However, similar effects can occur in drinking or ground water ozonation applications. This was shown for the decomposition of the organic phosphate pesticide diazinon (phosphorotoic acid <5,<5-diethyl-o[6-methylethyl)-4-pyrimidinylJether) in aqueous solution by ozonation. This compound was found to considerably affect the surface tension of the aqueous solution, even at low concentrations (c(M) < 10 mg L l) and, thus, also influenced the oxidation mechanism (Ku et al., 1998). 

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. 

Micelles are colloidal particles formed by the concentration-dependent aggregation of surfactant molecules (1). In an aqueous environment micelles form when the hydrophobic portions of the surfactant molecules begin to associate at a surfactant concentration that is referred to as the "critical micelle concentration", or CMC, as a result of hydrophobic effects In water, a micelle has a hydrophobic core and a charged surface that is the result of the orientation of ionizable or hydrophilic functional groups out into the bulk solution At concentrations prior to the CMC the surfactant molecules migrate to the solution-air interface which disturbs the structure of the water molecules and results in a decrease in the solution s surface tension (2), At concentrations greater than the CMC, increasing... 

The effective surfactant dose upon dilution was not inhibitory, and is less than the CMC in the soil-water systems. This dose to attain the CMC is nominally about 0.06% (v/v) or about 0.001 mol/L for Triton X-100 for a soil water ratio of 1 8 g/mL, as shown in Figure 3 for solubilization data or in reference 52 for surface-tension data. Therefore, the data in Figure 10 demonstrate recovery of phenanthrene biomineralization upon dilution of surfactant to sub-CMC aqueous-phase concentrations in soil-water systems. 

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