Influence of Quartz,Kaolin, and Organic Matter on the Critical Micelle Concentration of Tween Surfactants and their Application in Diesel-Contaminated Soil Washing

Surfactant solutions are commonly used for the remediation of petroleum-contaminated soil due to their good petroleum removal performance, time-saving capability, and cost effectiveness. However, applying surfactants in excess concentrations could make oil recovery difficult. Moreover, residual surfactants in soil are toxic to microorganisms and plants. Thus, it is crucial to identify a suitable surfactant concentration for soil washing applications. The main objective of this study was to evaluate the effect of soil minerals (quartz and kaolin) and organic matter (OM) on the critical micelle concentration (CMC) of polyethoxylated sorbitan ester surfactants (Tween 20, 40, 60, and 80) and its effect on diesel removal from diesel-contaminated soil by soil washing. The results showed that Tween surfactants with shorter carbon chain lengths required higher CMC for diesel removal from quartz, while those with longer chains needed higher CMC for kaolin cleanup. FTIR results illustrated that oxygenated functional groups of Tween surfactants played an important role in their adsorption on quartz, while alkyl chains of Tween surfactants were responsible for their adsorption on kaolin. At a certain OM concentration, quartz and OM exhibited antagonistic effects, resulting in CMC reduction. In soil washing application, maximum diesel removal could be achieved from kaolin, in the presence of which surfactants exhibited the highest CMC. Based on FTIR results, the adsorbed surfactant could reduce the hydrophobicity of the kaolin surface, thus preventing the re-deposition of detached diesel.     

Mixed Micelles of Trisiloxane Based Silicone and Hydrocarbon Surfactants Systems in Aqueous Media: Dilute Aqueous Solution Phase Diagrams, Surface Tension Isotherms, Dilute Solution Viscosities, Critical Micelle Concentrations and Application of Regular Solution Theory

Mixtures of trisiloxane type nonionic silicone surfactant (SS) with sodium dodecylsulfate, tetradecyltrimethylammonium bromide or tert-octylphenol ethoxylated with 9.5 ethylene oxide groups were studied in water at 30 °C by dilute aqueous solution phase diagrams, surface tension and dilute solution viscosity methods. The cloud points for the silicone surfactant aqueous solutions increased upon addition of hydrocarbon surfactants indicating the formation of hydrophilic complexes in mixture solutions. The scrutiny of the surface tension isotherms plotted as a function of SS concentration revealed that competitive adsorption effects are the characteristic features in these mixtures depending upon the SS concentration. Otherwise the isotherms exhibited two break points and the difference of concentration between the two break points increased with the increase in SS concentration indicating the cooperative nature of interactions. The micellar mole fractions of individual surfactants were determined by Rublingh's regular solution theory; interaction parameters and activity coefficients were evaluated and interpreted in terms of synergistic type interactions in these mixtures. The surface active parameters in mixture solutions were estimated and their analysis shows that the molecular species in the mixture solutions have a preferential tendency for adsorption at the air/water interface than in association form in the bulk solution. The effect of hydrocarbon surfactants on the intrinsic viscosity of SS micelles was monitored and related to the enhanced hydration in mixed micelles.     

Salt‐Induced Modulation of the Krafft Temperature and Critical Micelle Concentration of Benzyldimethylhexadecylammonium Chloride

In this work, the effect of some sodium salts on the Krafft temperature (T_K) and critical micelle concentration (CMC) of benzyldimethylhexadecylammonium chloride (C16Cl) in aqueous solution has been studied. It was observed that the T_K can be modulated to lower and higher values and the CMC can be depressed significantly upon the addition of the electrolytes. More chaotropic Br^? and I^? raise the T_K with an increase of the concentration of the ions. On the other hand, less chaotropic NO₃^? initially lowers and then raises the T_K. Kosmotropic F^?, SO₄^2? and CO₃^2? gradually lower the T_K with increasing concentration of the electrolytes. The more chaotropic ions form contact ion pairs with the surfactant and decrease the solubility with a consequent increase in the T_K. On the other hand, kosmotropic ions, being extensively hydrated in the bulk, remain separated from the surfactant by hydrated layers of water molecules. As a result, a significant electrostatic repulsion exists between the charged headgroups of the surfactant, resulting in a decrease in the T_K. The CMC of the surfactant decreases significantly in the presence of these ions. The surface tension at the CMC (γ_CMC) also decreases in the presence of all the salts except for F^?. The electrostatic repulsion between the charged headgroups is significantly reduced because of screening of the surface charge of both micelles and adsorbed monolayers by the associated counterions, resulting in a decrease in both the CMC and γ_CMC.     

The Effect of Polar Head and Chain Length on the Physicochemical Properties of Micellization and Adsorption of Amino Alcohol-Based Surfactants

In this work, we have synthesized a series of quaternary ammonium from amino alcohols and n-bromoalkanes. The compounds are referred to as C_nEtOH, C_nPrOH, and C_niPrOH (where n = 12 and 14 carbons, EtOH = ethanol, PrOH = propanol, iPrOH = iso-propanol). Their structures were checked using the usual spectroscopic methods [¹H, ¹³C nuclear magnetic resonance (NMR) and infrared (IR)]. Their physicochemical properties in aqueous solution were studied using conductivity, surface tension, and ultra violet (UV)–visible absorption spectroscopy measurements. This study was conducted to show the effect of the linear hydrophobic chain and the location of the OH polar group with respect to the N⁺ quaternary ammonium on the physicochemical properties of the surfactants. The comparison between the physicochemical properties of the surfactants studied shows a distinct effect of the position of the OH group on the critical micelle concentration (CMC), the ionization degree (α), the area occupied at the interface (A_min), the free energy of adsorption (), and the free energy of micellization (). The intermolecular interaction between the synthetic surfactants and the methyl orange (OM) dye is related to the degree of hydration of the micelle, proven by the hypsochromic displacement of OM wavelength (λ_max) and ionization (α) of the micelles. The CMC, the degree of ionization, and the degree of hydration of the micelle follow the same trend.     

A Mathematical Approach to a More Accurate Determination of Critical Micelle Concentration and Other Thermodynamic Parameters of 14‐2‐14 Gemini Surfactant in Water–Organic Solvent Mixed Media at Variable Temperatures

To explore how the solvent characteristics influence the self‐aggregation of the cationic gemini surfactant dimethylene‐1,2‐bis(tetradecyldimethylammonium bromide) (14‐2‐14) and to obtain various energetic parameters, conductometric experiments were performed on the binary mixtures in the presence of commonly used organic solvents; formamide (FA), acetonitrile (AN) and 2‐methoxyethanol (ME) in aqueous solutions at varying temperatures (298.15–323.15 K) and compositions. The procedure suggested by Carpena et al. has been utilized to analyze conductivity–concentration plots in order to obtain critical micelle concentration (CMC) and degree of counterion dissociation (α) of the micelles. This method provides more accurate results as compared to conventional treatments, and the experimental error for the evaluation of micellar parameters is reduced significantly. The results revealed that, although the process of micellization becomes less favorable with the increase in composition of FA, AN and ME in mixed systems, the increase in CMC at compositions lower than 20% (v/v) of the organic solvents is relatively less, indicating that water character is dominant in the bulk phase. As the enthalpy of micellization became more negative, the corresponding entropy change became less positive and enthalpy–entropy compensation phenomenon has been observed for 14‐2‐14 in all the mixtures within the studied temperature range.     

A Systematic Study of Mixed Surfactant Solutions of a Cationic Ester-Bonded Dimeric Surfactant with Cationic, Anionic and Nonionic Monomeric Surfactants in Aqueous Media

A novel cationic biodegradable dimeric (gemini) surfactant, ethane-1,2-diyl bis(N,N-dimethyl-N-hexadecylammoniumacetoxy) dichloride (16-E2-16), containing an ester-linked spacer was synthesized. Its pure and mixed micellization properties with monomeric surfactants cetyl trimethyl ammonium chloride, cetyl pyridinium chloride, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, cetyl alcohol ethoxylate (20EO) and tert-octylphenol ethoxylate (9.5EO) were investigated by surface tension measurements at 30 °C. The critical micelle concentration (CMC) of 16-E2-16 is well below that of cetyl trimethyl ammonium chloride containing the same number of carbon atoms in the hydrophobic tail per polar head. At different mole fractions of the gemini surfactant, the CMCs of the gemini-conventional binary mixtures were determined and were found to be less than the ideal CMC values in all the cases indicating synergistic interactions. Aggregation number and Stern–Volmer constant, obtained by the fluorescence quenching technique, also support the synergistic behavior of the surfactant systems.     

入塔气预热器的结构、焊后热处理及水压试验程序

介绍了鲁奇低压法合成甲醇装置中入塔气预热器的结构、焊后热处理及其水压试验程序,对类似设备的设计、制造具有一定的参考价值。