Water-pentanol systems

Silica Gels. The acid-catalyzed alkoxide sol-gel process produces gels (17). Frib-erg and coworkers (40-50) pioneered the extension of this process to silica synthesis in microemulsions both aqueous and nonaqueous microemulsions were used. For aqueous microemulsions, experiments were conducted mostly with the SDS/ pentanol/water/acid system. A representative flow diagram is shown in Figure 2.2.9. The nonaqueous microemulsion systems utilized included CTAB/decanol/ decane/formamide and AOT/decane/glycerol (44-46,49,50). The experimental approach followed the sequence nonaqueous microemulsion preparation, water addition, and then TEOS addition. 

FIG. 8.13 Two representations of a portion of the phase diagram for the water-benzene-potassium oleate-pentanol system. The unshaded regions represent homogenous solutions, (a) Redrawn, with permission, from S. Friberg and I. Burasczeska, Prog. Colloid Polym. Sci., 63, 1 (1978). (b) Redrawn, with permission, from C. U. Herrmann, U. Wurz, and M. Kahlweit, In Solution Chemistry of Surfactants, Vols. 1 and 2 (K. L. Mittal, Ed.), Plenum, New York, 1979. 

In this paper, a molecular thermodynamic approach is developed to predict the structural and compositional characteristics of microemulsions. The theory can be applied not only to oil-in-water and water-in-cil droplet-type microemulsions but also to bicontinuous microemulsions. This treatment constitutes an extension of our earlier approaches to micelles, mixed micelles, and solubilization but also takes into account the self-association of alcohol in the oil phase and the excluded-volume interactions among the droplets. Illustrative results are presented for an anionic surfactant (SDS) pentanol cyclohexane water NaCl system. Microstructur al features including the droplet radius, the thickness of the surfactant layer at the interface, the number of molecules of various species in a droplet, the size and composition dispersions of the droplets, and the distribution of the surfactant, oil, alcohol, and water molecules in the various microdomains are calculated. Further, the model allows the identification of the transition from a two-phase droplet-type microemulsion system to a three-phase microemulsion system involving a bicontinuous microemulsion. The persistence length of the bicontinuous microemulsion is also predicted by the model. Finally, the model permits the calculation of the interfacial tension between a microemulsion and the coexisting phase. 

For soap/alcohol combinations — g will depend not only on the soap counter ion but also on the alcohol/soap ratio. Furthermore, when a certain alcohol/soap ratio is exceeded (=2 for the potassium oleate system) S becomes Independent of the water content of the lamellar phase. This condition applies for Inverse structures and the water/pentanol/potassium oleate inverse micellar system will be examined for the structure determining ratio in Table I. 

The o c experimental results for the water/pentanol/potas-slum oleate system (18,19) show that a pentanol/potasslum oleate molecular ratio of 5.5 and lower should give a premlcellar aggregate/lamellar liquid crystal transition instead of the pre-micellar aggregate/Inverse micelle transition at high alcohol/ soap ratios. 

Figure 7. The onset of Inverse mlcelllzatlon In the pentanol solution In the water, pentanol (C5OH), potassium oleate (KOL) system (V) was changed to a small degree at the addition of decane (0) but to a pronounced degree by benzene ( ) (Reprinted with permission from ref. 23. Copyright 1978 Academic Press.)...

For microemulsion system (hexanol system), since it contains water spheres in a continuous oil medium, the addition of water forms more spherical droplets. The continuous medium is still an oil phase and therefore, the electrical resistance is maintained at a high value in the range of lO-- ohms (70). However, for cosolubilized system (pentanol system), as the amount of water is increased, the average distance between alcohol molecules as well as between water molecules would change and this consequently would influence the hydrogen bonding ability of water and alcohol molecules, which in turn would influence the chemical shift of the resonance peak. Moreover, as one adds more and more water in cosolubilized system, it becomes more electrically conducting and, hence exhibits a continuous decrease in the electrical resistance (70). 

Figure 3. W/S pseudoternary diagrams at T = 21.5 °C ( in volume) of the water-dodecane-SDS-pentanol system. Top W/S = 1 bottom W/S = 1.4. L, Lg, and L designate respectively an isotropic phase, a birefringent phase and a flow birefringent liquid phase.

The demixing curves in the W/S pseudoternary diagrams for the hexanol and pentanol systems have been calculated according to the above theoretical treatment. These lines have been determined in the following way. The calculation of the state equation is applied to a dilution line along such a line the inverse micelles have a constant radius R. The micelles contain the whole water (volume Vw), the surfactant (volume V ) and a part of the alcohol V. The rest of alcohol is in the oil continuous phase. We suppose that the alcohol-oil ratio in the continuous phase is constant and is equal to k. Besides, in the calculation of the micellar radius R one assumes that the surfactant and the alcohol molecules which are situated at the interface have a constant area per chain s. In mos of the previous studies s has been found constant and equal to 25 A2. This value is taken equal for the alcohol and surfactant chains. Consequently ... 

Figure 1. Phase map of the Pentanol/CTAB/Water/Hexadecane System. The emulsifier (E) [40% CTAB, 60% Pentanol, w/w] plus water (W) plus Hexadecane oil (0) = 100% by weight. The clear single phase region is denoted by (I).

In this study, the phase equilibrium in the binary mixtures that are expected to be found in the flash distillation was modeled with the Predictive Soave-Redlich-Kwong (PSRK) equation of state [4], using modified molecular parameters r and q. Five binary ethanol + congener mixtures were considered for new yield values for parameters r and q. The congeners considered were acetic acid, acetaldehyde, furfural, methanol, and 1-pentanol. Subsequently, the model was validated with the water + ethanol binary system, and the 1 -pentanol + ethanol + water, 1-propanol + ethanol + water, and furfural + ethanol + water ternary systems. 

Figure 1 Phase diagrams at 25°C of four ternary systems, (a) Water-pentanol-SDS. (From Refs. 22 and 23.) (b) Water-hexanol-SDS. (From Refs. 22 and 23.) (c) Water-octanol-SDS. (From Ref. 79.) (d) Water-decanol-SDS. (From Ref. 80.) Lj, L2, isotropic phases H, hexagonal phase R, rectangular phase L , lamellar phase L4, vesicle phase N, nematic phase. The dashed boundaries have not been determined accurately. is a critical point.

The phase diagrams of two quaternary mixtures made of sodium dodecylsulfate (SDS)-water-dodecane and hexanol (system A) or pentanol (system B) have been investigated in detail [22,23]. In both cases, sections of the three-dimensional diagram with constant water/surfactant ratio have been examined. These cuts were chosen because they allow a good description of the oil region and also because the water/SDS ratio, termed X in the following, fixes the size of the droplets in the inverse microemulsion phase and the thickness of the bilayers in the oil-rich lamellar phase. In the description of the quaternary mixtures, we emphasize the details of the evolution of the phase equilibria as X is varied. We have focused our attention not only on the characterization and the location of the boundaries of the various phases but also on the equilibria between the phases. 

Figure 15 shows the effect of added salt on the stability of the three oil-rich phases L2, L, and L3.0 found in the section A = 1.55 of the phase diagram of the water-dodecane-SDS-pentanol system at low alcohol content. The three phases still exist at very high... 

A. Structural Studies in the Water-Pentanol-Potassium Oleate-Benzene System... 

Figure 30 Dielectric relaxation times at 10°C of (a) dode-cane u-tanol/Brij 97/water microemulsion (system 1) and (b) dodecane/pentanol/Cj2(EO)g/water microemulsions (s5rstem 2), for different water contents. (From Ref 141. With permission from Elsevier Science.)...

The function of hydrotropes may vary in different systems. This has been observed in sun-screen microemulsions prepared with water, pentanol, sodium dodecyl sulfate (SDS) and a hydrotrope (13). Three different hydrotropes were tested, i.e. p-aminobenzoic acid (PABA), octyldimethyl-p-aminobenzoic acid (ODP) and 2-hydroxy-4-methoxy-5-sulfobenzophenone (HMSB). Their effects are presented in Table 18.2. 

Efficiency. It has been shown that an increase of the microemulsion pentanol content can increase the efficiency [5], Conversely, a drastic decrease of efficiency has been observed upon increasing the heptane content m the microemulsion [5]. The toluene efficiency dropped from 7000 plates with Microemulsion 1 (without heptane) to 3300 plates with Microemulsion 3 (heptane 0.59% w/w). The decylbenzene peak efficiency was divided by 8 with the same addition of heptane (1150 plates and 140 plates, respectively) [5], It was speculated that the significant decrease in the kmetics of the solute exchange between the stationary phase and the microemulsion droplets was linked to physicochemical structural changes of the system [5]. The large solubility power of o/w microemulsion systems, up to 4 g/L of decylbenzene in a 90% water rich system, produced a unique selectivity. Unfortunately the low-efficiency problem hinders the use of such systems. 

Friberg, S.E., Venable, R.E., Kim, M., and Neogi, R, Phase equilibria in water, pentanol, tetradecyltrialkylammonium bromide systems. Colloids Surfaces, 15, 285, 1985. 

Poly (ethylene glycol) (PEG), PEG I and PEG II are purchased from Fluka and used without further purification. The average molecular weights of the two PEG samples are determined by gel permeation chromatography (GPC) (compare Table 1). The commercially available pentanol (> 99%, Fluka), xylene (> 99%, Roth) and sodium do-decylsulfate (SDS, > 99%, Fluka) are used as obtained. CdCl2 and (NH4)2S are purchased by Merck-VWR, and water is purified with the Modulab PureOne water purification system (Continental). 

System A. Water-pentanol + dodecane 1 1 (by weight)-octaethylene glycol mono n-dodecyl ether) [hereafter designated as Ci2(EO)8]. This system was investigated along the water dilution line for which the surfactant/alcohol/ oil weight ratio is 2 1 1. Henceforth, this dilution line is marked as W5 (see Fig. 10). 

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