Styrene Solubilization and Adsolubilization on an Aluminum Oxide Surface Using Linker Molecules and Extended Surfactants

The impact of lipophilic linker and extended surfactant properties on admicelle formation and styrene adsolubilization were evaluated through adsorption and adsolubilization studies on aluminum oxide. While linker-based systems achieved a higher maximum adsorption than extended surfactants, the extended surfactants reached maximum adsorption at a lower aqueous surfactant concentration. Results of solubilization and adsolubilization studies are summarized by the extent of solute solubilization into micelles and admicelles, as captured through the micellar partition coefficient, K _mic, and the admicellar partition coefficient, K _adm. The extended-surfactant-based micelles showed greater solubilization capacity than linker-based micelles. Relative to the effect of the number of propoxy groups for extended surfactants with the same alkyl chain length, the results show that the solubilization capacity increases when the PO number increases for both C12,13- and C14,15-based surfactant series. Thus, adsolubilization using extended-surfactant-based admicelles showed adsolubilization enhancement but required lower amounts of surfactants to form admicelles. These results thus provide insights into external and internal linker-based and extended-surfactant-based admicellar systems and highlight the differences observed between them and admicelles based on conventional surfactant systems.

Ethoxy Carboxylate Extended Surfactant: Surface Charge of Surfactant-Modified Alumina, Adsolubilization and Solubilization of Phenylethanol and Styrene

Adsolubilization of contaminants by surfactant-modified material is an important phenomenon for surfactant-based environmental technologies. Recently, extended surfactants have been shown to enhance the adsolubilization capacity of organic solutes. In this study, two extended surfactants (ethoxy propoxylated carboxylate extended surfactant—C16PO4EO5C and propoxylate extended sulfate surfactant—C16PO4S) were selected for modifying positively charged alumina surfaces with the aim of enhancing adsolubilization of organic solutes with varying degrees of polarity (phenanthrene, styrene, and phenylethanol). The nature of the charged surface as a function of extended surfactant adsorption was evaluated through the zeta potential measurements. The results showed that at maximum bilayer coverage, the zeta potential of the alumina surface remained constant and was oppositely charged (negative) to the unmodified alumina (positive). Zeta potential measurements showed that the adsorbed bilayer of carboxylate-based extended surfactant produced more negatively charged surface. Surfactant desorption results showed that the surfactant-modified surface retained their negatively charge, albeit reduced, indicating that partial desorption occurred but not to the point that the positively charged alumina surface was realized. The adsolubilization results suggest a benefit of the ethoxy groups in adsolubilizing the polar phenylethanol in the palisade layer.     

Solubilization of unilamellar liposomes by betaine-type zwitterionic/anionic surfactant systems

The mechanisms governing the solubilizing interactions between zwitterionic/anionic mixed surfactant systems at different molar fractions of the zwitterionic surfactant (X_zwitter) and neutral or electrically charged unilamellar liposomes were investigated. The mixed systems were formed by N-dodecyl-N,N-dimethylbetaine and sodium dodecyl sulfate in the presence of piperazine-1,4-bis-(2-ethanesulfonic acid) buffer at pH 7.20. Unilamellar liposomes formed by egg phosphatidylcholine, in some cases together with stearylamine or phosphatidic acid, were used. Solubilization was detected as a decrease in static light-scattering of liposomes. Two parameters were regarded as corresponding to the effective surfactant/lipid molar ratios (Re) at which the surfactant system (i) saturated the liposomes, Re_sat, and (ii) led to a total solubilization of liposomes, Re_sol. From these parameters the bilayer/aqueous medium surfactant partition coefficients for the saturation (K_sat) and complete bilayer solubilization (K_sol) were determined. When X_zwitter was 0.40, The Re and K parameters showed a maximum, whereas the critical micellar concentration (CMC) of these systems exhibited a minimum, regardless of the electrical charge of bilayers. Given that the ability of the surfactant systems to saturate or solubilize liposomes is inversely related to the Re_sat and Re_sol parameters, these capacities appear to be directly correlated with the CMC of the mixed systems. The similarity of both K_sat and K_sol (particularly for X_zwitter=0.2–0.8) suggests that a similar partition equilibrium governs both the saturation and the complete solubilization of bilayers, the free surfactant concentration (S_a,S_b), remaining almost constant with similar values to the CMC for each mixed system studied.     

Solubilization of selected polycyclic aromatic compounds by nonionic surfactants

Solubilization of selected polycyclic aromatic compounds (PAC) by biodegradable nonionic surfactants, Tergitol 15-S-X (X=7 or 9) and Neodol 25–7, was investigated and correlated with micellar properties of these surfactants. These PAC include dibenzofuran, phenanthrene, acenaphthene, fluoranthene, and 9-chloroanthracene. Tergitol surfactants are mixtures of secondary ethoxylated alcohols, and Neodol 25–7 is a mixture of similar species but has the alcohol group in the primary position. These surfactants have the same chain length of hydrophobic tails and similar numbers of ethylene oxides. The results show that the Neodol surfactant yields micelles having larger hydrophobic core volume and renders a higher solubilization capacity for the PAC solubilizates in comparison with Tergitol surfactants. In general, aggregation numbers and micellar sizes both increase at elevated temperatures still below the cloud point. The micellewater partition coefficients of these PAC by the nonionic surfactants were well correlated to their octanol-water partition coefficients. Moreover, an estimated log K _ow value of 9-chloanthracene is 4.78.     

Study of the Interaction Between Methyl Orange and Mono and Bis-Quaternary Ammonium Surfactants

The solubilization and interaction of an azo-dye (methyl orange) with dodecyl trimethyl ammonium bromide and cationic gemini surfactants in the series of alkanediyl α,ω-bis[(dimethyl alkyl ammonium)bromide)] referred to as (m-s-m), m = 10, 12, 14 and s = 2, 3, 4 were investigated by means of UV–Vis spectroscopy. Aggregation with the anionic dye was reflected by a hypsochromic shift with a decrease in the intensity of the absorption band. The results also show a bathochromic shift followed by a sharp increase in the intensity of the maximum absorption band λ_max after the critical micellar concentration (CMC). This indicates that the dye solubility increased with increasing surfactant concentration. It was also observed that the aggregation of surfactant and dye takes place at a surfactant concentration far below the CMC of the individual surfactant. The effects of the chain length as well as the spacer length of gemini surfactants on the critical aggregation concentration and CMC were also examined. Moreover, the partition coefficients between the bulk water and surfactant micelles K _S and K _X as well as the Gibbs energies of distribution of dye between the bulk water and surfactant micelles were determined using the pseudo-phase model. The effect of the hydrophobic chain length and spacer of gemini surfactants on the distribution parameters is also reported.     

Recovering phenanthrene from spiked sand by a combined remediation process of micellar solubilization and cloud-point extraction

A remediation process, which combines the micellar solubilization and the cloud-point extraction technique by a nonionic surfactant Tergitol 15-S-7, was used to decontaminate phenanthrene, as a model hydrophobic pollutant, from spiked sand samples. A first-order kinetics model was employed to describe the solubilization behavior of phenanthrene well. It was observed that presence of surfactant decreased the mass-transfer coefficient of phenanthrene from sand surface to surfactant solutions, however, higher solubilization rate was obtained due to enhanced aqueous solubility and, thus, the larger driving force resulted from solublization. Cloud-point extraction was used to concentrate the phenanthrene solubilized in the washing solutions in an attempt to minimize the amount of wastewater. The extraction was carried out, subsequently, at room temperature by adding sodium sulfate to suppress the cloud-point low enough to induce phase-separation of the surfactant-rich phase with a minimal phase volume from the coexisting water phase. Recoveries higher than 93% were achieved in the combined process of micellar solubilization and cloud-point extraction on ultimate removal of immobilized phenanthrene sorbed on sands. The results showed that this combined process is efficient in recovering phenanthrene sorbed and immobilized on sands from contaminated sites, and produces only minimal amount of wastewater, i.e. less than 3% of its original volume.     

The Effect of NaCl on the Krafft Temperature and Related Behavior of Cetyltrimethylammonium Bromide in Aqueous Solution

This paper presents the effect of NaCl on the Krafft temperature (T _K), surface adsorption and bulk micellization of cetyltrimethylammonium bromide (CTAB) in aqueous solution. The critical micelle concentration (CMC) of CTAB in the presence of NaCl increased and then decreased with increasing temperature. Thus, the CMC–temperature data can be represented by a bell-shaped curve. The micellar dissociation (fraction of counterion binding) and energetic parameters (free energy, enthalpy and entropy changes) of both adsorption and micellization were calculated. The processes were found to be both enthalpy and entropy controlled and appeared to be more and more enthalpy driven with increasing temperature. An enthalpy–entropy compensation rule was observed for both adsorption and micelle formation. The T _K of the surfactant decreased significantly in the presence of NaCl, which is a sharp contrast to the usual behavior of the effect of electrolytes on the T _K of classical ionic surfactants. The surface excess concentrations decreased with increasing temperature. However, the values were much higher in the presence of NaCl compared to the corresponding values in pure water. The solubilization behavior of a water-insoluble dye, Sudan red B (SRB), in the micellar system was studied by the UV–visible spectrophotometric technique. The molar solubilization ratio in the presence of NaCl was found to be about three times higher than that in pure water, indicating that the solubilization of SRB in the CTAB micelles significantly increases in the presence of NaCl.     

Solubilization of model stratum corneum liposomes by quaternary ammonium surfactants

The solubilizing interactions of a series of quaternary ammonium surfactants [alkyl chain lengths C-12 (DoTAB), C-14 (TeTAB), and C-16 (HeTAB)] with liposomes formed by a mixture of lipids modeling the stratum corneum (SC) lipid composition (40% ceramides, 25% cholesterol, 25% palmitic acid, and 10% of cholesteryl sulfate) were investigated. Surfactant/lipid molar ratios (Re) and bilayer/aqueous phase partition coefficients (K) were determined by monitoring changes in static light scattering of the system during solubilization. Free surfactant concentration was always similar to the critical micelle concentration (CMC). A general assumption for phosphatidylcholine (PC) liposomes suggests that the free surfactant concentration must reach CMC for solubilization to occur. This assumption can be applied to SC liposomes in this study, and indicates that liposome solubilization was mainly driven by mixed micelle formation. The Re and K parameters fell as the surfactant alkyl chain length decreased or CMC increased. Thus, a higher CMC corrsponds to an increased ability of these surfactants to saturate or solubilize SC liposomes and to a lower degree of partitioning into liposomes or affinity with these bilayer structures. The overall balance of these opposing tendencies shows that TeTAB had the highest effectiveness with respect to the saturation and solubilization of SC structures in terms of total surfactant needed to produce these effects. Different trends in surfactant interaction with SC liposomes were observed when comparing Re and K parameters with those for PC liposomes. Because SC liposomes were more resistant to the surfactant action, the affinity of surfactants with these bilayer structures was higher in all cases.     

Reversible Solubilization of Typical Polycyclic Aromatic Hydrocarbons (PAH) by a Gas Switchable Surfactant

Surfactant‐enhanced remediation (SER) is one of the most effective remediation methods for polycyclic aromatic hydrocarbons (PAH) contaminated soils. However, mass deployment of SER has been restricted due to the shortage of the separation, recycle technology of the surfactant and its operation costs. This research mainly studied the reversibility of 2‐n‐lauryl‐1,1,3,3‐tetramethyl guanidine (DTMG) surfactant and its influence on reversible solubilization of typical PAH. Experimental results showed that the reversibility of the DTMG surfactant is excellent. The critical micellar concentration (CMC), surface tension and pH of DTMG in CO₂/N₂ conditions undergo reversible changes promptly. DTMG·CO₂ shows a strong solubilization capacity for PAH; the apparent solubilities of the selected PAH pyrene, phenanthrene and anthracene in 4 mmol/L of DTMG·CO₂ solution were about 32.4, 17.1 and 14.6 times higher than in water, respectively. The corresponding molar solubilization ratios were 5.4 × 10^?3, 2.80 × 10^?2 and 1.1 × 10^?3, much higher than those with DTMG. More than 50 % of the PAH in surfactant solutions could be released through gas control at each surfactant concentration, and improved release efficiency was achieved at low surfactant concentrations. In brief, such results in this work introduce a facile method to meliorate the SER technology.     

Solubilization of model polycyclic aromatic hydrocarbons by nonionic surfactants

Solubilization of model polycyclic aromatic hydrocarbons (PAHs) by the readily biodegradable nonionic surfactants, Tergitol 15-S-X (X=7,9 and 12), consisting of mixtures of secondary ethoxylated alcohols was investigated at temperatures below their cloud points. Their solubilization capacities for phenanthrene were compared to those of three other commonly used surfactants, e.g. Triton X-100 and Tween 20 as well as Tween 80. Correlation between the micelle-water partition coefficients and the octanol-water partition coefficients in Tergitol 15-S-7 solutions indicated that the hydrophobicity of PAHs, i.e., their octanol-water partition coefficients, could be used in predicting the solubilization efficiency of PAHs by this nonionic surfactant. Effects of temperature and salinity on solubilization capacity of Tergitol 15-S-7 surfactant for phenanthrene were also investigated along with the micellar properties. The change in hydrodynamic radius and aggregation number of micelles with temperature was measured by the dynamic and static laser light scattering techniques. Results showed that increasing aggregation number and micellar size at higher temperature when cloud point is approached gives rise to the higher solubilization capacity of this surfactant. Effect of salinity on the enhancement of phenanthrene solubility was also discussed in terms of conformation changes in the micelles due to the possible coordination of sodium cations and oxygen atoms on the ethylene oxide groups of the surfactant.     

Determination of pK a Values of Oxocholanoic Acids by Potentiometric Titration

The pK _a and the maximum solubility values of cholic, deoxycholic salts and their oxo-derivatives have been measured by the method of potentiometric titration. In the monomer phase (under the critical micellar concentration, CMC), the bile salts have different pK _a values, as a result of their structural differences (the number of hydroxyl and oxo groups in the steroid skeleton) and different hydration properties of the acid anions. In the micellar phase (above the CMC), the bile salts have higher pK _a values than in the monomer phase (under the CMC). This increase in the pK _a values is greater in more hydrophobic bile salts (cholate and deoxycholate), than in less hydrophobic oxo derivatives, which can be explained by the different aggregation numbers of these bile salts. The oxo-derivatives are more likely to form dimeric micelles, where the carboxylic groups are situated on the two sides of the micelle, not causing any electrostatic repulsion. In the more hydrophobic bile salts, aggregation numbers are higher, which causes electrostatic repulsion of the nearby situated carboxylic anions and consequential protonation of these anions (which leads to the stabilization of the micelle). The maximum solubility values are higher for the oxo-derivatives. If the steroid skeleton of the bile salt is more hydrophobic, the capacity to solubilize the unionized bile acid is higher, i.e. a smaller amount of the bile acid anion is needed for the solubilization of the bile acid monomer. The oxo-derivatives are less hydrophobic, but alongside their hydrophobicity, the structure of the micelle determines the solubilization capacities.     

Solubilization and Adsolubilization of Polar and Nonpolar Organic Solutes by Linker Molecules and Extended Surfactants

Adsolubilization reaches its maximum when a surfactant adsorbed onto the solid–liquid interface achieves complete bilayer or maximum adsorption. The attempt to enhance the adsolubilization of organic solute is accomplished by increasing interaction between the hydrophobic core of adsorbed admicelles and the organic solute. Solubilization and adsolubilization were studied with linker-based and extended-surfactant-based systems. Extended surfactants have propylene oxide (PO) groups of intermediate polarity inserted between hydrophobic and lipophilic moieties in the surfactant molecule. This study evaluated the adsolubilization of polar (phenylethanol) and nonpolar (ethylcyclohexane) solutes into conventional linker-based and extended-surfactant-based admicelles. The results demonstrated that the extended-surfactant-based systems showed higher solubilization capacity than the conventional sodium dodecyl sulfate alone or with linker. For the polar solute, the presence of PO group has a greater effect than the number of PO groups or the tail length, while for the nonpolar solute as the number of POs groups and the tail length increased, the adsolubilization capacity also increased. Preliminary explanations for these observations are provided.

Enhancement of Styrene Adsolubilization and Solubilization by Rhamnolipid Biosurfactant‐Linker Mixtures onto an Aluminum Oxide Surface

The polarity of rhamnolipid, a relatively hydrophilic biosurfactant, can be enhanced by the addition of linker molecules. In this work, rhamnolipid biosurfactant‐modified surfaces were prepared with and without a combination of linkers (1‐butanol, 1‐octanol, and 1‐dodecanol) to investigate effects of linker molecules on styrene adsolubilization and solubilization. Results showed that styrene adsolubilization increased with increasing carbon chain lengths of the linker molecules whereas the solubilization of styrene exhibited the opposite effect. Decreasing the carbon atoms in the linker molecules resulted in higher styrene solubilization capacity because of the change in polarity of the three‐dimensional surfactant aggregates. The higher adsolubilization capacity indicated the enlargement of surfactant tails that was created a larger adsolubilization region in the admicelle while the lesser solubilization of styrene indicated the decreasing of affective area per molecule of the surfactant‐linker system (butanol > octanol > dodecanol).     

Interaction Between Ionic Liquids and Gemini Surfactant: A Detailed Investigation into the Role of Ionic Liquids in Modifying Properties of Aqueous Gemini Surfactant

Tuning physicochemical properties of aqueous surfactant solutions comprised of normal or reverse micelles by external additives is of utmost importance due to the enormous application potential of surfactant‐based systems. Unusual and interesting properties of environmentally benign ionic liquids (IL) make them suitable candidates for this purpose. To understand and establish the role of IL in modifying properties of aqueous gemini surfactants, we studied the effect of the IL, 1‐hexyl‐3‐methylimidazolium bromide ([Hmim][Br]) and 1‐octyl‐3‐methylimidazolium bromide ([Omim][Br]) on the properties of the aqueous cationic gemini surfactant 1,6‐hexanediyl‐α,ω‐bis(dimethyltetradecyl)ammonium bromide (14‐6‐14,2Br^?). The behavioral changes were investigated by measuring the critical micelle concentration (CMC) using electrical conductance, surface tension, dye solubilization and fluorescence probe measurements at 298.15 K. It was observed that the CMC of 14‐6‐14,2Br^? gemini surfactant decreases with addition of IL, thus favoring the micellization process. An increase in micellar size was observed at lower IL concentration using dynamic light scattering, with a decrease in aggregation number (N_agg) determined from fluorescence probe quenching measurements. It is noteworthy that the extent of modulation of the micellar properties is different for both the IL due to their structural differences. IL behave like electrolytes at lower concentrations and cosurfactants at higher concentrations and form mixed micelles with the cationic gemini surfactant showing an increase in N_agg.     

The study of Sunset Yellow anionic dye interaction with gemini and conventional cationic surfactants in aqueous solution

In the present study, the interaction of an anionic azo dye, Sunset Yellow, with two cationic gemini surfactants with different spacer lengths (s = 3, 6 methylene groups) and their monomeric counterpart, dodecyl trimethyl ammonium bromide (DTAB), was investigated by surface tension, UV–Vis spectroscopy, and zeta potential measurements. The critical micelle concentration (CMC) was determined from plots of the surface tension (γ) as a function of the logarithm of total surfactant concentration. Moreover, the values of binding constants (K_b) of dye-surfactant complexes were calculated by UV–Vis spectroscopy. The UV–Vis spectra showed that the dye–surfactant interaction occurred in the solution at concentrations far below the CMC of each surfactant. The gemini surfactant with a shorter spacer showed stronger interaction with dye in comparison to DTAB and the gemini with longer spacer. The effect of surfactant chemical structure on solubilization of dye-surfactant aggregates at surfactant concentration above CMC was investigated by zeta potential.     

Changes in phospholipid bilayers caused by sodium dodecyl sulfate/nonionic surfactant mixtures

The interaction of mixtures of sodium dodecyl sulfate (SDS) and oxyethylenated nonylphenol (30 mol of ethylene oxide) [NP(EO)₃₀] with phosphatidylcholine liposomes was investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles, and bilayer solubilization was measured as a decrease in the static light scattered by liposome suspensions. Three parameters were described as the effective surfactant/lipid molar ratios (Re) at which the surfactant system: (i) resulted in 50% CF release (Re _50%CF); (ii) saturated the liposomes (Re _SAT); (iii) led to complete solubilization of these structures (Re _SOL). The corresponding surfactant partition coefficients (K _50%CF, K _SAT, and K _SOL) were determined from these parameters. The free surfactant concentrations S _W were lower than the mixed surfactant critical micellar concentration at subsolubilizing levels, whereas they remained similar to these values during saturation and solubilization of bilayers. Although the Re values increased linearly as the mole fraction of the SDS rose (X _SDS), the K parameters showed maximum values at X _SDS 0.6 for K _50%CF and approximately at X _SDS 0.2 for K _SAT and K _SOL, respectively. Thus, the lower the surfactant contribution in the surfactant/lipid system, the higher the X _SDS at which the maximum bilayer/water partitioning of added mixed surfactant systems occurred. As a consequence, the influence of SDS in this partition appears to be more significant at the sublytic level (monomeric effect), whereas the influence of NP(EO)₃₀ seems to be greater during saturation and solubilization of liposomes via formation of mixed micelles.     

Enhanced sorption of phenanthrene on activated carbon in surfactant solution

Distribution of a hazardous hydrophobic organic compound (HOC) and a nonionic surfactant in aqueous/activated carbon systems was investigated. Phenanthrene was selected as a representative HOC and Triton X-100 as a surfactant. Three activated carbons that differed in size (Darco 20-40, 12-20 and 4-12 mesh sizes) were used in the adsorption experiments. The system was analyzed using a mathematical partitioning model and compared with intrinsic sorption of phenanthrene without the effect of sorbed surfactant. Phenanthrene was sorbed onto activated carbon in a greater amount than an estimated value by intrinsic sorption, even though surfactant molecules covered most of surfaces. The sorbed surfactant was much more effective as a sorbent for phenanthrene, in the range of 1.2-98 for effectiveness factor, than was activated carbon, particularly at high surfactant doses. We introduced surface molar solubilization ratio (MSR_s) for sorbed micelles of surfactant and mathematically estimated using effectiveness factor and available carbon fraction of activated carbon after surfactant sorption. The MSR_s for sorbed surfactant was 5-46 times higher than the MSR for micellar surfactant in bulk solution. The sorbed surfactant onto activated carbon can more effectively remove hazardous organic compounds in liquid environmental samples.     

Solubilization of phospholipid bilayer caused by surfactants

The interaction of surfactants with liposomes eventually leads to the rupture of such structures and the solubilization of the phospholipid components. In this paper, solubilization is regarded as a decrease in light scattering of liposome suspensions. To this end, in accordance with the nomenclature, adopted by Lichtenberg, three parameters were considered as corresponding to the effective surfactant/lipid molar ratios (Re) at which light scattering starts to decrease, Re_sat; reaches 50% of the original value, Re₅₀; and shows no further decrease, Re_sol. These parameters corresponded to the Re at which the surfactant (i) saturated the liposomes, (ii) resulted in a 50% solubilization of vesicles and (iii) led to a total solubilization of liposomes. The surfactants tested were the nonionic surfactant octylphenol ethoxylated with 10 units of ethylene oxide or Triton X-100 (OP-10EO), two anionic surfactants, sodium dodecyl sulfate and sodium dodecyl ether sulfate, and an amphoteric surfactant dodecyl betaine (D-Bet). Unilamellar liposomes formed by egg phosphatidylcholine containing increasing amounts of phosphatidic acid were used. The Re parameters were the lowest for D-Bet, followed by OP-10EO, whereas the anionic surfactants always showed the highest values regardless of the electrical charge of the lipid bilayers. These parameters seem also to be inversely related to the critical micelle concentration (CMC) of the surfactant, except for OP-10EO. Moreover, the CMC values of the surfactant/lipid systems at 0.5 mM lipid concentration corresponded in all cases to the surfactant concentration at which liposomes were saturated by surfactants. As a consequence, this ratio can be regarded as an interesting parameter associated with the mixed micelle formation in liposome solubilization.     

Adsorption, Desorption and Adsolubilization Properties of Mixed Anionic Extended Surfactants and a Cationic Surfactant

Anionic and cationic surfactant mixtures exhibit desirable synergism, but are limited by their tendency to form precipitates. This research evaluates the adsorption, adsolubilization and desorption of mixtures of carboxylate-based anionic extended surfactants and a pyridinium-based cationic surfactant. The mixture of cetylpyridinium chloride (CPC), selected as the cationic surfactant, with four anionic extended surfactants were studied. The anionic surfactants studied were alkyl propoxylated ethoxylated carboxylate with average number of carbon chain length of 16 and 17 or 16 and 18 with 4?mol of propylene oxide groups and either 2 or 5?mol of ethylene oxide groups. The adsorption of anionic extended and cationic surfactant mixtures onto a negatively charged metal oxide surface (silica dioxide) was evaluated. The adsolubilization of phenylethanol, styrene and ethylcyclohexane were evaluated for these mixed surfactant systems. The desorption potential of individual and mixed surfactant systems was also evaluated by varying the number of washing (desorption) steps. It was found that the plateau adsorption of mixed anionic extended surfactant and cationic surfactant occurred at lower surfactant concentration than that of the CPC alone, although the maximum adsorption capacity of CPC was not enhanced in our mixed surfactant systems. Adsolubilization capacities of these mixed surfactant systems are higher than that of the individual surfactant system. For desorption studies, these mixed surfactant systems showed lower stability than the individual surfactant system.     

Synthesis and Surface Tension Study of the Spacer Chain Length Effect on the Adsorption and Micellization Properties of a New Kind of Carboxylate Gemini Surfactant

A series of carboxylate gemini surfactants, which contain two hydrocarbon chains linked by amide groups, two carboxylate groups, a flexible alkane spacer were synthesized by three-step reactions and named alkylidene–bis-(N,N′-dodecyl-carboxypropylamides) (2C₁₂H₂₅CnAm; n = 2, 3, 4, 6, 8 is the number of methylene groups of the spacer), their structures were confirmed by FTIR,¹H NMR, and LC–MS/TOF, and their purity checked by HPLC. The micellar properties with increasing spacer chain length of these gemini surfactants were determined by surface tension methods. The critical micelle concentration (CMC) varies slightly with spacer chain length; surface tension at CMC(γ_CMC), the tendency of micellization versus adsorption, CMC/C₂₀, the minimum area per surfactant molecule at the air/solution interface (A_CMC), all decrease with increasing spacer chain length; surface reduction efficiency, pC₂₀, the surface excess at the air/solution interface (Г_CMC) increase with increasing spacer chain length. The results probably indicate that increasing spacer chain length of these carboxylate gemini surfactants will increase spacer incorporation into the double hydrophobic chain.