Inverse lamellar mesophase

Note 5 The lyotropic equivalent of a smectic A mesophase is known as a lamellar mesophase where layers of amphiphilic molecules are separated by layers of solvent, normally water, or by oil in an inverse lamellar mesophase. 

In addition to the cubic and/or inverse cubic forms described above, further transitional forms exist between the lamellar phase and the hexagonal mesophase (cubic, type II) or inverse hexagonal mesophase (cubic, type III) [6]. In contrast to the discontinuous phases of types I and IV, cubic mesophases of type II and III belong to the bieontinuous phases (Fig. 4f). A range of lyotropic mesophases are possible, depending on the mesogen concentration, the lipophilic or hydrophilic characteristics of the solvent, and the molecule itself [6]. 

The study by low-angle X-ray diffraction and electron microscopy of concentrated solutions of the copolymers in preferential solvents for polybutadiene (iso-prene, butadiene) or for poly(a-methyl styrene) (styrene, a-methylstyrene, methyl methacrylate, methylethyl ketone) and of copolymers in the dry state obtained by slow evaporation of the solvent from the mesophases have shown the existence of three types of structure hexagonal, lamellar, and inverse hexagonal depending upon the copolymer composition84,85. The factors governing the structural type and the structural parameters are the same as in the case of polystyrene-polybutadiene copolymers85. ... 

Non-lamellar lipid mesophases (Fig. 4) may also be identified by their characteristic small-angle diffraction pattern. The structure of the inverse hexagonal lipid-water mesophase (denoted as Hu) is based on cylindrical water rods, which are surrounded by lipid monolayers. The rods are packed in a two-dimensional hexagonal lattice with Bragg peaks positioned at... 

Fig. 4. Schematic drawing of lipid-water mesophases (Lc, lamellar crystalline Lps Pp., lamellar gel L , lamellar liquid-crystalline Qn, Qn°, Qn , inverse bicontinuous cubics Hu, inverse hexagonal). The cubic phases are represented by the G, D, and P minimal surfaces, which locate the midplanes of fluid hpid bilayers.

The binary system of 8 and water has several eutectica and its melting temperature as well as that of the upper solid-solid transition (Cr2->Cr3) decreases with growing amounts of water, however, the lower solid-solid transition (Cri —> Cr2) remains constant. With growing water concentration the Cr3 phase is replaced by the N mesophase which occurs in a very narrow concentration range from 1 to 2 wt% of water in the mixture (see Fig. 10). This was the first observation of an inverse nematic N2L phase in a binary system of an amphiphile with water [83]. At higher water concentrations lamellar phases occur at first, starting at... 

Lyotropic mesophases usually formed from such substances are beside the lamellar phase the inverse hexagonal and different types of inverse cubic phases. Nanoparticles based on lamellar structures ((multilamellar) vesicles, liposomes) will not be... 

There is a linear relationship between the crystallization temperatures and the inverse lamella thicknesses, which is quite in accordance with Gibbs-Thomson equation. There is also a linear relationship between the melting temperatures and the inverse lamella thicknesses. Crossover of these two linear curves is considered to be the triple point of mesophase transition. Recently, the crossover was reproduced in the molecular simulations of lattice polymers, and the interpretation was updated to an uplimit of instant thickening at the lateral growth front of lamellar crystals (Jiang et al. 2016). 

In the presence of water, surfactants and lipids give rise to a variety of phases referred to as lyotropic phases or mesophases.i The most important of these phases are the lamellar, hexagonal, cubic micellar, and cubic bicontinuous phases denoted by L, H and V, and Q, respectively (see Figure 1.11 in Chapter 1). The subscripts 1 or 2 attached to these phase symbols indicate that the phase is direct (water continuous) or inverse (discontinuous water domains). Many other lyotropic phases have been identified that differ from the main ones by the state of the alkyl chain (crystalline or disordered) and of the head group arrangement (ordered or disordered). In the particular case of the lamellar phase, additional variations come from the possible different orientations adopted by the alkyl chains with respect to the plane of the lamellae (angle of tilt of the chain) and also from the state of the surface of the lamellae that can be planar or rippled. Numerous detailed descriptions have been given for the equilibrium state of the various phases that surfactants and lipids can form in the presence of water. 

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