Surfactants amphiphilicity

The use of cosolvents and designed surfactants (amphiphiles/stabilizers) can improve solubility. 

These are stable micelles that are formed with polymeric surfactants. Amphiphilic block copolymers such as the pluronics (polyoxyethylene-polyoxypropylene block copolymers) are able to self-assemble into polymeric micelles and hydrophobic drugs may be solubilized within the core of the micelle or, alternatively, conjugated to the micelle-forming polymer. Although micelles are rather dynamic systems that continuously exchange units between the micelle structure and the free units in solution, those composed of polyoxyethylene - poly(aspartic acid) have been found sufficiently... 

In addition to those formed by surfactant amphiphiles, two other types of lyotropic mesophases are generally recognized, neither of which exhibits a cmc. The first of these are lyotropic phases of rigid-rod polymers that can form mesophases in both aqueous and non-aqueous solvents " these mesophases are of the nematic or hexagonal type. Examples include polymeric metal acetylide complexes and DNA." The other type is usually formed from flat and largely aromatic molecules which stack to give lyotropic columnar phases, also referred to as chromonic phases." " This latter class is formed from systems with ionic or strongly hydrophilic peripheral functions, and forms mesophases... 

The HLB Number in Surfactant Amphiphilic Molecules (A Value between 0 and 60) Defining the Affinity of a Surfactant for Water or Oil/ Has a Crucial Influence on the Particle Size... 

Kunieda, H. (1989) Phase behaviors in water/nonionic surfactant/hydrocarbon and water/nonionic surfactant/ amphiphilic oil system. J. Colloid Interface Sci., 133, 237-243. 

Ill) Improved stabilization of liposomes can be achieved by incorporating a small amount of PEG-lipids and cholesterol. (IV) Microemulsions consist of a surfactant (amphiphile) monolayer covering oil. (V) Micelles can contain a hydrophobic nanoparticle. (VI) Bilayer on nanoparticles of silica, mica, glass, or iron oxide. Reproduced from Mulder, W. J. M. Strijkers, G. J. van Tilborg, G. A. F. etal. NMR Biomed. 2006, 19,142. ... 

Surfactant Amphiphilic molecule generally perceived as having a polar headgroup, either charged or neutral, and a long-chain hydrocarbon tail. 

The surfactant packing parameter v /aolc can be used to predict what types of nanostructures in microemulsions can form using specific surfactants. Amphiphilic molecules with 0.5 < v/aok < 1 tend to form three-component o/w and... 

Mixtures of aqueous electrolytes, hydrocarbons, and amphiphilic compounds have been the subjects of extensive research, especially those systems forming amorphous isotropic solutions, called microemulsions. Several books and papers have treated this subject [1-5]. The term microemulsion was first introduced by Hoar and Schulman [5]. Microemulsions are thermodynamically stable, isotropic, transparent colloidal solutions of low viscosity, consisting of three components a surfactant (amphiphile), a polar solvent (usually water), and a nonpolar solvent (oil) [1-7]. The surfactant monomers in these fluids reside at oil water interface and effectively lower the interfacial-free energy, resulting in the formation of optically clear, thermodynamically stable formulations. The innate formation of colloidal particles is typically up to nanometer scale globular droplets each... 

When dispersed in aqneous media, the hydrophobic component constitutes the core while the hydrophilic block corona serves to stabilize the miceUar structure. In contrast to low molar mass surfactants, amphiphilic block copolymers have highly tunable composition and assembly characteristics. The constraints between the core-forming blocks, the interaction between chains in the corona, and the surface energy between the solvent and the core dictate the shape and size of the micellar structures [43]. An important property of amphiphilic block copolymers is the ability to enhance solubility of hydrophobic substances. As with low molar mass surfactants, the hydro-phobic core of the micellar structures formed by amphiphilic block copolymers can serve as a compatible microenvironment for sequestration of water-insoluble compounds. 

For readers who would like to learn more about the chemistry and use of surfactant (amphiphilic) molecules, we recommend the following literature. ... 

Figure 9.2. Mechanisms for the stabilization of emulsions (a) adsorbed ions—specific-ion adsorption (b) colloidal sols—adsorption of polymer chains (c) polymeric stabilizers— solid particles (d) surfactants—amphiphile adsorption.

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