Discontinuous cubic phases

This phase should not be confused with the "I" discontinuous cubic phase formed in some systems, which consists of a cubic packing of closed aggregates. 

Uddin, M.H., Kanei, N., and Kunieda, H. (2000) Solubilization and emulsification of perfume in discontinuous cubic phase. Langmuir, 16, 6891-6897. 

A great many short-chain surfactants do not display either the hexagonal or lamellar liquid crystal as the separating phase above the Krafft eutectic they exhibit a cubic phase instead. Because the hexagonal liquid crystal is often found next to this cubic phase (at higher compositions), it may be presumed that this cubic phase has the discontinuous phase structure. The discontinuous cubic-phase structure consists of discrete micelle-like structural elements arrayed in various ways to form isotropic phase structures having cubic symmetry. A large family of such cubic structures exists [81,82]. 

The discontinuous cubic phase is, without exception (so far as is known), the solubility boundary that exists just above the Krafft eutectic in zwitterionic surfactants. This phase is also the saturating phase at the solubility boundary in many quaternary ammonium salts (such as dodecyltrimethylammonium chloride). It is also prominent in polyfunctional quaternary ammonium surfactants such as dodecyl-tris(2-hydroxyethyl)ammonium chloride [23]. It is interesting that the cubic liquid-crystal solubility boundary is not often found when lipophilic proximate substituent groups do not exist on or near the primary hydrophilic group, as in alkylammonium chlorides (RNH3, Cl ). In contrast, structurally... 

They are repulsive and work perpendicular to the interface. Repulsive interactions induce micelle ordering at values of the surfactant volume fraction and with symmetry that depend on the micelle shape.Spherical micelles close pack into a cubic array, forming the discontinuous cubic phase I. Rodlike micelles pack into a hexagonal array, forming the hexagonal phase H. Bilayers pack into the lamellar phase An important point is that this simple approach leads one to predict for a surfactant that forms spherical micelles (P < 1/3) the following sequence of phases as the surfactant concentration is increased ... 

Micellar cubic (OD), hexagonal columnar (ID), lamellar (2D), and bicontin-uous cubic (3D) nanostructures are formed by self-assembly of 13. For the complexes with IiC104, the ionic conductivities show discontinuous changes following the phase transitions with change of temperature or molecular structure of the dendritic moiety. For example, the conductivity of the complex of 13 with LiC104 drops from 4.6 x 10 6 to 1.2 x 10 9 S cm, along the phase transition from crystalline lamellar to micellar cubic phases. 

A recent study has revealed a previously unknown phase transition in FeCla at about 250 K [94]. There is a small discontinuous decrease in the chemical isomer shift with decreasing temperature of 0-003 mm s" which has been confirmed by extremely careful measurement. A change in the close-packed chlorine lattice to a face-centred cubic one by a shearing motion of adjacent chlorine layers was postulated and subsequently verified by X-ray diffraction. There is also the suggestion of a return to the hep structure at 165 K so the cubic phase may be metastable. 

Ionic conduction has been shown to occur in MHFg (M = K, Rb, or Cs) in both the a (tetragonal) and the / (cubic) phases. Plots of the zero-frequency conductivities versus T show discontinuities at the a-/S transition temperatures moreover, the gradients for the phases are all essentially the same (A 20 kcal), whereas there are considerable differences between the... 

In the case of a balanced relation between the different molecular parts a SmA phase is observed. Excessive space demand of one of these parts results in the formation of a columnar mesophase or, in extreme situations, even in discontinuous cubic mesophases. Bicontinuous cubic mesophases may occur in the area between the SmA and the columnar regions. 

According to Fig. 3, classical thermotropic smectic phases of amphotropic liquid crystals are (SmA ), colunmar hexagonal (Col ), bicontinuous cubic (Cub, i), or discontinuous cubic (Cubjis) [169]. All these meso-phases include a disclination surface between the hydrophilic and the lipophilic parts of the unordered molecules. This surface can be uncurved (SmA), curved in one direction (columnar), curved in two directions with the same sign (discontinuous cubic), or curved in two directions with opposite sign (bicontinuous cubic). 

In contrast to the bicontinuous cubes, the less studied micellar cubic phases have positive Gaussian interfacial curvatures and are discontinuous, consisting of discrete micellar aggregates [164]. The structure of four micellar cubic phase has so far been established. 

Figure 4.11 Schematic representation of spherical reverse micellar structure formed in discontinuous cubic (b) phase. The radius of the micelle is r, the radius of the hydrophilic...

Among the inverted type non-lamellar phases, various studies have been reported on the formation of bicontinuous cubic (V2) phases, the hexagonal (H2) phase, and the discontinuous cubic (I2) phase of the symmetry Fd3m [81, 88, 89],... 

Figure 3.4 The temperature-concentration phase diagrams of BPS-m (m=5,10,20, and 30) with BmimPFj. The phase abbreviations are as follows micellar phase (1 ), discontinuous cubic liquid crystal phase (1 ), hexagonal liquid crystal phase (H ), lamellar liquid crystal phase (L ), lamellar gel phase (L ), reverse micellar phase (L ), ionic liquid phase (IL), and two-phase separation (II). The chemical structure of j0-sitosterol ethoxylates as a typical example of BPS-m is also shown in this figure. Reproduced from Sakai et al. [37] with permission from Japan Oil Chemists Society.

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