Adsorption and coalescence in mixed surfactant systems: Water−hydrocarbon interface

Major commercial uses of surfactants involve a mixture of these compounds. The properties of the monolayer formed at the water?hydrocarbon interface depend upon the interaction between the surfactant molecules. The presence of salt influences the interactions between the surfactants in the monolayer and in the micelle. In this work, these interactions in presence and in absence of a 1:1 salt were studied and the results were analyzed using the nonideal solution theory. An anionic, a cationic and a nonionic surfactant were used. The stability of emulsions is significantly affected by the interaction between the surfactants. To study this effect, coalescence of cyclohexane drops at a flat water?cyclohexane interface was studied in the mixed surfactant systems, and the results were compared with single surfactant systems. The effect of salt on coalescence time was studied. The results were analyzed using the film drainage and stochastic theories of coalescence. Seven film drainage models were used to predict the coalescence time, and the values predicted by these models were compared with the experimental data. The parameters of the stochastic model were analyzed based on the properties of the systems.     

Acid- and base-catalyzed epoxy-phenol thermosets from catechol,resorcinol and hydroquinone: A structure–property study

In order to better understand the design rules of epoxy–phenol thermosets we will report on the chemistry and (thermo)mechanical properties of cured epoxy–phenol thermoset films. Ortho-, meta- and para-isomers of dihydroxybenzene (DHB) were reacted with the diglycidyl ether of bisphenol A (DGEBA) in the presence of an acid catalyst or triphenylphosphine (PPh₃). The glass transition temperatures (T_g) of the cross-linked films decreases in the order of meta- (T_g = 115°C) > ortho- (T_g = 102°C) > para-DHB (T_g = 96°C) as measured by differential scanning calorimetry. Uniaxial tensile testing of cross-linked films showed excellent stress–strain behavior. The average ultimate strength values ranged from 65 to 82 MPa and the average values of the strain-at-break ranged from 4.8% to 6.9% at 25°C for all cross-linked films. When a PPh₃ was used, the network properties were profoundly different. The base catalyzed thermoset of DGEBA and meta-DHB shows a T_g of 85°C, which is 30°C lower than the T_g of the acid-catalyzed analog. Tensile films appear to be more ductile, as they exhibit a strain-at-break of 20%. The results of this study confirm that simple dihydroxybenzene hardeners can be used to prepare cross-linked films with excellent thermomechanical properties.     

Analysis of sulfoxylated methyl esters (Φ-MES): Sulfonic acid composition and isomer identification

Derivatization of a C₁₂Φ-methyl ester sulfonic acid by using iodide-trifluoroacetic anhydride in dimethylformamide in a one-step reaction yielded derivatized sulfonic thiotrifluoroacetates. The latter have been analyzed by gas chromatography-mass spectrometry (MS) and liquid chromatography-MS techniques so that, for the first time, the acid composition and the mono sulfonic acid isomer distribution are shown.     

Phase diagram study and thermodynamic modeling of the Na2O–Al2O3–ZrO2 system

The phase diagram of the Na₂O–Al₂O₃–ZrO₂ system was experimentally studied at 1500°C–1650°C by a classical equilibration/quenching method and differential thermal analysis followed by X-ray diffraction phase analysis and electron probe micro-analysis. A sealed Pt crucible was utilized to prevent the volatile loss of Na₂O during high-temperature phase equilibrium experiments and the hydration upon quenching. The phase diagram of the Na₂O–Al₂O₃–ZrO₂ system was revealed for the first time. Based on the present experimental data and available binary modeling results in literature, the thermodynamic modeling of the ternary system was performed using the Calculation of Phase Diagram method and the phase diagram of the entire the Na₂O–Al₂O₃–ZrO₂ system was constructed and the optimized thermodynamic properties for all solids and liquid phase within the ternary system were obtained.     

Polycarboxylate superplasticizers of acrylic acid–isobutylene polyethylene glycol copolymers: monomer reactivity ratios,copolymerization behavior and performance

Acrylic acid–isobutylene polyethylene glycol (AA-TPEG) copolymers are typical of polycarboxylate superplasticizers (PCEs). AA-TPEG copolymers are prepared via free-radical polymerization with potassium persulfate as the initiator. The obtained copolymers were characterized by gel permeation chromatography (GPC) and infrared spectra (FTIR). The GPC method can break through the former limitations of the instruments and receive instantaneous unreacted and instantaneous monomer concentrations and not the initial monomer feeds. Since TPEG monomer is highly bulky, the common calculation methods for determining monomer reactivity ratios in copolymerization based on terminal copolymerization equation are not suitable. However, this study created non-linear least squares curve fitting of terminal copolymerization equation (NLLSQ-T) and penultimate copolymerization equation (NLLSQ-P) methods, which used Python’s NumPy, SciPy, and SymPy libraries to generate code and did numerical computations, bringing greater accuracy of monomer reactivity ratios. The monomer reactivity ratios were calculated with Fineman–Ross, Kelen–Tüdös, YBR, NLLSQ-T, and NLLSQ-P methods and found to be r _AA = 10.888, r′ _AA = 1.131, r _TPEG = 0.012, and r′ _TPEG = 0.042 for AA-TPEG copolymers. Moreover, this study also explored specific copolymerization behavior of similar structure of copolymers with steric hindrance under penultimate copolymerization equation, such as dependence of the mole fractions in the copolymer on the mole fractions of unreacted monomers in solution, variation of copolymer compositions with conversion and sequence length distribution. The fluidity and flow loss of pastes containing PCEs were investigated, and the appropriate PCEs dosages resulted in a better workability of cement pastes.     

Ternary nucleation: kinetics and application to water–ammonia–hydrochloric acid system

The ternary nucleation of an ideal mixture of three alcohols and a non-ideal mixture of water, ammonia and hydrochloric acid, which is relevant in atmosphere, have been investigated theoretically. In the ideal mixture of three alcohols, the nucleation rates obtained using simplified kinetic approach are compared with the nucleation rates given by a detailed kinetic model. The simplified model is seen to underestimate nucleation rates by 2–3 orders of magnitude. This is mainly due to the crude estimate for the Zeldovich factor in the simplified model. We have proposed a modification to the simplified model. The improved model gives order-of-magnitude estimates for the nucleation rates. The ternary nucleation of water–ammonia–hydrochloric acid is studied with the improved model. The results have been compared with binary nucleation of water and ammonium chloride. The results show that water–ammonia–hydrochloric acid mixture is effectively a two-component system.     

Insights into the adsorption performance and mechanism of Cr(Ⅵ) onto porous nanocomposite prepared from gossans and modified coal interface:Steric,energetic,and thermodynamic parameters interpretations

Herein,iron oxide/hydroxides deposits(gossans) were utilized,for the first time,in the fabrication of magnetite nanoparticles(MNPs) to load modified coal(MC).The as-synthesized MNPs@MC composite was characterized via different techniques and utilized for the Cr(Ⅵ) remediation.Experimental studies supported by theoretical treatment were applied to offer a new overview of the Cr(Ⅵ) adsorption geometry and mechanism at 25-45℃.Experimental results suggested that the Cr(Ⅵ) uptake was mainly governed ...     

Structure–property relationship for poly(lactic acid) (PLA) filaments: physical,thermomechanical and shape memory characterization

Physical, thermomechanical, and shape memory properties of two different samples of poly(lactic acid) (PLA) multifilament yarns were determined using various complementary techniques. The birefringence and crystalline fraction of one sample was higher than the other filaments sample indicating higher molecular orientation and compactness. For both filaments, two distinct morphological features with different sizes in the order of few nanometers (less than 50 nm) were found using AFM and SAXS techniques. The glass transition temperature (T_g) of the samples were ranged from 61 °C to 76 °C depends on the sample and the methods of measurement. Partial storage modulus (E′) increase above T_gas well as additional small peak in loss modulus (E″) of the lower crystallinity sample was assigned to recrystallization. The multiple overlapped peaks in the E″ and tan δ curves and subsequent crystallization along with exothermic peak right after T_g suggests the existence of both relaxed and oriented amorphous regions. The rigid crystalline regions prevented the shrinkage and enhanced dimensional stability. Multifilament yarn with higher crystallinity and total molecular orientation showed higher modulus (both dynamic and static) and strength and lower elongation at break. The oriented non-crystalline regions in the multifilament yarn sample led to moderate modulus and strength along with high elongation at break. The shape recovery of both samples with different structural parameters stayed almost constant (~50 %) upon the deformation temperature rise.     

Degradation of surfactant used in iron mining by oxidation technique: Fenton,photo-Fenton,and H2O2/UV—A comparative study

Reuse of water in mining helps reduce the volume of tailings directed to dams, avoiding overloads and ruptures, as occurred in Brumadinho, Brazil. Water reuse in mining requires treatment mainly for removing the surfactant substances used. Photo-Fenton and UV/H₂O₂ showed 96% to 98% degradation results of anionic surfactants within 5 minutes, suggesting this technique is faster than biological systems that can take days. This paper aims to study the degradation of a surfactant used in the flotation process by UV/H₂O₂, Fenton, and photo-Fenton oxidation techniques. The compound was characterized by FTIR and MALDI-TOF. In degradation experiments, the variation in reactants concentrations was evaluated with hydrogen peroxide, iron sulphate heptahydrate, and oxalic acid. We used a synthetic solution of surfactant in the reverse flotation of ore with 180 mg/L. The reaction was monitored with TOC analysis and a spectrophotometer throughout the reaction. The UV/H₂O₂ and Fenton system were studied by varying peroxide and iron concentrations, with 120 minute tests. Additionally, photo-Fenton concentrations, the pH variation (1.5-8.0), temperature (15°C, 21°C, and 60°C), and time were evaluated. The results showed the most efficient degradation was that using photo-Fenton, which achieved total TOC removal using 4500 mg/L of peroxide and 364 mg/L of iron for 330 minutes, while the UV/H₂O₂ system achieved 29% and 49% TOC removal of the Fenton. It is verified that the oxidative processes can be applied to degrade the surfactants present in the water recovered from the flotation processes.     

Synthesis of new diacid monomers and poly(amide-imide)s: study of structure–property relationship and applications

Two diimide-diacid monomers 4,4′-bis[4″-(trimellitimido)phenyl isopropylidene-4″′-phenoxy]diphenyl sulfone and 4,4′-bis[4″-(trimellitimido)phenylisopropylidene-4″′-phenoxy] were synthesized. The structures of the monomers were characterized by FT-IR and ¹H-NMR spectroscopy. A series of novel poly(amide-imide)s were prepared from this two diacids and aromatic diamines through phosphorylation reaction. The PAIs were characterized by FT-IR, ¹H-NMR, XRD, TGA, and DSC, solution viscosity, solubility test and electrical properties. Poly(amide-imide)s showed excellent solubility due to the presence of flexible groups and isopropylidene unit in the polymer backbone. They also exhibited good thermal stability and the temperatures at which 10% weight loss occurred in the range 385–465 °C. These PAIs found to have a dielectric constant in the range 3.25–4.20 at 10 kHz and have excellent electrical insulation character and can be used as insulation materials for electrical items operating at elevated temperatures.     

EPR study on oxygen handling properties of ceria, zirconia and Zr–Ce (1 : 1) mixed oxide samples

The characteristics of ceria, zirconia and Zr–Ce (1 : 1 molar ratio) samples prepared by using inverse microemulsions have been studied to obtain information on the modifications produced in the oxygen handling properties of the single oxides by the formation of the mixed oxide. The structural characteristics of the samples are compared on the basis of XRD and Raman spectroscopy data, which show that the Zr–Ce sample forms a homogeneous mixed oxide structure corresponding to the (pseudocubic) tetragonal phase t″ while CeO₂ presents, as expected, a cubic fluorite structure and ZrO₂ is formed mainly by a tetragonal phase with only traces of the thermodynamically most stable monoclinic phase. Evaluation by EPR of the type and intensity of superoxide radicals generated upon oxygen adsorption on the outgassed samples reveals a higher surface reducibility in the mixed oxide sample, associated vacancies defects being generated on it in higher amounts and at lower temperatures than on pure ceria. It is also shown that both Ce and Zr ions participate in the oxygen chemisorption process on the mixed oxide sample, actually giving rise to much larger amounts of O₂ ^-–Zr⁴⁺ species than the pure ZrO₂ sample; the latter species show a higher thermal stability than O₂ ^-–Ce⁴⁺ species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,characterization and correlation with the catalytic activity of efficient mesoporous niobia and mesoporous niobia–zirconia mixed oxide catalyst system

Mesoporous mixed oxide has always remained as a subject of interest due to diffusion relaxation and generation of new surface potential and acidity by mixing of different stoichiometries of metal oxide. To deliver more insight on niobia based catalyst, herein, we have synthesized mesoporous niobia and five different mole ratios of niobia–zirconia mixed oxide. The catalysts were characterized by XRD, N₂-physisorption, FTIR, UV–Vis and NH₃-TPD techniques. Less distorted NbO₆ octahedra and NbOH or Nb–OH–Zr are found to act as Bronsted center responsible for reaction. The results established the role of Kung model to generate acidic sites in mesoporous mixed oxide.     

Synthesis,structure and luminescent property of a new europium-based coordination polymer constructed from biphenyl-3,4′,5-tricarboxylic acid

A new 3D lanthanide metal–organic framework Eu(BPT)(DMF)(H₂O)•(H₂O)_0.5] (1) has been synthesized by self-assembly of Eu(III) ions and ligand biphenyl-3, 4′, 5-tricarboxylate under solvothermal reaction conditions. X-ray crystallography reveals that 1 exhibits a (3, 6)-connected topology, with dinuclear europium clusters as 6-connected nodes and C₂-symmetric ligands BPT as 3-connected nodes. In addition, the luminescence sensitization of 1 via excitation of the ligand is highly efficient.     

Thermo-responsive block copolymer micelle-supported (S)-α,α-diphenylprolinol trimethylsilyl ether for asymmetric Michael addition of nitroalkenes and aldehydes in water

An amphiphilic block copolymer PNIPAM₅₃-b-(PS₃₀-co-P4AMS₁₀) was facilely prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. The immobilization of (S)-α,α-diphenylprolinol trimethylsilyl ether onto the block copolymers was then performed through using copper-catalyzed alkyne-azide cycloaddition (CuAAC), and the generating amphiphilic diblock copolymer supported chiral catalyst PNIPAM₅₃-b-(PS₃₀-co-P4AMS₁₀)/proTMS was self-assembled into micelles with regular diameters about 50 nm in aqueous solution. The micellar catalyst was further used for the asymmetric Michael reaction between propanal and trans-β-nitrostyrene in water. Using only 1 mol% micellar catalyst, the corresponding Michael addition products could be obtained in good yields and high enantioselectivities as well as good diastereoselectivities. In addition, this micellar catalyst could be reused at least for four times. Moreover, the micellar catalyst could be applied for the asymmetric addition reaction of 4-chlorocinnamyl aldehyde and nitromethane, and thus constructing the baclofen pharmaceutical intermediate.     

From C–S–H to C–A–S–H: Experimental study and thermodynamic modelling

It has long been known that the stoichiometry of C–S–H varies with the calcium hydroxide concentration in solution. However, this issue is still far from understood. We revisit it in both experimental and modelling aspects. A careful analysis of the solubility confirms the existence of three different C–S–H phases, defined as Ca₄H₄Si₅O₁₆, Ca₂H₂Si₂O₇ and Ca₆(HSi₂O₇)₂(OH)₂, respectively. The variation of the Ca/Si ratio of the three phases has been described by surface reactions: the increase of the Si content is accounted for by silicate bridging, the increase of calcium content and the surface charge are accounted for by reactions involving silanol groups via deprotonation and complexation with calcium. In the presence of Al in solution, the uptake of Al by C–S–H is experimentally observed. The Al content increases with Al concentration. C–A–S–H formation is modelled by the competition between silicate and aluminate tetrahedra for the bridging of the dimeric silicates in C–S–H.     

Band gap engineering and microwave dielectric properties evolution of mixed (Sr,La, Ce) TiMgO3 titanate–aluminate system

A mixed perovskite titanate-aluminate [(1-x)(Sr_0.6La_0.2Ce_0.2Ti_0.8Mg_0.2O₃)-xNdAlO₃ for x = 0.1 to 0.4] solid solution was successfully synthesized. X-ray diffraction patterns (XRD) and Rietveld refinement results indicated a stable perovskite phase with a cubic structure, in which Nd³⁺ occupies the A-site randomly while Al³⁺ occupies the B-site. No additional reflection spots (superlattice reflections) were detected in the HRTEM pattern (see SAED), confirming the cubic symmetry. All samples showed small Urbach tails, mainly due to compositional disorder. Microstructural analysis based on atomic force microscopy (AFM) showed no traces of impurity phases. For x = 0.4, excellent microwave dielectric properties (MWD) are obtained with a quality factor (Q × f) of 37,131 GHz at f = 5.2801 GHz, relative permittivity (ε_r) of 43, and temperature coefficient of resonant frequency (τ_f) of +1.3 ppm/°C. Variations in ε_r, Q × f values, and τ_f may be related to changes in relative density (ρ_rel), ion polarizability, optical band gap, and tolerance factor, respectively.     

Oxidative dehydrogenation of n-butane: a comparative study of thermal and catalytic reaction using Fe–Zn mixed oxides

In order to investigate how the presence of surface hydroxyl groups on oxide surfaces affects the interaction with the supported metal, we have modified a well-ordered alumina film on NiAl(110) by Al deposition and subsequent exposure to water. This procedure yields a hydroxylated alumina surface as revealed by infrared and high-resolution electron energy loss spectroscopy. By means of scanning tunneling microscopy, we have studied the growth of rhodium on the modified film at 300 K. Clear differences in the particle distribution and density are observed in comparison to the clean substrate. While, in the latter case, decoration of domain boundaries as typical defects of the oxide film governs the growth mode, a more isotropic island distribution and a drastically increased particle density is found on the hydroxylated surface. From infrared data, it can be deduced that the growth is connected with the consumption of the hydroxyl groups due to the interaction between the metal deposit and the hydroxylated areas. This finding is in line with photoemission results published earlier. This revised version was published online in July 2006 with corrections to the Cover Date.     

The CO2 absorption and desorption performance of the triethylenetetramine + N,N-diethylethanolamine + H2O system

Post-combustion CO₂ capture (PCC) process faces significant challenge of high regeneration energy consumption. Biphasic absorbent is a promising alternative candidate which could significantly reduce the regeneration energy consumption because only the CO₂-concentrated phase should be regenerated. In this work, aqueous solutions of triethylenetetramine (TETA) and N,N-diethylethanolamine (DEEA) are found to be efficient biphasic absorbents of CO₂. The effects of the solvent composition, total amine concentration, and temperature on the absorption behavior, as well as the effect of temperature on the desorption behavior of TETA-DEEA-H₂O system were investigated. An aqueous solution of 1 mol·L^-1 TETA and 4 mol·L^-1 DEEA spontaneously separates into two liquid phases after a certain amount of CO₂ is absorbed and it shows high CO₂ absorption/desorption performance. About 99.4% of the absorbed CO₂ is found in the lower phase, which corresponds to a CO₂ absorption capacity of 3.44 mol·kg^-1. The appropriate absorption and desorption temperatures are found to be 30℃ and 90℃, respectively. The thermal analysis indicates that the heat of absorption of the 1 mol·L^-1 TETA and 4 mol·L^-1 DEEA solution is -84.38 kJ·(mol CO₂)^-1 which is 6.92 kJ·(mol CO₂)^-1 less than that of aqueous MEA. The reaction heat, sensible heat, and the vaporization heat of the TETA-DEEA-H₂O system are lower than that of the aqueous MEA, while its CO₂ capacity is higher. Thus the TETA-DEEA-H₂O system is potentially a better absorbent for the post-combustion CO₂ capture process.