Ionic liquid-based surfactants structures

Ionic Liquid-Based Surfactants Synthesis, Moiecuiar Structure,... 

A new one phase method for the synthesis of uniform monodisperse crystalline Ag nanoparticles in aqueous systems was developed by using newly synthesized mono and dihydroxylated ionic liquids and cationic surfactants based on 1,3-disubstituted imidazolium cations and halogens anions. The hydroxyl functionalized ionic liquids and hydroxyl functionalized cationic surfactants simultaneously act both as the reducing and protective agent. By changing the carbon chain length, alcohol structure and anion of the hydoxy-functionalized 1,3-imidazolium based ionic liquids and the hydroxyl functionalized cationic surfactants the particle size, uniformity and dispersibility of nanoparticles in aqueous solvents could be controlled (Dorjnamjin et al, 2008). 

Most highly polar and ionic species are not amenable to processing wifli desirable solvents such as carbon dioxide or any other solvent such as water that has a higher eritieal temperature well above the deeomposition temperature of many solutes. In sueh instanees, the combination of the unique properties of supercritical fluids wifli Arose of micro-emulsions can be used to inerease the range of applications of supercritical fluids. The resulting thermodynamically stable systems generally contain water, a surfactant and a supercritical fluid (as opposed to a non-polar liquid in liquid miero-emulsions). The possible supercritical fluids that could be used in these systems inelude earbon dioxide, efliylene, ethane, propane, propylene, n-butane, and n-pentane while many ionic and non-ionic surfactants can be used. The major difference between the liquid based emulsions and the supercritical ones is the effect of pressure. The pressure affeets the miscibility gaps as well as the micro structure of the micro-emulsion phase. 

Surfactants have a unique long-chain molecular structure composed of a hydrophilic head and hydrophobic tail. Based on the nature of the hydrophilic part surfactants are generally categorized as anionic, non-ionic, cationic, and zwitter-ionic. They all have a natural tendency to adsorb at surfaces and interfaces when added in low concentration in water. Surfactant absorption/desorption at the vapor-liquid interface alters the surface tension, which decreases continually with increasing concentrations until the critical micelle concentration (CMC), at which micelles (colloid-sized clusters or aggregates of monomers) start to form is reached (Manglik et al. 2001 Hetsroni et al. 2003c). 

Electrostatic interactions occur between the ionic head groups of the surfactant and the oppositely charged solid surface (head down adsorption with monolayer structure) [56]. Acid-base interactions occur due to hydrogen bonding or Lewis acid-Lewis base reactions between solid surface and surfactant molecules (head down with monolayer structure) [57]. Polarisation of jt electrons occurs between the surfactant head group which has electron-rich aromatic nuclei and the positively charged solid surface (head down with monolayer structure) [58]. Dispersion forces occur due to London-van der Waals forces between the surfactant molecules and the solid surface (hydrophobic tail lies flat on the hydrophobic solid surface while hydrophilic head orients towards polar liquid) [59]. 

Very recently, the self-assembly of poly(y-benzyl-i,-glulamalc)-fo-poly(i,-lysine) rod-coil copolypeptide via ionic complexation was reported by Ikkala, Hadjichristidis and coworkers [65]. Complexation between the anionic surfactants dodecyl benzenesulfonic acid and the cationic poly(L-lysine) chains occurs via proton transfer from the acid group to the base, resulting in electrostatically bonded comb-like structures, and fluid-like liquid crystalline structures at room temperature due to efficient plasticization of dodecyl benzenesulfonic acid. 

Neutron Diffraction - The one example reported this year involved an exploration of the structural features of the liquid-air interface affected by adsorbed sugar-based ionic surfactant 7,7-bis[(l,2,3,4,5-pentahydroxyhexana-mido)-methyl]-n-tridecane. ... 

Generally, amphiphilic molecules self-assemble to form micelle, microemulsion, lyotropic liquid crystal and vesicle. Moreover, long-chain ILs can act as ionic surfactants and form similar self-assembly in water or oil. Qiu et al. summarized the studies of IL based microemulsions from the p>erspective of the role of ILs (Qiu Texter, 2008). ILs participated in the formation of the microemulsions, in which ILs replaced oil, water or surfactants. Hao et al. reviewed the self-assembled structures (such as micelles, microemulsions, liquid crystals and vesicle) in ILs, which acted as the solvent (Hao Zemb, 2007). In this p>art, we summarized the IL based organized assemblies, in which IL participated in the formation of micelles, microemulsions, vesicles and liquid crystals rather than acted as solvents. 

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