Amphiphiles self-organized structures

Fixation of hydrophilic units as side-groups of a hydrophobic macromolecular chain leads to water-soluble polysoaps [205], exhibiting a similar diversity of self-organized structures like the monomeric analogues. A detailed review can be found in [206]. In contrast to polyelectrolytes and ionomers described above, the association of the amphiphilic groups of polysoaps occurs preferentially intramolecularly. As a consequence the solution viscosity remains low, even for highly concentrated solutions [207] and no critical micelle concentration (CMC) can be found up to extreme dilutions [208,209]. 

Figure 22.28 and Figure 22.29 show, respectively, the H and C-NMR spectra of the oligoesters prepared from epoxidized sunflower oil methyl esters (methyl biodiesel from sunflower oil) and di-l,2-cyclohexanedicarboxylic anhydride using triethylamine as initiator. These materials are soluble in common organic solvents such as acetone, ethanol, tetrahydrofurane, and chloroform, but insoluble in water. Oligoesters from epoxidized biodiesel can be used as intermediate materials for the synthesis of polyelectrolytes by saponification reactions with aqueous solution of sodium or potassium hydroxide at room temperature (Fig. 22.27). The products obtained after saponification present solubility in water. Amphiphilic materials, such as the polyelectrolytes prepared from epoxidized biodiesel, have hydrophobic and hydrophilic segments. They can spontaneously self-organize in a wide variety of structures in aqueous solution. Understanding the dynamics of the formation and transition between the various self-organized structures is important for technological applications.

The macroscopic morphologies of the self-organized structures derived from the aggregation of [GOjfullerene molecules have received considerable attention due to their tunable physical and chemical properties. This section deals with recent approaches seeking to exploit amphiphilic interactions of functionaUzed [GOjfullerene derivatives to build new nano architectures. 

As the number of hydrophobic sequences in an amphiphilic polymer chain increases, intrapolymer hydrophobic association, as well as interpolymer association, becomes an important process to determine overall self-organized structures. This is particularly so with amphiphilic random or alternating copolymers in which hydrophobic and hydrophilic units are randomly or alternately distributed on a polymer chain. Intrapolymerassociating structures are of critical importance to determine interpolymerassociating structures. In general, intrapolymer hydrophobic association is dominant in dilute solutions, whereas interpolymer association also occurs in a semidilute or concentrated regimen. In random copolymers with a strong tendency for intrapolymer association, unimolecular micelles (unimer micelles) may be formed as a consequence of intrapolymer closed association. 

A typical biomembrane consists largely of amphiphilic lipids with small hydrophilic head groups and long hydrophobic fatty acid tails. These amphiphiles are insoluble in water (<10 ° mol L ) and capable of self-organization into uitrathin bilaycr lipid membranes (BLMs). Until 1977 only natural lipids, in particular phospholipids like lecithins, were believed to form spherical and related vesicular membrane structures. Intricate interactions of the head groups were supposed to be necessary for the self-organization of several ten thousands of... 

Vesicles [10, 11] these aggregates of insoluble natural or artificial amphiphiles in water can have various shapes (spherical, cylindrical). Depending on the preparation conditions, small unilamellar or large multilamellar vesicles can be produced. The structures meet the self-organization criterion, because they are, albeit on a long time scale, dynamic and not in thermodynamic equilibrium, which would in many cases be a macroscopically phase separated lamellar phase. 

Self-aggregating amphiphiles can broadly be divided into hydrotropes and surfactants. The main difference between hydrotropes and surfactants lies in the fact that hydrotropes are typically not sufficiently hydrophobic to cooperatively self-aggregate and form organized structures, whereas surfactants form distinct aggregates such as micelles and vesicles above their critical aggregation concentrations. 

We have already seen in Chapter 5, on self-organization, how and why amphiphilic molecules tend to form aggregates such as micelles, vesicles, and other organized structures. 

Although not strictly LB films, there are other types of self-assembled films containing Q-state MCs that resemble LB films. One example involves the self-assembly of the amphiphile DTG into an organized film by slow evaporation of solvent from a dispersion of the amphiphile (40). The structure of the cast film has the head-... 

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