Neat phases

An example for a partially known ternary phase diagram is the sodium octane 1 -sulfonate/ 1-decanol/water system [61]. Figure 34 shows the isotropic areas L, and L2 for the water-rich surfactant phase with solubilized alcohol and for the solvent-rich surfactant phase with solubilized water, respectively. Furthermore, the lamellar neat phase D and the anisotropic hexagonal middle phase E are indicated (for systematics, cf. Ref. 62). For the quaternary sodium octane 1-sulfonate (A)/l-butanol (B)/n-tetradecane (0)/water (W) system, the tricritical point which characterizes the transition of three coexisting phases into one liquid phase is at 40.1°C A, 0.042 (mass parts) B, 0.958 (A + B = 56 wt %) O, 0.54 W, 0.46 [63]. For both the binary phase equilibrium dodecane... 

Bulk Properties. Because of viscosity and stability requirements for product manufacture and processing, the appearance of mesomorphous phases in mixtures with water is very important. In the case of dodecyl monoglycol ether sulfate and dodecyl sulfate, a highly viscous middle phase is observed up to a concentration of 80 %. For the corresponding diglycol ether compound, however, the middle phase is present only in a concentration range up to about 65 % ( ). Above this concentration, a lamellar neat phase exists. 

The middle phase is much more viscous than the neat phase, though the concentration of the latter is higher. If a concentrated system of an alkyl ether sulfate and water existing initially as a neat phase is stepwise diluted, the range of the middle phase will be reached. This is accompanied by a steep increase in viscosity. The formation of the neat phase allows the manufacture and handling of highly concentrated fluid preparations. This property, however, can lead to processing problems upon dilution. 

Figure 9 shows the effect of acyl chain length (N) on the binary phase diagram of G type nonionics. The area of neat phase spreads with increasing N and the extension of the area takes rapid strides between N of 12 and 14. This N is just in accord with that of the sharp minimum in the cloud point - N curve of the G type. The same thing has also been found for the relation between the effect of OE number on the area of the neat phase and the minimum in the cloud point - OE number curve of CiaGE j (m = 2 - 4). 

Figure 8. Binary phase diagram of Cj GE -water system. G gel phase, N neat phase, I isotropic solution, II two liquid phase...

At relatively low concentrations of surfactant, the micelles are essentially the spherical structures we discussed above in this chapter. As the amount of surfactant and the extent of solubilization increase, these spheres become distorted into prolate or oblate ellipsoids and, eventually, into cylindrical rods or lamellar disks. Figure 8.8 schematically shows (a) spherical, (b) cylindrical, and (c) lamellar micelle structures. The structures shown in the three parts of the figure are called (a) the viscous isotropic phase, (b) the middle phase, and (c) the neat phase. Again, we emphasize that the orientation of the amphipathic molecules in these structures depends on the nature of the continuous and the solubilized components. 

Recently, Sato and Hatano 67 69) found a new type of chiral lyotropic mesophase composed of Tween 80, sorbitan mono-9-octadecenoate poly(oxy-l,2-ethanediyl), and water, and discussed the ICD of achiral solute molecules intercalated into the lyotropic mesophase. As the concentration of Tween 80 is increased, three distinct phases are obtained micelle, neat phase, and reversed micelle, in that order. In the region of the volume ratio of Tween 80/(Tween 80 + water) of 0.40 to 0.63 under crossed Nicol-prisms, a focal conic texture was observed. This result indicates that the... 

T extures of lyotropic mesophases have been the object of numerous observations by optical (1,2,3) and electronic (4, 5, 6,7) microscopy. Except for the pioneering work of Lehmann (1) and Friedel (2) who intended to identify the various kinds of defects which constitute the textures, the purpose of these observations was to recognize the different existing phases—lamellar, hexagonal (or in the soaps language neat phase, median phase, etc.)—in correlation with x-ray data. 

Use of liquid crystalline phases Surfactants produce liquid crystalline phases at high concentrations. Three main types of Hquid crystals can be identified hexagonal phase (sometimes referred to as middle phase) cubic phase and lamellar (neat phase). All of these structures are highly viscous and also show elastic responses. If produced in the continuous phase of suspensions, they can eliminate sedimentation of the particles. These Hquid crystalline phase are particularly useful for application in liquid detergents which contain high surfactant concentrations. Their presence reduces sedimentation of the coarse builder particles (phosphates and silicates). 

The phase diagram of sodium dodecyl sulfate-water is representative of many ionic systems (Figure 3.7) [5], In Figure 3.7 Liquid is the aqueous micellar phase Ha is the hexagonal lyotropic liquid crystal, sometimes called the middle phase and La is the lamellar lyotropic liquid crystal, sometimes called the neat phase. On the surfactant-rich side, several hydrated solid phases are present. 

The closed loop is not the only characteristic of the nonionic surfactant-water binary phase diagram. Like the ionic surfactant-water mixture, nonionic surfactants, at higher concentration in water, exhibit lyotropic mesophases. Figure 3.14 shows a typical binary phase diagram exhibiting the full lyotropic mesophase sequence II, cubic isotropic phase HI, direct hexagonal phase (middle phase) VI, special cubic ( viscous phase) La, lamellar phase (neat phase). Note the presence of the two-phase domains surrounding each mesophase, the critical point on top of each, and the zero-variant three-phase feature. 

In refluxing toluene the main reaction is the 1,3-dipolar isomerisation apparently via the interceptable CF3-dipole. In neat phase at higher temperatures reduction to the thioaminal and elimination of dimethylsulftde become the major reactions. Further results arise from trifluorothioamidium salts with varying N-substitution. Addition of cyanide furnished substituted thioaminals with two captor substituents and their thermal behaviour was studied (refs. 1, 13, Scheme 10). 

The order of the line widths of the waxy phases deserves some comment. There is some correlation between the line widths and the lengths of the hydrocarbon portion of the molecules. With perhaps the exception of NaL, the line widths increase as the chains become shorter. At most temperatures the order of the line widths is NaM > NaL > NaP > NaS. It is expected that a longer chain will be more mobile and thus have a sharper line. The order of the line widths in a given soap is without exception subwaxy > waxy > superwaxy > subneat the neat phase is not found in the temperature range covered in this study. As expected, the line widths decrease with increasing temperature. 

The two most common lyotropic mesophases are designated neat and middle 26), Both are members of the family of mesomorphic structures derived by Hermann 12). The neat phase structure is generally accepted as being made up of parallel, equidistant sheets of double molecules separated by solvent 4, 21, 22). Neat phase is optically anisotropic and flows easily. Figure 11 indicates the structure 22) and a cross-sectional view of one of the layers. 

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