Solubilization-emulsification mechanisms of detergency

More documents

Recommendations

Info

182 C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 3.5. Water-surfactant-polar soil systems Hydrocarbons and triglycerides are frequently referred to as non-polar soils, while long-chain fatty acids and alcohols are termed polar soils. In this section we consider only the case of pure polar soils. Ekwall has studied the phase behavior of many anionic surfactant-water-polar soil systems [56]. Figure 14 is a partial ternary diagram at 50ºC for the water-sodium octylsulfonate-n-hexanol system, which has been investigated in recent years by Kunieda and Nakamura [57]. A matter of interest for later sections of this paper is that the region of coexistence of L1 and L2 phases near the water-hexanol axis is bounded by a three-phase triangle involving these phases and the lamellar liquid crystal La. In other cases, including the water-sodium octanoate-n-decanol system that was studied extensively by Ekwall's group, careful examination of the dilute region reveals that the D' (or L3) phase replaces Lα, in the three-phase triangle which terminates the L1-L2 region [58]. In this system a second three-phase triangle D'-Lα-L2 also exists, the arrangement Fig. 14. Phase behavior of the sodium octylsulfonate-water-nhexanol system in the dilute region at 50ºC [57]. Reprinted with permission of the American Chemical Society. being similar to that shown in Fig. 8 for triglyceride systems. In almost all diagrams of this type involving relatively long-chain compounds, the lamellar phase and its associated multiphase regions are prominent although other liquid crystalline phases may be present as well at high surfactant concentrations [56]. Kunieda and Nakamura [57] showed that the addition of NaCl to the system of Fig. 14 caused the D' phase to appear and the dilute portion of the phase diagram to resemble Fig. 8. The higher salinity is likely to make the surfactant-alcohol bilayers more flexible and enables them to assume the locally saddleshaped configuration necessary for formation of the sponge-like microstructure of the D' phase for slightly lipophilic conditions. Apparently only the lamellar structure is possible for more rigid bilayers. When the surfactant is non-ionic, the same behavior, i.e. the appearance of the D' phase and a shift from a diagram resembling Fig. 14 to one resembling Fig. 8, can be effected by increasing the temperature, as Kunieda and Miyajima [591 showed for the water-n-dodecyl octaoxyethylene monoether (C12E8)-n-decanol system. Here. too. the ability to form the D' phase at temperatures above about 14ºC is probably the result of increased flexibility of the surfactant-alcohol bilayers. 3.6. Mixtures of non-polar and polar soils As mentioned in section 3.2, the addition of rather lipophilic amphiphilic compounds reduce, the PIT of non-ionic surfactant-water-hydrocarbon systems. Long-chain alcohols and (undissociated) fatty acids ate of this type, as Fig. 15 shows for the addition of oleyl alcohol to systems containing water, n-hexadecane, and several non-ionic -surfactants [12]. Note that 5% oleyl alcohol in the system by oil phase reduces the PIT in the C12E6 about 35ºC. Similar results were found by the same authors for oleic acid. When enough polar soil is present that the system is above its PIT but the surfactant is
C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 183 Fig. 15. PIT values for non-ionic surfactant-water-nhexadecane-oleyl alcohol systems [12]. Reprinted with permission of the American Oil Chemists' Society. below its cloud point, one might expect that phase behavior in the dilute region would be similar to that described in the preceding section, i.e. the L 1-L 2 region would terminate in a three-phase region involving either the D' or the La phase. Experiments at 30ºC with C 12E 7 and oils having ratios of n-hexadecane to oleyl alcohol of 3/1 and 1/1, respectively, showed that such behavior did, in fact, occur, with the third phase being the lamellar liquid crystal Lα [60]. However, in contrast to the situations shown in Fig. 8 and 14 where the oil phase solubilizes modest amounts of water, L 2 phases in these systems extended to compositions containing up to 75-80% water which were in equilibrium with aqueous micellar solutions. Evidently, the presence of hydrocarbon and of the double bond in the alcohol chain makes the surfactant films sufficiently flexible so that the L 2 phase can invert continuously and become water continuous, ultimately reaching compositions comparable to those of the D' phase in systems such as that shown in Fig. 8. The relevance of this behavior to detergency is discussed later. When the long-chain alcohol is mixed with a liquid triglyceride instead of with a hydrocarbon, multiphase regions containing the D' phase are prominent, as is shown in Fig. 16 [61] for the C 12E 6-water-triolein-oleyl alcohol system. The sequence of phases observed with increasing temperature in Fig. 16 for oils having oleyl alcohol contents exceeding about 20% is the same as was found for the water-non-ionic surfactant-triolein systems discussed in section 3.3, as may be seen, for instance, along the right-hand boundary of Fig. 12 for water-C 12E 4- Fig. 16. Partial phase diagram of C12E6-water-triolein-oleyl alcohol system with 10 wt.% surfactant, 45 wt.% water, and 45 wt.% mixed oil [61]. The symbol IV denotes the four-phase region W + D'+ D + O.
Page 1 and 2: Colloids and Surfaces A: Physicoche
Page 3 and 4: C.A. Miller and K.H. Raney/Colloids
Page 13: C.A. Miller and K.H. Raney/Colloids
Page 47: C.A. Miller and K.H. Raney/Colloids

Solubilization-emulsification mechanisms of detergency

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?