Journal of Colloid And Interface Science (v.300, #2)
Editorial Board (CO1).
A characterization study of some aspects of the adsorption of aqueous Co2+ ions on a natural bentonite clay by T. Shahwan; H.N. Erten; S. Unugur (447-452).
The natural bentonite used in this study contained montmorillonite in addition to low cristobalite. The uptake of aqueous Co2+ ions was investigated as a function of time, concentration, and temperature. In addition, the change in the interlayer space of montmorillonite was analyzed using XRPD, and the distribution of fixed Co2+ ions on the heterogeneous clay surface was recorded using EDS mapping. The sorbed amount of Co2+ appeared to closely follow Freundlich isotherm, with the sorption process showing apparent endothermic behavior. The relevance of the apparent Δ H o values is briefly discussed. Analysis of the Co-sorbed bentonite samples using SEM/EDS showed that the montmorillonite fraction in the mineral was more effective in Co2+ fixation than the cristobalite fraction. XRPD analysis demonstrated that the interlayer space of montmorillonite was slightly modified at the end of sorption.X-ray diffraction patterns of montmorillonite before (i) and after Co2+ sorption (ii, iii, iv). The figures show slight changes in the d 001 features of montmorillonite following sorption.
Keywords: Co2+; Bentonite; Adsorption;
Some remarks on the calculation of the pore size distribution function of activated carbons by Piotr A. Gauden; Artur P. Terzyk; Piotr Kowalczyk (453-474).
Different authors investigated the effects of geometric and energetic heterogeneities on adsorption and on carbon characterization methods. In most theoretical studies carbon structure is modeled as parallel infinite graphite walls that form ideal slit-shaped pores of the fixed widths. In the literature there is the lack of systematic studies showing the influence of pore structural and Lennard-Jones (LJ) potential parameters on the pore-size distribution functions. Moreover, the parameters characterizing the properties of the adsorbed phase and the heterogeneity of the adsorbent surface should be taken into account. The Nguyen and Do method with proposed by us ASA algorithm, were utilized for the assessment of the porosity from the series of almost few thousands numerically generated local adsorption isotherms. The values of the mentioned-above parameters are varied over the wide range (ca. ±20%) of the reference ones. Different types of the theoretical and experimental adsorption isotherms (nitrogen at 77 K) were taken into account as the global ones. They were related to the mechanism of the primary, secondary or mixed micropore filling. The variations in some above-mentioned parameters have significant effects only for PSDs (and for average pore widths) corresponding to the primary micropore filling mechanism. On the other hand, for the process of the secondary micropore filling, the influence of these parameters (without the BET coefficient for adsorption on a “flat” surface, c s , B ) is rather insignificant. Nevertheless the differences between local and global adsorption isotherms (in the whole range of relative pressures) the absence of micropores having pore half width equal to ca. 1 nm on PSDs was observed for studied adsorbate–adsorbent systems with exceptions of the strictly microporous adsorbents and/or the low values of c s , B . Comparison of the experimental data with the generated theoretical isosteric enthalpy of adsorption indicates that the phenomenal uptake observed from experiment can be explained in terms of the reasonable solid–fluid interaction parameters. Therefore, we varied the heterogeneity of the adsorbent surface via the strength and the range of the solid–fluid potential and the parameter c s , B in order to reproduce the experimental data of enthalpy of adsorption. Note that similar procedure was applied by Wang and Johnson to reproduce some hydrogen adsorption data measured for carbon nanofibres. The analysis of the obtained results shows that the selection of the values of the parameters of the intermolecular interactions and the quantities characterizing the properties of the adsorbed phase and the heterogeneity of the adsorbent walls for molecular simulations should be made with care and the influence of possible errors should be considered.
Keywords: Adsorption; Activated carbon; Porosity; Micropores; Adsorption; Thermodynamics;
AFM study of forces between silica, silicon nitride and polyurethane pads by Igor Sokolov; Quy K. Ong; Hasan Shodiev; Nina Chechik; David James; Mike Oliver (475-481).
Interaction of silica and silicon nitride with polyurethane surfaces is rather poorly studied despite being of great interest for modern semiconductor industry, e.g., for chemical–mechanical planarization (CMP) processes. Here we show the results from the application of the atomic force microscopy (AFM) technique to study the forces between silica or silicon nitride (AFM tips) and polyurethane surfaces in aqueous solutions of different acidity. The polyurethane surface potentials are derived from the measured AFM data. The obtained potentials are in rather good agreement with measurements of zeta-potentials using the streaming-potentials method. Another important parameter, adhesion, is also measured. While the surface potentials of silica are well known, there are ambiguous results on the potentials of silicon nitride that is naturally oxidized. Deriving the surface potential of the naturally oxidized silicon nitride from our measurements, we show that it is not oxidized to silica despite some earlier published expectations.Surface potentials of polyurethane pads used in chemical–mechanical planarization (CMP) process are derived from measured AFM data as well as using the streaming-potentials method. Data are shown for different acidity. Interaction of silica and silicon nitride probe with the pads are also measured.
Keywords: AFM; Surface potential; Surface forces; DLVO; Silica; Silicon nitride; Chemical–mechanical planarization;
Comparison of complexed species of Eu in alumina-bound and free polyacrylic acid: A spectroscopic study by G. Montavon; C. Hennig; P. Janvier; B. Grambow (482-490).
The speciation of Eu complexed with polyacrylic acid (PAA) and alumina-bound PAA (PAAads) was studied at pH 5 in 0.1 M NaClO4. Structural parameters were obtained from 7F0 →5D0 excitation spectra measured by laser-induced fluorescence spectroscopy as well as from Eu LIII-edge extended X-ray absorption fine structure (EXAFS) spectra. The coordination mode was also investigated by infrared spectroscopy. To elucidate the nature of the complexed species, Eu–acetate complexes were used as references. The spectroscopic techniques show that two carboxylate groups with 2–3 (EuPAA) and 4–5 (EuPAAads) water molecules are coordinated to Eu in the first coordination sphere. For EuPAAads, the coordination between carboxylate groups and Eu appears to be bidendate. A similar coordination is probable for EuPAA but the EXAFS data indicate a slightly distorted coordination. The results show that the degree of freedom of carboxylate groups is not the same for free or adsorbed PAA. For PAA, the degree of freedom is constrained by the flexibility of the methylene chain. When PAA is adsorbed on alumina, the polymer chains cannot any more be treated as independent chains. One may rather assume formation of aggregates that form an organic layer at the mineral surface presenting a complex arrangement of carboxylate groups.The question addressed in this study is to assess the effect of the adsorption of an organic polyelectrolyte onto a mineral phase on its complexation properties for metal ions.
Keywords: Polyacrylic acid; Eu; LIFS; FTIR; EXAFS; Speciation; Adsorption; Ternary system;
Removal of phosphate from aqueous solution by zeolite synthesized from fly ash by Jiangang Chen; Hainan Kong; Deyi Wu; Zhanbo Hu; Zaosheng Wang; Yanhua Wang (491-497).
Fifteen Chinese fly ashes were converted hydrothermally into zeolites, and phosphate immobilization capacity (PIC) of the synthesized zeolites and the corresponding raw fly ashes were determined using an initial phosphate concentration of 1000 mg/L. Results showed that there was a remarkable increase in PIC (from 1.2 to 7.6 times) following the synthesis process. Fractionation of immobilized phosphorus indicated that Fe + Al-P increased most significantly and consistently among all the phosphorus fractions following the conversion of fly ash to zeolite. The PIC and Ca + Mg-P were closely related to Ca content (with r values of 0.9683 and 0.9651, respectively) rather than Mg content (with r values of 0.3920 and 0.3212, respectively). The r values of PIC and Fe + Al-P with Fe content (with r values of 0.4686 and 0.6385, respectively) were higher than those with Al content (with r values of −0.7857 and −0.3770, respectively). Although calcium and iron components were mainly involved in phosphate immobilization, there was no significant change of Ca and Fe content following the conversion of fly ash to zeolite. Increase in dissociated Fe2O3 and specific surface area probably accounted for the enhancement in PIC of synthesized zeolites compared with corresponding fly ashes. The PIC value of zeolites showed a significant correlation with dissociated Fe2O3 ( r = 0.6186 ). The specific surface area increased 26.0–89.4 times as a result of the conversion of fly ash to zeolite. The maximum removal of phosphate occurred within different pH ranges for zeolites which were synthesized from high, medium and low calcium fly ashes and this behavior was explained by the reaction of phosphate with calcium and iron components.Fly ashes with different calcium contents were converted hydrothermally into zeolites, and the maximum phosphate immobilization capacities of the synthesized zeolites occurred within different pH range.
Keywords: Fly ash; Synthesized zeolite; Phosphate; Immobilization; Composition; Correlation;
Removal of phenol from aqueous phase by using neutralized red mud by Ali Tor; Yunus Cengeloglu; Mehmet Emin Aydin; Mustafa Ersoz (498-503).
The objective of this study is to remove the phenol from aqueous solution by using the neutralized red mud in batch adsorption technique. The study was carried out as functions of contact time, pH, initial phenol concentration, red mud dosage and effect of salt addition. The experiments demonstrated that maximum phenol removal was obtained in a wide pH range of 1–9 and it takes 10 h to attain equilibrium. The adsorption data was analyzed using the Langmuir and the Freundlich isotherm models and it was found that the Freundlich isotherm model represented the measured sorption data well. The influence of addition of salt on phenol removal depends on the relative affinity of the anions for the red mud surface and the relative concentrations of the anions.Effect of initial phenol concentration on the removal of phenol. Red mud dose: 8 g/L, pH 6, agitation speed: 700 rpm and temperature: 25 ± 1 °C.
Keywords: Adsorption; Equilibrium isotherm; Freundlich isotherm; Langmuir isotherm; Phenol; Red mud;
Sulfate adsorption and surface precipitation on a volcanic ash soil (allophanic andisol) by Munehide Ishiguro; Tomoyuki Makino; Yasunobu Hattori (504-510).
Sulfate strongly adsorbs on metal oxides and soils with variable charges. However, its surface precipitation has not been clearly evaluated and its adsorption mechanism has been in dispute. In the present study, an allophanic andisol, a typical volcanic ash soil having both negative and positive variable charges, was used to identify the adsorption mechanism of sulfate. Sulfate adsorption isotherms were obtained by a batch method at pH values of 4, 5, 6, and 7 in a wide range of concentrations in an Na–H–SO4–OH system. Theoretical isotherms were applied to the measured values for the evaluation. The surface precipitation was detected by the measured adsorption isotherms, and the BET isotherm confirmed the presence of multilayer adsorption. Stronger and weaker adsorption sites were suggested by using the Langmuir isotherm for the monolayer adsorption. The adsorption energies obtained from the Langmuir equation and recent spectroscopic analysis suggested that the stronger adsorption corresponded to an inner-sphere surface complex and that the weaker adsorption corresponded to outer-sphere surface complexation. The BET and Langmuir equations showed three types of adsorption mechanisms for the sulfate adsorption on the soil.The BET and Langmuir equations showed three types of adsorption mechanisms for the sulfate adsorption on the soil in an Na–H–SO4–OH system.
Keywords: Surface precipitation; Sulfate adsorption; BET equation; Langmuir equation; Allophanic soil; Variable charge; Adsorption isotherm; Multilayer adsorption;
Kinetics of phosphate adsorption on goethite: Comparing batch adsorption and ATR-IR measurements by Carina Luengo; Maximiliano Brigante; Juan Antelo; Marcelo Avena (511-518).
The adsorption kinetics of phosphate on goethite has been studied by batch adsorption experiments and by in situ ATR-IR spectroscopy at different pH, initial phosphate concentrations and stirring rates. Batch adsorption results are very similar to those reported by several authors, and show a rather fast initial adsorption taking place in a few minutes followed by a slower process taking place in days or weeks. The adsorption kinetics could be also monitored by integrating the phosphate signals obtained in ATR-IR experiments, and a very good agreement between both techniques was found. At pH 4.5 two surface complexes, the bidentate nonprotonated (FeO)2PO2 and the bidentate protonated (FeO)2(OH)PO complexes, are formed at the surface. There are small changes in the relative concentrations of these species as the reaction proceeds, and they seem to evolve in time rather independently. At pH 7.5 and 9 the dominating surface species is (FeO)2PO2, which is accompanied by an extra unidentified species at low concentration. They also seem to evolve independently as the reaction proceeds. The results are consistent with a mechanism that involve a fast adsorption followed by a slow diffusion into pores, and are not consistent with surface precipitation of iron phosphate.The adsorption kinetics and species evolution of phosphate on goethite can be monitored by ATR-IR.
Keywords: Adsorption kinetics; Oxide–water interface; Surface complexes; Adsorption mechanism;
Adsorption of hexyl- α , ω -bis(dodecyldimethylammonium bromide) gemini surfactant on silica and its effect on wettability by Meiwen Cao; Xiaoyan Song; Jinben Wang; Yilin Wang (519-525).
The adsorption of hexyl- α , ω -bis(dodecyldimethylammonium bromide) (C12C6C12Br2) gemini surfactant on silica and its effect on wettability have been studied. The structure of the adsorbed aggregates experiences an evolving course with the increase of C12C6C12Br2 concentration. It is from no aggregates to circular islands, then to semicontinuous islands, and at last to the two-bilayer structure. No matter what kind of aggregates are in existence, their thickness values are to be the same 3.3 ± 0.3 nm . The fraction of silica surface covered by the surfactant aggregates also varies from nearly zero at 0.05 mM to ∼0.92 at 5.0 mM. The variation of contact angle against C12C6C12Br2 concentration shows two distinct regions. The upward shift indicates that the surfactant molecules are adsorbed with their hydrophobic tails facing air upon increasing concentration, while the downward shift reveals that the surfactant aggregates are in existence with the hydrophilic headgroups facing air. IR spectra suggest that two different courses are involved with the increase of the surfactant concentration. One possible course is that the surfactant tails pack more closely and orderly, and the other may be that the spacer changes from stretched profile to bended conformation upon increasing the surfactant concentration.
Keywords: Gemini surfactant; Adsorption; Surfactant aggregates; Silica surface; Solid–solution interface; AFM;
Kinetics and thermodynamics of bromophenol blue adsorption by a mesoporous hybrid gel derived from tetraethoxysilane and bis(trimethoxysilyl)hexane by Laijiang You; Zhijian Wu; Taehoon Kim; Kangtaek Lee (526-535).
A mesoporous hybrid gel is prepared with tetraethoxysilane (TEOS) and bis(trimethoxysilyl)hexane (TSH) as precursors without using any templating agent. Nitrogen sorption, TG-DTA, FTIR, and point of zero charge (PZC) measurement are used to characterize the gel. The gel has a specific surface area of 695 m2 g−1 with a pore size of 3.5 nm, a pore volume of 0.564 cm3 g−1, and a point of zero charge (PZC) of 6.2. The kinetics and thermodynamics of bromophenol blue (BPB) adsorption by the gel in aqueous solution are investigated comprehensively. The effects of initial BPB concentration, pH, ionic strength, and temperature on the adsorption are investigated. Kinetic studies show that the kinetic data are well described by the pseudo-second-order kinetic model. Initial adsorption rate increases with the increase in initial BPB concentration and temperature. Adsorption activation energy is found to be 62.5–67.5 kJ mol−1 depending on the initial BPB concentration. Internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in the initial BPB concentration, solution acidity, and ionic strength, but decreases with the increase in temperature. The thermodynamic analysis indicates that the adsorption is spontaneous and exothermic. The adsorption isotherms can be well described with Freundlich equation indicating the heterogeneity of the hybrid gel surface. Electrostatic and hydrophobic interactions are suggested to be the dominant mechanism for adsorption.
Keywords: Bromophenol blue; Adsorption kinetics; Adsorption thermodynamics; Adsorption mechanism; Mesoporous hybrid gel; Bis(trimethoxysilyl)hexane;
The inhibition of calcium carbonate crystal growth by the cysteine-rich Mdm2 peptide by E. Dalas; A. Chalias; D. Gatos; K. Barlos (536-542).
The crystal growth of calcite, the most stable calcium carbonate polymorph, in the presence of the cysteine-rich Mdm2 peptide (containing 48 amino acids in the ring finger configuration), has been investigated by the constant composition technique. Crystallization took place exclusively on well-characterized calcite crystals in solutions supersaturated only with respect to this calcium carbonate salt. The kinetic results indicated a surface diffusion spiral growth mechanism. The presence of the Mdm2 peptide inhibited the crystal growth of calcite by 22–58% in the concentration range tested, through adsorption onto the active growth sites of the calcite crystal surface. The kinetic results favored a Langmuir-type adsorption model, and the value of the calculated affinity constant was k aff = 147 × 10 4 dm 3 mol −1 , a ads = 0.29 .
Keywords: Calcium carbonate; Calcite; Inhibition; Mdm2 peptide;
Design of an NO photoinduced releaser xerogel based on the controlled nitric oxide donor trans-[Ru(NO)Cl(cyclam)](PF6)2 (cyclam = 1,4,8,11-tetraazacyclotetradecane) by Kleber Queiroz Ferreira; José F. Schneider; Pedro A.P. Nascente; Ubirajara Pereira Rodrigues-Filho; Elia Tfouni (543-552).
The immobilization and properties of the nitric oxide donor trans-[Ru(NO)Cl(cyclam)](PF6)2, Ru―NO, entrapped in a silica matrix by the sol–gel process is reported herein. The entrapped nitrosyl complex was characterized by spectroscopic (UV–vis, infrared (IR), X-ray photoelectron, and 13C and 29Si MAS NMR) and electrochemical techniques. The entrapped species exhibit one characteristic absorption band in the UV–vis region of the electronic spectrum at 354 nm and one IR ν NO stretching band at 1865 cm−1, as does the Ru―NO species in aqueous solution. Our results show that trans-[Ru(NO)Cl(cyclam)](PF6)2 can be entrapped in a SiO2 matrix with preservation of the molecular structure. However, in a SiO2/SiNH2 matrix, the complex undergoes a nucleophilic attack by the amine group at the nitrosonium. Irradiation of the complex, entrapped in the SiO2 matrix, with light of 334 nm, resulted in NO release. The material was regenerated to its initial nitrosyl form by reaction with nitric oxide. Trans-[Ru(NO)Cl(cyclam)]2+ is entrapped in a SiO2 xerogel without loss of integrity, delivers NO under irradiation with light and it can be regenerated. Amino functionalized xerogel reacts with the coordinated NO.
Keywords: Nitric oxide; Sol–gel; Xerogel; Ruthenium; Nitrosyl; Controlled; Photochemistry; Cyclam; Silica; Aminopropylsilica; Nucleophilic; Attack;
Behavior of yeast cells in aqueous suspension affected by pulsed electric field by H. El Zakhem; J.-L. Lanoisellé; N.I. Lebovka; M. Nonus; E. Vorobiev (553-563).
This work discusses pulsed electric fields (PEF) induced effects in treatment of aqueous suspensions of concentrated yeast cells (S. cerevisiae). The PEF treatment was done using pulses of near-rectangular shape, electric field strength was within E = 2 – 5 kV / cm and the total time of treatment was t PEF = 10 −4 – 0.1 s . The concentration of aqueous yeast suspensions was in the interval of C Y = 0 – 22 (wt%), where 1% concentration corresponds to the cellular density of 2 × 10 8 cells / mL . Triton X-100 was used for studying non-ionic surfactant additive effects. The electric current peak value I was measured during each pulse application, and from these data the electrical conductivity σ was estimated. The PEF-induced damage results in increase of σ with t PEF increasing and attains its saturation level σ ≈ σ max at long time of PEF treatment. The value of σ max reflects the efficiency of damage. The reduced efficiency of damage at suspension volume concentration higher than φ Y ≈ 32 vol% is explained by the percolation phenomenon in the randomly packed suspension of near-spherical cells. The higher cytoplasmic ions leakage was observed in presence of surfactant. Experiments were carried out in the static and continuous flow treatment chambers in order to reveal the effects of mixing in PEF-treatment efficiency. A noticeable aggregation of the yeast cells was observed in the static flow chamber during the PEF treatment, while aggregation was not so pronounced in the continuous flow chamber. The nature of the enhanced aggregation under the PEF treatment was revealed by the ζ-potential measurements: these data demonstrate different ζ-potential signs for alive and dead cells. The effect of the electric field strength on the PEF-induced extraction of the intracellular components of S. cerevisiae is discussed.This work discusses the PEF induced effects in treatments of concentrated yeast cells (S. cerevisiae) aqueous suspensions. The nature of enhanced aggregation under the PEF treatment was revealed by the measurements of ζ-potentials: the data evidence the difference of ζ-potential signs between alive and dead cells.
Keywords: Electric fields; Aqueous suspensions; Electrical conductivity; Percolation; Saccharomyces cerevisiae; Yeast; Non-ionic surfactant; Triton X-100;
Easy preparation and characterization of highly fluorescent polymer composite microspheres from aqueous CdTe nanocrystals by Minjie Li; Hao Zhang; Junhu Zhang; Chunlei Wang; Kun Han; Bai Yang (564-568).
Fluorescent microspheres were easily fabricated from aqueous CdTe nanocrystals (NCs). The NCs, which had negative charges on the surface, were first extracted to chloroform by cationic surfactant octadecyl-p-vinyl-benzyldimethylammonium chloride (OVDAC) and then swollen into performed polystyrene (PS) microspheres. Through this method, strong photoluminescence (PL) of aqueous NCs was inherited in the resultant composite microspheres. Moreover, the NCs were firmly stabilized in the microspheres, withstanding not only polar solvents but also nonpolar solvents. UV–vis spectrum, PL spectrum, TEM, and confocal fluorescence microscopy were used to characterize the product.
Keywords: CdTe nanocrystals; Surface coating; Swelling; Polymer; Fluorescent microspheres;
Wet-chemical synthesis of crystalline BaTiO3 from stable chelated titanium complex: Formation mechanism and dispersibility in organic solvents by Nimai Chand Pramanik; Sang Il Seok; Bok Yeop Ahn (569-576).
Crystalline barium titanate nanoparticles were synthesized in solution at low temperature (70 °C) from acetylacetone chelated titanium complex and barium hydroxide. Very fine crystalline solids were characterized to cubic phase of BaTiO3 by X-ray diffraction studies of the air-dried samples. It was observed that the crystalline barium titanate was formed in solution at Ba/Ti molar ratio ⩾2.5. The dependence of the reaction temperature and the Ba(OH)2 concentration (in terms of Ba/Ti molar ratio) on formation of crystalline BaTiO3 in solution-phase was studied, and a plausible mechanism toward the formation of crystalline BaTiO3 was also proposed. Crystallite sizes of the BaTiO3 were found to be in the range 33–50 nm, while the average particle sizes, measured by dynamic light scattering method were in the range 70–100 nm. The crystalline BaTiO3 prepared from acetylacetone chelated titanium complex was highly dispersible in organic medium such as N-methyl-2-pyrillidone (NMP) and N , N -dimethyl formamide (DMF).The crystalline BaTiO3 prepared from acetylacetone chelated titanium complex with barium hydroxide in alcohol–water medium was highly dispersible in organic medium such as N-methyl-2-pyrillidone (NMP) and N , N -dimethyl formamide (DMF).
Keywords: Crystalline BaTiO3; Wet-chemical synthesis; Chelated titanium complex; Formation mechanism; Dispersion in organic solvent;
Steady electro-optic characteristics of noninteracting colloidal particles by Maria Stoimenova; Svetla Miteva (577-583).
In previous papers on the electro-optic effects of β-FeOOH particles we proposed a new procedure for analysis of the low frequency behavior of charged particles. The procedure is based on comparison of characteristic field intensity curves on an appropriate scale and helps to test the dependence of the slow effects on particle surface electric polarizability (relaxing in the kilohertz domain). The results stimulated us to test the applicability of the method to other samples and to reconsider the literature data on the electro-optic behavior of charged colloids in the hydrodynamic domain. The aim of the present paper is to demonstrate on a series of samples similar features of the electro-optic responses of charged particles in the relaxation interval of particle rotation. The analysis leads to a new hypothesis for explanation of the complicated low frequency behavior of charged particles. The superposition of two slow effects (linear and quadratic with field intensity), relaxing in the relaxation interval of particle rotation, can explain the complicated frequency curves in this domain. One of the slow effects is observed for all polarizable particles. It is of negative sign and displays the features of an induced dipole effect dependent on the “kilohertz” induced moment. It corresponds to a slow stage of the surface polarization process related to electrokinetic charge. The linear slow effect shows permanent dipole like behavior and appears only at certain ionic content of the medium. It shows no direct dependence on counterion mobility and on the “kilohertz” induced moment and is probably due to surface charge nonuniformity.
Keywords: Electro-optic spectroscopy of colloids; Low frequency anomalies in colloidal electro-optics;
Preparation, characterization and surface study of poly-epsilon caprolactone magnetic microparticles by Misara Hamoudeh; Hatem Fessi (584-590).
Magnetic microparticles (MMP) have shown to be applied in increasing applications in various fields of biotechnology and medicine. One of their most promising utilization is the magnetic resonance imaging (MRI) in which superparamagnetic substances as magnetite are used in a nanometric size (less than 30 nm) and encapsulated within locally injected biodegradable microparticles. In this paper, magnetite has been encapsulated in polymer-based microparticles. The MMP have been prepared by an emulsion evaporation method. The different parameters influencing the particles size were investigated. The size was found to decrease as the stirring speed or the stabilizer amount (to certain limit) increases. The encapsulation efficacy was more than 90% yielding a magnetite loading of up to 30%, w/w. The X-ray photoelectron spectroscopy (XPS) showed less than 2% of iron atoms at the microparticles surface. The zeta potential response of MMP towards pH variation was very similar to that of magnetite-free microparticles confirming the encapsulation of magnetite within the microparticles. X-ray diffraction assays showed that magnetite crystalline structure was conserved after emulsification and MMP formation. Vibration simple magnetometer (VSM) showed a superparamagnetic profile of the MMP with a magnetic saturation increasing with the increased magnetite amount in the microparticles. These magnetic microparticles can enable clinicians to control microparticles distribution after a local administration in tumors by MRI. They can also be administered to target a defined tumor area by focusing a magnetic field on the surfaces covering the cancerous tissue.Magnetic microparticles with superparamagnetic behavior can be used in various application in medicine and biotechnology. MRI and magnetic targeting are among their most promising application in cancer treatment.
Keywords: Magnetite; Magnetic microparticles (MMP); Magnetic resonance imaging (MRI); Superparamagnetism; Encapsulation efficacy; Simple emulsion; Vibration simple magnetism (VSM); Surface study;
Synthesis and characterization of photoluminescent In-doped CdSe nanoparticles by Craig K. Knox; Sterling D. Fillmore; Dawn M. Call; Dan G. Allen; Bret C. Hess; Robert C. Davis; William E. Evenson; Roger G. Harrison (591-596).
Indium-doped CdSe nanoparticles have been synthesized and characterized. Their light absorption, photoluminescence, and structure are similar to undoped CdSe nanoparticles. The greater part of the In associated with the nanoparticles is removed when the nanoparticles undergo ligand exchange by pyridine. As observed with undoped nanoparticles, a ZnS capping layer on the indium-doped nanoparticles results in enhanced nanocrystal photoluminescence. Also, the ZnS cap enhances the retention of In by the nanoparticles. Elemental analysis shows ligand exchange causes CdSe to be lost and capping with ZnS results in the loss of Se. We conclude that In-doped nanoparticles have most of the In on their surface, capping helps the nanoparticles retain the In, and they do not have altered electronic properties.CdSe nanoparticles have been synthesized with indium present. Indium is incorporated in the nanoparticles after capping with ZnS.
Keywords: CdSe; In-doped; Nanoparticles; Photoluminescence; ZnS capping;
Langmuir–Blodgett monolayers of InP quantum dots with short chain ligands by K. Lambert; L. Wittebrood; I. Moreels; D. Deresmes; B. Grandidier; Z. Hens (597-602).
We demonstrate the organization of nearly monodisperse colloidal InP quantum dots at the air/water interface in Langmuir monolayers. The organization of the particles is monitored in situ by surface pressure–surface area measurements and ex situ by AFM measurements on films transferred to mica by Langmuir–Blodgett deposition. The influence of different ligands on the quality of the monolayer formed has been studied. We show that densely packed monolayers with little holes can be formed using short chain ligands like pyridine and pentamethylene sulfide. The advantage of using short chain ligands for electron tunneling to or from the quantum dots is demonstrated using scanning tunneling spectroscopy.The influence of different ligands on the monolayer quality has been studied, while the advantage of using short chain ligands for electron tunneling is demonstrated using scanning tunneling spectroscopy.
Keywords: Colloidal InP nanoparticles; Quantum dots; Semiconductor nanocrystals; Monolayer; Langmuir–Blodgett; Thin films; Scanning tunneling spectroscopy;
Stabilization of gamma alumina slurry for chemical–mechanical polishing of copper by Myung-Geun Song; Jin-ho Lee; Yoon-Gyu Lee; Ja-ho Koo (603-611).
Stabilization of γ-alumina suspension for chemical–mechanical polishing (CMP) of copper was investigated. Citric acid and poly(acrylic acid) (PAA) ( M w = 5000 ) were used as dispersant. The stability of suspension was evaluated from the changes in viscosity, particle size and zeta potential. It appears that metastable γ-alumina mainly due to its high specific surface area and to the presence of aluminol groups on its surface is progressively transformed to bayerite (β-Al(OH)3) by hydration procedure. Citric acid molecules were adsorbed onto γ-alumina surface effectively and exhibited the excellent hydration inhibition effect. Although citrate–alumina surface complexes give barrier to the flocculation, the repulsion potential is based mainly on the electrostatic repulsion, thereby steric hindrance caused by the adsorption of these small molecules is very weak. The electrosteric repulsion, which provides more effective dispersion stability than electrostatic repulsion force, can be expected by using polyelectrolyte such as PAA; however, adsorbed layers of PAA onto solid/liquid interface are loosely formed. Therefore, a large amount of PAA was required to inhibit the surface hydration of γ-alumina suspension, thereby the excess addition of PAA decreased the electrosteric repulsion and re-bridging of the dispersant between particles caused an increase in suspension viscosity. Therefore, synergistic effect can be expected in mixed dispersant system of citric acid and PAA, since small citric acid molecules are adsorbed faster than PAA, inhibiting the progress of surface hydration, and then adsorbed PAA layers exhibit the effective electrosteric repulsion interaction between particles with a small amount compared with PAA alone. It was revealed that the γ-alumina slurry dispersed by mixed dispersant exhibited the improved removal rate of Cu layer by CMP polishing test.Proposed adsorption model of mixed monolayer coverage with poly(acrylic acid) and citric acid molecules onto the γ-alumina surface in aqueous slurry for Cu CMP.
Keywords: Chemical–mechanical polishing; CMP; Copper; γ-Alumina; Dispersion stability; Wet grinding; Mixed dispersant;
Preparation of zinc oxide nanorods using pulsed laser ablation in water media at high temperature by Yoshie Ishikawa; Yoshiki Shimizu; Takeshi Sasaki; Naoto Koshizaki (612-615).
ZnO columnar single crystals were formed by pulsed laser ablation in deionized water and surfactant aqueous solutions of lauryl dimethylaminoacetic acid (LDA) and cetyltrimethylammonium bromide (CTAB) at 80 °C. ZnO particles produced by laser ablation were dissolved at a higher temperature than 60 °C, and then crystalline growth to columnar structure proceeded. While large ZnO columnar crystals were obtained in deionized water, the crystals prepared in surfactant solution were smaller than those in deionized water due to inhibition of crystalline growth by surfactant adsorption on ZnO surfaces. The size of ZnO nanorods depended on how surfactant molecules adsorb on ZnO surface.ZnO columnar single crystals, 500–600 nm long and 200 nm wide, were formed by pulsed laser ablation in deionized water at 80 °C.
Keywords: Pulsed laser ablation in liquid; ZnO; Nanorod;
Coupled chemical processes at clay/electrolyte interface: A batch titration study of Na-montmorillonites by Myriam Duc; Fabien Thomas; Fabien Gaboriaud (616-625).
The present work addresses the protolytic charge of montmorillonite, which occurs on the broken-bond sites at the particle edges. The purpose is to overcome the general difficulty arising in potentiometric titration due to coupled side reactions, which severely impede the titrant budget (partial dissolution of the clay and of secondary phases, hydrolysis and readsorption of dissolved species, cation exchange). Batch potentiometric titrations were carried out on the montmorillonite fractions extracted from two bentonites (MX80 and SWy2) to quantify their protolytic charge. The effects of equilibration time (24 h and 7 days), pH from 4 to 10, and ionic strength (0.1 and 0.01 mol L−1) were extensively studied for the MX80 sample. Quantification of dissolution was achieved by analysis of the equilibrium solutions for dissolved species and by La3+ exchange of the readsorbed species. The results clearly show that secondary phases such as iron- or silica-rich minerals contribute to the dissolved species, according to the nature of the raw bentonite. Furthermore, readsorption affects significant amounts of dissolved species. The overconsumption of proton/hydroxide due to dissolution, readsorption, and hydrolysis of dissolved species was evaluated using a self-consistent thermodynamic calculation. The ability of such calculation to correct the raw titration curves in order to extract the titrable surface charge of montmorillonite was evaluated by comparison with the continuous titration procedure. Especially in the alkaline domain, correcting the raw batch titration curves for the measured side reactions failed to reproduce the continuous titration curves. These observations demonstrate the limitations of the batch titration method and the superiority of fast, continuous methods for quantifying the dissociable surface charge of clays.This study deals with the surface charge of 2:1 clays, and with the impact of side reactions (cation exchange, dissolution, hydrolysis, readsorption) on its quantification by batch titration. The raw titration curves were corrected according to the quantified consumption of titrant by the side reactions. The corrected curves satisfactorily reproduced the continuous titration curves in the acidic to neutral domain. In the basic domain, strong discrepancy remained. These results show the limitations of the batch titration curves in the determination of the surface charge of unstable solids, compared to the continuous method.
Keywords: Montmorillonite clay; Acid–base properties; Batch titration; Potentiometric titrimetry; Dissolution/readsorption;
Preparation of a thermosensitive cobalt phthalocyanine/N-isopropylacrylamide copolymer and its catalytic activity on thiol by Wenxing Chen; Baoyan Zhao; Yong Pan; Yuyuan Yao; Shenshui Lu; Shiliang Chen; Lijuan Du (626-632).
A thermosensitive copolymer of cobalt tetra(N-acryliccarbonyl)aminophthalocyanine (Co-TACAPc) and N-isopropylacrylamide (NIPA) was prepared through redox polymerization in aqueous solution, and its catalytic activity for oxidation of 2-mercaptoethanol was investigated. The products of Co-TACAPc and its copolymer were characterized by elemental analysis, IR, UV/vis, and TGA. The copolymer can be dissolved into most solvents, particularly into water over a wide range of pH. The copolymer also revealed a lower critical solution temperature (LCST) phenomenon at 32.6 °C in water; i.e., it was soluble in cold water (below 32.6 °C) but insoluble in hot water (above 32.6 °C). As a result, in contrast to Co-TACAPc, the copolymer is able to serve as a homogeneous catalyst on oxidation of 2-mercaptoethanol below 31.0 °C and be recovered with increasing temperature due to its lower solubility above 31.0 °C.A thermosensitive copolymer of cobalt tetra(N-acryliccarbonyl)aminophthalocyanine (Co-TACAPc) and N-isopropylacrylamide (NIPA) was prepared through redox polymerization in aqueous solution, and its catalytic activity for oxidation of 2-mercaptoethanol was investigated.
Keywords: Cobalt tetra(N-acryliccarbonyl)aminophthalocyanine; Catalytic oxidation; N-Isopropylacrylamide; 2-Mercaptoethanol; Thermosensitive polymer;
Synthesis and electrochemical properties of chemically substituted LiMn2O4 prepared by a solution-based gel method by Ben-Lin He; Wen-Jia Zhou; Yan-Yu Liang; Shu-Juan Bao; Hu-Lin Li (633-639).
Lithium manganese oxide, LiMn2O4, and its substituted samples LiM0.05Mn1.95O4 (M = Al, Co, and Zn) were first prepared by a cost-saving and effective new solution-based gel method using a mixture of acetate and ethanol as the chelating agent. The physical properties of the synthesized samples were investigated by thermogravimetry/differential thermal analysis, X-ray diffraction, and scanning electronic microscopy. The as-prepared powders were used as positive materials for a lithium-ion battery, whose charge/discharge properties and cycle performance were examined. The results revealed that all the substituted samples had better cycle performance than pure LiMn2O4. Among these synthesized materials, the LiCo0.05Mn1.95O4 sample had the best cycle performance. After 30 cycles, its capacity loss was only 3%. Therefore, cyclic voltammetry and electrochemical impedance spectroscopy were employed to characterize the reactions of Li ion insertion into and extraction from LiCo0.05Mn1.95O4 electrodes.The cyclic voltammograms of all samples show two symmetrical couples of peaks which represented two redox reactions for LiMn2O4 and LiCo0.05Mn1.95O4. As substitution manganese with cobalt, the redox peaks of the LiCo0.05Mn1.95O4 electrode are sharp and show well defined splitting, which indicates that the Co-doped LiCo0.05Mn1.95O4 powders are more crystalline than pure LiMn2O4 and also explains that the cycle performance of LiCo0.05Mn1.95O4 is better than LiMn2O4.
Keywords: Lithium-ion batteries; LiMn2O4; LiCo0.05Mn1.95O4; Spinel; Solution-based gel method;
Surface oxidation of polyethylene using an atmospheric pressure glow discharge with liquid electrolyte cathode by H.S. Choi; T.G. Shikova; V.A. Titov; V.V. Rybkin (640-647).
This study investigated the action of an atmospheric pressure air glow discharge (APGD) with aqueous electrolyte cathode onto the surface of polyethylene (PE) films. Distilled water and aqueous solutions of KCl and HCl were utilized as a cathode. The surface properties of PE were characterized by contact angle measurement followed by surface free energy calculation, Fourier transform infrared by attenuated total reflectance (FTIR-ATR), and XPS. After treating the PE surface, we observed OH groups, C＝O groups in ester, ketone, and carboxyl groups, and C＝O groups in unsaturated ketones and aldehydes. For a treatment time of 20 min and a discharge current of 40 mA, atomic concentrations of O and N were 12% and 2%, respectively, under distilled water application. Modification processes were able to improve the surface free energy of PE.An atmospheric pressure glow discharge with liquid electrolyte cathode was quite promising for the surface oxidation of polyethylene films without generating low molecular weight oxidized products.
Keywords: Atmospheric pressure plasma with liquid electrolyte cathode; Polymers; Surface composition; Modification; Polyethylene;
Formation of hydrotalcite in aqueous solutions and intercalation of ATP by anion exchange by Hiroki Tamura; Jun Chiba; Masahiro Ito; Takashi Takeda; Shinichi Kikkawa; Yasuteru Mawatari; Masayoshi Tabata (648-654).
The formation reaction and the intercalation of adenosine triphosphate (ATP) were studied for hydrotalcite (HT), a layered double hydroxide (LDH) of magnesium and aluminum. Hydrotalcite with nitrate ions in the interlayer (HT-NO3) was formed (A) by dropwise addition of a solution of magnesium and aluminum nitrates (pH ca. 3) to a sodium hydroxide solution (pH ca. 14) until the pH decreased from 14 to 10 and (B) by dropwise addition of the NaOH solution to the solution of magnesium and aluminum nitrates with pH increasing from 3 to 10. The precipitate obtained with method B was contaminated with aluminum hydroxide and the crystallinity of the product was low, possibly because aluminum hydroxide precipitates at pH 4 or 5 and remains even after HT-NO3 forms at pH above 8. With method A, however, the precipitate was pure HT-NO3 with increased crystallinity, since the solubility of aluminum hydroxide at pH above and around 10 is high as dissolved aluminate anions are stable in this high pH region, and there was no aluminum hydroxide contamination. The formed HT-NO3 had a composition of [Mg0.71Al0.29(OH)2](NO3)0.29⋅0.58H2O. To intercalate ATP anions into the HT-NO3, HT-NO3 was dispersed in an ATP solution at pH 7. It was found that the interlayer nitrate ions were completely exchanged with ATP anions by ion exchange, and the interlayer distance expanded almost twice with a free space distance of 1.2 nm. The composition of HT-ATP was established as [Mg0.68Al0.32(OH)2](ATP)0.080⋅0.88H2O. The increased distance could be explained with a calculated molecular configuration of the ATP as follows: An ATP molecule is bound to an interlayer surface with the triphosphate group, the adenosine group bends owing to its bond angles and projects into the interlayer to a height of 1 nm, and the adenosine groups aligned in the interlayer support the interlayer distance.An ATP molecule intercalated into hydrotalcite stretches up into the interlayer space supporting the interlayer free space. The adenosine groups of the ATP bind the two hydrotalcite layers by attractive interactions.
Keywords: Hydrotalcite; ATP; Layered compound; Intercalation; Intercalate; Ion exchange;
An electrical impedance spectroscopic (EIS) study on transport characteristics of ion-exchange membrane systems by Jin-Soo Park; Jae-Hwan Choi; Jung-Je Woo; Seung-Hyeon Moon (655-662).
This study aimed at investigating ion-exchange membrane systems using impedance spectroscopy. Nyquist plots showed that the impedance obtained in this study described the ion-exchange membrane system well, as consisting of (i) an ion-exchange membrane immersed in solution, (ii) electrical double layers at the membrane surface, and (iii) diffusion boundary layers arising from the interface between the ion-exchange membrane and the electrolyte solutions. Taking into account the physical and electrochemical understanding of the ion-exchange membrane system, an equivalent circuit was suggested to quantitatively analyze each component of the ion-exchange membrane system. To confirm the reliability of the proposed equivalent circuit, the resistance and capacitance were estimated from the impedance data and the values were compared with other experimental results (e.g., I – V curves). The comparison showed good agreement and validated the equivalent circuit. Moreover, the impedance measurements made it possible to confirm the electroconvective effects in the over LCD region.
Keywords: Ion-exchange membrane; Electrical impedance spectroscopy; Nyquist plot; Equivalent circuit; Electroconvective effects;
Nature identification and morphology characterization of cation-exchange membrane fouling during conventional electrodialysis by Erik Ayala-Bribiesca; Gérald Pourcelly; Laurent Bazinet (663-672).
The aim of this work was to study the effect of a concentrate solution pH value and of the composition in calcium, carbonate, and protein of a diluate solution to be treated by conventional electrodialysis on the fouling of cation-exchange membranes (CEM). It appeared that after demineralization of solutions containing CaCl2 and CaCl2 + Na2CO3 using a concentrate solution maintained at a pH of 12, mineral fouling appeared on both sides of the CEM. The nature of the deposits was identified as calcium hydroxide and/or carbonate on both surfaces. The mineral fouling presented an aggregation-like crystal following a carnation-like pattern of aggregates of small rhombohedral crystals with CaCl2 added alone, while CaCl2 + Na2CO3 yielded a smoother spherical crystal. Protein fouling was detected only on the CEM surface in contact with the diluate after demineralization of a solution containing CaCl2 + Na2CO3 using a concentrate pH value of 2.
Keywords: Electrodialysis; Cation-exchange membrane; Fouling; Protein; Calcium; Carbonate; pH;
Dynamics of water droplets detached from porous surfaces of relevance to PEM fuel cells by A. Theodorakakos; T. Ous; M. Gavaises; J.M. Nouri; N. Nikolopoulos; H. Yanagihara (673-687).
The detachment of liquid droplets from porous material surfaces used with proton exchange membrane (PEM) fuel cells under the influence of a cross-flowing air is investigated computationally and experimentally. CCD images taken on a purpose-built transparent fuel cell have revealed that the water produced within the PEM is forming droplets on the surface of the gas-diffusion layer. These droplets are swept away if the velocity of the flowing air is above a critical value for a given droplet size. Static and dynamic contact angle measurements for three different carbon gas-diffusion layer materials obtained inside a transparent air-channel test model have been used as input to the numerical model; the latter is based on a Navier–Stokes equations flow solver incorporating the volume of fluid (VOF) two-phase flow methodology. Variable contact angle values around the gas–liquid–solid contact-line as well as their dynamic change during the droplet shape deformation process, have allowed estimation of the adhesion force between the liquid droplet and the solid surface and successful prediction of the separation line at which droplets loose their contact from the solid surface under the influence of the air stream flowing around them. Parametric studies highlight the relevant importance of various factors affecting the detachment of the liquid droplets from the solid surface.The detachment process of water droplets from porous material surfaces used with PEM fuel cells is investigated experimentally and computationally.
Keywords: Water droplet detachment; Carbon gas-diffusion layer; Fuel cell; Modelling;
Viscous-gravity spreading of time-varying liquid drop volumes on solid surfaces by Rachid Chebbi (688-696).
Viscous-gravity spreading of liquid drops of time-dependent volume over a solid surface is considered. A self-similar solution for the drop configuration is obtained, in the case the liquid drop volume varies as a power-law function of time, along with the spreading laws in both cases of cylindrical and axisymmetric geometries. Results compare favorably with published experimental results and previous theoretical work. The limitations of the model are discussed, along with a comparison with viscous gravity spreading of oil on water. The validity of using approximate spreading laws is considered, and an approximate method is suggested to provide the dynamics of spreading in the general case where the drop volume does not necessarily vary as a power-law function of time.The dynamics of viscous-gravity spreading of time-varying liquid drop volumes on solid surfaces is described for cylindrical and axisymmetric geometries.
Keywords: Drop spreading; Liquid spreading; Viscous-gravity spreading; Spontaneous spreading; Spreading laws; Variable volume;
Effect of oxygen plasma treatment on the surface properties of tin-doped indium oxide substrates for polymer LEDs by Zhong Zhi You; Jiang Ya Dong (697-703).
The effect of oxygen plasma treatment on the surface properties of tin-doped indium oxide (ITO) substrates and the changes in surface properties of treated ITO substrates with ageing time were investigated by X-ray photoelectron spectroscopy (XPS), contact angle and surface free energy measurements. Experimental results show that oxygen plasma treatment increases the oxygen concentration, decreases the carbon concentration, and enhances the surface free energy and polarity, and thereby improves the surface properties of ITO substrates. However, the improved ITO surface properties tended to decay and the surface free energy decreased, with ageing time. In addition, the ageing effect of treated ITO substrates on the performance of polymer light-emitting diodes (LEDs) was studied with respect to the driving voltage, electroluminescent luminance and efficiency. We observe that the ITO substrates aged for various times result in significant differences in optical and electrical characteristics which become worse as the ageing time increases. The optical and electrical performance of polymer LEDs is closely related to the surface properties of ITO substrate and the interface characteristics of ITO/polymer.The effect of oxygen plasma treatment on the surface properties of ITO substrates and the subsequent influence on the performance of polymer LEDs were investigated.
Keywords: Tin-doped indium oxide (ITO); Surface property; Polymer light-emitting diodes (LEDs);
Observation and modelling of barrel droplets on vertical fibres subjected to gravitational and drag forces by Benjamin J. Mullins; Roger D. Braddock; Igor E. Agranovski; Roger A. Cropp (704-712).
Extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment or flow of drops from fibres as airflow velocity increases. A detailed experimental study of the aforementioned processes was conducted using glass filter fibres and H2O aerosol, which coalesce on the fibre to form barrel droplets with small contact angles. The droplets were predominantly observed in the Reynolds transition (or unsteady laminar) flow region. The droplet oscillation appears to be induced by the onset of vortexes in the flow field around the droplet as the increasing droplet size increases the Reynolds number. Flow in this region is usually modelled using the classical two-dimensional Karman vortex street, and there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and inhibiting such oscillation. The agreement between the model and experimental results is acceptable for both the radial and transverse oscillations.Reynolds numbers at which droplet activation (commencement of oscillation— O A ) and deactivation (cease of oscillation— O D ) occurs as a function of drop size (b). A straight line has been fitted to each data set using linear regression. R 2 ( O A ) = 0.25 , R 2 ( O D ) = 0.27 . The two datasets were shown to be significantly different ( p = 5.2 × 10 −7 ) using a t-test ( t = − 7.28 , df = 20 ).
Keywords: Fibre wetting; Drag; Filtration; Liquid aerosols; Mists;
Micellar solubilization of tributylphosphate in aqueous solutions of Pluronic block copolymers by J. Causse; S. Lagerge; L.C. de Menorval; S. Faure (713-723).
Solubilization of tributylphosphate (TBP), a polar oil, in various micellar solutions of Pluronic has been investigated by turbidimetry emphasizing the effect of temperature and the role of the PPO and PEO blocks on the phase behavior of the three components systems (Pluronic–TBP–water). [Temperature–composition] diagrams allow monophasic and diphasic domains to be delimited. Two temperatures are shown to have a determining effect on the phase behavior (TBP solubilization); the well known cloud point temperature (CPT, here defined for the three components system) and the solubilization minimum temperature (SMT) which is defined as the lowest temperature allowing solubilization of TBP in the system. Both temperature depend on the copolymer structure and, interestingly, are directly related to the TBP concentration in the medium. Monophasic microemulsions are observed when the temperature ranges between the SMT and the CPT. When T < SMT , the phase separation occurs and is related to the formation of TBP in water emulsion droplets. When T > CPT the system separates in two phase due to the co-precipitation of TBP and Pluronic. Moreover an unexpected evolution of the CPT with the TBP content clearly indicates the occurrence of a structural change of the microemulsions which allows higher quantities of TBP to be solubilized. But the structural change does not allow alone higher quantities of TBP to be solubilized. A well compromise between the SMT and the CPT must be also observed so as to obtain a large extent of monophasic domain after the restructuration. The best compromise is obtained with Pluronics with intermediate hydrophobic character. Reversely, hydrophobic and hydrophilic Pluronics exhibit a very small extent of monophasic domain after the restructuration which does not allow benefit by the structural change.Evolution of the cloud point temperature (CPT) and the solubilization minimum temperature (SMT) of a micellar Pluronic (L64) solution following addition of tributylphosphate. SMT = lowest temperature allowing solubilization of TBP in the system.
Micellar solubilization of tributylphosphate in aqueous solutions of Pluronic block copolymers by J. Causse; S. Lagerge; L.C. de Menorval; S. Faure (724-734).
The solubilization of tributylphosphate (TBP), a polar oil, in various micellar solutions of Pluronic has been investigated by 1H NMR spectroscopy. Partial phase diagrams of the three components systems (Pluronic–TBP–water) have shown two characteristic temperatures, called CPT and SMT, which control the phase behavior (see Part I); Both temperature depend on the copolymer structure and, interestingly, are directly related to the TBP concentration in the medium. Monophasic microemulsions are observed only when the temperature ranges between the SMT and the CPT. Moreover, the evolution of the CPT with the TBP content clearly indicated the occurrence of a structural change of the microemulsions which allows higher quantities of TBP to be solubilized. In this second part, 1H NMR studies of TPB/micellar systems have essentially focused on elucidating the nature of the interactions between TBP and micelle, or on the location of the solubilized species, mainly from the dependence of chemical shifts or linewidths on TBP concentration. Especially, the NMR spectra of the microemulsions before and after the structural change have been compared with those obtained for pure solution of Pluronic in D2O at different temperatures and in CDCl3. The analysis of the 1H NMR chemical shifts suggests a structural transformation of the TBP–Pluronic micelles in the sense of an hydrophobic TBP–PPO core becoming more and more dense as the TBP concentration increases. Especially, 1H NMR data evidence an evolution of the hydration state of the hydrophobic core following addition of TBP in the micellar solutions. During the addition of TBP, the microemulsion structure turns from spherical swelled micelles to nanodroplets of pure TBP stabilized by the Pluronic (pure nanophase of TBP stabilized by the copolymer). It is shown that the structural change strongly depends on the temperatures (CPT and SMT, see Part I) and on the copolymer structure.Evolution of the cloud point temperature (CPT) and the solubilization minimum temperature (SMT) of a micellar Pluronic (L64) solution following addition of tributylphosphate. SMT = lowest temperature allowing solubilization of TBP in the system.
Bubble motion measurements during foam drainage and coarsening by G. Maurdev; A. Saint-Jalmes; D. Langevin (735-743).
We have studied bubble motion within a column of foam allowed to undergo free drainage. We have measured bubble motion upward with time and as a function of their initial positions. Depending on the gas used, which sets the coarsening and drainage rates, different bubble upward motion types have been identified (constant speed, acceleration or deceleration) and explained in relation with liquid downward flows. The proofs of the consistency between bubble upward motion and liquid downward flow are obtained both by comparing the bubble motion curves to the liquid drainage ones, and by comparing the time variations of the liquid fraction extracted from bubble motion to direct liquid fraction measurements by electrical conductimetry. The agreement between bubble position tracking and electrical conductivity shows in particular that it is possible to determine the drainage regime from such simple bubble motion measurements. This work also allowed us to demonstrate a special case of foam coarsening and expansion, occurring when the foam gas is less soluble than the outside one, caused by diffusion of this external gas into the foam. All these results allow us to build a picture of drainage and coarsening seen from the bubble point of view.
Keywords: Foams; Drainage; Coarsening; Bubble;
Modification to the cumulant analysis of polydispersity in quasielastic light scattering data by P.A. Hassan; S.K. Kulshreshtha (744-748).
The electric field correlation function of light scattered from a polydispersed population of spherical particles having log–normal distribution with varying polydispersity is simulated. The correlation function with different polydispersity is compared with the method of cumulants over a wide range of correlation time. The large positive deviation of the method of cumulants at long correlation time is identified. This necessitates the truncation of the data at long correlation time or use of an appropriate weighting function to eliminate errors in the analysis. A modified cumulant analysis is used to overcome the limitation of truncating the correlation function. QELS data from polydisperse samples of micelles, liposomes and polyaniline nanoparticles are compared using the two methods. This method can be extended to the analysis of other multi-exponential decays such as stress relaxation, positron annihilation and NMR relaxation.
Keywords: QELS; Cumulant analysis; Polydispersity; Micelles; Emulsions; Liposomes; Nanoparticles;
Solubilization of pyrene in aqueous micellar solutions of gemini surfactants C12-s-C12⋅2Br by Ou Zheng; Jian-Xi Zhao (749-754).
Solubilization of pyrene in aqueous micellar solutions of quaternary ammonium gemini surfactants C12-s-C12⋅2Br has been examined by UV spectra and steady fluorescence spectra at 30 °C. The results showed that pyrene molecules were incorporated in the palisade layers of the micelles and interacted with the quarterary ammonium head groups through cation–π interaction, resulting in red shift of the UV absorption spectrum. C12-s-C12⋅2Br ( s = 3 , 4 , 6 ) micelles have stronger ability for solubilization of pyrene than conventional surfactant C12TABr micelles. With increasing spacer length of C12-s-C12⋅2Br, the micelles become more adaptable to solubilizing pyrene, which even forms the dimers as in the case of s = 3 , 4 , 6 , while pyrene solubilizes in the micelles ( s = 2 ) mainly in single-molecule form due to the more compact structure of the micelle in comparison with that at s > 2 .C12-s-C12⋅2Br micelles have stronger ability for solubilization of pyrene than the conventional surfactant C12TABr micelle. With s increasing, the micelles become more adaptable to solubilizing pyrene, which even forms dimers as in the case of s = 3 , 4 , and 6, while pyrene solubilizes in the micelles ( s = 2 ) mainly in single-molecule form.
Keywords: Gemini surfactants; Pyrene; Micellar solubilization; Interaction;
Phase behavior, interfacial composition and thermodynamic properties of mixed surfactant (CTAB and Brij-58) derived w/o microemulsions with 1-butanol and 1-pentanol as cosurfactants and n-heptane and n-decane as oils by Rajib K. Mitra; Bidyut K. Paul; Satya P. Moulik (755-764).
Phase diagrams of pseudo-quaternary systems of cetyltrimethylammonium bromide (CTAB)/polyoxyethylene(20)cetyl ether (Brij-58)/water/1-butanol (or 1-pentanol)/n-heptane (or n-decane) at fixed ω ( = [water]/[surfactant]) of 55.6 were constructed at different temperatures (293, 303, 313, and 323 K) and different mole fraction compositions of Brij-58 ( X Brij - 58 = 0 , 0.5, and 1.0 in CTAB + Brij-58 mixture). Pure CTAB stabilized systems produced larger single-phase domains than pure Brij-58 stabilized systems. Increasing temperature increased the single-phase domain in the Brij-58 stabilized systems, whereas the domain decreased in the CTAB stabilized systems. For mixed surfactant systems (with X Brij = 0.5 ) negligible influence of temperature in the studied range of 293 to 323 K on the phase behavior was observed. Interfacial compositions of the mixed microemulsion systems at different temperature and different compositions were evaluated by the dilution method. The n a i (number of moles of alcohol at the interface) and n a o (number of moles of alcohol in the oil phase) determined from dilution experiments were found to decrease and increase respectively for CTAB stabilized systems, whereas an opposite trend was witnessed for Brij-58 stabilized systems. The energetics of transfer of cosurfactants from oil to the interface were found to be exothermic and endothermic for CTAB and Brij-58 stabilized systems, respectively. At equimolar composition of CTAB and Brij-58, the phase diagrams were temperature insensitive, so that the enthalpy of the aforesaid transfer process was zero.Phase behavior of mixed surfactant (CTAB and Brij-58) derived w/o microemulsions with 1-butanol and 1-pentanol as cosurfactants and n-heptane and n-decane as oils has been studied. Interfacial composition and the related thermodynamic properties of these systems have been determined using the dilution method.
Keywords: Microemulsion; Mixed surfactant; Phase behavior; Interfacial composition; Thermodynamic properties;
Cloud point curve of nonionic surfactant related to the structures of mesoporous materials by J.L. Blin; R. Bleta; M.J. Stébé (765-773).
We have investigated the phase behavior of a fluorinated surfactant R 7 F ( EO ) 7 in water. The cloud point is situated at 19 °C for 2 wt% of surfactant. Using this surfactant, mesoporous materials have been synthesized with micellar solution prepared either at 10 °C (below the cloud point) or at 40 °C (above the cloud point). Results show that whatever the syntheses conditions, only wormhole-like structure is recovered. The effect of perfluorodecalin addition on the fluorinated surfactant/water system was also investigated. Swollen micelles, microemulsion, and lamellar ( L α ) liquid crystals were identified. When perfluorodecalin is added, the cloud point is shifted toward higher temperature. As regards the mesoporous syntheses, perfluorodecalin plays a dual role. First, incorporation of perfluorodecalin leads to the formation of well ordered materials. Secondly, the pore size enlargement occurs when perfluorodecalin is added. Our results evidence that the ratio between the volume of the hydrophilic headgroup ( V H ) and the hydrophobic part ( V L ) of the surfactant is not an efficiency parameter to explain the ordering improvement of mesoporous materials and that we should rather consider the existence of the cloud point curve, which disturbs the cooperative templating mechanism (CTM).
Keywords: Fluorinated surfactant; Nonionic surfactant; Phase diagram; Cloud point curve; Liquid crystal; Mesoporous; Silica; Pore ordering; Swelling agent;
Aggregation behavior of polypropylene oxide with electric charges at both ends in aqueous solution by Tohru Inoue; Kohei Yamashita (774-781).
The aggregation behavior of polypropylene oxide (PPO) with positive charges at both ends was investigated in aqueous solution by means of the measurements of solution turbidity, dynamic light-scattering, differential scanning calorimetry, and dye solubilization. The positive charges were produced by protonation of terminal NH2 groups attached to the polymer composed of 33 PO units. It was found that the aggregation behavior is quite sensitive to temperature. At low temperature, the polymer dissolves in water as a unimer. When temperature is increased, the unimer solution undergoes a phase separation to give a turbid solution. Further increase in temperature produces a transparent micellar solution. The aggregation of the polymer molecules must be induced by the dehydration of PPO chain caused by temperature increase. According to the analysis of heat absorptions associated with the melting of the solid mixture and the phase separation of the unimer solution, it is suggested that approximately 10% dehydration of PPO chain causes the phase separation. The temperature–composition phase diagram of aqueous mixture of this polymer was constructed on the basis of turbidity and DSC experiments, which reveals the aggregation behavior of this polymer in aqueous medium as a function of concentration and temperature.The phase diagram of aqueous mixture of PPO with NH+ 3 groups at both ends was constructed, which reveals the aggregation behavior of this polymer as a function of concentration and temperature.
Keywords: Amphiphiloic polymer; Polypropylene oxide; Aggregation behavior; Micelle formation; Clouding phenomenon; Phase diagram; Light-scattering; Differential scanning calorimetry;
NMR diffusometry and conductometry study of the host–guest association between β-cyclodextrin and dodecane 1,12-bis(trimethylammonium bromide) by Celia Cabaleiro-Lago; Markus Nilsson; Artur J.M. Valente; Massimo Bonini; Olle Söderman (782-787).
Surfactants form association complexes with cyclodextrins. In the present investigation we have used NMR-diffusometry and electrical conductivity to follow the interactions which take place between β-cyclodextrin and a bolaform surfactant: dodecane 1,12-bis(trimethylammonium bromide). Both 1H NMR self-diffusion and conductometry data indicate the formation of a 1:1 inclusion complex. Assuming this stoichiometry, it was possible to calculate the association constant; from the analysis of the self-diffusion coefficients of free β-cyclodextrin and the bolaform surfactant an association constant K = 3 × 10 3 M −1 was obtained while the analysis of conductivity data gave a comparable value of K = 2.5 × 10 3 M −1 .
Keywords: Bolaform surfactant; Cyclodextrin; Self-diffusion; Conductivity; Association constants;
Temperature and pressure effects on zeta potential values of reservoir minerals by Karina Rodríguez; Mariela Araujo (788-794).
An experimental study of the effect of temperature and pressure on zeta potential of typical reservoir minerals, including quartz, kaolinite, and calcite, is presented. Experiments included the design and construction of an electrophoretic cell for zeta potential measurements at variable pressure and temperature. Electrolyte concentration was varied in the range from 0.0001 to 0.1 M in the pH range from 2 to 9. For all the minerals it is found that the zeta potential decreases with temperature at a rate characteristic of each mineral; values are around −2.3 mV/°C for quartz, −0.96 mV/°C for kaolinite, and −2.1 mV/°C for calcite for pressure values less than 45 psi. The effect of pressure is found to depend on the mineral nature and pH of the electrolytic solution. In the case of quartz, a systematic increase in the value of the zeta potential with pressure is observed, whereas a decreasing trend is measured for the kaolinite. In the case of calcite, a decreasing trend is observed for pressures up to 45 psi, whereas the experimental data suggest an increasing trend for higher pressure values.It is found that the zeta potential of the three minerals decrease with temperature with characteristic rates, whereas with pressure, the response is a function of mineral nature and pH of electrolytic solution.
Keywords: Reservoir minerals; Zeta potential; Quartz; Kaolinite; Calcite; Pressure;
Effects of heavy metals and oxalate on the zeta potential of magnetite by Murat Erdemoğlu; Musa Sarıkaya (795-804).
Zeta potential is a function of surface coverage by charged species at a given pH, and it is theoretically determined by the activity of the species in solution. The zeta potentials of particles occurring in soils, such as clay and iron oxide minerals, directly affect the efficiency of the electrokinetic soil remediation. In this study, zeta potential of natural magnetite was studied by conducting electrophoretic mobility measurements in single and binary solution systems. It was shown that adsorption of charged species of Co2+, Ni2+, Cu2+, Zn2+, Pb2+, and Cd2+ and precipitation of their hydroxides at the mineral surface are dominant processes in the charging of the surface in high alkaline suspensions. Taking Pb2+ as an example, three different mechanisms were proposed for its effect on the surface charge: if pH < 5, competitive adsorption with H3O+; if 5 < pH < 6, adsorption and surface precipitation; and if pH > 6, precipitation of heavy metal hydroxides prevails. Oxalate anion changed the associated surface charge by neutralizing surface positive charges by complexing with iron at the surface, and ultimately reversed the surface to a negative zeta potential. Therefore the adsorption ability of heavy metal ions ultimately changed in the presence of oxalate ion. The changes in the zeta potentials of the magnetite suspensions with solution pH before and after adsorption were utilized to estimate the adsorption ability of heavy metal ions. The mechanisms for heavy metals and oxalate adsorption on magnetite were discussed in the view of the experimental results and published data.The changes in the zeta potentials of magnetite suspensions with solution pH before and after adsorption of Co2+, Ni2+, Cu2+, Zn2+, Pb2+, Cd2+, and oxalate anion were utilized to estimate the adsorption ability of heavy metal ions. The mechanisms for heavy metals and oxalate adsorption were discussed in the view of the experimental results and published data.
Keywords: Magnetite; Zeta potential; Heavy metals; Oxalate; Adsorption;
Determining molecule–carbon surface adsorption energies using molecular mechanics and graphene nanostructures by Thomas R. Rybolt; Rachael A. Hansel (805-808).
Five model surfaces were developed using molecular mechanics with MM2 parameters. A smooth, flat model surface was constructed of three parallel graphene layers where each graphene layer contained 127 interconnected benzene rings. Four rough surfaces were constructed by varying the separation between a pair of graphene nanostructures placed on the topmost layer of graphene. Each nanostructure contained 17 benzene rings arranged in a linear strip. The parallel nanostructures were moved closer together to increase the surface roughness and to enhance the molecule–surface interaction. Experimental adsorption energy values from the temperature variation of second gas–solid virial coefficients values were available for 16 different alkanes, haloalkanes, and ether molecules adsorbed on Carbopack B (Supelco, 100 m2/g). For each of the five different surface models, sets of 16 calculated adsorption energies, E cal ∗ , were determined and compared to the available experimental adsorption energies, E ∗ . The best linear regression correlation between E ∗ and E cal ∗ was found for a 1.20 nm internuclei separation of the surface nanostructures, and for this surface model the calculated gas–solid interaction energies closely matched the experimental values ( E ∗ = 1.018 E cal ∗ , r 2 = 0.964 ).Experimental adsorption energies ( E ∗ ) for 16 different adsorbate molecules on a carbon surface were correlated by molecular mechanics calculated adsorption energies ( E cal ∗ ) based on a rough graphene surface model.
Keywords: Adsorption; Henry's law; Adsorption; Virial coefficients; Molecular mechanics surface energy; Adsorption energy;
Interpretation of surface-tension isotherms of n-alkanoic (fatty) acids by means of the van der Waals model by K.D. Danov; P.A. Kralchevsky; K.P. Ananthapadmanabhan; A. Lips (809-813).
Here we apply the two-dimensional van der Waals model to interpret surface-tension isotherms of aqueous solutions of n-alkanoic (fatty) acids. We processed available experimental data for a homologous series of eight acids, from pentanoic to dodecanoic (lauric). Only three adjustable parameters have been varied to fit simultaneously all experimental curves. Excellent agreement between the theoretical model and the experiment has been obtained. The determined parameter values comply well with the molecular properties and allow one to calculate the surfactant adsorption, surface elasticity, and the surface pressure vs area isotherms. For the dodecanoic acid, the van der Waals model indicates the existence of a surface phase transition.By means of the two-dimensional van der Waals model, experimental surface-tension isotherms of eight normal alkanoic acids are simultaneously fitted, and the respective adsorptions, surface pressures and elasticities are determined.
Keywords: n-Alkanoic acids; Normal fatty acids; Surface-tension isotherms; Adsorption; Surface (Gibbs) elasticity; Surface pressure;
Adsorption of methyl mercaptan on surface modified activated carbon by Hisashi Tamai; Hisato Nagoya; Takeshi Shiono (814-817).
The influence of surface modification of activated carbon on the adsorption of methyl mercaptan in N2 was investigated. The modification of the activated carbon was carried out by treatment with HNO3/H2SO4 solutions, heat-treatment in Ar, and adsorption of cetylamine. Acid-treatment increased the adsorption of methyl mercaptan compared with the original activated carbon, and the adsorbed amounts increased with ratio of H2SO4 in HNO3/H2SO4 solutions. This result suggests that hydrogen bonding between acidic groups formed by acid-treatment and thiol groups of methyl mercaptan plays a role in adsorption of methyl mercaptan on activated carbon.Activated carbons treated with HNO3/H2SO4 solutions (AC-At(1), (2), (3)) enhanced the adsorption of methyl mercaptan, compared with the original activated carbon (AC).
Keywords: Activated carbon; Surface modification; Methyl mercaptan adsorption;
Comment on “Electrorheological behavior of copper phthalocyanine-doped mesoporous TiO2 suspensions” by Cheng Hai Hong; Bong Jun Park; Hyoung Jin Choi (818-819).
We comment on the electrorheological (ER) behavior of copper phthalocyanine (CuPC)-doped mesoporous TiO2 suspensions. Our Cole–Cole plot not only fits the dielectric spectra of the two CuPC-doped mesoporous TiO2 templated ER fluids with CuPC/cetyltrimethylammonium (CTAB) molar ratios of 0.10 and 0.15, respectively, but also provides a better explanation of their polarizability by differentiating their ER performance.The Cole–Cole plot not only fits the dielectric spectra of the two CuPC-doped mesoporous TiO2 templated ER fluids with CuPC/CTAB molar ratios of 0.10 and 0.15, but also provides a better explanation of their polarizability by differentiating their ER performance.
Keywords: Electrorheological fluid; Mesoporous; Dielectric spectrum; Polarization;
Aspects of ionic diffusion through thick matrices of charged particles by S. Chatterji (820-825).
A review of the literature on ionic diffusion through matrices of charged particles shows that many workers have reported higher diffusivity of co-ions than of counterions. If these observations are correct then the requirement of electroneutrality of bulk solutions is violated. In those experiments other, not looked for, ions must have been taking part. It therefore appears that complete chemical analyses of solutions of both up- and downstream sides should be carried out, otherwise misleading inferences may be drawn, with practical consequences. Some researchers have studied transport of water under osmotic pressure differentials across clay membranes. However, a diffusing ion, during its transport from higher concentration to lower concentration, always carries its water of hydration. This second water transport process has not received attention. This suggests that at a critical concentration two transport processes will cancel each other. Attention has been drawn to this second type of water flow and its consequences. In ionic diffusion, each side of the membrane–outside solution interface is subject to the effects of the Nernst layer and Donnan zone. However, these layers and zones are seldom treated quantitatively. This has been carried out in this paper by two different methods. Both methods give identical thicknesses of the Nernst layer and Donnan zone. Finally, the effects of the presence of soluble bivalent salts on the diffusivity of different types of ions have been commented up on. In these cases some of the co-ions diffuse to the upstream side.(1) The thicknesses of interfacial layers (see figure) have been evaluated quantitatively. (2) A literature survey shows number of anomalies, e.g., violation of electro-neutrality, etc. These need clarifications. Ways have been suggested for resolution of these anomalies.
Keywords: Ion; Diffusion; Charged matrix; Electrical potential; Nernst layer; Donnan zone; Ultrafiltration;
Comment on “The surface potential of a spherical colloid particle: Functional theoretical approach” by C. Grosse; J.J. López-García; J. Horno (826-827).
In a work published in this journal by Z.W. Wang, G.Z. Li, D.R. Guan, X.Z. Yi, and A.J. Lou [J. Colloid Interface Sci. 246 (2002) 302], an iterative method for the determination of the potential around a colloidal particle is presented. It is claimed that successive terms of the iteration series converge to the exact solution of the Poisson–Boltzmann equation. This claim seems to be unfounded when the analytical expressions of the iteration terms are compared with well established numerical data.Reduced electric potential in the electrolyte solution surrounding a charged spherical particle of radius R. Comparison of the “exact” numerical solution with the Debye–Hückel approximation, and the results of the first and second iterations by Wang et al. [J. Colloid Interface Sci. 246 (2002) 302]. Calculations performed for z = 1 , κ R = 2 , and z e ψ ( R ) / ( k T ) = 6 .
Keywords: Poisson–Boltzmann equation; Spherical colloid particle;
Author Index for Volume 300 (828-830).