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.     

Synthesis,Quantum Chemical Calculations and Properties of Nonionic and Nonionic–Anionic Surfactants Based on Fatty Alkyl Succinate

Two surfactants based on maleic anhydride were synthesized by esterification with fatty alcohols C₁₀, C₁₂ and C₁₄ to produce half esters [I–III]. Nonionic surfactant monoesters [I–III]a–c synthesized by ethoxylation of [I–III] with different moles of ethylene oxide [6, 8 and 10] in the presence of K10 clay as an untraditionally catalyst. The later products were sulfonated to produce nonionic–anionic surfactants [IV–VI]a–c. The structures of synthesized surfactant were elucidated by FTIR and ¹H-NMR data. Their surface activity and biodegradability were determined. All the synthesized surfactants showed good surface activity and biodegradability, but anionic-nonionic type has better effect than nonionic one. Quantum chemical calculations were utilized to explore the electronic structure and stability of these compounds. Computational studies have been carried out at the PM3 semiempirical molecular orbitals level, to establish the highest occupied molecular orbital–lowest unoccupied molecular orbital, ionization potential energy and ESP mapping of these compounds. Also, the absorption, distribution, metabolism, elimination and toxic properties were studied to gain a clear view of the oral bioavailability of these compounds.     

Interaction Between an Anionic and an Amphoteric Surfactant. Part I: Monomer–Micelle Equilibrium

A mixture of anionic and amphoteric surfactants is composed of three components at intermediate pH levels: anionic, cationic (protonated amphoteric), and zwitterionic (unprotonated amphoteric). Knowledge of the composition of each surfactant in both monomer and micellar forms (monomer–micelle equilibrium) is important in applications using this mixture. Hydrogen ion titration of the mixed surfactant solution as a function of surfactant composition is combined with the pseudophase separation model and regular solution theory for the three-surfactant mixture to calculate the concentration of each surfactant in monomer and in micelle forms at different pH levels. The specific systems studied here contain sodium dodecyl sulfate (SDS) and dimethyldodecylamine oxide (DDAO), which are used in a wide range of consumer products. The degree of protonation of monomeric DDAO is not affected by the presence of SDS, indicating an insignificant formation of ion pairs between these monomers. However, the presence of SDS in micelles shifts the micellar pK _a of DDAO protonation significantly and the method used here allows the quantification of partial fugacities of each individual surfactant in micelle form. The composition in the monomer phase at each pH will aid in understanding and predicting solution compositions corresponding to anionic/amphoteric surfactant precipitation boundaries, which is the focus of the subsequent paper in this series.

Adsorption of Anionic–Cationic Surfactant Mixtures on Metal oxide Surfaces

This research evaluates the adsorption of anionic and cationic surfactant mixtures on charged metal oxide surfaces (i.e., alumina and silica). For an anionic-rich surfactant mixture below the CMC, the adsorption of anionic surfactant was found to substantially increase with the addition of low mole fractions of cationic surfactant. Two anionic surfactants (sodium dodecyl sulfate and sodium dihexyl sulfosuccinate) and two cationic surfactants (dodecyl pyridinium chloride and benzethonium chloride) were studied to evaluate the effect of surfactant tail branching. While cationic surfactants were observed to co-adsorb with anionic surfactants onto positively charged surfaces, the plateau level of anionic surfactant adsorption (i.e., at or above the CMC) did not change significantly for anionic–cationic surfactant mixtures. At the same time, the adsorption of anionic surfactants onto alumina was dramatically reduced when present in cationic-rich micelles and the adsorption of cationic surfactants on silica was substantially reduced in the presence of anionic-rich micelles. This demonstrates that mixed micelle formation can effectively reduce the activity of the highly adsorbing surfactant and thus inhibit the adsorption of the surfactant, especially when the highly adsorbing surfactant is present at a low mole fraction in the mixed surfactant system. Thus surfactant adsorption can be either enhanced or inhibited using mixed anionic–cationic surfactant systems by varying the concentration and composition.

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Behavior of Anionic Surfactants and Short Chain Alcohols Mixtures in the Monolayer at the Water–Air Interface

Measurements of the surface tension of aqueous solution of mixtures of sodium dodecyl sulfate (SDDS) with methanol and ethanol in SDDS concentration range from 10⁻⁵ to 10⁻² M and mixtures of sodium hexadecyl sulfonate (SHS) with methanol and ethanol at SHS concentration from 10⁻⁵ to 8 × 10⁻⁴ M and for methanol and ethanol from 0 to 21.1 and, 11.97 M, respectively, were carried out at 293 K. Moreover, the surface tension of aqueous solution mixtures of SDDS with propanol in the concentration range from 0 to 6.67 M taken from the literature was also considered. The results obtained indicate that it is possible to describe the relationship between the surface tension and molar concentration or molar fraction of alcohol by Szyszkowski and Connors equations. However, the Fainerman and Miller equation allows us to predict the isotherm of the surfactant tension at constant anionic surfactants concentration at which their molecules are present in the solution in the monomeric form if the molar area of surfactants and alcohols can be determined. Based on the surface tension isotherms, the Gibbs surface excess of anionic surfactants and alcohols concentration at water–air interface was determined and then recalculated for Guggenheim-Adam surface excess concentration of these substrates, and next the molar fraction of alcohols and surfactants in the surface layer was determined. These molar fractions were discussed with regard to surfactant and alcohol standard free energy of adsorption at the water–air interface determined from Langmuir and Aronson and Rosen equations. The standard free energy of adsorption determined in these ways was compared to that deduced on the basis of pC₂₀ and Lifshitz van der Waals-components of the anionic surfactant and alcohol tails.     

Synergistic Behavior Between Zwitterionic Surfactant α-Decylbetaine and Anionic Surfactant Sodium Dodecyl Sulfate

Here, we present experimental surface tension isotherms of mixed solutions of a zwitterionic surfactant α-decylbetaine (DB) and an anionic surfactant sodium dodecyl sulfate (SDS) in different molar ratios. These mixed solutions show a composition dependency with respect to both surface tension effectiveness and critical micelle concentration. The pseudo-regular solution theory has been used to evaluate the interaction parameters in the micelle, β ^m and at the surface, β ^s. The results revealed that the mixed solutions of DB/SDS behave synergistically in both surface tension reduction effectiveness and mixed micelle formation at all mole fractions investigated. The values of adsorption area per surfactant molecule at air/solution interface were estimated, which provides some useful information on evaluating the interaction between DB and SDS in mixed adsorbed monolayers. The solubilization behaviors of toluene in DB/SDS mixed solutions were also investigated to help in understanding the structure of mixed micelles of DB and SDS.     

A Star-Shaped Anionic Surfactant: Synthesis,Alkalinity Resistance,Interfacial Tension and Emulsification Properties at the Crude Oil–Water Interface

In this research, a star‐shaped surfactant was synthesized through the chlorination reaction, alkylation reaction and sulfonation reaction of triethanolamine, which is composed of three hydrophobic chains and three sulfonate hydrophilic groups. The critical micelle concentration (CMC) of the surfactant was measured by the surface tension method, and the results showed that it had high surface activity with CMC of 5.53 × 10^?5 mol/L. The surfactant was superior in surface active properties to the reference surfactants SDBS and DADS‐C₁₂. The interfacial tension (IFT) of the studied crude oil–water system (surfactant concentration 0.1 g/L, NaOH concentration 0.5 g/L, and experimental temperature 50 °C) dropped to 1.1 × 10^?4 mN/m, which can fulfil the requirement of surfactants for oil displacement. An aqueous solution of the surfactant and crude oil was emulsified by shaking, which formed a highly stable oil‐in‐water (O/W) emulsion with particle size of 5–20 μm. The oil displacement effect was almost 12%.     

Characterisation and modelling of CNT–epoxy and CNT–fibre–epoxy composites

Abstract

This research presents an experimental and theoretical investigation on the effects of carbon nanotube (CNT) integration within neat epoxy resin (nanocomposites) and a carbon fabric–epoxy composite (multiscale composites). An approach is presented for the prediction of mechanical properties of multiscale composites. This approach combines woven fibre micromechanics (MESOTEX) with the Mori-Tanaka model which was used for the prediction of mechanical properties of nanocomposites in this research. Nanocomposite and multiscale composite samples were manufactured using cast moulding, resin infusion, and hand lay-up process. The CNT concentrations in the composite samples were from 0 to 5 wt-%. The samples were characterised using tensile, shear and flexural tests. The discrepancy between the theoretical predictions and the experimental observations was hypothesised to be due to dispersion and bonding issues and SEM images are presented in support of the hypothesis.     

Efficient extraction of phenol from wastewater by ionic micro-emulsion method: Anionic and cationic

Phenolic wastewater is one of the priorities in the field of wastewater treatment, which poses a serious threat to the human health and nature environment. In this paper, cationic cetyltrimethylammonium bromide(CTAB) and anionic sodium oleate(Na OL) microemulsions were utilized to extract phenol from the wastewater. The optimal extraction factors were investigated by exploring the effects of microemulsion composition ratio and extraction conditions on the phenol extraction performance. Furthermo...     

Effect of Inorganic Additives on a Conventional Anionic–Nonionic Mixed Surfactants System in Aqueous Solution

The interaction between an anionic surfactant (sodium dodecyl sulfate) and a nonionic surfactant [polyoxyethylene (9.5) octyl phenyl ether] in aqueous salt solution was investigated using the surface tension method. The critical micelle concentration values were determined for the individual surfactants and their corresponding mixtures. The interaction parameter between the surfactants in the mixed micelles, the activity and activity coefficients in the mixed micelles, and the thermodynamic parameters were calculated using various approaches, viz., Clint, Rubingh, and Maeda models. It was observed that the critical micelle concentration of the mixed surfactants system reveals little deviation from ideality.     

Colloidal Stability and Sintering of Yttria–Silica and Yttria–Silica–Alumina aqueous suspensions

The aim of this work was to produce dense yttrium silicate materials by slip casting, with more than 90% of Y₂SiO₅ phase. The rheological behaviour of concentrated aqueous slips was studied considering the effect of the dispersing additives, solids content and pH. The densification kinetics was examined as a function of temperature and time, and the reactions were analysed in the light of the equilibrium phase diagrams. Deflocculation of the slips was achieved by either an electrostatic mechanism using tetraethylammonium hydroxide, thus requiring a high concentration of base, and by a polyelectrolyte through an electrosteric mechanism, which provided more reliable results. In the binary system Y₂O₃–SiO₂, a very low grade of sintering was obtained at 1600°C. The use of alumina allows sintering through a liquid phase, reaching 90% theoretical density.     

Synthesis and characterizations of BNT–BT and BNT–BT–KNN ceramics for actuator and energy storage applications

Dielectric and ferroelectric properties of 0.93Bi_0.5Na_0.5TiO₃–0.07BaTiO₃ (BNT–BT) and 0.93Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–0.01K_0.5Na_0.5NbO₃ (BNT–BT–KNN) ceramics were studied in detail. An XRD analysis confirmed the single perovskite phase formation in both the samples. Room temperature (RT) dielectric constant (ε_r) ~1020 and 1370, respectively at 1 kHz frequency were obtained in the BNT–BT and BNT–BT–KNN ceramics. Temperature dependent dielectric and the polarization vs. electric field (P–E) studies confirmed the coexistence of ferroelectric (FE) and anti-ferroelectric (AFE) phases in the BNT–BT and BNT–BT–KNN ceramics. Substitution of KNN into the BNT–BT system decreased the remnant polarization, coercive field and the maximum strain percentage. The energy storage density values ~0.485 J/cm³ and 0.598 J/cm³ were obtained in the BNT–BT and BNT–BT–KNN ceramics, respectively. High induced strain% in the BNT–BT ceramics and the high energy storage density in the BNT–BT–KNN ceramics suggested about the usefulness of these systems for the actuator and the energy storage applications, respectively.     

The preparation and properties of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics

Two series (N-9 and N-18 series) of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics were designed. Nominal compositions of the glass samples in equivalent percent (eq%) are xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 91O: 9 N and xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 82O: 18 N (x=0, 2, 4, 6), respectively. The obtained samples were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Densities, Vickers hardness, fracture toughness, glass transition temperature, and thermal expansion coefficient data were established for each sample. Effect of Zr and N content on glass network structure, thermal and mechanical properties was investigated. It was found that the addition of zirconia is effective in preparing Y–Si–Al–O–N oxynitride glasses with lower glass transition temperature and higher hardness.     

Unique and contrasting mixed-metal lithium–calcium and lithium–barium hexamethyldisilazide complexes

Addition of lithium hexamethyldisilazide to calcium or barium bis(hexamethyldisilazide) in THF resulted in the synthesis of two unique but very different mixed-metal complexes: X-ray crystallography shows these to be, respectively, the heterobimetallic complex [Ca{N(SiMe₃)₂}₃Li(THF)] (1), containing two calcium–lithium bridging amide ligands and the remarkable co-crystalline compound [Ba{N(SiMe₃)₂}₂(THF)₃][Li₂{N(SiMe₃)₂}₂(THF)₂] (2).     

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.     

Synthesis and Structural Analysis of Co–Zn–Cd Ferrite by Williamson–Hall and Size–Strain Plot Methods

The work aimed at studying the structural properties of Cd-doped cobalt zinc ferrite (Co_0.5Zn_0.5Cd_0.2Fe_1.8O₄) prepared by simple, low-cost solid-state reaction method and characterized by XRD techniques. The X-ray analysis confirms the formation of ferrite particles with a cubic spinel structure. Crystallite size D, lattice constant a, micro strain ε, X-ray density Δ_X, dislocation density ρ _D , hopping lengths (L_A and L_B), bond lengths (A–O and B–O), ionic radii (r_A and r_B), texture coefficients [TC(hkl)], and mechanical properties are also reported.     

Microstructure and mechanical properties of TiC–TiN–Zr–WC–Ni–Co cermets

Cermet cutting tools are widely used for semi-finishing and finishing work on steel and cast iron. However, their brittleness is still an unavoidable limitation for their utilizations. Zirconium was added to improve the fracture toughness of Ti(C, N) based cermets. The microstructure and the fracture surfaces of cermets were studied by using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results reveal that Zr dissolved and formed solid solutions during the sintering process. The amount of grains with typical core/rim structure decreases and that of coreless grains increases with increasing Zr addition. Moreover, the fracture toughness is improved clearly due to the increased amount of the coreless grains, the spinodal decomposition in cermets, as well as the crack deflection and crack branching mechanisms. Additionally, hardness and relative density were also measured, respectively.     

Electrocaloric and pyroelectric properties of PZT and PMN–PNN–PZT thin films

The electrocaloric effects (EC) of PZT and PMN–PNN–PZT films were evaluated. PZT and PMN–PNN–PZT thin films with a thickness of 500 nm were fabricated by state-of-the-art chemical solution deposition from a precursor solution with PZT and (PMN?PNN)/PZT=30/70. The polarization hysteresis loop was found to be slim and nonlinear, with smaller hysteretic behavior compared with PZT. The pyroelectric properties evaluated from polarization change and current measurement show that the properties of PMN–PNN–PZT films are superior to those of non-doped PZT films. The electrocaloric temperature changes ΔT due to applied ΔE were calculated. PZT and PMN–PNN–PZT films exhibited ΔT of 2.1 K and 3.6 K at 237.5 °C under a field of 500 kV/cm, respectively. Thermal-electrical energy converters based on pyroelectric effects were investigated for energy harvesting and possible use in ultralow-power sensor modules. The possibilities of pyroelectric energy harvesting using these PZT films were also investigated.     

Measurement and Correlation of Liquid–Liquid Equilibrium Data for Ethanol–Water–KF and Ethanol–Water–K2CO3 Systems

The liquid–liquid equilibrium data for two ternary systems, ethanol–water–KF and ethanol– water–K2CO3, were determined at 25℃. Experiments show that by adding KF or K2CO3 into the ethanol–water system two phases are formed: an ethanol-rich phase with negligible salt and a water-rich phase with negligible ethanol, thus water can be separated out easily. A mathematical calculation of the liquid–liquid equilibrium data was carried out with the Pitzer theory on water activity in the aqueous phase, and with the Wilson or NRTL or UNIQUAC equations for that in the ethanol phase, which is in good agreement with experimental data.     

Preparation and properties of Ge–Ga–La–S–AgI chalcogenide glass

Chalcogenide glasses of 65GeS₂–(25–x)Ga₂S₃–10AgI–xLa₂S₃ (x=0, 1, 3, and 5 mol%) were fabricated through the traditional melt-quenching method. The effects of addition of La₂S₃ on physical, thermal and optical properties of the glass system were investigated. The results showed that the fabricated glasses possess considerably high glass transition temperature, exhibit improved mechanical property and excellent infrared transmission. A redshift at the visible absorbing cut-off edge is observed with increasing of La₂S₃ content. The direct and indirect optical band gap values are also calculated. Raman spectra analysis indicated that the band at 265 cm⁻¹ decreased in amplitude and a new peak at 230 cm⁻¹ was detected manifesting the formation of La-S bond in the network. In addition, the mid-infrared emission at 3.74 µm of the glasses doped with Tm³⁺ ions was achieved. The results indicated that the glasses are promising materials for mid-infrared applications such as imaging, remote sensing and lasers.