Structured surfactant

Surfactant structure Surfactant-lype antistats Surfactol Surfadones Surfilcon-A Surflan Surfonic Surfynol Surfynol 104 Surgam [33005-95-7] Surgery... 

Below the CMC, the surfactant mixing in monolayers composed of similarly structured surfactants approximately obeys ideal solution theory. This means that the total surfactant concentration required to attain a specified surface tension for a mixture is intermediate between those concentrations for the pure surfactants involved. For mixtures of ionic/nonionic or anionic/cationic surfactants, below the CMC, the surfactant mixing in the monolayer exhibits negative deviation from ideality (i.e., the surfactant concentration required to attain a specified surface tension is less than that predicted from ideal solution theory). The same guidelines already discussed to select surfactant mixtures which have low monomer concentrations when micelles are present would also apply to the selection of surfactants which would reduce surface tension below the CMC. 

A micelle is a dynamic structure. Surfactants leave the micelle and go into solution while other surfactants enter the micelle from solution. The timescales involved depend critically on the specific structure of the surfactant, in particular on the length of the hydrocarbon chain. For example, the residence time of a single dodecylsulfate (CH3(CH2)h0S03 ) in a SDS micelle at 25° C is 6 /xs [525], If we reduce the chain length by two methylene units to decyl sulfate (CH3(CH2)g0S03 ) the residence time decreases to roughly 0.5 /us. Tetradecyl sulfate (CH3(CH2)i30S03 ), which has two methylene units more than dodecylsulfate, typically remains 83 /its in a micelle. 

Surfactants act as solubilizers, stabilizers, emulsiLers, and wetting agents. They can also causi toxicity and disrupt normal membrane structure. Surfactant toxicity is directly related to its concentration. This should be considered by the pharmaceutical formulator so levels below the toxic concentration will be used for a particular application. Many of the toxic effects of the surfactants are related to their physicochemical properties and their interaction with biological membranes and other macromolecular assemblies. The observed protein binding and lipid solubilization is directly... 

This new family of mesoporous silica and aluminosilicate compounds were obtained by the introduction of supramolecular assemblies. Micellar aggregates, rather than molecular species, were used as structure-directing agents. Then, the growth of inorganic or hybrid networks templated by structured surfactant assemblies permitted the construction of novel types of nanostructured materials in the mesoscopic scale (2-100 nm) [110,113,117],... 

Depending on their chemical structure, surfactants capable of forming micelles are usually classified into cationic e.g. ammonium salts), anionic e.g. sulfates, carboxylates), ampholytic e.g. zwitterionic salts), and non-ionic surfactants (usually containing polyoxyethene chains) cf. Table 2-10 in Section 2.5. 

Foaming properties can be quantitatively related to surfactant chemical structure, surfactant physical properties, and test conditions using the technique of multiple correlation analysis.(11) The current studies were restricted to linear correlation equations to permit the analyses to be performed on a small microcomputer. While non-linear equations having higher correlation coefficients than obtained herein can be developed, theoretical insights are often limited due to the complexity of the various terms of such equations. The quality of the correlations were assessed using the correlation coefficient (r ) criteria of Jaffe (12)... 

C linkages and are hydrolytically unstable others do not contain a silicone-carbon bond and are stable. In general, higher-viscosity silicone copolymers are more efficient and wiU provide foams with finer cell structures. Surfactants are used at the 0.5% to 1% level in rigid urethane foams. With too little silicone foam, cell structure is large. Too much silicone does not affect the foam properties, but is wasteful. There is no known health hazard with the use of silicones (20). 

Variables identified as important in the achievement of the low IFT in a W/O/S/electrolyte system are the surfactant average MW and MW distribution, surfactant molecular structure, surfactant concentration, electrolyte concentration and type, oil phase average MW and structure, temperature, and the age of the system. Salager et al. (1979b) classified the variables that affect surfactant phase behavior in three groups (1) formulation variables those factors related to the components of the system-surfactant structure, oil carbon number, salinity, and alcohol type and concentration (2) external variables temperature and pressure (3) two-position variables surfactant concentration and water/oil ratio. Some of the factors affecting IFT-related parameters are briefly discussed in this section. Some other factors, such as cosolvent, salinity, and divalent, are discussed in Section 7.4 on phase behavior. Healy et al. (1976) presented experimental results on the effects of a number of parameters. 

Graciaa, A., Fortney, L.N., Schechter, R.S., Wade, W.W., Yiv, S., 1982. Criteria for structuring surfactants to maximize solubilization of oil and water part 1-commercial nonionics. SPEJ (October), 743-749. 

This term is connected with assemblies of typically structured surfactants above a critical micelle concentration (cmc) or a critical vesicle concentration (cvc). The aggregates have colloidal dimensions and are spherically shaped [44]. 

At constant surfactant concentration, C, in the solution, a plot of (y0 — yt) versus f1/2 should be linear, if adsorption is diffusion-controlled (generally true, for simple-structured surfactants) and permits evaluation of Dap from the slope of the plot. 

The amphiphilic nature is the indispensable attribute of the structure of any surfactant. The nonpolar, "solvophobic" part of fluorosurfactants constitutes usually with perfluoroalkyl, co-hydroperfluoroalkyl or perfluoroether chain of normal or branched structure. Surfactants with semifluorinated carbon chains are not quite effective as the ones with completely fluorinated carbon chains. Usually the optimum perfluorocarbon chain length is from 6 to 10 carbon atoms. Three industrially important methods of fluorosurfactants synthesis are known [123-126] ... 

C. Either mechanical or pneumatic foam whipping of the oligomer or polymer solution or emulsion contact of the inhibiting vapor phase in the presence of a structural surfactant. The foam is then fixed by lacing the polymer walls. 

Anderson and Wennerstrom [33] calculated the geometrical obstruction factors of the self-diffusion of surfactant and solvent molecules in ordered bicontinuous microstructures, which serve as good approximations also for the disordered bicontinuous microemulsions and L3 (sponge) phases. The geometrical obstruction factor is defined as the relative diffusion coefficient DIDq, where D is the diffusion coefficient in the structured surfactant system and Z)q is the diffusion coefficient in the pure solvent. In a bicontinuous microemulsion the geometrical obstruction factor depends on the water/oil ratio. An expansion around the balanced (equal volumes of water and oil) state gives, to leading order. 

Fig. n To study the structure surfactants on surface, these AFM images (150 x 150 nm) were recorded in electrostatic repulsion mode. They show two different gemini surfactants, (CmH2m+l)[N+(CH3)2](CH2)n[N (CH3)2](CH2)j with m-n-j of 18-3-1 (a) and 12-4-12 (b), in aqueous medium on mica. The concentrations were 3.0 and 2.2 mM, respectively. Both are above the critical micellar concentration. (The figure is reproduced with kind permission from S. Manne [202].)... 

For example, whereas low area headgroup surfactants (high g values, g= 1) favour lamellar liquid crystal type phases or cubic phases with low curvature, such as the Ia-3d bicontinuous gyroidal structure, surfactants with higher area headgroups with lower g values favour strongly curved micellar shapes, such as cylindrical rods (MCM-41) or spheres (e.g. SBA-1, SBA-2). 

It was shown in the early 1990s that nanoscale porosity of silicas can conveniently be generated in a predictable way using smfactant micelles as templates." This approach can be used to form cylindrical pores (diameter 2-30 nm), " spherical pores (diameter 3-27 nm), and other periodic porous structures. Surfactants that are suitable as mieellar templates include alkylammonium surfactants, oligomeric alkyl-poly(ethylene oxide) surfactants, and block copolymers with poly (ethylene oxide) block(s). " The micelle-templating approach has been extended to some other compositions relevant for the manufacture of on-chip insulations, including polymethylsilsesquioxane (formula unit SiOi 5-./2(CH3)(0H),) and... 

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