Surfactants efficiency

The surface excess concentration of surfactant corresponding to saturation of the surface or interface. Example one indicator of effectiveness is the maximum reduction in surface or interfacial tension achievable by a surfactant. This term has a different meaning from surfactant efficiency. 

Foam characteristics used as an estimated of the surfactant efficiency as foaming agents... 

Surfactant surface activity is most completely presented in the form of the Gibbs adsorption isotherm, the plot of solution surface tension versus the logarithm of surfactant concentration. For many pure surfactants, the critical micelle concentration (CMC) defines the limit above which surface tension does not change with concentration, because at this stage, the surface is saturated with surfactant molecules. The CMC is a measure of surfactant efficiency, and the surface tension at or above the CMC (the low-surface-tension plateau) is an index of surfactant effectiveness (Table XIII). A surfactant concentration of 1% was chosen where possible from these various dissimilar studies to ensure a surface tension value above the CMC. Surfactants with hydrophobes based on methylsiloxanes can achieve a low surface tension plateau for aqueous solutions of —21-22 mN/m. There is ample confirmation of this fact in the literature (86, 87). 

Surfactant Efficiency The equilibrium solution surfactant concentration needed to achieve a specified level of adsorption at an interface. Example One such measure of efficiency is the surfactant concentration needed to reduce the surface or interfadal tension by 20 mN/m from the value of the pure solvent(s). This term has a different meaning from surfactant effectiveness. See also references 14 and 15. 

Effective compatibilization of binary polymer blends by addition of a copolymer reduces the dispersed particles size and Vj [Anastasiadis et al, 1987 Wu, 1987 Patterson et ai, 1971]. An illustration is shown on Figure 4.15. The effect of compatibilizer addition is similar to the emulsification of the classical emulsions. In the former systems, the compatibilizer effect on the drop size and Vj follows the same behavior as the emulsion drop size reduction upon addition of a surfactant. The latter behavior is usually described as the titration curve that characterizes the surfactant efficiency. The shape of the titration curve depends on the type of emulsifier and the emulsification process, e.g., mixing time and equipment. However, the amount of emulsifier to saturate the interface also depends on the affinity of emulsifier to the dispersed phase, the size of the dispersion, the orientation of the emulsifier at the interface and its ability to prevent flocculation and coalescence [Djakovic et al., 1987]. A similar behavior is to be expected for polymer blends upon addition of a compatibilizer. 

Surfactant efficiency can be expressed as the surfactant concentration needed to reduce the surface or interfacial tension by 20 mN m from the value of the pure solvent(s). Surfactant effectiveness, on the other hand, refers to the maximum reduction in surface or interfacial tension achievable by a surfactant (corresponding to saturation of the surface or interface). To give some sense of the extent to which surfactants can lower surface and interfacial tension, many hydrocarbon surfactants, at high concentrations (above the critical micelle concentration (cmc) see Section 3.5.3) can lower the surface tension of water at 20 "C from 72.8 to about 28 mN m . Polysiloxane surfactants can reduce it further, to about 20 mN m , and perfluoroalkyl surfactants can reduce it still further, to about 15 mN m . Similarly, hydrocarbon surfactants can reduce the interfacial tension of water - mineral oil from about 40 mN m down to about 3 mN m . ... 

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. 

On a molecular basis, the conflicting factors can be seen conceptually as arising from the different roles of the molecular structure in the adsorption process. Surfactant efficiency is related to the extent of adsorption at the interface as a function of bulk surfactant concentration. At a concentration well below that at which micellization becomes a factor, efficiency can be structurally related to the hydrophobicity of the surfactant tail and the nature... 

One of the most important effects of surfactant synergy in liquid hard-surface cleaners is that the overall concentration of active ingredients can be reduced. More importantly, the amount of adjunct materials—builders, solvents, and the like—that must be added are decreased as the surfactant efficiency and effectiveness is increased due to synergy. While this has the effect of increasing... 

Function in Formula Multifunctional substantive conditioner for skin and hair products. Adds mild surfactancy. Efficient thickener... 

Equation 5.20 demonstrates that the surfactant efficiency can be reflected in both of the solid content and particle size. Interestingly, no significant difference among the solid contents was observed between surfactants with different topologies (Table 5.2), which means the efficiency can be simply reflected in (R) or A p. 

Since the surfactant efficiency is directly related to the thermodynamics of chain transfer from bulk to interface, it is reasonable to expect that chain modifications that alter that characteristic, such as changes in the hydrophobic character of the surfactant, will produce corresponding changes in the value of pC2o- The linear relationship between the number of -CH2- linkages in a chain and the adsorption efficiency for a variety of hydrophilic groups illustrated in Figure 3.8. 

The complex relationship between the molecular structure of a smfactant and its impact on surfactant efficiency and effectiveness can be illustrated by the case of a series of nonionic POE surfactants in which the number of OE units is held constant and the hydrocarbon chain length is increased (Table 3.3). In the series it is found that the siuface excess at surface saturation Tn, decreases regularly from 4.4 x 10 ° mol/cm for Cm to 2.7 x 10 for Ce, while the a iin remains relatively constant. This would indicate that while the efficiency of surfactant adsorption is increasing with the length of the hydrocarbon chain, the overall effectiveness of the material is relatively unchanged. 

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