Temperature effects oxyethylene surfactants

Nonionic Oxyethylene Surfactants Display Special Temperature Effects 440... 

NONIONIC OXYETHYLENE SURFACTANTS DISPLAY SPECIAL TEMPERATURE EFFECTS... 

Another example of chemical-potential-driven percolation is in the recent report on the use of simple poly(oxyethylene)alkyl ethers, C, ), as cosurfactants in reverse water, alkane, and AOT microemulsions [27]. While studying temperature-driven percolation, Nazario et al. also examined the effects of added C, ) as cosurfactants, and found that these cosurfactants decreased the temperature threshold for percolation. Based on these collective observations one can conclude that linear alcohols as cosurfactants tend to stiffen the surfactant interface, and that amides and poly(oxyethylene) alkyl ethers as cosurfactants tend to make this interface more flexible and enhance clustering, leading to more facile percolation. 

CMC determinations as a function of temperature utilizing the change of the amount of solubilized water are inaccurate. This procedure has been frequently applied. In this way, for example, the effect of the temperature on the CMC of hexa-oxyethylene dodecylether in cyclohexane183) was determined. The CMC loses its well defined meaning in a ternary system, viz. to represent a thermodynamic property of the particular surfactant/solvent system (see Paragraph 2.2). 

Nonionic surfactants dissolve in aqueous solutions through hydrogen bonding between the water molecules and the oxyethylenic portion of the surfactant. These interactions are weak but enough in number to maintain the molecule in solution up to the cloud point temperature, at which the surfactant separates as a different phase (4). Figure 3 shows that electrolytes like calcium chloride, potassium chloride, or sodium chloride reduce the cloud point of Triton X-100. Hydrochloric acid instead promoted a salting-in effect similar to that observed for ethanol. 

The effect of temperature and surfactants on the viscosity of coal-water mixtures is shown in [281]. It has been shown that the volume content of coal in suspension can be increased while preserving its flowability at a certain surfactant content. Stable and pseudo-plastic suspensions were obtained both with anionic surfactants containing electrolyte, and with ethoxylated alkylphenols with a high content of oxyethylene groups. But the rate of reduction of the apparent viscosity begins to decrease with increasing temperature which seems to be connected with the change of the surfactant structure in solution and adsorption layers. 

The solubilization behaviors of water and aqueous ammonia solutions in the NP5/cyclohexane/water microemulsion system are compared in Fig. 4 [78]. It can be seen that replacing water with ammonium hydroxide solution shifts the solubilization curve to lower temperatures. The observed ammonia effect is attributable to a competition between hydroxyl ions and the oxyethylene groups of the surfactant for interaction with water molecules. The microemulsion-based alkoxide sol-gel systems provide an interesting example of reactant effects on microemulsion phase stability. In this case, water serves multiple roles, including that of a reaction medium (i.e., microemulsion water pools) and a reactant [for alkoxide hydrolysis, Eq. (13)]. Thus, consumption of water via the alkoxide... 

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