Chain Length Compatibility Research Articles

The importance of sub-angstrom distances in mixed surfactant systems for technological processes

The spacing between atoms and molecules at interfaces and within materials is extremely important in determining the properties of such interfaces and materials. In surfactant monolayers at the air-water interface, it has been shown that small changes in molecular packing lead to large changes in the interfacial properties. Changes in intermolecular distance as small as 0.04 Å have been attributed to the effect of mixing surfactants of different chain lengths. This paper discusses the effect of these sub-angstrom distance changes on foaming, micellar stability, melting points, bubble size, surface viscosity, lubrication, environmental remediation, enhanced oil recovery, and microemulsion stability that result from chain length compatibility.

Effect of Chain Length Compatibility on Micellar Stability in Sodium Dodecyl Sulfate/Alkyltrimethylammonium Bromide Solutions

The effect of chain length compatibility on the micellar stability was investigated for mixtures of sodium dodecyl sulfate (SDS) and alkyltrimethylammonium bromides (CnTAB, n = 8, 10, 12, 14, 16) at a 20/1 molar ratio. It was observed that the surface properties of surfactant solutions were influenced by the chain length compatibility of the surfactant molecules. The slow micellar relaxation time (τ2), which directly correlates to the micellar stability, was determined using the pressure-jump technique. The addition of CnTAB to SDS solutions results in a significant increase in the relaxation time compared to SDS alone, showing a maximum for the SDS/C12TAB system. The high micellar stability results in minimum surface tension, maximum surface viscosity, maximum micellar lifetime, maximum foam stability, and minimum foamability. The higher micellar stability as observed for SDS/C12TAB is attributed to both the chain length compatibility and the Coulombic interaction of the surfactant head groups, resulting...

Water Solubilization and Chain Length Compatibility in Nonionic Microemulsions

The BSO (Bansal, Shah, O'Connell) equation ( J. Colloid Interface Sci. 75, 462, 1980) was derived as an empirical condition for maximum water solubilization in microemulsions stabilized by anionic surfactants, in relation to the cosurfactant (alcohol) and oil chain lengths. The present study examines, for the first time, the applicability of this equation for nonionic microemulsions. By constructing pseudo-ternary phase diagrams and measuring the area of the single phase regions as well as the water contents at the boundary, we find that the solubilization capacity is directly related to the alcohol chain length only if the alcohol solubility in both the aqueous and oleic phases is limited. In addition, we try to integrate the concept of chain length compatibility with the competition between the natural curvature and the critical radius of the interface. The attempt to unify the experimental results may serve as a guideline for optimization of microemulsion systems.

Double-tailed surfactants and their chain length compatibility in water-in-oil emulsions

The effect of carbon number has been studied with three different series of double tailed surfactants, viz. poly(isobuty1ene)succinic anhydride esterified with diand triethanolamine esters of n-alkylsuccinic anhydride and poly(isobuty1ene)succinic anhydride esterified with ((n-alky1oxy)propyl)diethanolamine. The primary hydrocarbon chain of the surfactants comprised polyisobutylene of approximately 34 backbone carbon number and the secondary hydrocarbon chain comprises n-alkyl groups varying from CS to Cz0. The results indicate that the surface properties at the water-oil interface correlate well with chain length compatibility effects in the mixed surfactant and cosurfactant systems.

Solubilization and phase equilibria of water-in-oil microemulsions: II. Effects of alcohols, oils, and salinity on single-chain surfactant systems

The solubilization and phase equilibria of water-in-oil (w/o) microemulsions have been studied to elucidate how the molecular structure of various components of microemulsions and salinity influence two interfacial parameters of the system, namely the spontaneous curvature and elasticity of interfacial films. Most solubilization and phase equilibria data presented are explained by the change of these two parameters. It is indicated that oil can influence the property of an interfacial film by a solvation effect. Oil molecules with small molecular volume or high aromaticity produce a strong solvation effect and consequently lead to a greater penetration of oil molecules into the surfactant chain layer, thus increasing the rigidity and curvature of the interface. The addition of alcohol exhibits strong effects on the elasticity and spontaneous curvature of an interface. Decreasing alcohol chain length can increase the fluidity of the interfacial film and hence increase the attractive interdroplet interaction. On the other hand, increasing alcohol chain length often increases the rigidity and curvature of an interface. For alcohols which increase the interfacial fluidity, increasing alcohol partitioning at the interface will increase the fluidity and natural radius of the interface. The addition of electrolytes results in tighter molecular packing at the interface and a decrease in the natural radius and interfacial fluidity. There often exists an optimal salinity for a given w/o microemulsion system at which a maximum brine solubilization occurs. The maximum solubilization is interpreted as a result of counteracting effects of attractive interdroplet interaction of fluid interfaces and the bending stress of rigid interfaces. As a result of this study, phenomenological guidelines for the formulation of microemulsions have been proposed. It is inferred that the addition of a small amount of alcohol at optimal salinity together with the condition of chain length compatibility can result in the largest possible brine solubilization in a given w/o microemulsion.

Alkyl “chain length compatibility” and solubilization in water-in-oil microemulsions

Donnees theoriques et considerations du cas des microemulsions eau-huile formees d'eau, d'alcanes normaux de C 6 a C 16 , de stearate de sodium et de pentanol

INTERFACIAL COMPOSITION OF MICROEMULSIONS: MODIFIED SCHULMAN-BOWCOTT MODEL

The interfacial composition of oil-external microemulsions formed with sodium stearate, pentanol, brine and various oils (octane, dodecane and hexadecane) was determined in terms of moles of alcohol per mole of surfactant present at the interface (nii a/n3,) using a modified three compartment Schulman-Bowcott model. The modified model takes into account the solubility of pentanol in aqueous and hydrocarbon phases. For a constant brine/surfactant ratio, it was found that the value of (nii a/n3,) was highest for dodecane containing microemulsion which corresponded to the maximum solubilization of brine in this microemulsion at optimal salinity. This behavior is explained on the basis of chain length compatibility in microemulsions. The optimal salinity for solubilization increased with the chainlength of oil.

Correlation of chain length compatibility and surface properties of mixed foaming agents with fluid displacement efficiency and effective air mobility in porous media

The effects of chain length compatibility and surface properties of mixed foaming agents on fluid displacement efficiency and effective air mobility in porous media were investigated. Sodium dodecyl sulfate (C/sub 12/H/sub 25/SO/sub 4/Na) and various alkyl alcohols (e.g., C/sub 8/OH,C/sub 10/OH,C/sub 12/OH,C/sub 14/OH, and C/sub 16/OH) were used as mixed foaming agents. It was observed that the surface properties of surfactant solutions and flow behavior of foams through porous media were influenced by the chain length compatibility of the surfactant molecules. The increase in the length of porous media improved fluid displacement efficiency while breakthrough time per unit length decreased slightly with increase in the length of porous media. For mixed surfactant systems, a minimum in surface tension, a maximum in surface viscosity, a minimum in bubble size, a maximum in breakthrough time, a maximum in fluid displacement efficiency, and a minimum in effective air mobility were observed when the two components of the surfactant system had the same chain length. These results indicate that the surface properties of foaming solutions and molecular packing at interfaces exhibit a striking correlation with breakthrough time, fluid displacement efficiency, and effective air mobility in porous media.

Influence of alkyl chain length compatibility on microemulsion structure and solubilization

The solubilization capacity of water/oil microemulsions formed with fatty acid soaps and alcohols was studied as a function of alkyl chain length of oil (C 8 to C 16), soap (C 14 and C 18), and alcohol (C 4 to C 7). For n-butanol with both soaps, the maximum amount of water solubilized in the microemulsion continuously decreased with increasing oil chain length whereas for n-heptanol the solubilization capacity continuously increased. For pentanol with both soaps and for hexanol with sodium stearate, the solubilization reached a maximum when the oil chain length, l o, plus that of the alcohol, l a, was equal to that of the surfactant, l s, (i.e., l a + l o = l s). When excess water was added to these systems, a birefringent aqueous phase in equilibrium with an isotropic upper phase formed if l a + l o < l s whereas a different phase behavior, namely, the formation of two isotropic phases, was observed if l a + l o ⩾ l s. Both of these observations indicate a chain length compatibility effect similar to that observed in monolayers, foams, emulsions, and lubricants. The solubilization behavior is interpreted in terms of partitioning of alcohol among oil, water, and the interface depending upon the chain length of oil and alcohol, as well as in terms of molecular packing at the interface in relation to the disorder produced by the chain length compatibility effect. It was concluded from the oil-alcohol titration study that the molar ratio of alcohol to soap at the interface increases with oil chain length. We propose that the increase in the alcohol/soap molar ratio leads to increased spacing between carboxyl groups resulting in a greater degree of ionization. Electrical resistance and dielectric constant measurements yielded results consistent with this interpretation. At a given water/oil ratio, the electrical resistance of microemulsions decreases, the dielectric constant increases, and the thickness of ionic atmosphere within the water droplets increases as the oil chain length is increased. These phenomena are consistent with the concept that microemulsions form, and vary their structure, under the influence of surfactant and alcohol partitioning between aqueous and oleic phases and the consequent interfacial activity of both species. Here, the partitioning of alcohol and soap is subtly varied by changing the oil chain length.

The Effect of Chain Length Compatibility on Molecular Area, Intermolecular Spacing, Dispersion Energies and Evaporation Resistance of Mixed Monolayers

AbstractUsing mixed monolayers of alkyl alcohols, it was established that the unequal chain lengths cause an expansion in the area/molecule in mixed monolayers. Assuming the cross‐sectional area of molecules to be circles, it was shown that a difference of two methylene groups between the two components of the mixed monolayer causes an increase in the intermolecular spacing of about 0.05 A. The small increase in intermolecular spacing strikingly decreases the resistance of mixed monolayers to evaporation of water. The surface viscosity was found to be maximum when the chain‐lengths of the components were equal. The dispersion energy between alcohol molecules in the mixed monolayer was calculated using Salem's approach. It was found that a small increase in intermolecular spacing (0.05Å) can decrease the dispersion energy by 6.7 kJ/mol. The magnitude of this decrease is about 1/4 of the energy of a hydrogen bond. It was further shown that the small increase in intermolecular spacing, decreases the melting point of mixed crystals by about 9°C. The chainlength compatibility of mixed surfactants also influences the bubble size, bubble stability, emulsion stability, lubrication, contact angle and wettability. In summary, using the monolayer approach, it was experimentally shown that a small change of 0.05 Å in intermolecular spacing, brought about by a difference of 2 methylene groups between the two surfactant molecules, can strikingly influence the dispersion energy between the molecules. The small change in dispersion energy influences the characteristics of many engineering processes such as bubbles, foams, emulsions, lubrication and wettability.

Thermodynamic aspects of polymer compatibility

Abstract