Micelles, rod-like

The concentration at which surfactants form rodlike micelles is called CMCII. Critical micelle concentration is almost independent of temperature while CMCII increases with temperature. Spherical micelles, rod-like or thread-like micelles, and vesicles are the three most common microstructures seen in dilute DR surfactant solutions. 

Self-assembled microstructures of water and surfactant with or without oil have been the subject of intense research for several decades because of their rich structural variety. Microstructures ranging from spherical micelles, rod-like micelles, bicontinuous micro emulsions and liquid crystalline phases have broad commercial and scientific applications including nanomaterial synthesis, controlled delivery, coatings and detergents among many others. 

The obtained PCL diol was modified with a-bromopropionyl to yield a tel-echelic ATRP macroinitiator. After ATRP of styrene, the obtained PS-b-PCL-b-PEG-fc-PCL-fc-PS revealed interesting self-assembly behavior in water forming spherical micelles, rod-like micelles, vesicles, lamellae and large compound micelles depending on the block copolymer composition and concentration (Figure 12.11). The same author also extended this concept to the synthesis of... 

Figure B3.6.4. Illustration of tliree structured phases in a mixture of amphiphile and water, (a) Lamellar phase the hydrophilic heads shield the hydrophobic tails from the water by fonning a bilayer. The amphiphilic heads of different bilayers face each other and are separated by a thin water layer, (b) Hexagonal phase tlie amphiphiles assemble into a rod-like structure where the tails are shielded in the interior from the water and the heads are on the outside. The rods arrange on a hexagonal lattice, (c) Cubic phase amphiphilic micelles with a hydrophobic centre order on a BCC lattice.

Cetyltrimethylammonium 4-vinylbenzoate (33) forms rod-like micelles that can be stabilized by radical polymerization. The resulting structure, was observed by small-angle neutron scattering to retain its original rod-like architecture and showed enhanced thermal stability and did not dissociate upon dilution. 

As an example, take the manufacture of mesoporous silica (amorphous Si02) with uniformly sized pores. Rod-like micelles of alkyltrimethylammonium ions form in an aqueous solution of an alkyltrimethylammonium halide. The micelles have a positive electric... 

Rod-like micelles of surfactant molecules with a liquid-crystalline order. The aqueous solution is located between the micelles. Spheres = hydrophilic ends of the surfactant molecules, black zigzag lines = long alkyl groups... 

The amphipathic compounds shown in Scheme 2 can form a disc-like micelle(7). The shape of a molecular aggregate depends on the shape of the constituent molecules(8). For instance, conical molecules with large polar head groups prefer to form spherical micelles while cylindrical molecules tend to give flat aggregates. Trans-azobenzene is a rod-like molecule whereas the cis-form is bent. 

Note 3 A polymer composed of molecules that have rigid rod-like groups or chains may form LC mesophases in solution under suitable conditions. These are sometimes described as lyotropic but, as the solvent does not induce the formation of aggregates or micelles, this term is not appropriate. 

FIGURE 6.4 Micelles swollen with solubilized monomer. As the concentration increases the micelles change from spherical, as shown, to more rod-like in appearance. 

Esumi K, Matsuhisa K, Torigoe K (1995) Preparation of Rod like Gold Particles by UV Irradiation Using Cationic Micelles as a Template. Langmtur 11 3285-3287... 

Zeolitic structures with pore sizes of 2000 to 10000 pm are known as mesoporous solids, and can be formed by a method known as liquid crystal templating (LCT). The combination of a suitable cationic surfactant together with silicate anions form arrays of rod-like surfactant micelles (Figure 3.7) surrounded by a polymeric siliceous framework. On calcination the mesoporous structure is formed. 

Increasing the concentration of surfactants in water to a level above the CMC leads to the formation of rod-like micelles and, subsequently, liquid crystals [251]. Both liquid crystals and liquid-crystalline polymers [252] have been used as media for small particle generation [253, 254] and have also acted as piezoelectric devices [255]. Of particular interest are metallomesogens, the metal complexes of organic ligands which exhibit liquid crystalline behavior [255],... 

The new surfactants have to answer several criterions 1- lower cost and commercially available, 2- possibility of self-assemble into rod-like micelles with dimension larger than those formed by CTMA+ and controllable phases. 

Figure 2. Synthetic scheme for macroporous transition metal oxides. Double templating is achieved by the co-existence of rod-like micelles and vesicles or microbubbles.

---