Surface viscosity critical micelle concentration

Performance Indices Quality Factors Optimum E1LB Critical micelle concentration (CMC) Soil solubilization capacity Krafft point (ionic surfactants only) Cloud point (nonionic surfactants only) Viscosity Calcium binding capacity Surface tension reduction at CMC Dissolution time Material and/or structural attributes... 

Schick and Fowkes (11) studied the effect of alkyl chain length of surfactants on critical micelle concentration (CMC). The maximum lowering of CMC occurred when both the anionic and nonionic surfactants had the same chain length. It was also reported that the coefficient of friction between polymeric surfaces reaches a minimum as the chain length of paraffinic oils approached that of stearic acid (12). In order to delineate the effect of chain length of fatty acids on lubrication, the scuff load was measured by Cameron and Crouch (13). The maximum scuff load was observed when both hydrocarbon oil and fatty acid had the same chain length. Similar results of the effect of chain length compatibility on dielectric absorption, surface viscosity and rust prevention have been reported in the literature (14-16). 

In sufficiently dilute aqueous solutions surfactants are present as monomeric particles or ions. Above critical micellization concentration CMC, monomers are in equilibrium with micelles. In this chapter the term micelle is used to denote spherical aggregates, each containing a few dozens of monomeric units, whose structure is illustrated in Fig. 4.64. The CMC of common surfactants are on the order of 10 " -10 mol dm . The CMC is not sharply defined and different methods (e.g. breakpoints in the curves expressing the conductivity, surface tension, viscosity and turbidity of surfactant solutions as the function of concentration) lead to somewhat different values. Moreover, CMC depends on the experimental conditions (temperature, presence of other solutes), thus the CMC relevant for the expierimental system of interest is not necessarily readily available from the literature. For example, the CMC is depressed in the presence of inert electrolytes and in the presence of apolar solutes, and it increases when the temperature increases. These shifts in the CMC reflect the effect of cosolutes on the activity of monomer species in surfactant solution, and consequently the factors affecting the CMC (e.g. salinity) affect also the surfactant adsorption. 

The history of the physicochemical properties of A -acylamino acid started from the patent by Hentrich et al. [27], Since then, Staudinger and Becer reported the solubility and viscosity of A -acylsarcosinate [28] Naudet measured the surface tension and interfacial tension of aqueous solutions of A -acylseri-nate and At-acylleusinate [46], Tsubone measured the surface tension and critical micelle concentration (cmc) of various A -acylamino acids and investigated the effect of structural differences of amino acids and length of fatty acid residue on these surface activities [29], Heitmann [30] further investigated the cmc of Af-acyl cysteine, serine, and glycine and indicated that the-SH in cysteine stabilized the micelle structure with its hydrophobic nature. Ooki reported the surface activities of At-acylsarcosinate [47]. 

Surfactant/suspending agent molecules adsorb at liquid-liquid interfaces until equilibrium is reached between the adsorbed layer and ihe bulk fluid. The interfacial tension decreases with increasing bulk concentration until the critical micelle concentration (CMC) is reached. The interfacial tension remains constant beyond the CMC. Figure 12-27 shows a typical dependence of interfacial tension on surfactant concentration. Surface viscosity behavior is different. The viscosity remains practically constant up to the CMC and increases beyond it. The CMC is an equilibrium phenomenon. As surface area is created by agitation, surfactant molecules leave the CMC cluster, transfer to the aqueous phase, and then transfer to the liquid-liquid interface. Adsorption and protective action are not... 

The intrinsic viscosity [t]] of the coagulant protein was measured for protein concentration, c, in the range 0.02—0.15 g/mL in 0.1 M NaCl. Solution environment such as presence of surfactants can affect protein conformation. To study interactions SDS and SDBS with the cor ulant protein, capillary viscosities of the surfactant/protein solutions were measured using a capillary viscometer. The protein concentration (% w/v) was kept constant at 0.05% whereas the surfactant concentration was varied up to concentrations higher than the critical micelle concentration (CMC). The protein solution was used as the reference standard for surfactant dissolved in 0.05% protein. The SDS (99% purity) was supplied by Sigma-Aldrich whereas SDBS was supplied by Fluka, and both surfactants were used without further purification. The measurements of surface tension, fluorescence, and circular dichroism spectral correlation coefficients of SDS solutions in the presence of protein were done in similar manner, and the details are described elsewhere [15-18]. 

The critical micelle concentration of a surfactant solution can be determined by measuring surface tension, electric conductivity, osmotic pressure, light scattering, viscosity, dye solubilization, and other physical properties [107] (see Chapter 9). The cmc in aqueous solution can be determined also from a change in the chemical environment indicated by the -NMR chemical shift (5) [140), plotted as a function of inverse surfactant concentration (Fig. 6.14). The intersection in the lines indicates the cmc. 

Emulsifiers are known to play a very important role in emulsion polymerization. To appreciate the role of an emulsifier, we must understand the physicochemical properties of emulsifier solutions. When an emulsifier is dissolved in water, several physical properties of the solution (e.g., osmotic pressure, conductivity, relative viscosity, and surface tension) change. Figure 7.1 shows these changes as a fimction of the molar concentration of the emulsifier. Beyond a particular level of concentration, there is a sudden change in the slope of these physicochemical properties, as shown in the figure. This concentration is called the critical micelle concentration (CMC). 

From our experiments we cannot completely exclude the possibility of micelle formation of CHP in water. We found however little evidence for such micelles. The viscosity and light absorption of CHP solutions for example, are normal. We conclude therefore that no aggregates are formed in PMA-CHP solution that contain more than one PMA molecule. Our results can be quite well explained by the molecular model proposed by Lovrien [12]. With our results however a more refined mechanism can be formulated. Upon increasing the concentration of chrysophenine in an aqueous solution of PMA, the binding to the macromolecular surface increases. It reaches a critical level around a CHP concentration in solution of 0.001 M. A further increase of the CHP concentration leads to a level of bound dye that forces the polymer globule to open up to some extent. Thus new sites for dye binding become available, etc. Potentiometric titration is a more sensitive technique for recording the start of this process than is viscosity. However either technique demonstrates the cooperative nature of the phenomenon. 

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