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Experimental results of measurements of refractive index and light scattering yield interesting information about the structure of the L2-phase. In accordance with previously presented studies they show that one, with respect to the role of water, has two main regions, one extending from the water-free phase up to a content of water of about 40% and the other at water contents above about 55%. An intermediate transition region lies between about 40% and 55% of water. In the first main region the incorporation of water into the acid octanoate molecules influences the magnitude of the refractive index decrement and light scattering intensity. In the latter region, the partial contributions of water and the amphiphilic substance for the magnitude of the refractive index remain almost unchanged, but here it seems to be the distribution into different domains, bordering each other, of the two types of water, that in the domains with hydrated polar groups and that in the domains with unbound bulk-water, which causes the changes in the intensity of the light scattering. The structure of the L2-phase, among others, the diversity on the molecular level and the very high concentrations of the active amphiphilic components in large parts of the phase, render quantitative estimations of particle size impossible on the basis of light scattering measurements. Information about phase structure obtained from other experimental investigations, however, makes it possible to show the connection between phase changes on the molecular level and changes in the light scattering intensity. This has also created a basis for some, although partially hypothetical, explanations of which factors play a role in the changes mentioned, as with information about the structure. Among the latter it may be mentioned that the amphiphilic substance, up to very high water contents, retains some of the properties that the first 40% of water have caused. The differences in properties between unbound bulk-water and water bound to the polar groups are considerable; the influence of the bulk-water on the phase properties seems to vary with the manner of its distribution and the properties of the bound water are different, depending on whether it belongs to the solvation water shell of the sodium ion, or whether it is bound via hydrogen bridges.

Measurements of water pressure and electrical conductivity have contributed to show that the extended, isotropic liquid L2-phase region in the system sodium octanoate/ octanoic acid/water may be divided into several subregions, inside which the character of the system is different. In the non-aqueous part of the phase and at low contents of water and more than about three moles of octanoic acid per mole of sodium octanoate the character is that of a solution of acid sodium octanoate in octanoic acid. At high water contents the L2-phase has the character of a solution of acid sodium octanoate in water. Intermediately there is a large region where the character of the phase is reminiscent of a hydrated acid sodium octanoate in fluid state. In this region the content of octanoic acid is below three moles per mole of sodium octanoate and the maximal water content is about that bound to the polar groups.

The influence of decanol solubilization on the viscosity and the water vapor pressure of sodium octanoate solutions has been studied. The incorporation of decanol in the micelles causes an increase in the viscosity as well as in the vapor pressure at all concentrations above the CMC. The increase in viscosity is caused by the increased volume fraction of the micellar substance and is particularly obvious above the 3rd critical concentration, where the amount of hydrated micellar substance is so high that crowding between the micelles occurs. Under some circumstances the viscosity increase is somewhat retarded by the decrease of the charge density in the boundary layers of the micelles caused by the incorporation of decanol. The increase of water vapor pressure is due to the fact that the concentration of octanoate and sodium ions in the intermicellar solution is lower in the decanol-containing system than in the pure octanoate solutions and to the fact that the charge density in the boundary layer of the micelles decreases by the incorporation of decanol. The latter is more significant the higher the micellar concentration.

The influence of sodium chloride addition upon the ability of aqueous sodium octanoate solutions to solubilize decan-1-ol has been studied. At low octanoate concentrations an addition of neutral salt increases the solubilizing capacity; this depends on the displacement of cmc toward lower concentrations, thereby causing an increase in the content of micellar matter. At high octanoate concentrations the neutral salt exerts the opposite effect; this is obviously a result of the increased number of counterions bound to the mixed micelles and the earlier formation of mesophases caused thereby. Between the limiting association concentration and the second critical concentration, within which region of the neutral salt-free system water-rich mesophases are formed (water-rich D, B, and C phase), the addition of sodium chloride causes a decrease in the water content of the mesophase. Above the second critical concentration where even in the absence of sodium chloride a water-poor mesophase (D phase) is formed, there will primarily be an increase in the octanoate content of the phase. The composition of the middle phase (E phase) seems to be rather unaffected by sodium chloride addition. At high neutral salt addition the formation of mesophases is replaced by the formation of crystalline sodium octanoate; simultaneously, the aqueous solubility of octanoate markedly decreases.

1. Das System Palmitinsaure–Natriumpalmitat ist sowohl mit der sogenannten „Auftaumethode” wie durch Aufnehmen von Zeittemperaturkurven bei dem Erstarren der Schmelzen untersucht worden. Die Untersuchung nach dem erstgenannten Verfahren umfast das Konzentrationsgebiet 0–75 Mol-% Natriumpalmitat, die nach dem zweiten das Gebiet von 0–58 Mol-% Natriumpalmitat.

Nuclear magnetic resonance line-widths of 23Na have been determined at several compositions in two isotropic solution phases and five mesomorphous phases in the sodium caprylate-decanol-water system. The results obtained demonstrate that the rate of nuclear magnetic relaxation of 23Na+ is primarily determined by the number of water molecules per sodium ion. this indicates that in all the phases investigated, the sodium ions are predominantly coupled to water molecules. A comparison with 81Br nuclear magnetic relaxation data shows that the bonding of sodium ions is markedly different from that of bromide ions in systems containing association colloids and water. This diversity is found to be due to differences in ion-water coupling.

The properties and structures of aqueous sodium caprylate solutions : V theactivity of water and sodium caprylate

1. Eine von S a m t e r vorgeschlagene Schnellmethode, das Blei durch Oxydation mit Persulfat und durch nachheriges Titrieren des entstandenen Bleisuperoxyds zu bestimmen, ist naher gepruft worden. Die Oxydation ist, teils mit Ammoniumpersulfat in ammoniakalischer Losung, teils mit Kaliumpersulfat in natriumhydroxydhaltiger Losung ausgefuhrt worden. Das Bleisuperoxyd wurde nach R u p p und S i e b l e r mit Arsentrioxyd und Kaliumbromat bestimmt. Die Bleisuperoxydausbeuten sind durchweg zu niedrig, etwa 96 – 97%, gefunden worden. 2. Die ausgefuhrten Analysen zeigen, dass bei der Oxydation mit Persulfat immer etwas Blei in der Losung geblieben ist und dass der Superoxydniederschlag das Blei auch in anderer Form wie Bleisuperoxyd enthalten hat.

Properties and structure of the decanolic solutions in the sodium caprylate-decanol-water systems : I. the region of existence of the isotropic decanolic solutions

The dependence on the concentration of the density, viscosity, refractive index, and light scattering has been studied in aqueous solutions of cetyltrimethylammonium bromide between 0.036% (c.m.c.) and 26%. The results are discussed in relation to results of other studies. Above the c.m.c. there are more or less spherical, strongly hydrated micelles composed of about 95 CTAB molecules. From 9% to 11% upwards the micelles are deformed to rod-shaped micelles owing to the increasing crowding in the solution. At 26% the isotropic micellar solution is transformed via a narrow two-phase region to mesomorphous middle soap with rod-shaped hydrated CTAB aggregates in hexagonal array.

Phase equilibria diagrams at 20°C are presented for the systems AOT- p -xylene-water, AOT-caprylic acid-water, and AOT- n -decanol-water. In all these systems occur 2 solution phases, L 1 and L 2 , and 3 mesophases, F, I 2 , and D. The mesophase F, which includes pure AOT, has a reversed two-dimensional hexagonal structure with long mutually parallel AOT rods where the sodium sulfonate groups are oriented toward the center. Water is incorporated in the polar cores, whereby the rods swell. Hydrocarbon is located around the rods and between their outer paraffin chains. The isotropic mesophase I 2 has a body-centered cubic structure; also in this phase the AOT molecules are oriented with the polar groups inwards. The mesophase D has a lamellar structure of the neat-soap type. In the AOT- p -xylene-water system the water-free solution in region L 2 is micellar and contains cylindrical, nearly spherical, and largely unsolvatized micelles of the reversed type. The aggregation number is 23 and the diameter about 22–23A. The arrangement of the AOT molecules in them resembles that in the aggregates of the water-free mesophase of region F. When water is solubilized it is taken up in the polar core and the micelles will swell; their nearly spherical shape is retained. Only when the volume fraction of micellar substance exceeds about 0.74 will the micelles deform and grow out to cylindrical aggregates of the same type as in the water-rich region of phase F. In the L 2 solutions of the AOT-caprylic acid-water and AOT-decanol-water systems the interaction between the hydrophilic groups of the added organic substances and the polar groups of the AOT will split up the original AOT aggregates and result in small composite entities. In the presence of water their aggregation will increase. The “microemulsions” of Schulman are in many cases identical in principle with the micellar solutions of reversed type that occur in the L 2 solutions of many ternary amphiphile systems. The stabilizing amphiphilic layer consists in these “microemulsions” of a combination of association colloid and alcohol whereas this layer in the system of AOT-hydrocarbon-water consists only of one component. In the case of thermodynamically stable micellar solutions the term “micro-emulsions” is a misnomer and should not be used in this connection.

The properties and structures of aqueous sodium caprylate solutions : VII activities of caprylate anions, and counter ion binding to the micelles

Die Phasengleichgewichte im Drei-Komponentensystem Natriumkaprylat-Dekanol-Wasser wurden untersucht und die Resultate in einem Dreieckdiagramm dargestellt. Es treten zwei Gebiete mit isotropen Losungen auf, und zwar das eine mit Wasser, das andere mit Dekanol als Losungsmittel.

The properties and structures of aqueous sodium caprylate solutions : V measurements of the activity of sodium ions

The properties and structures of aqueous sodium caprylate solutions : II theviscosities of sodium caprylate solutions at 20 C measured with capillaryviscometers

Properties and structure of the decanolic solutions in the sodium caprylate-decanol-water system : II density and viscosity of the solutions

The relationship between various kinds of solubilization and the formation of mesophases is elucidated. In aqueous solutions of association colloids there are three processes by which mesomorphous phases form: (i) the separation of the micellar substance in mesomorphous form on reduction of the water content, (ii) the separation of the micellar substance at lower concentrations, from the c.m.c. upwards, as a result of the changes that the micelles undergo on solubilization of foreign amphiphilic and lipophilic substances, and (iii) below the c.m.c. through the formation of aggregates between the solubilizate and the molecules or ions of the association colloids. The last of these processes is typical of the solubilization of fatty acids and liquid monohydric alcohols. In systems of sparingly soluble amphiphilea that do not give micellar aqueous solutions but take up water with swelling, mesophases often form through this “solubilization” of water, a process that is often promoted by the presence ...

The properties and structures of aqueous sodium caprylate solutions : III the viscosities at temperatures between 20 and 40 C