Contact angle of surfactant solutions on precipitated surfactant surfaces. III. Effects of subsaturated anionic and nonionic surfactants and NaCl

The contact angles of saturated calcium dodecanoate (CaC₁₂) solutions containing a second subsaturated surfactant on a precipitated CaC₁₂ surface were measured by using the drop shape analysis technique. The subsaturated surfactants used were anionic sodium dodecylsulfate (NaDS), anionic sodium octanoate (NaC₈), and nonionic nonylphenol polyethoxylate (NPE). Comparing at the critical micelle concentration (CMC) for each surfactant, NaC₈ was the best wetting agent, followed by NaDS, with NPE as the poorest wetter (contact angles of 32⁰, 42⁰, and 62⁰, respectively). Surface tension at the CMC increased in the order NaC₈<NPE<NaDS, and subsaturated surfactant adsorption increased in the order NPE≪NaDS (1.4 vs. 84 μmole/g); adsorption of the NaC₈ was not measurable. Interfacial tension (IFT) reduction at the solid-liquid interface due to subsaturated surfactant adsorption is an important contribution to contact angle reduction, in addition to surface tension reduction at the air-water interface. Surfactant adsorption onto the soap scum solid is crucial to solid-liquid IFT reduction and to good wetting. The fatty acid was the best wetting agent of the three surfactants studied, probably because calcium bridging with the carboxylate group synergizes surfactant adsorption onto the solid of the higher molecular weight soap. NaCl added to NaDS surfactant results in depressed CMC, lower surface tension at the CMC, decreased NaDS adsorption onto the solid, and decreased reduction in solid-liquid IFT. The contact angle is not dependent on the NaCl concentration for NaDS. The NaCl causes an increased tendency to form monolayers, which decrease air-water surface tension, but a decreased tendency to form adsorbed aggregates on the solid; the two trends offset each other, so wettability is not affected by added salt. The Zisman equation does not describe the wetting data for these systems well except for NaDS, further emphasizing the danger of ignoring solid-liquid IFT reduction in interpreting wetting data in these systems.     

Contact angle of surfactant solutions on precipitated surfactant surfaces

In this study, the contact angle of a saturated aqueous surfactant solution onto the surface of a precipitate of that surfactant is investigated. Those precipitates include fatty acids (C₁₀, C₁₂, C₁₄, C₁₆, and C₁₈), sodium salts of fatty acids (C₁₄, C₁₆, and C₁₈), calcium salts of fatty acids (C₈, C₁₀, C₁₂, C₁₄, C₁₆, and C₁₈). On virgin surfaces, free fatty acids and calcium salts of fatty acids have advancing contact angles (θ_A) between 77 and 92°, with little dependence on alkyl chain length for C₁₂ and higher alkyl chains. The sodium salt of a fatty acid has a lower θ_A than the free fatty or the calcium salt of the soap. The calcium salt of dodecyl sulfate has a lower θ_A than the calcium salt of dodecanoic acid (θ_A = 46 vs. 82°), but the calcium salt of the 18-carbon hydrophobes showed nearly the same contact angle for the soap and the alkyl sulfate. Greasiness, or slipperyness, or a scummy feel of a precipitated surfactant does not necessarily correspond to a hydrophobic surface.     

Adsorption of Binary Mixtures of Anionic Surfactants at Water–Air and Poly(Tetrafluoroethylene)–Water Interfaces

Measurements of the surface tension (γ _LV ) and the advancing contact angle (θ) on poly(tetrafluoroethylene) (PTFE) were carried out for aqueous solutions of sodium decyl sulfate (SDS) and sodium dodecyl sulfate (SDDS) and their mixtures. The results obtained indicate that the values of the surface tension and the contact angle of solutions of surfactants on PTFE surface depend on the concentration and composition of the surfactants mixture. On the curves presenting the relationship between the surface tension, contact angle and monomer mole fraction of SDDS (α) in the mixture of SDDS and SDS, there is a minimum at α equal to 0.8 which together with the negative values of the interaction parameters indicate that synergism occurs in surface tension and contact angle reduction almost in the range of concentration corresponding to the saturated monolayer of surfactants at the water–air interface. The results and calculations obtained also indicate that for single surfactants and their mixtures at a given concentration in the bulk phase, the values of surface excess concentration of the surfactants at water–air and PTFE–water interfaces are nearly the same, which suggests that the orientation of SDDS and SDS molecules at both interfaces in saturated monolayer should be vertical to the interfaces. Taking into account the values of the monomer mole fractions of the surfactants in a mixed monolayer at the water–air interface and values of the contact angle of a single surfactant on the PTFE surface, it is possible in a simple way to predict the values of the contact angle of a mixture at a given concentration and composition.     

Chemical structure/property relationships in surfactants. 17. N-substituted-N-acyl glycinates in pure and synthetic hard river water

The surface properties [effectiveness of surface tension reduction (γ_CMC), critical micelle concentration (CMC), efficiency of surface tension reduction (pC ₂₀), maximum surface excess concentration (Γ_CMC), minimum area/molecule at the interface (A _min), and the CMC/C ₂₀) ratio] of well-purified N-substituted glycine derivatives, having the structural formula RC(O)N(R′)CH₂COONa, where RC(O)=lauroyl, myristoyl, or oleoyl, and R′=Et, Pr, Bu, CH₂CH₂OH or CH₂CH₂CH₂OCH₃, were investigated at 25°C in hard river water and distilled water. These surfactants show greater surface activity in hard river water than in distilled water. The effect of both the main alkyl chain R and the N-substituent R′ on surface properties was elucidated, the oleoyl group showing properties equivalent to that of a C₁₆ saturated acyl group. A linear relationship was observed between the pC ₂₀ or CMC values and the number of carbon atoms in the alkyl chain R or in R′ when it was alkyl. With increase in the number of carbon atoms in either R or the N-substituent R′ when it is alkyl, both pC ₂₀ and micelle-forming ability increase, although the effect of R′ on the foregoing two surface properties is lower than that of R. When R′ is (CH₂)₃OCH₃, however, the results suggest that R′ is only partly removed from contact with the aqueous phase either upon adsorption at the water/air interface or upon micellization. It increases A _min, is equivalent only to an ethyl group in its effect on pC ₂₀ and to a methyl group in its effect on CMC, and, in contrast to the effect of R′ when it is alkyl, produces no increase in the CMC/C ₂₀ ratio. As a result, γ_CMC increases with R when R′ is alkyl and decreases with R when R′ is (CH₂)₃OCH₃.     

Preparation of a New Oligomeric Surfactant: N,N,N′,N″,N″-Pentamethyl Diethyleneamine—N,N″-Di-[Tetradecylammonium Bromide] and the Study of its Thermodynamic Properties

A new oligomeric surfactant: N,N,N′,N″,N″- pentamethyl diethyleneamine—N,N″-di-[tetradecylammonium bromide] referred to as 14-2-N(CH₃)-2-14 was synthesized, purified and characterized by Elemental Analysis, ¹H and ¹³C NMR and Electrospray. The micellar properties of this compound were determined by electrical conductivity and surface tension methods. Optical microscopy was also employed to study the behavior of anhydrous surfactant and the binary water/surfactant system as a function of temperature. The critical micellar concentration (cmc), degree of counterion binding and thermodynamic parameters of micellization (standard molar Gibbs energy, enthalpy and entropy of micellization) were determined by electrical conductivity measurements in the temperature range [24–54 °C]. Surface tension measurements also provide information about the dependence of the surface tension at the cmc (γ_cmc), pC₂₀ (negative logarithm of the surfactant’s molar concentration C₂₀, required to reduce the surface tension by 20 mN/m, the surface excess (Γ_max) at air/solution interface, the minimum area per surfactant molecule at the air/solution interface (Amin), surface pressure at the cmc (П_cmc), critical packing parameter(CPP) and the standard free energies of micellization ( \Updelta G_m⁰\Updelta G_{m}^{0}) and of adsorption ( \Updelta G_\textads⁰ \Updelta G_{\text{ads}}^{0} ).     

Viscosity Adjustment of Aqueous Micellar Solutions of Gemini Surfactants by Interaction with Additional Surfactants

The viscosity of aqueous micellar solutions depends on the size and shape of the aggregates and thus can be adjusted by addition of another surfactant interacting with the original component, which alters the geometry of the molecule-pair consisting of two surfactants and influences strongly the size and shape of the mixed micelles. Ethanediyl-α,ω-bis(dimethyl dodecyl ammonium bromide), referred to as C₁₂-2-C₁₂·2Br, forms generally large micelles. Addition of a cationic surfactant (dodecyltrimethylammonium bromide, C₁₂TMABr) or a nonionic surfactant (alkyl polyoxyethylene ether, C _m E _n ), the mixed micelle size is reduced violently since the electrostatic repulsion between the same charged heads of C₁₂-2-C₁₂·2Br and C₁₂TMABr or the steric hindrance of the PEO chain of C _m E _n in the palisade layers of the mixed micelle, which leads to a decrease in the packing parameter P of the molecule-pair. As a result, the zero-shear viscosity (η ₀) of the mixed solution reduces rapidly. In contrast, on adding an oppositely charged surfactant, η ₀ of the mixed solution increases strongly since the P of the molecule-pair increases through electrostatic attraction between the oppositely charged heads. The typical cases occur in the mixtures of the anionic gemini surfactant, O,O′-bis(sodium 2-lauricate)-p-benzenediol C11pPHCNa, and the cationic surfactant C₁₂-2-C₁₂·2Br, C₁₂TMABr or its homologue with a different size of heads.     

Activity and stability ofPenicillium cyclopium lipase in surfactant and detergent solutions

Activity and stability of an alkaline lipase fromPenicillium cyclopium var.album (PG 37) were studied in surfactant and detergent solutions. Three anionic surfactants [Na salts of C₁₂SO₄ ^? (sodium dodecyl sulfate), C₁₂ØSO₃/^? (linear alkyl benzene sulfonate), and C₁₁COO^? (laurate)] and four homologous series of nonionic surfactants of C_12–15 polyoxethylenated fatty alcohols (AEO₃, AEO₅, AEO₇, and AEO₉) were evaluated. At a concentration range of 3.2–40 μM, sodium dodecyl sulfate and laurate stimulated the activity of PG 37 lipase. At concentrations greater than 5.6 μM, linear alkylbenzene sulfonate inhibited PG 37 lipase activity. Nonionic surfactants, AEO₅ and AEO₇, in the concentration range of 0.25–20 mM, enhanced and stabilized the activity of PG 37 lipase. The presence of PG 37 lipase in detergent formulaton improved detergency ～20%. The mechanism of inhibition of the lipolytic activity of PG 37 lipase is proposed to be partly due to the formation of inactive (BR)_n-E complex between the hydrophobic moiety of the surfactants and the surface of the lipase. Conversely, formation of a soluble (RB)_n-E complex between the hydrophilic group of the surfactant and lipase may account for the increased lipolytic activity of PG 37 lipase.     

Synthesis, characterization and surface properties of 1-N-l-tryptophan-glycerol-ether surfactants

A novel homologous series of 1-N-l-tryptophanglycerol-ether surfactants was synthesized and characterized. The precursor compounds, 3-alkyloxy-1-chloropropan-2-ols, were prepared from epichlorohydrin and aliphatic alcohols with alkyl chain lengths of 9–16 carbon atoms. Tryptophan was then attached to the monosubstituted glycerol backbone from its α-amino group through an α-NH-C bond. Structural assignment of the new compounds was made on the basis of elemental analysis and spectroscopic data. Critical micelle concentrations of the new surfactants, as well as the negative logs of the surfactant concentrations required to reduce the surface tension of the solvent by 20 mN/m (pC ₂₀) and the interfacial areas occupied by the surfactant molecules, were calculated from aqueous surface tension measurements using the Wilhelmy plate technique.     

Gemini surfactant controlled preparation of well-ordered lamellar mesoporous molybdenum oxide

A series of well-ordered lamellar mesoporous molybdenum oxides were prepared using gemini surfactant [C _n H_2n+1N⁺(CH₃)₂–(CH₂)₂–N⁺(CH₃)₂C _n H_2n+1] · 2Br⁻(denoted as C _n-2-n , n = 12, 14 and 16) as the structure-directing agent and ammonium heptamolybdate tetrahydrate (NH₄)₆Mo₇O₂₄ · 4H₂O as the precursor. The obtained samples were characterized by X-ray powder diffraction, thermal analysis, transmission electron microscopy and nitrogen adsorption–desorption. Results showed that contrary to complete structure collapse after removing tetradecyltrimethylammonium bromide (TTAB) from molybdenum oxide/TTAB composite, the lamellar mesostructure was retained after removal of C _n-2-n from corresponding composite. The effects of alkyl chain length and concentration of gemini surfactants on the structure of the mesoporous molybdenum oxide were also investigated. The specific surface area of extracted sample was as high as 116 m² g⁻¹. The maintenance of the lamellar mesostruture was due to the strong self-assembly ability of gemini surfactants and the strong electrical interaction between gemini surfactants and molybdenum oxide.     

Micellization of an anionic gemini surfactant having <Emphasis Type="Italic">N,N</Emphasis>-dialkylamide,carboxyl, and carboxylate groups in aqueous NaCl solutions

The micellization of an anionic gemini surfactant, (CH₂)₂[N(COC₁₁H₂₃)CH(CO₂H)CH₂(CO₂H)]₂·2NaOH, abbreviated as GA, having N,N-dialkylamide, carboxyl, and carboxylate groups, in aqueous solutions of NaCl at pH 5.0 was investigated by means of surface tension and of fluorescence, using pyrene as a probe. The l ₁/l ₃ vs. log surfactant molar concentration (C) plots showed two values of critical micelle concentration (cmc). Of the two values, the higher cmc value was close to that measured by the surface tension method, meaning that the lower cmc value may be caused by the formation of small, non-surface-active soluble premicellar aggregates. Evidence for the existence of these premicellar aggregates includes the fact that the lower of the two cmc values for GA was not observed in the l ₁/l ₃ vs. log C plots for (CH₂)₂[N(COC₁₁H₂₃)CH₂CH₂CO₂Na]₂, abbreviated as 212, in 0.001–0.3 M NaCl at pH 11.0, since the only cmc value obtained was close to that from surface tension data. Plots of log molar concentration of Na⁺ in the solutions vs. log cmc, or Corrin-Harkins plots, revealed that the lower cmc values decrease with an increase in Na⁺ concentration, and when [Na+]=1 M, the values reach the decreasing higher cmc value. This means two mechanisms of GA aggregation occured in at the same aqueous solutions of NaCl. In the first one, “monomeric form” → “micelle I” → “micelle II,” and in the second, “monomeric form” → premicelle → micelle II.” The degree of micelle ionization, or β, for the higher cmc values is 0.97 at 10⁻² M≦[Na⁺]≦0.1 M. This large β value indicates that the GA molecules, as a result of the structural characteristic attributable to the simultaneous presence of N,N-dialkylamide and carboxylate groups in the molecule, may be almost fully dissociated even at the cmc. The β value for the lower cmc is 0.75. This indicates that the existence of a non-monomeric state at concentrations below the cmc determined from surface tension data, which is additional evidence for the premicellar aggregation.     

Dynamic surface tension of aqueous surfactant solutions. 6. Compounds containing two hydrophilic head groups and two or three hydrophobic groups and their mixtures with other surfactants

Dynamic surface tensions (γ_t)—measured by the maximum bubble pressure method—of some surfactants containing two hydrophilic (sulfonate) groups and two or three hydrophobic groups in the molecule (“gemini surfactants”), and of their mixtures with a nonionic surfactant or an amine oxide, have been measured at 25°C in 0.1 M NaCl. Linearity of the plots of surface pressure vs. square root of the surface age indicated that the systems studied were all diffusion-controlled. For the individual surfactant systems, the apparent diffusion coefficient decreases with an increase in the number of alkyl chains and the bulkiness of the surfactant molecules. For the mixtures, when interaction between the two surfactants is weak, γ_t at short times (t<1s) is close to that of the component with the lower surface tension; at longer times, it is closer to that of the component with the lower equilibrium surface tension. When interaction is strong, γ_t at short times is greater than that of either component. The molar ratio at which maximum effect on γ_t is observed depends upon the strength of the interactions between the two surfactants.     

Water-retaining ability of diacylglycerol

The water-in-oil emulsification characteristics and the adsorption properties of DAG at the oil/water interface were investigated for DAG having different FA compositions. The water-retaining ability of DAG is dependent on the FA composition but is not dependent on the interfacial tension at the oil/water interface in a simple way. The water-retaining ability is very different between uni-chain DAG (two FA have the same chain length) and complex-chain DAG (one FA is oleic acid and the other has a shorter alkyl chain). Uni-chain DAG, having long FA chains (R=C₁₂ or C_18∶1) have the ability to emulsify water at the volume fraction of 80% (ϕ80%), but uni-chain DAG with short or medium chain-length FA (R=C₃, C₄, C₆, C₈) show little ability to retain water. For complex-chain DAG, all the DAG studied here (R₁=C_18∶1, R₂=C₂−C₁₂) have the ability to emulsify water at ϕ80%. The stability of the emulsions, however, varies with the chain length of the R₂ FA (R₂ stability order: C₂, C₃>C_18∶1, C₁₀>C₈>C₄, C₆). The relationship between the water-retaining ability and the molecular structure of DAG is discussed from the viewpoint of intra- and intermolecular interactions between the FA chains.     

A New Type of Sulfobetaine Surfactant with Double Alkyl Polyoxyethylene Ether Chains for Enhanced Oil Recovery

A new type of sulfobetaine with double alkyl polyoxyethylene (n) ether chains, dicoconut oil alcohol polyoxethylene (n) ether methylhydroxylpropyl sulfobetaine (diC_12–14E _n HSB) was synthesized using a commercial nonionic surfactant, coconut oil alcohol polyoxethylene (n) ether, as raw material and its properties as a surfactant for enhanced oil recovery (EOR) in the absence of alkali was studied. The purified product is a mixture of homologues with mainly C₁₂/C₁₂, C₁₂/C₁₄ and C₁₄/C₁₄ alkyl chains and widely distributed EO chains (n = 2.2 on average) with an average molar mass of 742.6 g/mol. The diC_12–14E_2.2HSB has an improved aqueous solubility at 25 °C compared with didodecylmethylhydroxylpropyl sulfobetaine (diC₁₂HSB), a homologue without an EO chain, and is highly surface active as reflected by its low CMC (4.6 × 10^?6 mol/L), high saturated adsorption (6.8 × 10^?10 mol/cm²) and small cross sectional area (0.24 nm²/molec.) at the air/water interface. With a hydrophile–lipophile balance well matched with Daqing crude oil/connate water system, the sulfobetaine can reduce Daqing crude oil/connate water interfacial tension to ultra-low values at 45 °C in the absence of alkali, and displays a low saturated adsorption at the sandstone/water interface (0.0024 mmol/g), reduced by 69 and 92 % respectively in comparison with that of the corresponding carboxyl betaine, diC_12–14E_2.2B and its homologue without an EO chain, didodecylmethylcarboxyl betaine (diC₁₂B). With these excellent properties diC_12–14E_2.2HSB gives a high tertiary recovery, 18.4 % original oil in place, when mixed with other hydrophobic and hydrophilic sulfobetaines in surfactant-polymer (SP) flooding free of alkali. The insertion of EO chains in combination with the replacement of carboxyl betaine by sulfobetaine is therefore very efficient for improving the properties of the double chain hydrophobic carboxyl betaines as surfactants for SP flooding free of alkali.     

Synthesis and Surface Properties of Novel Gemini Imidazolium Surfactants

Five new Gemini imidazolium surfactants were synthesized from imidazole and 1-bromoalkane (C₈, C₁₀, C₁₂, C₁₄, C₁₆) to get 1-alkylimidazole, which was further reacted with 1,3-dichloropropan-2-ol to form the surfactant molecule, 1,1′-(propane-1,3-diyl-2-ol) bis(3-alkyl-1H-imidazol-3-ium) chloride. The structures of the five new surfactants and intermediates were characterized by ¹H-NMR, ¹³C-NMR and IR spectra. Thermal properties of the five new surfactants were studied with thermogravimetric analysis and differential scanning calorimetry, the five new surfactants showed a transition from a crystalline phase to a thermotropic liquid–crystalline phase at around ca. 100 °C, which transformed to an isotropic liquid phase at around ca. 165 °C. The five new surfactants critical micelle concentrations (CMC) in the aqueous solutions were determined by surface tension and electrical conductivity methods. The surface tension measurements provided a series of parameters, including critical micelle concentration (CMC), surface tension at the CMC (γ _CMC), adsorption efficiency  (pC ₂₀), and effectiveness of surface tension reduction (π_CMC). In addition, with application of the Gibbs adsorption isotherm, maximum surface excess concentration (Γ_max) and minimum surface area/molecule (A_min) at the air–water interface were obtained. The parameters β (degree of counterion binding to micelles), ΔG _ads ^θ (Gibbs free energy of adsorption), and ΔG _mic ^θ (Gibbs free energy change of micellization) were also derived. The results indicated that the five new Gemini surfactants exhibited very low CMC and a good efficiency in lowering the surface tension of water. The foamability and foam stability of the five new surfactants were also examined at different CMC.     

Characterization of Microemulsion Systems Formed by a Mixed 1,3-Dioxolane Ethoxylate/Octyl Glucoside Surfactant System

The phase behavior of microemulsion systems containing water (or 1.0 wt% NaCl_aq), isooctane, and the binary surfactant system consisting of n-octyl-β-d-glucopyranoside, C₈βG₁, and the acid-cleavable alkyl ethoxylate, 4-CH₃O (CH₂CH₂O)_7.2, 2-(CH₂)₁₂CH₃, 2-(CH₂)CH₃, 1,3-dioxolane, or “cyclic ketal” (“CK-2,13”), was determined. Large temperature-insensitive one, two, and three-phase microemulsion-phase regions were obtained when equal masses of the two surfactants were employed, suggesting that C₈βG₁ reduces the temperature sensitivity of CK-2,13’s ethoxylate group. Addition of C₈βG₁ to CK-2,13 greatly improves the latter’s low efficiency, evidenced by the formation of a three-phase microemulsion system for surfactant concentrations at low fractions of total surfactants for systems with equal mass ratios of water to oil and CK-2,13 to C₈βG₁. Analysis of the phase diagrams also suggests that CK-2,13 and C₈βG₁ impart hydrophobic and hydrophilic character, respectively, to the surfactant mixture, and that addition of salt further increases the hydrophilicity of C₈βG₁, presumably because of the salting-in of the latter. Analysis of small-angle neutron scattering data revealed that the mixed surfactant system formed spherical oil-in-water microemulsions, and that increasing the CK-2,13 fraction among the surfactants reduced the critical microemulsion concentration but slightly increased the nanodroplet size.

Nonionic surfactant properties of methoxypolyoxyethylene dodecanoate compared with polyoxyethylene dodecylether

Nonionic surfactant properties of methoxypolyoxyethylene dodecanoate [C₁₂-EFME; C₁₁H₂₃CO-(OCH₂CH₂) _n CH₃] with varying ethylene oxide (EO) adduct distributions were compared with those of polyoxyethylene dodecylether [C₁₂-alcohol ethoxylate (AE); C₁₂H₂₅O(CH₂CH₂O) _n H]. The gelling region of C₁₂-EFME was much smaller than that of C₁₂-AE due to the effects of the ester bond and the terminal methyl group. When the EO adduct distribution of EFME is narrowed, the cloud point and the ability to lower interfacial tension do not change appreciably. Other effects of narrow distribution on EFME performance include a decrease in the gellation region and better foam breaking and wetting.     

Purification,Surface Tensions,and Miscibility Gaps of Alkyldimethyl and Alkyldiethylphosphine Oxides

Alkyldimethyl (C _n DMPO) with chain lengths of n = 8 (octyl), 10 (decyl), 12 (dodecyl), and 14 (tetradecyl) as well as alkyldiethyl (C _n DEPO) phosphine oxides with chain lengths of n = 10, 12, and 14 were synthesized and purified to study how the adsorption properties and the location of the miscibility gap of these surfactants depend on the size of the head group and on the length of the alkyl chain. After surfactant purification, the surface tension isotherms were determined from which the cmc, the minimum surface tension σ_cmc, the maximum surface concentration Γ_max, and the minimum surface area A _min were obtained. As expected, for one homologous series, a decrease in the cmc and an increase in Γ_max was observed with increasing alkyl chain length. For two surfactants of the same alkyl chain length, the cmc values of the C _n DEPO surfactants are approximately two times lower than those of the C _n DMPO surfactants. However, the Γ_max values of C _n DEPO are lower than those of C _n DMPO as two ethyl chains are sterically more demanding than two methyl chains. In addition to the adsorption properties, the location of the miscibility gap as a function of the alkyl chain length and the head group size was studied. Its location depends on the total number of carbon atoms and not primarily on the length of the main alkyl chain. This observation reflects the decreasing water solubility which can be tuned by increasing the length of either the main alkyl chain or of the shorter head group chains.     

Synthesis and Surface Active Properties of a Novel Linear Dodecyl Diphenyl Ether Sulfonate Gemini Surfactant

The linear dodecyl diphenyl ether sulfonate gemini surfactant (C₁₂-DLADS) has been synthesized by a new route from lauric acid according to a five-step reaction sequence consisting of acidification, Friedel?CCrafts acylation, Clemmensen reduction, sulfonation and a neutralization reaction. The surfactant and intermediates were characterized by ¹H-NMR, HPLC/MS and elemental analysis. The properties have been studied by surface tension (?? _CMC) and conductivity measurements. The thermodynamic parameters of micellization were calculated. The test results show that C₁₂-DLADS has lower critical micelle concentration (CMC) and better capability for lowering the ?? _CMC. The ?? _CMC and CMC are 36.04?mN/m and 6.03?×?10^?4?mol/L respectively at 45?°C. Moreover, with the increase in temperature, the conductivity of C₁₂-DLADS increased, while the counterion binding K ₀ decreased. The thermodynamic data show that the micellization process for the surfactant C₁₂-DLADS is entropy driven.     

Surface rearrangement of vinyl acetate and acrylate terpolymer adhesives investigated by dynamic contact angles

Terpolymer solution-based adhesives of vinyl acetate and acrylates with different long alkyl side chains were prepared by radical polymerization. Dynamic contact angles of the adhesives-coated films measured by the Wilhelmy plate technique indicated that the reorientation of the adhesive surface varied with the length of the alkyl side chain. It was found that the changes of advancing contact angles (θ_a) and receding contact angles (θ_r) were relatively great within the range of lower immersion speeds at various temperatures, but approaching a certain velocity the contact angles became stable. The lower activation energies of the change in contact angles revealed that the rearrangement of surface groups can be achieved by small-scale secondary transitions. In addition, the activation energies required for rearrangement from apolar to polar medium and the reverse process were different. ©1997 SCI     

Glucamine-based gemini surfactants I: Gemini surfactants from long-chain <Emphasis Type="Italic">N</Emphasis>-alkyl glucamines and α,ω-diepoxides

N-Alkyl glucamines can be reacted with α,ω-diepoxides to yield gemini (dimeric) surfactants similarly to the reaction of glucamine with terminal epoxides. Under the conditions chosen for this work, epoxides were quantitatively converted in the presence of an equimolar amount of amine to gemini surfactants. Reactions could be carried out under mild conditions (70°C) in methanol, and products were obtained quantitatively by removing the solvent. The combination of N-octyl glucamine, N-decyl glucamine, or N-dodecyl glucamine with diepoxides of α,ω-diolefins having chain lengths of C₈, C₉, C₁₀, or C₁₄ resulted in gemini surfactants differing in spacer length and length of hydrophobic alkyl chains. Surface-active properties were studied by measuring surface tension and evaluating foaming properties. Tensiometric studies showed the reduction of surface tension down to 29–33 mN/m and critical micelle concentrations often in the range of 3–150 mg/L. Comparison of a selected gemini surfactant [1,8-bis(N-dodecyl glucamino-2,7-octane diol] with its corresponding “single surfactant” demonstrated the enhancement of surface-active properties afforded by the gemini structure.