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BACKGROUND: The oil industry has a big impact on the environment by itself and by using chemically synthesized surfactants. Biosurfactants are an ecofriendly alternative, especially rhamnolipids produced by Pseudomonas aeruginosa. Rhamnolipids in a determined concentration decrease the liquid surface tension, and this allows access oil hydrocarbon to be degraded. The objective of this research is to characterize the biosurfactant produced by the native strain P. aeruginosa 6K‐11 by determining its critical micelle concentration (CMC), Krafft point, and emulsifying activity. RESULTS: Experiments were initially performed with rhamnolipid produced by P. aeruginosa 6K‐11 growing on Siegmund‐Wagner medium with 1% of waste oil as carbon source and at 31.26 °C, 186 rpm after 42 h of incubation. After that, the biosurfactant was purified according to acid precipitation methodology. The first conductivity measurement, 34 μS/cm, was obtained with 12.5 g/L of rhamnolipid by using an APERA conductivity meter. The rhamnolipid CMC was 5.86 g/L due to the conductivity measurements graph and 0.49 was the dissociation degree. The equations of both lines were found by the method of least squares. The rhamnolipid has produced 1.97 Units of Emulsifying Activity (UEA) and 50% stability was observed based on the E24 Index. The highest conductivity achieved under 39 °C, as calculated from a conductivity against temperature graph, was the Krafft point. CONCLUSION: These findings give important parameters to characterize the P. aeruginosa 6K‐11 biosurfactant activity that can be used to accelerate oil biodegradation in bioremediation processes. © 2024 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The structural state of ionic surfactant sodium dodecyl sulfate (SDS) on passing through the Krafft point (classical characteristic parameter determining the relationship between surfactant solubility and micelle formation) was studied by two independent physical methods, NMR and dielectric spectroscopies. It was established that the micellar structure of concentrated SDS solution is preserved on cooling down to 10 °C, which is much lower than the reported Krafft point of SDS lying near 18 °C. [ABSTRACT FROM AUTHOR]

Everlasting pursuit of high energy efficiency as well as meeting fluctuant temperatures raise various lighting requirements, which is driving the originality of thermochromic smart windows (SWs). SWs with dual‐temperature response upon rational designs are identified as an effective approach to regulate solar radiation and protect privacy. Here, combining the Krafft point (Tk) of ionic surfactants and the volume phase transition temperature (VPTT) of gels toward SW materials is utilized to achieve a transition of opacity‐transparence‐opacity as temperature change, maintaining transparency at an intermediate temperature range with favorable optical modulation parameters. Cationic surfactant, hexadecylpyridinium bromide (HPB), and poly(N‐isopropylacrylamide) (PNIPAM) are combined using Tk and VPTT to serve as the dual thermo‐responsive switches for regulating solar radiation and protecting privacy. Tk of HPB can be adjusted by adding salts and VPTT is turned by introducing hydrophilic and hydrophobic comonomer. This work provides a realizable pathway by which in situ adjustable parameters may be performed and operated in external environment conditions, completely changing the smart window materials. [ABSTRACT FROM AUTHOR]

Abstract Everlasting pursuit of high energy efficiency as well as meeting fluctuant temperatures raise various lighting requirements, which is driving the originality of thermochromic smart windows (SWs). SWs with dual‐temperature response upon rational designs are identified as an effective approach to regulate solar radiation and protect privacy. Here, combining the Krafft point (Tk) of ionic surfactants and the volume phase transition temperature (VPTT) of gels toward SW materials is utilized to achieve a transition of opacity‐transparence‐opacity as temperature change, maintaining transparency at an intermediate temperature range with favorable optical modulation parameters. Cationic surfactant, hexadecylpyridinium bromide (HPB), and poly(N‐isopropylacrylamide) (PNIPAM) are combined using Tk and VPTT to serve as the dual thermo‐responsive switches for regulating solar radiation and protecting privacy. Tk of HPB can be adjusted by adding salts and VPTT is turned by introducing hydrophilic and hydrophobic comonomer. This work provides a realizable pathway by which in situ adjustable parameters may be performed and operated in external environment conditions, completely changing the smart window materials.

Krafft point is one of the key properties of anionic surfactants to indicate their solubility in an aqueous phase. Below the Krafft point, the surfactant is a useless solid. We have developed a prediction model for the Krafft point based on the Marrero and Gani Group Contribution (GC) concept. Literature data were analyzed and a new third‐order level was proposed to improve the model accuracy. The Krafft points of 53 anionic surfactants were collected including alkyl sulfonate, alkyl sulfate, alkyl benzene sulfonate, alkyl ethoxy sulfate, alkyl ester sulfonate, alkyl ester sulfate, alkyl disulfate, alkyldiphenylether disulfonates, alkyl diester sulfonate, alkyl naphthalene sulfonate, and fluorocarbon surfactants. The coefficients of the fractional groups in a surfactant molecule reveal the dependence of the Krafft point on the internal structure. Compared to the more complicated models such as those based on advanced statistical concept, the GC model for the Krafft point developed in this work gives a higher accuracy with a simpler calculation. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The effect of glycerol with sodium chloride (NaCl) on the phase behaviour of sodium dodecyl sulfate (SDS) near the Krafft point was studied by surface tension analysis using the pendant drop method. The critical micelle concentration (CMC) and Krafft Temperature (T K) of SDS in water: glycerol mixtures, across the full composition range, and in NaCl solutions within 0.005–0.1 M were obtained. The pendant drop method successfully allowed us to determine the Krafft point of SDS in high glycerol systems where other traditional methods (e.g. conductivity) have been ineffective. Overall the addition of glycerol increases the CMC and the T K , thus shifting the Krafft point of SDS to higher temperatures (increasing crystallisation temperatures) and higher SDS content in the presence of glycerol, which is interpreted as a result of the reduction in solvent polarity which opposes micellization. The addition of NaCl to the SDS – water-glycerol systems brings the CMC back down, while having no significant effect on the T K. Our results establish a robust route for tuning the Krafft point of model surfactant SDS by adjusting solvent quality and salt content. [ABSTRACT FROM AUTHOR]

The mixed micellization of the anionic surfactant sodium oleate (NaOL) and three anionic surfactants (NaDC, AOT, SDS) of different structures in 0.01 mol/L NaCl solution was investigated by surface tension measurement at different temperatures. All the investigated mixtures exhibited nonideal behaviors as the experimental critical micelle concentration (CMC) values were less than thevalues calculated by using the Clint’s equation. Negative βmvalues calculated by using Rubingh’s equation and |ln(CMC1/CMC2)| < |βm| proved synergism in the three systems of higher αNaOLor lowerαNaOL. An interesting phenomenon of double inflection points was observed for pure NaOL and mixtures of highαNaOL. The negative ΔG0mvalues for the mixed systems imply that the micelle formations are spontaneous process. The NaOL/NaDC system was also studied in buffer solution (pH 8, 12) at 30°C which also exhibited nonideal behavior. Synergism existed at pH 12 but not at pH 8 for the NaOL/NaDC system. It is noteworthy that there were no double inflection points for NaOL/NaDC system in buffer solution (pH 8, 12). Krafft point and calcium stability data show that these three anionic surfactants can improve the water solubility and hard-water resistance of soap. [ABSTRACT FROM AUTHOR]

Short branched alkyl polyoxypropylene sulfates, sodium isohexyl polyoxypropylene sulfate (i-HPS) and sodium isooctyl polyoxypropylene sulfate (i-OPS) were synthetized via propoxylation, sulfation, and neutralization three-step reactions, and characterized by FT-IR and 1 H NMR. Their Krafft points were measured and the results were all below freezing point. Their critical micelle concentrations (cmc) and minimum surface tension (γ cmc ) determined by equilibrium surface tension were 54.74 mmol L − 1 and 32.12 mN m − 1 for i-HPS, 15.57 mmol L − 1 and 33.33 mN m − 1 for i-OPS, respectively. The measurement of dynamic surface tension indicated that both the equilibrium values of surface tension and the time required for reaching the equilibrium decreased with the increasing concentration of surfactant solutions. The spreading ability on paraffin film researched through dynamic contact angle revealed that the droplet of i-HPS solution presented a minimum contact angle of 58.9° at a concentration of 150 mmol L − 1 , while the equilibrium contact angle of i-OPS droplet was 52.8° under the same condition. Their salt tolerance measurement showed that 1.0 wt% i-HPS solution and 1.0 wt% i-OPS solution could endure 183.1 g L − 1 , 143.9 g L − 1 NaCl, 206.3 g L − 1 , 198.4 g L − 1 MgCl 2 , and 229.7 g L − 1 , 217.9 g L − 1 CaCl 2 , respectively. [ABSTRACT FROM AUTHOR]

A branched alkyl polyoxyethylene ether alcohol sulfate, sodium isooctyl polyoxyethylene ether sulfate (i-OE 3 S), was synthesized and its physic-chemical properties were investigated systematically. The experiment on Krafft point gave a result that the Krafft temperature of i-OE 3 S was below 0 °C. The measurement of static surface tension showed that the critical micelle concentration (cmc) and surface tension at cmc (γ cmc ) of i-OE 3 S were 21.67 mmol·L − 1 and 27.4 mN·m − 1 , respectively. From the results of dynamic surface tension (DST) measurements, we could obtain that the adsorption of i-OE 3 S at air/liquid interface is controlled by the mixed diffusion–kinetic mechanism. Spherical assemblies with a diameter in the range of 263 to 606 nm in water were observed by transmission electron microscopy (TEM). The spreading performance of i-OE 3 S aqueous solution on paraffin film was investigated by dynamic contact angle and the results demonstrated that i-OE 3 S possessed an excellent spreading ability. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study of the kinetics of methane hydrate formation in the presence of ionic surfactants with equal carbon chain length, such as sodium dodecyl sulfate (SDS), dodecylamine hydrochloride (DAH), dodecyltrimethylammonium chloride (DTAC) and N-dodecylpropane-1,3-diamine hydrochloride (DN 2 Cl). Methane hydrates were formed at 274 K with incipient gas pressure of 15 MPa in an unstirred isochoric/isothermal reactor containing aqueous solutions at different initial surfactant loadings. It was found that addition of DTAC had little effect on methane hydrate formation whereas SDS, DAH, and DN 2 Cl had pronounced promoting effects. This result coincides with the fact that the Krafft point of DTAC is below 273 K and those of SDS, DAH, and DN 2 Cl are near room temperature. At a given initial surfactant loading, the effectiveness of the surfactants for reducing the induction time of methane hydrate formation followed the order of SDS > DAH > DN 2 Cl. SDS also gave higher hydrate growth rates than DAH and DN 2 Cl. At 1000 and 2000 ppm, however, DN 2 Cl gave slightly higher final methane uptake than SDS. It was also found that during the nucleation or induction period, addition of SDS, DAH and DN 2 Cl instead of DTAC, considerably reduced methane mole fraction in the liquid phase. Possible promotion mechanisms of surfactants during the hydrate nucleation period were discussed. [ABSTRACT FROM AUTHOR]

Three counterion coupled gemini (cocogem) surfactants in the series 1,6-bis( N, N-alkyldimethylammonium) adipate, referred as n-6- n ( n = 12, 14, 16), were synthesized, purified and characterized by H NMR and C NMR. Their physicochemical properties were investigated by electrical conductivity and surface tension measurements. The degree of ionization, critical micelle concentration (CMC), surface excess at the air/solution interface (Γ), minimum area per surfactant molecule at the air/solution interface ( A), surface tension at the CMC ( γ), and p C (negative log of the surfactant molar concentration, required to reduce the surface tension of water by 20 mN m) were calculated. Increase in tail length of the surfactants increases the efficiency of surfactants to decrease the surface tension of water. Thermodynamic parameters, viz. molar free energy at the maximum adsorption attained at CMC ( G), standard Gibb's energy of micellization ( $$ \Updelta G_{\text{mic}}^{\text{o}} $$ ), and standard Gibbs energy of adsorption ( $$ \Updelta G_{\text{ad}}^{\text{o}} $$ ), were also calculated. The $$ \Updelta G_{\text{mic}}^{\text{o}} $$ and $$ \Updelta G_{\text{ad}}^{\text{o}} $$ values show that the monomers were preferred to be adsorbed at the air/water interface and then in the micellar formation in the bulk. Additionally, fluorescence measurements were used to find the aggregation number. Other relevant surface properties (Krafft point, emulsion stability, foaming ability, micellar stability and dye solubilization ability) were also evaluated. These results suggest that with respect to emulsion formation, micellar stability and dye solubilization, the cocogem with a 16-carbon chain gives better results, producing 89 % more stable foams and shows better aggregational behavior. [ABSTRACT FROM AUTHOR]

The unsaturated long-chain carboxybetaine and hydroxy sulfobetaine were synthesized by the reaction of unsaturated octadecyl tertiary amine with sodium chloroacetate and 3-chloro-2-hydroxypropanesulfonic acid sodium salt, respectively. The structures of the two betaines were characterized by IR and H-NMR spectroscopy. The Krafft points of the two betaines are below 0 °C and the isoelectric points are at pH 8.2 and 8.0, respectively. The surface tensions ( γ) at the critical micelle concentrations (CMC) were measured to investigate the surface activities of the prepared compounds when the pH is equal to 4.0, 6.5 and 10.0 at 50 °C, respectively. Meanwhile, the corresponding saturated betaines were synthesized and determined for comparison. The double bond in the non-polar tail leads to a slightly higher CMC and a lower γ. Though the CMC of the unsaturated betaine is slightly higher than that of saturated betaine for the double bond in the non-polar tail, the applied range of the unsaturated betaine is broader than corresponding saturated betaine for low Krafft point. The CMC and Г of the four betaines increase, but the pC decreases, with increasing pH. As a whole, the impact of pH on the performance of the four betaines is not very obvious. [ABSTRACT FROM AUTHOR]

Abstract: In this work we show how a new promising green and highly water-soluble surfactant can be designed based on recent progress in the knowledge of counterion–headgroup binding and crystallization behavior. The result is the combination of a most classical surfactant anion, dodecylsulfate (DS), with choline (Ch), a natural green cation. The advantage of the physiological metabolite choline is its bulky structure that prevents ChDS from easy crystallization and thus leads to a considerable lowering of the Krafft point down to 0°C. The counterion–headgroup binding is reflected by the aqueous phase behavior of ChDS. Conductivity, surface tension, and cryo-TEM measurements allow the characterization of the dilute micellar region, while the penetration scan technique enables the establishment of a preliminary aqueous phase diagram. In addition, the influence of different mono- and divalent salts on the solubility of ChDS is investigated. The results are compared to the alkali sulfate and alkylcarboxylate homologs, and reveal that ChDS is less sensitive towards addition of salts than, for instance, choline carboxylates due to an increased counterion–headgroup association. Further, cytotoxicity tests on HeLa and SK-Mel 28 cells are presented and compared to other surfactants, showing that ChDS is no more harmful than its sodium counterpart SDS. Taken together, our findings highlight that the harmless green cation choline is of great potential for the design of new surfactants. [Copyright &y& Elsevier]

A homologue series of sodium secondary n-alkanesulfonates (C, C and C) were obtained by photosulfochlorination process with two different reaction conditions. Different length chains with different isomeric distributions of n-alkanesulfonates are expected to present variations in physicochemical properties. In this investigation, the relationships between their isomeric distribution and their chain length and micellar behaviors were thoroughly explored. Their CMC at different temperatures were determined using specific conductivity and surface tension measurements. Through surface tension isotherms, the surface activities (γ) were obtained. The surface absorption amounts (Γ) and the molecular areas ( A) were calculated using Gibb's equation. As expected, these surfactants exhibit good surface properties. It was shown that the CMC values increase with increasing the percentage of secondary isomers, with a surface tension decrease. It was also shown that the CMC values decrease with increasing chain length. The HLB values were calculated for each surfactant and the results obtained suggest that they are O/W emulsifiers. The foam properties of synthesized surfactants were evaluated and compared to those obtained for commercial samples. It was shown that the foamability is influenced both by the length of the hydrophobic moiety and the percentage of secondary isomers. It can be easily concluded that the C sulfonates show the best foaming properties independently of their isomeric distribution. The Krafft point values obtained indicate that the micellization and the surfactant solubility mainly depend on the proportion of secondary isomers and the length of hydrophobic moiety. [ABSTRACT FROM AUTHOR]

Abstract: The aggregation properties of 2-, 3-, and 4-fluorobenzoic acids (2FBA, 3FBA, and 4FBA, respectively) and their salts with hexadecyltrimethylammonium cations (HTA2FB, HTA3FB, and HTA4FB) in water were studied with a battery of techniques. Their activity at the air/solution interface has been also studied. The position of the fluorine atom in the acid affected the solubility, adsorption, and aggregation in the pure acids solutions. The 4FBA is less water soluble, more hydrophobic, and has the lower critical aggregation concentration of the three isomers. The behavior of the HTA2FB compound in aqueous solution is different from that of HTA3FB and HTA4FB. The critical micelle concentration, critical concentration for sphere-to-rod-like micelle transition, and Krafft point of HTA3FB and HTA4FB are lower than those of the other surfactant but their surface activities are higher. The differences between the HTA2FB and the other two surfactants have been explained on the basis of the regular solution theory of mixed micelles and in light of the analysis of the hydration shell of the acids through molecular dynamic simulations. The results of the present work suggest that the different behaviors are due to a combination of different dehydration tendencies and the steric possibility of inclusion of the counterions in the micelle palisade layer. The formation of rod-like micelles by HTA2FB, while the tetradecyltrimethylammonium 2-fluorobenzoate only forms spherical aggregates, is explained on the basis of the packing parameter. The mentioned factors are complementary to others presented in literature. These conditions may be used in the rational design of micelles by means of molecular dynamics simulations, reducing the trial-and-error approach used to date. [Copyright &y& Elsevier]

Synthesis and surfactant properties and biodegradation of succinylated alkyl polyxylosides is described for the first time. The esterification of succinic anhydride with alkyl polyxylosides was achieved without solvent and the substitution degree controlled over a certain range. The surfactant properties were studied as a function of substitution degree. Their biodegradation was studied following OECD guidelines. The results have confirmed that the new synthetic approach described in this paper is a potentially economical and efficient method for the preparation of a new range of environmental friendly surfactants. [ABSTRACT FROM AUTHOR]

Abstract: We have used electrical impedance spectroscopy to determine the influence of temperature on the electric characteristics of ionic surfactant/water and ternary systems composed by surfactant/salt/water and ionic surfactant/phospholipid/water, with the purpose of understanding the physical meaning of melting point of surfactants (called Krafft point) based on the fitting of Nyquist diagrams from the use of modified Randles circuit and to analyze the influence of salts actuating as lyotropic or hydrotropic electrolytes. The parameters obtained from the study of Gouy–Chapman double layer allow that important information about ionic and molecular distribution can be obtained in direction to describe the phase transition from hydrated solid surfactant to micelles in aqueous solutions. [Copyright &y& Elsevier]

Abstract: Anomalous double cloud point of ethylene oxide–propylene oxide triblock copolymer L62 in an aqueous solution is usually ascribed to impurities in the polymeric nonionic surfactant. In this article, the partial phase diagrams of block copolymers L62, L61, and L92 (including their mixtures) in aqueous solutions with and without the presence of 1-butanol have been determined, which indicates that double cloud point is not a peculiar character of L62 in an aqueous solution. Based on a further analysis of phenol solubilization in clear L62 aqueous solutions, a schematic phase diagram of polymeric nonionic surfactants in an aqueous solution is proposed. The schematic phase diagram was supported not only by our experimental results but also in line with the reported results in the literature. [Copyright &y& Elsevier]

Abstract: Didodecyldimethylammonium bromide (DDAB) (1.0mM) vesicles in water were investigated by differential scanning calorimetry (DSC) to highlight the existing kinetic asymmetry in the gel–liquid crystalline (LC) state transitions. The experiments were performed in the range of temperature, scan rate and pre-scanning time 5–45°C, 15–90°C/h and 0–16h, respectively, in the up- and down-scanning modes. Depending on the input parameters and number of heating–cooling cycles, the DSC thermograms exhibit a sharp peak, a broad band or a flat shape. A melting temperature T m =15.6–16.0°C, given by the peak position, was obtained independently of the scan rate used in the up-scanning mode. The data reveal that DDAB vesicles exhibit much slower kinetics for the LC to gel state than for the opposite transition. Such an asymmetry is supported by: (a) the absence of peak for shorter pre-scanning times but longer scan rates, (b) the increasing intensity of the DSC peak with increasing pre-scanning time and decreasing scan rate, and (c) the complete absence of peak in the down-scan mode. Longer pre-scanning time, however, yields crystal precipitates due to a Krafft phenomenon, which also reduces the peak intensity. The overall results depend on whether the sample is fresh or not, that is, after some heating–cooling cycles, the melting peak requires a longer pre-scanning time to be detected. The kinetic asymmetry explains, for example, the lack of any DSC melting peak reported for “non-fresh” DDAB vesicles, which was as yet unexplained. [Copyright &y& Elsevier]

Abstract: Amiodarone aqueous systems at concentrations C ⩽3mg/mL were studied with different techniques (conductivity, solubility, ion-selective electrodes, pH, viscosity, polarizing microscopy, computational simulation, electron microscopy and fluorescence at various temperatures. The Krafft point (TK =70.6°C) was determined. A partial phase diagram was plotted showing the critical micelle concentration (CMC) dependence on temperature, the solubility and a transition between a coacervate and an unstable gel below TK as a function of temperature. The nature of aggregates below TK at different concentrations was determined. Micellization is an entropy-driven process which is probably caused by a strong dehydration of the amiodarone backbone on micellization. CMC, micelle aggregation number and TK given in earlier literature were misinterpreted in the original articles and are re-interpreted in this work. [Copyright &y& Elsevier]

Abstract: The melting behavior of polyethyleneglycol dodecyl ethers (C12E6, C12E7, and C12E8) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), was investigated by means of differential scanning calorimetry (DSC). The melting temperature as a function of the surfactant concentration, combined with the cmc curve and cloud point curve, provided phase diagrams for the surfactant/bmimBF4 mixtures in solvent-rich region. The characteristic feature of the mixtures is an existence of the Krafft temperature which is usually not observed with aqueous solutions of nonionic surfactants. The heat of fusion as a function of the surfactant concentration provided the interaction energy between the surfactant and bmimBF4. The interaction energy shows a linear dependence on the length of polyoxyethylene (POE) chain of the surfactants, which suggests that the solvation takes place around the POE chain. [Copyright &y& Elsevier]

Abstract: Long-chain amines, used in potash ore flotation as collectors, are insoluble in NaCl–KCl saturated brine. In commercial applications, these amines are melted at 70–90 °C, dispersed in acidic solution of hydrochloric or acetic acids, and such emulsions are then introduced to the flotation pulp. To model the commercial potash ore flotation process, dodecyl amine, used in this study, was melted at 70 °C, dispersed in hydrochloric acid aqueous solution and was added to a KCl–NaCl saturated brine at room temperature. This results in the precipitation of the amine. The present study summarizes the influence of the conditions on the particle size and morphology of the precipitating amine particles. Methyl isobutyl carbinol (MIBC), common frother in flotation processes, was shown to affect amine dispersion when added into a hot amine emulsion prior to mixing with a saturated brine. This study demonstrates that the precipitating amine particles are selectively abstracted by KCl particles, but not by NaCl particles. [Copyright &y& Elsevier]

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Abstract: Triton X-45, a nonionic surfactant with a low hydrophile–lypophile balance value and dispersible in aqueous solution at room temperature, has a Krafft point above the room temperature. The cloud point of Triton X-45 in an aqueous solution is different from the conventional aqueous nonionic surfactant micelle solution. It was further confirmed by a determination of the effect of additives on the phase behavior of aqueous solutions containing Triton X-45. The experimental fact eliminates the prevalent concept that the cloud point of Triton X-45 is below room temperature, which is helpful to exploit a biocompatible medium for a microbial growth and then for whole cell microbial transformation in a nonaqueous medium. [Copyright &y& Elsevier]

Abstract: Sodium dodecyl sulfate (SDS) can accelerate nucleation and growth of gas hydrates in a quiescent system. The objective of this paper is to investigate whether or not SDS micelles form in the meta-stable region of methane hydrates by the direct measurement of aqueous SDS concentration. The SDS solubility in water with high-pressure methane is identical to that under atmospheric pressure at a temperature range of 270–282 K; thus, the Krafft point under these methane hydrate-forming conditions does not shift from the normal Krafft point (281–289 K) under atmospheric pressure. The mole fraction of methane in SDS solution is independent of aqueous SDS concentration at a hydrate-forming condition. These results suggest that at temperatures below the normal Krafft point, no SDS micelles are present in the aqueous phase even in a high-pressure methane environment. [Copyright &y& Elsevier]

Abstract: Conductivity, density, and sound velocity measurements as functions of temperature were made on tetraethylammonium perfluorooctylsulfonate solutions to determine the Krafft point, the dependence on temperature of the critical micelle concentration, the micellar ionization degree, and several thermodynamic properties: Gibbs free energy, enthalpy and entropy of micellization, apparent molar partial volume, thermal expansion coefficient, and the adiabatic compressibility factor of both micellized and unmicellized surfactants. Important changes occur at about 30 °C. Results are interpreted on the basis of dehydration of surfactant on micellization and on temperature increase. [Copyright &y& Elsevier]

Abstract: The solubility of sodium soaps in dilute aqueous salt solutions has been systematically investigated by direct visual phase behavior observations. The added electrolytes, including simple inorganic salts and bulky organic salts, influence the solubility of sodium soaps in water, as represented by the varied soap Krafft point. Two inorganic salts, sodium chloride and sodium perchlorate, demonstrate a “salting-out” property. On the other hand, tetraalkylammonium bromides show an excellent ability to depress the soap Krafft point and enhance the soap solubility in water. With increasing the tetraalkylammonium ionic size, the degree of “salting-in” of soaps in water increases. However, solubility of pure tetraalkylammonium bromide in water decreases as the length of the alkyl chains increases. Furthermore, in the ternary water-tetrapentylammonium bromide (TPeAB)-sodium myristate (NaMy) system, we observed an upper cloud point phenomenon, which greatly shrinks the 1-phase micellar solution region in the phase diagram. This miscibility gap, together with the organic salt solubility limitation, restricts the use of tetraalkylammonium bromides with alkyl chains longer than 4 carbon atoms as effective soap solubility enhancement electrolytes. We also found that for sodium soap with a longer hydrocarbon chain, more tetrabutylammonium salt is required to reduce the soap Krafft point to room temperature. [Copyright &y& Elsevier]

General empirical relationships have been developed for estimating the Krafft point of anionic surfactants and cloud point of nonionic surfactants using the quantitative structure‐property relationship (QSPR) method. For the Krafft point, a six‐parameter structure‐property relationship (R 2 =0.941) was obtained for a diverse set of 46 anionic hydrocarbon surfactants and a three‐parameter relationship (R 2 =0.864) for 19 linear fluorocarbon anionic surfactants by employing topological, thermodynamic, and structural descriptors. For the cloud point of 64 nonionic surfactants with six representative structures, the best multiple linear regression model involved five parameters and had a correlation coefficient of R 2 =0.921. From these relations Krafft point or cloud point of surfactants can be estimated based on their molecular structure. [ABSTRACT FROM AUTHOR]

Abstract: In this work we studied and compared the physicochemical properties of perfluorinated (sodium perfluoroheptanoate, C7FONa, and perfluorooctanoate, C8FONa) and hydrogenated (sodium octanoate, C8HONa, decanoate, C10HONa, and dodecanoate, C12HONa) amphiphiles. First, we determined their Krafft points to study the solubility and appropriate temperature range of micellization of these compounds. The critical micelle concentration (cmc) and ionization degree of micellization (β) as a function of temperature (T) were estimated from conductivity data. Plots of cmc vs T appear to follow the typical U-shaped curve with a minimum . The results show that the surfactants with CF2/CH2 ratio of 1.5 between alkyl chains (C12HONa–C8FONa and C10HONa–C7FONa) have nearly the same minimum value for cmc against temperature. The comparison between the cmc of hydrogenated amphiphiles and the corresponding perfluorinated amphiphiles must be done at this point. Thermodynamic functions of micellization were obtained by applying different theoretical models and choosing the one that best fit our experimental data. Although perfluorinated and hydrogenated amphiphiles present similar thermodynamic behavior, we have found a variation of 1.3 to 1.7 in the CF2/CH2 ratio, which did not remain constant with temperature. In the second part of this study the apparent molar volumes and adiabatic compressibilities were determined from density and ultrasound velocity measurements. Apparent molar volumes at infinite dilution presented the ratio 1.5 between alkyl chains again. However, apparent molar volumes upon micellization for sodium perfluoroheptanoate indicated a different aggregation pattern. [Copyright &y& Elsevier]

Abstract: A series of dissymmetric gemini surfactants with the general formula [C12H25(CH3)2N(CH2)sN(CH3)2C14H29]Br2 designed as 12–s–14, where , 6, and 10, were synthesized and their physicochemical properties investigated. The effect of spacer length on Krafft temperature, adsorption at the air/solution interface, and association in aqueous solution was studied by tensiometry, conductometry, and cryo-transmission electron microscopy. The Krafft temperature was found to increase linearly with spacer length. In the submicellar concentration range the dissymmetric 12–s–14 surfactants display ion pairing and premicellar association. Adsorption at air/solution interfaces and micellization in aqueous solution are similar to the behavior of their symmetric counterparts and depend strongly on spacer length. [Copyright &y& Elsevier]

Sodium (3-dodecanoyloxy-2-hydroxy-propyl) succinate (SLGMS) is a conjugated anionic surfactant in which a glycerol residue connects with a hydrophilic sodium succinate and dodecanoate. Aqueous micellar phase (Wm), hexagonal (H1), bicontinuous cubic (V1), and lamellar (Lα) phases are successively formed with increasing the surfactant concentration in a binary SLGMS-water system. The Krafft point is below 0 °C. The effective cross sectional area per surfactant molecule, as, in the H1 phase is almost constant, 0.5 nm2, and the shape of cylindrical micelle is almost unchanged with surfactant concentration. The cmc value of SLGMS measured by means of surface tension, electrical conductivity, and fluorescence probe methods is in the range of 4∼9 × 10−5 mol/l that is much lower than that of sodium dodecanoate, 2 × 10−2 mol/l, or SDS, 8 × 10−3 mol/l. Hence, it is considered that the polar glycerol part in the SLGMS acts as a hydrophobic part. The solubilization of oil in the SLGMS solution is much higher than that in the SDS solution and this also suggests that the glycerol and succinic units act as lipophilic moieties. [ABSTRACT FROM AUTHOR]

For a sodium salt of α sulfonatomyristic acid methyl ester (14SFNa), one of the α-SFMe series surfactants, critical micellization concentration (CMC), solubility and degree of counterion binding (β) were determined by means of electroconductivity measurements at different temperatures (at every 5 °C) ranging from 15 to 50 °C. The phase diagram of 14SFNa in pure water was constructed from the CMC- and solubility-temperature data, in which the Krafft temperature (critical solution temperature) was found around 0 °C. The changes in the Gibbs energy, ΔG, enthalpy,ΔH, and entropy, ΔS, upon micelle formation as a function of temperature were evaluated taking β values into calculation. [ABSTRACT FROM AUTHOR]

The calcium salts of α-sulfonated fatty acid methyl esters were prepared, and the physico-chemical properties such as solubility, critical micelle concentration, aggregation number, and precipitation phase boundary were studied to clarify the reasons for the good hardness tolerance manifested by α-sulfonated fatty acid methyl esters. The Krafft point of the calcium salts of α-sulfonated fatty acid methyl esters were not necessarily lower than room temperature, but the rate of crystallization in hard water was extremely slow compared with the calcium salt of dodecyl sulfate, which has been known as an insufficient surfactant in terms of hardness tolerance. [ABSTRACT FROM AUTHOR]

Sodium α-sulfonated, fatty acid polyethylene glycol monoesters [CHCH(SONa)COO(CHO)H] and diesters [CHCH(SONa)COO(CHO)COCH(SONa)CH], where m=10-16 and n=1-35, were prepared by esterification of α-sulfonated, fatty acids with polyethylene glycols, followed by neutralization with NaOH. Crude products were purified by reversed-phase column chromatography on an octadecyl-modified silica gel. Characteristic solution behavior of these α-sulfonated fatty acid esters was, examined, and the following features were observed. All monoesters prepared in this work had Krafft points below 0°C and also possessed good calcium stabilities. Critical micelle concentrations of the monoesters increased monotonously, as a rule, with an increase in the number of oxyethylene units. These results suggest that the polyethylene glycol residue of the monoester behaves as a hydrophile. On the other hand, diesters possessed high water solubility, low foamability, and critical micelle concentrations that were lower by a factor of ten compared to those of the monoesters. [ABSTRACT FROM AUTHOR]

There has long been interest in methyl ester sulfonates (MES) derived from natural or renewable sources, such as palm oil, with considerable effort focused on process development. A major drawback with current process technology is the formation of dark brown impurities that create aesthetic and odor issues in the final product. These issues are usually addressed by bleaching rather than by chemical purification. This paper reports on a simple yet highly effective nonbleach, two-step process for purifying palm C16-18 potassium methyl ester sulfonates. The first step comprises addition of water to the impure surfactant mixture. Preferably, the temperature of the system is maintained above the Krafft point of the surfactant, thereby completely solubilizing the surfactant and associated impurities. Once completely dissolved, the surfactant mixture is allowed to cool, and the potassium-neutralized methyl ester sulfonate precipitates out selectively. In the second step, the purified surfactant is recovered by gravity- or pressure-filtration or by centrifugation, followed by drying. The process significantly improves C16-18 MES analytical purity and color without raising safety or environmental concerns. It also allows for the purification of products derived from lower-grade methyl esters, resolves odor issues, and does not require use of substantial amounts of solvent such as methanol. [ABSTRACT FROM AUTHOR]

A series of cationic cleavable surfactants was prepared by condensation of 2-alkyl-1,3-propanediols with 3-bromopropanal, followed by reaction with triethylamine. Each surfactant is a mixture of two diastereomers, and their precursors' stereochemical assignments were based onH nuclear magnetic resonance spectra and melting points. The critical micelle concentrations, Krafft points and destructibility of these surfactants were determined. [ABSTRACT FROM AUTHOR]

A series of di-anionic cleavable surfactants were prepared by the condensation of aldehydes with 2,2- bis(hydroxymethyl)-1,3-propanediol, followed by reaction with 1,3-propanesultone in the presence of sodium hydride. Surfactant 5a had a differentH nuclear magnetic resonance spectrum in DO than products 5b−d. This was rationalized by its different conformation, which originates from the self-coiling of its alkyl chain. The critical micelle concentrations, Krafft points and hydrolysis properties of these surfactants were determined. [ABSTRACT FROM AUTHOR]

This paper reports the influence of synthesis temperature on the structure of mesoporous silica materials templated with ionic surfactant. The results obtained allow for the prediction of optimal temperature value to be used in nonhydrothermal short-term synthesis. The model materials were mesoporous silicates of MCM-41 type. The samples were prepared under alkaline conditions using tetraethyl orthosilicate as a silica source and cetyltrimethylammonium bromide or octadecyltrimethylammonium bromide as templates. An increase in synthesis temperature led to a rougher surface and decrease in the long-range ordering of the materials obtained, while a slight temperature decrease produced additional porosity. The reasons for these structural disturbances were briefly explained. The best material structure was obtained by synthesis at a temperature slightly higher than the Krafft temperature of surfactant of the porosity template. [Display omitted] • Krafft point - a key factor in short-term synthesis of surfactant templated material. • Higher temperature increases the surface roughness of the silica material. • Too low temperature causes formation of additional pores in the silica structure. [ABSTRACT FROM AUTHOR]

Micellar solubilization can effectively dissolve low water-soluble compounds in aqueous environment, however, the micellar systems are not able to withstand dilution and maintain solubilization of poorly water-soluble drugs below critical micelle concentration. To overcome the drawbacks of conventional micellar solubilization, nonionic polyoxyethylated surfactants with Krafft points at or higher than body temperature were chosen to create novel micelle-based nanostructures as a delivery vehicle for poorly water-soluble compounds. A technique "thermo-spray process" was developed for the preparation of the nanostructures-containing formulation, in which the drug-containing micelle solution was first prepared and maintained at the elevated temperature above the Krafft point of the surfactant, then spray dried to solidify the obtained micelle-like nanostructure at room temperature. Lactose was used as an excipient to embed the nanostructures in the thermo-spray products. Water insoluble spherical nanoparticles with size range from 80 to 250 nm were obtained after reconstitution of the product at the temperature lower than Krafft point. When paclitaxel was used as model drug, the micelle-like nanostructures exhibited similar drug entrapment efficiency, solubility enhancement and drug release facilitation as conventional micelles, but provided lower critical micellar concentration at body temperature, and good encapsulation stability upon storage and dilution. These findings indicated that the developed thermo-spray product can serve as a promising delivery platform for drugs with low aqueous solubility. [ABSTRACT FROM AUTHOR]