Compatibility chain length

The difference in properties when the aliphatic chain of amine oxide contains more than 14 carbons is attributed to the mismatch of the hydrophobic chain with that of the SDS. The extra terminal segment results in a disruptive effect on the packing of the surface active molecules. The observed association behavior in the case of 0 2 C14-DAO with SDS is then also due to the maximum cohesive interaction between hydrocarbon chains in addition to the reduced electrostatic repulsion in the head groups. Solubilization of the 1 1 association is also determined by this chain length compatibility effect which may contribute to the absence of visible precipitation in C12/C12 and C2 2/ -14 mixtures. Chain length compatibility effects in different systems have been discussed by other investigators (24,25,26). 

Shah, D. O. and Shiao, S. Y. (1975). The chain-length compatibility and molecular area in mixed alcohol monolayers. In Goddard, E. D., ed. Monolayers, Advances in Chemistry Series 144 Am. Chem. Soc., Washington, DC, pp. 153-164. 

Effect of Chain Length Compatibility on Monolayers, Foams, and Macro- and Microemulsions... 

Schick and Fowkes (11) studied the effect of alkyl chain length of surfactants on critical micelle concentration (CMC). The maximum lowering of CMC occurred when both the anionic and nonionic surfactants had the same chain length. It was also reported that the coefficient of friction between polymeric surfaces reaches a minimum as the chain length of paraffinic oils approached that of stearic acid (12). In order to delineate the effect of chain length of fatty acids on lubrication, the scuff load was measured by Cameron and Crouch (13). The maximum scuff load was observed when both hydrocarbon oil and fatty acid had the same chain length. Similar results of the effect of chain length compatibility on dielectric absorption, surface viscosity and rust prevention have been reported in the literature (14-16). 

The gas/liquid and liquid/liquid systems are relevant to biomedical and engineering applications. The large interfacial area in foams, macro- and microemulsions is suitable for rapid mass transfer from gas to liquid or liquid to gas in foams and from one liquid to another or vice versa in macro- and microemulsions. The formation and stability of these systems may be influenced by the chain length compatibility which may also influence the flow through porous media behavior of these systems. Therefore, the present communication deals with the effect of chain length compatibility on the properties of monolayers, foams, macro- and microemulsions. An attempt is made to correlate the chain length compatibility effects with surface properties of mixed surfactants and their flow behavior in porous media in relation to enhanced oil recovery. 

For flow through porous media studies, the sandpacks used as porous media were flushed vertically with carbon dioxide for an hour to replace interstitial air. Distilled water was pumped and the pore volume (PV) of the porous medium was determined. By this procedure, the trapped gas bubbles in the porous media can be easily eliminated because carbon dioxide is soluble in water. For determining the absolute permeability of the porous medium, the water was pumped at various flow rates and the pressure drop across the sandpack as a function of flow rate was recorded. After the porous medium was characterized, the mixed surfactant solutions of known surface properties were injected. This was followed by air injection to determine the effect of chain length compatibility on fluid displacement efficiency, breakthrough time and air mobility in porous media. 

Figure 2. Schematic Diagram of the Chain Length Compatibility and the Thermal Motion of the Terminal Segments of Molecules.

Table I shows various surface and microscopic properties such as surface tension, surface viscosity, foaminess (i.e. foam volume generated in a given time) and bubble size in foams of the surfactant solutions as a function of chain length compatibility. The results indicate that a minimum in surface tension, a maximum in surface viscosity, a maximum in foaminess and a minimum in bubble size were observed when both the components of the mixed surfactant system have the same chain length. These results clearly show that the molecular packing at air-water interface influences surface properties of the surfactant solutions, which can influence microscopic characteristics of foams. The effect of chain length compatibility on microscopic and surface properties of surfactant solutions can be explained as reported in the previous section.

Table II shows the effect of chain length compatibility on oil recovery, fluid displacement efficiency, breakthrough time and effective gas mobility in porous media. For gas/liquid systems (e.g. Foams), a maximum in fluid displacement efficiency, a...

Table I. Effect of Properties Chain Length Compatibility on of Mixed Surfactant Solutions Surface ...

Table II. Effect of Chain Length Compatibility on Flow Through Porous Media Behavior of Foams and Macroemulsion Systems...

The Chain-Length Compatibility and Molecular Area in Mixed Alcohol Monolayers... 

The present study was designed to obtain a better understanding of the chain-length compatibility effect in terms of molecular areas of sur-... 

The trends in phase behavior as a function of oil-phase ACN indicate an optimum point in the neighborhood of pentane or hexane. This behavior is a consequence of the enthalpic and entropic components of the solvent-surfactant tail interaction [25,43]. Alkanes heavier than hexane are hindered in their ability to penetrate between the surfactant tails, which makes the combinatorial (chain length compatibility) effect the dominant one for these solvents. Alkanes lighter than hexane penetrate between surfactant tails very easily, but their enthalpic interaction with the tails is weak. At pentane and hexane, the combinabon of enthalpic and entropic effects is balanced. This balance favors the formation of the 2 configuration in Winsor systems. In reverse micelle systems, the optimum solvent-surfactant tail interaction stabilizes the reverse micelles against phase separation driven by micelle-micelle interactions. Also, there is a minimum in the attractive intermicellar dispersion interaction [13]. Therefore W reaches a maximum. 

Figure 9. Effect of Molecular Properties (e.g. Chain Length Compatibility) of Mixed Surfactants on Surface Properties of Foaming Agents, Bubble Size and Heavy Oil Recovery in Porous Media.

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