Structures nonionic surfactant micelles

J. Weiss, J.N. Coupland, D. Brathwaite, and D.J. McClements Influence of Molecular Structure of Hydrocarbon Emulsion Droplets on Their Solubilization in Nonionic Surfactant Micelles. Colloids Surfaces A 121, 53 (1997). 

Jafvert, C.T., Chu, W. and Vanhoof, P.L. (1995). A Quantitative Structure-Activity Relationship for Solubilization of Nonpolar Compounds by Nonionic Surfactant Micelles. ACS Symp.Ser., 594, 24-37. 

Weiss, J. et al.. Influence of molecular structure of hydrocarbon emulsion droplets on their solubihzation in nonionic surfactant micelles. Colloids Surf. A, 121, 53, 1997. 

Structure of Nonionic Surfactant Micelles in Organic Solvents A SAXS Study... 

This section is based on Ref. [69] and will describe the structure of monoglycerol-based nonionic surfactant micelles in n-alkanes. The effects of solvent properties, temperature, the alkyl chain length of surfactant, surfactant concentrahon, and added water or glycerol will be mainly discussed. The glycerol a-monomyristate (G14G1) is taken as the main surfactant. 

In the following section, structure of diglycerol fatty acid ester nonionic surfactant micelles in n-alkanes (straight-chain hydrocarbon oils from octane to hexadecane), and in two aromatic oils (phenyl octane and ethyl benzene) will be described. 

Araos MU, Warr GG (2008) Structure of nonionic surfactant micelles in the ionic liquid ethylammonium nitrate. Langmuir 24 9354-9360... 

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

Performance Indices Quality Factors Optimum E1LB Critical micelle concentration (CMC) Soil solubilization capacity Krafft point (ionic surfactants only) Cloud point (nonionic surfactants only) Viscosity Calcium binding capacity Surface tension reduction at CMC Dissolution time Material and/or structural attributes... 

In the remainder of this article, discussion of surfactant dissolution mechanisms and rates proceeds from the simplest case of pure nonionic surfactants to nonionic surfactant mixtures, mixtures of nonionics with anionics, and finally to development of myehnic figures during dissolution, with emphasis on studies in one anionic surfactant/water system. Not considered here are studies of rates of transformation between individual phases or aggregate structures in surfactant systems, e.g., between micelles and vesicles. Reviews of these phenomena, which include some of the information summarized below, have been given elsewhere [7,15,29]. 

Some surfactants aggregate at the solid-liquid interface to form micelle-like structures, which are popularly known as hemimicelles or in general solloids (surface colloids) [23-26]. There is evidence in favor of the formation of these two-dimensional surfactant aggregates of ionic surfactants at the alumina-water surface and that of nonionic surfactants at the silica-water interface [23-26]. 

The same effect is seen when a non—aromatic cationic surfactant/nonionic surfactant system is used. Since the nonideality of mixed micelle formation in this case is due almost entirely to the electrostatic effects and not to any specific interactions between the dissimilar hydrophilic groups, the geometrical effect just discussed will cause the EO groups to be less compactly structured... 

The equilibrium in these systems above the cloud point then involves monomer-micelle equilibrium in the dilute phase and monomer in the dilute phase in equilibrium with the coacervate phase. Prediction o-f the distribution of surfactant component between phases involves modeling of both of these equilibrium processes (98). It should be kept in mind that the region under discussion here involves only a small fraction of the total phase space in the nonionic surfactant—water system (105). Other compositions may involve more than two equilibrium phases, liquid crystals, or other structures. As the temperature or surfactant composition or concentration is varied, these regions may be encroached upon, something that the surfactant technologist must be wary of when working with nonionic surfactant systems. 

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