Surfactants or surfactant mixtures

As indicated above, miscibiUty gaps are small and intermediate lamellar liquid crystalline phases dissolve rapidly into the aqueous phase if the surfactant or surfactant mixture is rather hydrophihc with a high spontaneous curvature (low (v/la)), for instance at temperatures below Tq for pure nonionic surfactants. In this case dissolution, which converts lamellae of zero curvature to aggregates with significant curvature as surfactant concentration decreases, occurs spontaneously because it reduces system free energy. 

The relative tendency for surfactants or surfactant mixtures to form a micelle compared to a monolayer is approximately the same. However, the relative tendency to form an admicelle can be substantially different from that to form micelles or monolayers. This is because there can be specific interactions between the solid surface and the surfactants as well as intersurfactant interactions in the aggregate. The surfactant technologist can take advantage of this to design... 

The hydrophile-lipophile balance (HLB) system is the measure of the surfactant s polarity as well as other physical properties of surfactants and the emulsifying materials. The more lipophilic the surfactant is, the lower the HLB values will be. Table 4.5 empirically classifies and compares surfactants according to their optimum use. Table 4.6 shows the HLB values for a selected group of surfactants. The HLB value of the surfactant or surfactant mixture should be matched with that of the oil or the mixture of oils to ensure a stable emulsion. The required HLB values of a... 

Equivalent Alkane Carbon Number (EACN) Each surfactant or surfactant mixture in a reference series will produce a minimum interfacial tension (IFT) for a different n-alkane. For any crude oil or oil component, a minimum IFT will be observed against one of the reference surfactants. The EACN for the crude oil refers to the n-alkane that would yield minimum... 

Surfactant Any substance that lowers the surface or interfacial tension of the medium in which it is dissolved. Soaps (fatty acid salts) are surfactants. Detergents are surfactants or surfactant mixtures whose solutions have cleaning properties. 

Most concern the use of specific surfactants or surfactant mixtures that permit the lowering of the Leidenfi-ost temperature [2]. Others concern the increase of the oil viscosity contained in the emulsion [3 - 5] and/or the use of specific organic waxes [6]. Another approach concerns the thickening of the emulsion or the increase of its elongational viscosity [7]. 

Dispersant is a common term used to label chemical spill-treating agents that promote the formation of small droplets of oil that disperse throughout the top layer of the water column. Dispersants contain surfactants, chemicals like those in soaps and detergents, that have molecules with both a water-soluble and oil-soluble component. Depending on the nature of these components, surfactants cause oil to behave in different ways in water. Surfactants or surfactant mixtures used in dispersants have approximately the same solubility in oil and water, which stabilizes oil droplets in water so that the oil will disperse into the water column. This can be desirable when an oil slick is threatening a bird colony or a particularly sensitive shoreline. 

Meanwhile, there are a variety of large-scale applications of microemulsion systems. Many products used in daily life contain micro emulsions or formulations which are able to form microemulsions (some prominent examples are discussed in Chapters 8 and 9 of this book). Concentrates, surfactants or surfactant mixtures which can be used for microemulsification are frequently applied. All these materials are produced and handled in large quantities. In particular, oil-in-water (o/w) droplet and water-in-oil (w/o) droplet microemulsions are found in many products or technical processes today. Whereas their usage is not very different from ordinary solvents in most cases, the use of bicontinuous microemulsions poses specific problems which will be discussed later on. 

Surfactant Any substance that lowers the surface or interfacial tension of the medium in which it is dissolved. The substance does not have to be completely soluble and may lower surface or interfadal tension by spreading over the interface. Soaps (fatty acid salts containing at least eight carbon atoms) are surfactants. Detergents are surfactants or surfactant mixtures whose solutions have cleaning properties. Also referred to as surface-active agents or tensides. 

Conventional formulations of cleaners and detergents obligatorily include, independent of their trade form (powders, pastes, gels, liquids), the following components 1) active matter (i.e. a surfactant or surfactant mixtures) 2) substances activating the washing effect 3) auxiliaries perfumes, fillers, viscosity controllers etc. Formulators have to solve the following tasks here ... 

Between these systems and the so-called microenudshns a clear differentiation must be made. The microemulsions are often wrongly described as parenteral fat emulsions (142) and represent—from the physical point of view—a completely different. system. Microemuisions are thermodynamically. stable, single phase, transparent or opalescent, liquid, and in unsheared state arc optically isotropic systems consisting of several liquids that cannot be mixed together and are produced with the aid of surfactants or surfactant mixtures (88). The physical structure of these systems is the object of many investigations (5U6.64. 84,103,152), in which they are described either as swollen micelles or as critical solutions (47). 

We have restricted fliis presentation to involve only oil-continuous emulsions. The reason for excluding water-continuous systems is that the OAV emulsions are usually stabilized by means of ionic surfactants (or surfactant mixtures) and consequently the electric double-layer effects can be very large. The electrode polarization will normally also be very strong in many 0/W systems. For the TDS technique water-in-oil emulsions stabilized by means of non-ionie surfactants are very good model systems. 

In a recent work [417], the two-microemulsion method was used for synthesis. In microemulsion I, the continuous phase was prepared by mixing n-heptane with a surfactant or surfactant mixture from C12E4, C,2E5, i.e. penta(ethylene glycol)dodecyl ether, i.e. hexa(ethylene glycol)dodecyl ether or AOT. An... 

In order to improve the HLB number s practical imcrcsi. a second parameter was introduced to describe the oil phase nature, the so-called required HLB or HLB. so that a better description of the physicochemical environment would be attained. The oil HLB is the HLB of the surfactant that results in the niosi stable emulsion. In order to estimate the oil HLB. an HLB scan for emulsion stability has to be carried out. This is done by preparing several systems with the same oil and aqueous phases but different HLB surfactants or surfactant mixtures. so that a whole HLB scan is carried out. say. from deiinilel) lipirphilic (HLB = 2-4) to definitely hydrophilic (HLB > 14). 

The use of the HLB system for choosing the best emulsifier system for a given application originally required the performance of a number of experiments in which surfactants or surfactant mixtures with a range of HLB numbers are employed to prepare emulsions of the oil in question, and the stability of the resulting emulsions is evaluated by measuring the amount of creaming that occurred with time. The use of surfactant mixtures can become complicated by the fact that such... 

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