Journal of Colloid And Interface Science (v.311, #2)
Deposition efficiency of fractal-like aggregates in fibrous filters calculated using Brownian dynamics method
by Anna Bałazy; Albert Podgórski (pp. 323-337).
Nonspherical particles, such as fractal-like aggregates emitted by diesel engines, are commonly met in the ambient air. Some of them are believed to be carcinogenic to humans, thus their efficient removal is of crucial practical importance. A fibrous filter is the device commonly used for aerosol purification but the literature lacks experimental data concerning aggregates filtration. Effect of aggregates' parameters (fractal dimension, primary particle radius) as well as fiber diameter and air velocity on the filtration efficiency is investigated theoretically using the modified Brownian dynamics method. Three different expressions for the friction coefficient evaluation for the aggregates were examined. The results obtained indicate that structure of an aggregate, filter structure and process conditions strongly influence the aggregates deposition efficiency, which significantly differs from the values determined for mass-equivalent spherical particles. The results determined using the Brownian dynamics approach were compared with the values calculated using classical single fiber theory and noticeable discrepancy was observed for the most penetrating particles, while both approaches agree for the limiting cases of small or large particles. Peclet number based on the mobility radius and the interception parameter based on the outer radius are the proper criteria to describe diffusional and deterministic deposition of aggregates.
Keywords: Aerosol; Aggregate; Brownian dynamics; Cluster; Deposition; Fibrous filter; Filtration
Studies of the equilibrium and thermodynamics of the adsorption of Cu2+ onto as-produced and modified carbon nanotubes
by Chung-Hsin Wu (pp. 338-346).
This study evaluates the Cu2+ adsorption efficiency of as-produced carbon nanotubes (CNTs) and those modified by HNO3 and NaOCl. The surface area, pHpzc, pore volume, FTIR analyses, and average pore size of CNTs were determined to compare the differences between nanotubes before and after HNO3 and NaOCl modification. The HNO3 and NaOCl modifications increased the pore volume and the average pore size of CNTs; in contrast, the pHpzc was decreased. The modification processes produced some functional groups. The adsorption capacity of Cu2+ on as-produced and modified CNTs increased with the pH and temperature; however, the effects of the ionic strength on the adsorption of Cu2+ on as-produced and modified CNTs were negligible. The linear correlation coefficients of Langmuir and Freundlich isotherms were obtained and the results revealed that the Langmuir isotherm fitted the experimental results better than did the Freundlich isotherm. The adsorption capacity of Cu2+ followed the order NaOCl-modified CNTs > HNO3-modified CNTs > as-produced CNTs. Changes in the free energy of adsorption(ΔGo), enthalpy(ΔHo), and entropy(ΔSo) were determined. AllΔGo values were negative; theΔHo values of as-produced, HNO3-modified, and NaOCl-modified CNTs were 10.84, 17.08, and 67.77 kJ/mol and theΔSo values were 96.89, 122.88, and 319.76 J/mol K, respectively.Effects of pH (initial Cu2+ = 43.1 mg/L, ionic strength = 0.01 M, CNTs = 0.5 g/L, temperature = 300 K, and contact time = 24 h).
Keywords: Adsorption; Carbon nanotubes; Isotherm; Copper; Thermodynamics
Thermal stability of octadecyltrimethylammonium bromide modified montmorillonite organoclay
by Yunfei Xi; Qin Zhou; Ray L. Frost; Hongping He (pp. 347-353).
Organoclays are significant for providing a mechanism for the adsorption of organic molecules from potable water. As such their thermal stability is important. A combination of thermogravimetric analysis and infrared emission spectroscopy was used to determine this stability. Infrared emission spectroscopy (IES) was used to investigate the changes in the structure and surface characteristics of water and surfactant molecules in montmorillonite, octadecyltrimethylammonium bromide and organoclays prepared with the surfactant octadecyltrimethylammonium bromide with different surfactant loadings. These spectra collected at different temperatures give support to the results obtained from the thermal analysis and also provide additional evidence for the dehydration which is difficult to obtain by normal thermoanalytical techniques. The spectra provide information on the conformation of the surfactant molecules in the clay layers and the thermal decomposition of the organoclays. Infrared emission spectroscopy proved to be a useful tool for the study of the thermal stability of the organoclays.
Keywords: Adsorption; Thermal stability; Montmorillonite; Dehydration; Dehydroxylation; Infrared emission; Spectroscopy; Thermogravimetric analysis
Adsorption kinetics of phosphate and arsenate on goethite. A comparative study
by Carina Luengo; Maximiliano Brigante; Marcelo Avena (pp. 354-360).
The adsorption kinetics of phosphate and arsenate on goethite is studied and compared. Batch adsorption experiments were performed at different adsorbate concentrations, pH, temperatures and stirring rates. For both oxoanions the adsorption rate increases by increasing adsorbate concentration, decreasing pH and increasing temperature. It does not change by changing stirring rate. The adsorption takes place in two processes: a fast one that takes place in less than 5 min and a slow one that takes place in several hours or more. The rate of the slow process does not depend directly on the concentration of phosphate or arsenate in solution, but depends linearly on the amount of phosphate or arsenate that was adsorbed during the fast process. Apparent activation energies and absence of stirring rate effects suggest that the slow process is controlled by diffusion into pores, although the evidence is not conclusive. The similarities in the adsorption kinetics of phosphate and arsenate are quantitatively shown by using a three-parameters equation that takes into account both the fast and the slow processes. These similarities are in line with the similar reactivity that phosphate and arsenate have in general and may be important for theoretical and experimental studies of the fate of these oxoanions in the environment.Phosphate and arsenate show very similar adsorption behavior on goethite.
Keywords: Adsorption; Kinetics; Phosphorus; Arsenic; Metal oxides
Formation of complex Langmuir and Langmuir–Blodgett films of water soluble rosebengal
by S. Biswas; D. Bhattacharjee; R.K. Nath; S.A. Hussain (pp. 361-367).
This communication reports the formation of complex Langmuir monolayer at the air–water interface by charge transfer types of interaction with the water soluble N-cetylN,N,N-trimethyl ammonium bromide (CTAB) molecules doped with rosebengal (RB), with the stearic acid (SA) molecules of a preformed SA Langmuir monolayer. The reaction kinetics of the formation of RB-CTAB-SA complex monolayer was monitored by observing the increase in surface pressure with time while the barrier was kept fixed. Completion of interaction kinetics was confirmed by FTIR study. This complex Langmuir films at the air–water interface was transferred onto solid substrates at a desired surface pressure to form multilayered Langmuir–Blodgett films. Spectroscopic characterizations reveal some molecular level interactions as well as formation of microcrystalline aggregates depending upon the molar ratios of CTAB and RB within the complex LB films. Presence of two types of species in the complex LB films was confirmed by fluorescence spectroscopy.Schematic representation of RB-CTAB-SA complex Langmuir monolayer at the air–water interface.
Keywords: Langmuir–Blodgett films; UV–vis absorption spectroscopy; Fluorescence spectroscopy; Adsorption kinetics; Water soluble
Conductivity stopped-flow study of the kinetics of solutes uptake by colloidal particles of synthetic resins
by Marc Hébrant (pp. 368-374).
The uptake rates of acids (hydrochloric acid, sulfuric acid, perchloric acid and acetic acid) by colloidal solid particles (mean diameter 0.35 μm) of DEAE (diethylaminoethyl Sephadex) resin was studied by the means of the stopped flow technique equipped with a conductivity detection. This original experimental approach allows to avoid hydrodynamics perturbations during data acquisition. For the sake of comparison NaOH uptake or K+/H+ exchange by sulfonic Dowex resin particles experiments have also been performed. As stated in the literature we observed that the uptake rate limiting step is the solute diffusion in the solution layer surrounding the particles. To fit the experimental conductivity versus time curves on the basis of solutes diffusion concepts a simple mathematical equation fitting perfectly well the experimental data is proposed. The mathematical modeling of kinetic data obtained in non-stationary diffusion proposed here can substitute to the empiric pseudo-first- and -second-order models often used in environmental research.The stopped-flow technique as a new method for the study of the acid uptake and ion exchange on solid particles.
Keywords: Stopped-flow; Ion exchange; Colloid particles; Resin; Conductivity; Diffusion
Adsorption of phosphate and nitrate anions on ammonium-functionalized MCM-48: Effects of experimental conditions
by Rabih Saad; Khaled Belkacemi; Safia Hamoudi (pp. 375-381).
In this study, ammonium-functionalized MCM-48 (Mobil Composite Material No. 48) was used as an adsorbent to remove nitrate (NO−3) and monobasic phosphate (H2PO−4) anions from aqueous solutions. The effects of operating conditions such as temperature, adsorbent loading, initial anion concentration, pH, and the presence of competitive ions on the adsorption performances were examined. Results showed that adsorption capacity decreased with increasing temperature. The adsorption capacity increased with adsorbent loading and initial anion concentration. The removal of nitrate was maximum at pH<8, while phosphate removal was maximized at pH 5. The adsorption was almost unaffected by the presence of competitive ions in the case of phosphate anions. However, their presence adversely affected nitrate adsorption. Desorption of both anions was rapidly achieved within 10 min using NaOH at 0.01 M. Regeneration tests showed that the adsorbent retained its capacity after 5 adsorption–desorption cycles.Ammonium-functionalized MCM-48 was investigated as adsorbent to remove nitrate (NO−3) and monobasic phosphate (H2PO−4) anions from aqueous solutions. The effect of operating condition such as temperature, absorbent loading, initial anions concentration, pH, and the presence of competitive ions on the adsorption performances was examined.
Keywords: Adsorption; Nitrate; Phosphate; Ammonium-functionalized MCM-48; Desorption; Regeneration
Assessment on the removal of dimethyl phthalate from aqueous phase using a hydrophilic hyper-cross-linked polymer resin NDA-702
by Weiming Zhang; Zhengwen Xu; Bingcai Pan; Lu Lv; Qingjian Zhang; Qingrui Zhang; Wei Du; Bingjun Pan; Quanxing Zhang (pp. 382-390).
A hydrophilic hyper-cross-linked polymer resin (NDA-702) was synthesized, and the adsorption performance of dimethyl phthalate (DMP) on NDA-702 was compared with that on the commercial hydrophobic macroporous resin (Amberlite XAD-4) and granular activated carbon (AC-750). The kinetic adsorption of DMP onto NDA-702 and AC-750 is limited mainly by intraparticle diffusion and obeys the pseudo-second-order rate model, while the uptake on XAD-4 is limited mainly by film diffusion and follows the pseudo-first-order rate model. All the associated adsorption isotherms are well described by the Freundlich equation, and the larger uptake and stronger affinity of NDA-702 than AC-750 and XAD-4 probably result from the microporous structure, phenyl rings, and polar groups on NDA-702 polymer matrix. An interesting observation is that in the aqueous phase all the adsorbents spontaneously adsorb DMP driven mainly by enthalpy change, but the hydrophilic nature of NDA-702 and AC-750 surfaces results in less entropy change compared to hydrophobic XAD-4. Dynamic adsorption studies show that the high breakthrough and the total adsorption capacities of NDA-702 are 388 and 559 mg per gram dry resin at 313 K. Nearly 100% regeneration efficiency for the resin was achieved by methanol at 313 K.
Keywords: Removal; DMP; Porous materials; Adsorption; Kinetics; Isotherms; Dynamics
Saving time when measuring BET isotherms
by J.A. Poulis; C.H. Massen; E. Robens (pp. 391-393).
The measurement of adsorption isotherms and the determination of surface properties of a solid by means of the BET equation usually takes a lot of time as it involves measurement of several dynamic adsorption curves each at a given gas pressure. Two different timesaving approaches are suggested: (a) the beginning of a single dynamic curve is considered and (b) the beginnings of a number of different dynamic curves is considered. Approach (a) is less time consuming than approach (b), where approach (b) yields more accurate estimates of the BET-parameters. A discussion is given of the possibilities of using the time saving procedure of Jäntti for the two approaches.The measurement of a BET curve for the determination of the specific surface area usually takes a lot of time. We discuss the possibilities of using the time saving procedure of Jäntti.
Keywords: Adsorption; BET; Jäntti approach; Fast measurement; Surface
Electrokinetic effect and surface free energy behavior in the adsorption process of a reactive dye onto Leacril pretreated with polyethyleneimine ion
by E. Giménez-Martín; A. Ontiveros-Ortega; M. Espinosa-Jiménez; R. Perea-Carpio (pp. 394-399).
In a previous paper, we studied the adsorption of a polyelectrolyte, polyethyleneimine ion (PEI), onto Leacril in order to increase the amount of the reactive dye Remazol Brilliant Blue R (RBBR) taken up by these fibers. We observed that this polycation changes the fibers zeta potential sign at low concentration, ca. 0.03 g/L, and thus the RBBR adsorption onto Leacril is improved when implementing the PEI treatment. The aim of this work is to study the PEI effect related to the amount of dye adsorbed by Leacril. For this purpose, we present data on streaming potential, adsorption isotherms, and surface free energy component determination as a function of the PEI concentration used in the pretreatment, as well as a function of the RBBR concentration used in the dyeing solutions. Adsorption experimental results show that the amount of RBBR taken by the fibers increases with the PEI concentration used in the pretreatment, and this effect becomes significant at higher concentrations of RBBR solution. The zeta potential increases to positive values in the range of low concentrations of dye solution when Leacril fibers have been pretreated with the polyelectrolyte. From surface free energy component determinations it is worth noting that the electron-donor component,γ−, decreases with the RBBR concentration in the treatment. The results we have obtained suggest that the interaction between the amine group of the PEI previously adsorbed and the reactive β-sulfato-ethysulfonyl group of the dye can be responsible for the improvement in dye uptake.Pre-treating Leacril with increasing concentration of polyethyleneimine ion improve the adsorption of Remazol Brillant Blue R at room temperature. The results obtained show that despite hydrophobic interactions chemical reactions between the β-sulfato-ethylsulfonyl reactive group of dye molecule and the amino groups of PEI must be considered.
Keywords: Leacril; Polyelectrolyte; Reactive dye; Absorption; Zeta potential; Surface free energy; Textile fabrics
Spectroscopic studies on the interaction between human hemoglobin and CdS quantum dots
by Xing-Can Shen; Xin-Yan Liou; Li-Ping Ye; Hong Liang; Zuo-Yuan Wang (pp. 400-406).
The interaction between human adult hemoglobin (Hb) and bare CdS quantum dots (QDs) was investigated by fluorescence, synchronous fluorescence, circular dichroism (CD), and Raman spectroscopic techniques under physiological pH 7.43. The intrinsic fluorescence of Hb is statically quenched by CdS QDs. The quenching obeys the Stern–Volmer equation, with an order of magnitude of binding constant ( K) of 107. The electrostatic adsorption of Hb on the cationic CdS QDs surface is energetically favorable (ΔS0=70.22Jmol−1K−1,ΔH0=−23.11kJmol−1). The red shift of synchronous fluorescence spectra revealed that the microenvironments of tryptophan and tyrosine residues at theα1β2 interface of Hb are disturbed by CdS QDs, which are induced from hydrophobic cavities to a more exposed or hydrophilic surrounding. The secondary structure of the adsorbed Hb has a loose or extended conformation for which the content of α-helix has decreased from 72.5 to 60.8%. Moreover, Raman spectra results indicated that the sulfur atoms of the cysteine residues form direct chemical bonds on the surface of the CdS QDs. The binding does not significantly affect the spin state of the heme iron, and deoxidation is not expected to take place on the coated oxyhemoglobin. The change of orientation of heme vinyl groups was also detected.Raman spectra indicated that sulfur atoms of cysteine residues in Hb have direct chemical bonds with CdS QDs, whereas, the binding do not affect the spin state of the heme iron.
Keywords: Hemoglobin; CdS quantum dots; Binding constant; Conformational change; Thermodynamic parameters; Fluorescence spectroscopy; CD spectroscopy; Raman spectroscopy
Effect of propyl paraben on the dipalmitoyl phosphatidic acid vesicles
by Lata Panicker (pp. 407-416).
The effect of the preservative propyl paraben (PPB) on the phase transition and dynamics of dipalmitoyl phosphatidic acid (DPPA)-buffer (pH 7.4/9.3) vesicles has been studied using DSC and (1H and31P) NMR. These investigations were carried out with DPPA dispersion in both multilamellar vesicular (MLV) and unilamellar vesicular (ULV) forms. DSC results indicate that the mechanism by which PPB interact with the DPPA vesicles is similar in MLV and ULV and is independent of pH of the buffer used to form the dispersion. However, for a given concentration of PPB, the perturbation in DPPA bilayer is more when the dispersion is prepared in buffer pH 7.4. PPB affected both the thermotropic phase transition and the molecular mobility of the DPPA membrane. In the presence of PPB, the gel to liquid crystalline phase transition temperature (Tm) of the DPPA vesicles decreases hence increases membrane fluidity due to reduced headgroup–headgroup interaction. For all concentrations, the PPB molecules seem to get intercalated between the polar groups of the phospholipids with its alkyl chain penetrating into the co-operative region. At high PPB concentration, additional transitions are observed whose intensity increases with increasing PPB concentration. The large enthalpy values obtained at high PPB concentration suggest that presence of PPB makes the DPPA bilayer more ordered (rigid). The interesting finding obtained with MLV is that the stable gel phase of DPPA-buffer (pH 9.3/7.4) system in the presence of high PPB concentration becomes a metastable gel phase, this metastable gel phase on equilibration at 25 °C or when cooled to −20 °C transforms to a stable crystalline phase(s). The intensity of this new phase(s) increases with increasing PPB concentration. However, the transition temperatures of these new phases are not significantly changed with increasing PPB concentration. The effect of inclusion of cholesterol in the PPB-free and PPB-doped DPPA dispersion was also studied.The DSC heating scans of DPPA in buffer pH 9.3 and 7.4, containing increasing concentrations of PPB, obtained at a scan rate of 5 °C/min, and for equilibration time,τe≈0 are shown in figures (a) and (b), respectively.
Keywords: DPPA; Differential scanning calorimetry; NMR; ParabensAbbreviations; DSC; differential scanning calorimetric; PPB; propyl paraben; DPPA; dipalmitoyl phosphatidic acid; CM; chain melting; NMR; nuclear magnetic resonance
Synthesis and size control of monodisperse copper nanoparticles by polyol method
by Bong Kyun Park; Sunho Jeong; Dongjo Kim; Jooho Moon; Soonkwon Lim; Jang Sub Kim (pp. 417-424).
We describe herein the synthesis of metallic copper nanoparticles in the presence of poly(vinylpyrrolidone), employed as a protecting agent, via a polyol method in ambient atmosphere. The obtained copper particles were confirmed by XRD to be crystalline copper with a face-centered cubic (fcc) structure. We observed monodisperse spherical copper nanoparticles with a diameter range45±8 nm. The particle size and its distribution are controlled by varying the synthesis parameters such as the reducing agent concentration, reaction temperature, and precursor injection rate. The precursor injection rate plays an important role in controlling the size of the copper nanoparticles. On the basis of XPS and HRTEM results, we demonstrate that the surface of the copper is surrounded by amorphous CuO and that poly(vinylpyrrolidone) is chemisorbed on the copper surface.We describe the synthesis of metallic copper nanoparticles in the presence of poly(vinylpyrrolidone), employed as a protecting agent, via a polyol method in ambient atmosphere.
Keywords: Cu nanoparticles; Polyol synthesis; Particle size control; Surface characterization; Conductive ink
Functionalized polymer colloids bearing primary amino groups
by M. Schmitt; J. Wagner; G. Jung; R. Hempelmann (pp. 425-429).
Polymer colloids are prepared via radicalic emulsion polymerisation of butylacrylate. Functionalization with amino groups is achieved by copolymerisation of 2-amino-ethylmethacrylates. In order to over-compensate the positive surface charges resulting from the amino groups additionally vinylbenzenesulfonic acid is copolymerized. The size of the resulting particles is controlled by the molar ratio of amino to sulfonic acid groups. The suitability of amino groups for coupling reactions is demonstrated by electrophilic addition of fluorescein-5-isothiocyanate. The resulting particles are characterized by dynamic light scattering and zeta potential measurements as well as by optical spectroscopy. The suitability of labelled particles for optical tracer experiments is demonstrated by fluorescence correlation spectroscopy.Particle size distribution of polymer particles bearing primary amino groups. The size and size distribution can be tuned by the molar ratio of the copolymers vinylbenzenesulfonic (VBS) acid and 2-amino-ethylmethacrylate (AEMA).
Keywords: Emulsion polymerisation; Polymer colloids; Fluorescence labelling
Interaction forces between particles stabilized by a hydrophobically modified inulin surfactant
by Jérémie Nestor; Jordi Esquena; Conxita Solans; Paul F. Luckham; Michael Musoke; Bart Levecke; Karl Booten; Tharwat F. Tadros (pp. 430-437).
The adsorption isotherm of a hydrophobically modified inulin (INUTEC SP1) on polystyrene (PS) and poly(methyl methacrylate) (PMMA) particles was determined. The results show a high affinity isotherm for both particles as expected for a polymeric surfactant adsorption. The interactions forces between two layers of the hydrophobically modified inulin surfactant adsorbed onto a glass sphere and plate was determined using a modified atomic force microscope (AFM) apparatus. In the absence of any polymer, the interaction was attractive although the energy of interaction was lower than predicted by the van der Waals forces. The results between two layers of the adsorbed polymer confirms the adsorption isotherms results and provides an explanation to the high stability of the particles covered by INUTEC SP1 at high electrolyte concentration. Stability of dispersions against strong flocculation could be attributed to the conformation of the polymeric surfactant at the solid/liquid interface (multipoint attachment with several loops) which remains efficient at Na2SO4 concentration reaching 1.5 mol dm−3. The thickness of the adsorbed polymer layer in water determined both by AFM and rheology measurements, was found to be about 9 nm.Interaction forces as a function of separation distance, at different electrolyte concentrations.
Keywords: Hydrophobically modified inulin; Colloidal stability; Interaction forces; Atomic force microscopy
Thickening properties and emulsification mechanisms of new derivatives of polysaccharide in aqueous solution
by Eri Akiyama; Takamasa Yamamoto; Yuuko Yago; Hajime Hotta; Takeshi Ihara; Tomohito Kitsuki (pp. 438-446).
The thickening properties and association behavior of aqueous solutions of HHM-HEC (hydrophobically–hydrophilically modified hydroxyethyl cellulose) with various hydrophobic and hydrophilic substitution degrees were investigated. The HHM-HEC was used as an oil-in-water emulsifier and stable compositional regions were investigated as a function of polymer concentration and substitution degree. The viscosity of aqueous solutions of HHM-HEC increased drastically at lower concentration for HHM-HEC with a higher hydrophobic/hydrophilic substitution ratio. The intensity ratio of the first and third vibrational bands of pyrene (I1/I3) decreased with the increase of HHM-HEC concentration and theI1/I3 reached a lower plateau at a lower concentration for HHM-HEC with a higher hydrophobic/hydrophilic substitution ratio. The concentration ranges of HHM-HEC solutions which stabilize O/W emulsions differ by the hydrophobic/hydrophilic substitution ratio. However the viscosity ranges of these HHM-HEC solutions were almost the same regardless of the hydrophobic/hydrophilic substitution ratio. At the suitable concentration range for emulsification, HHM-HEC networks have two properties: (1) oil particle retention capacity and (2) laxation which can trap emulsified particles.
Keywords: Hydrophobically–hydrophilically modified hydroxyethyl cellulose; Amphiphilic water-soluble polymer; Oil-in-water emulsion; Hydrophobic modification; Hydrophilic modification; Physical network
Covalently closed microemulsions in presence of triblock terpolymers
by Stefanie Lutter; Brigitte Tiersch; Joachim Koetz; Adriana Boschetti-de-Fierro; Volker Abetz (pp. 447-455).
This paper is focused on the influence of polystyrene (PS)–poly(1,4-butadiene) (PB)–poly(ethylene oxide) (PEO) triblock terpolymers on the w/o microemulsion of the pseudo-ternary system water/sodium dodecylsulfate (SDS)/xylene-pentanol. Despite the insolubility of the copolymer in water as well as in the xylene–pentanol mixture, it can be incorporated into the w/o microemulsion and interactions between the triblock terpolymer molecules and the anionic surfactant headgroups can be detected by differential scanning calorimetry (DSC) measurements. Furthermore, dynamic light scattering measurements were used to determine the aggregate diameter of the modified microemulsions. For lower polymer concentrations large aggregates between 100 and 500 nm can be observed. Surprisingly, at a higher terpolymer concentration of 5 wt%, significant smaller aggregate diameters can be identified by dynamic light scattering and Cryo-SEM. One can conclude that the copolymers are incorporated in the inverse microemulsion droplets, where the PB blocks cover the water droplets. The thermally induced radical cross-linking of the butadiene units in the presence of azobisisobutyronitrile (AIBN) leads then to covalently closed nanocapsules with an average size of 10 nm.Scheme of a water-in-oil polymer-modified microemulsion covalently closed due to the crosslinking of butadiene units of triblock terpolymers.
Keywords: Triblock terpolymer; Microemulsion; Nanocapsules
Silver microflowers and large spherical particles: Controlled preparation and their wetting properties
by Wei Song; Huiying Jia; Qian Cong; Bing Zhao (pp. 456-460).
In this article, we report a simple wet-chemical method to prepare silver microflowers and large spherical particles. The formation of the two different microstructures of silver is based on the reduction of AgNO3 by para-phenylenediamine in aqueous medium at room temperature. The controlling of the silver microstructures can be achieved only by adjusting the concentration of the reactants. It is found that the two different silver microstructures display opposite wetting properties. Large spherical silver particles exhibit superhydrophilic properties with a contact angle (CA) of close to 0°, microflower-like silver particles exhibit highly hydrophobic properties with CA about 132°. X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and UV–vis spectra are used to characterize the chemical structure of the obtained products.Large spherical and microflower-like silver particles were obtained by simple wet-chemical method. It was found large spherical silver particles exhibit superhydrophilic properties with a contact angle (CA) of close to 0°, microflower-like silver particles exhibit highly hydrophobic properties with CA about 132°.
Keywords: Silver; Microflowers; Large spherical particles; Wetting properties
Nickel nanoparticles obtained by a modified polyol process: Synthesis, characterization, and magnetic properties
by Giselle G. Couto; João J. Klein; Wido H. Schreiner; Dante H. Mosca; Adilson J.A. de Oliveira; Aldo J.G. Zarbin (pp. 461-468).
The synthesis of nickel nanoparticles using poly( N-vinilpyrrolidone) (PVP) as protective agent was studied. The nanoparticles were prepared in air according to a modified polyol route, using nickel chloride as precursor and sodium borohydride as reducing agent. Samples with different nickel/PVP ratio were obtained. The X-ray diffraction and transmission electron microscopy (TEM) measurements indicate the occurrence of face-centered cubic metallic nickel nanoparticles with a medium diameter of 3.8 nm and good size dispersion. Fourier transformed infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) data show an effective interaction between the nickel nanoparticles surface and the carboxyl oxygen atoms of PVP. Magnetic measurements show single-domain nonideal superparamagnetism behavior due to dipolar magnetic coupling between particles.The picture represents a TEM image showing spherical PVP-coated Ni nanoparticles prepared by a modified polyol route.
Keywords: Nickel nanoparticles; Polyol; Magnetic measurements
Preparation of magnetite nanocrystals with surface reactive moieties by one-pot reaction
by Fengqin Hu; Zhen Li; Chifeng Tu; M.Y. Mingyuan Gao (pp. 469-474).
By one-pot reaction, biocompatible magnetite nanocrystals with surface reactive moieties were prepared through the thermal decomposition of Fe(acac)3 in 2-pyrrolidone usingα,ω-dicarboxyl-terminated poly(ethylene glycol) as surface capping molecule. The successful conjugation between the magnetite nanocrystals and 9-amino acridine on the one hand demonstrates the existence of free carboxylic groups from PEG binding on the particle surface, on the other hand may also lead to a new type of magneto-optical materials as well as magneto-drugs.By one-pot reaction, through the thermal decomposition of Fe(acac)3 in 2-pyrrolidone, biocompatible magnetite nanocrystals with surface reactive moieties were prepared usingα,ω-dicarboxyl-terminated poly(ethylene glycol) as a surface capping agent. An EDC-mediated coupling reaction was conducted to link 9-amino acridine (9-AA) with Fe3O4 nanocrystals to detect the existence of the carboxylic groups on the particle surface.
Keywords: Reactive surface moieties; Biocompatible Fe; 3; O; 4; nanocrystals; One-pot reaction
An experimental method for the measurement of the stability of concentrated magnetic fluids
by G.R. Iglesias; L. Fernández Ruiz-Morón; J. Insa Monesma; J.D.G. Durán; A.V. Delgado (pp. 475-480).
In this paper we present a device and method suited to the experimental determination of the sedimentation rate of concentrated suspensions of magnetic particles. The method is based on the measurement of the inductance of one or more sensing coils located at specified positions around a test tube containing the suspension. Such measurement is made possible by the determination of the resonant frequency of a parallel LC circuit in which L is the inductance of the sensing coil and C is the capacity of a capacitor chosen in such a way that the resonant frequency is easily measured. Upon calibration it is possible to relate the resonant frequency to the volume fraction of the particles at the coil location. The method is applied in the present work to the evaluation of the sedimentation kinetics of iron suspensions in base fluids of viscosities ranging from 0.3 to 100 mPa s and volume fractions of solids between 2.5 and 25%. Both if a single coil is used and if a set of three coils at different positions are employed, it is possible to detect the rate of accumulation of particles at the bottom of the container as well as a phenomenon of buoyancy of the largest particles brought about by the hydrostatic push of a dense fluid consisting of the smallest particles in the supporting liquid.
Keywords: Inductance; Magnetic fluids; Resonant frequency; Sedimentation kinetics; Stability
Heterogeneous photodegradation of bisphenol A with iron oxides and oxalate in aqueous solution
by F.B. Li; X.Z. Li; X.M. Li; T.X. Liu; J. Dong (pp. 481-490).
To understand the degradation of endocrine disrupting chemicals (EDCs) with existence of iron oxides and polycarboxylic acids in the natural environment, the photodegradation of bisphenol A (BPA) at the interface of iron oxides under UV illumination was conducted. Four iron oxides were prepared by a hydrothermal process and then sintered at different temperatures of 65, 280, 310, and 420 °C named “IO-65,” “IO-280,” “IO-310,” and “IO-420,” respectively. The prepared iron oxides were characterized by X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) methods. The XRD pattern of IO-65 showed a crystal structure of lepidocrocite ( γ-FeOOH) and that of IO-420 demonstrated a crystal structure of hematite ( α-Fe2O3), while IO-280 and IO-310 have the mixed crystal structures of maghemite ( γ-Fe2O3) and hematite. The BET results revealed that the specific surface areas decreased with the increase of sintering temperature. The results demonstrated that the photodegradation of BPA depends strongly on the properties of iron oxides and oxalate, and pH. The properties of iron oxides influenced strongly the dependence of the BPA degradation on the oxalate concentration. The optimal initial concentrations of oxalate for BPA degradation under UV illumination were determined to be 2.0, 2.0, 2.4, and 2.0 mM for IO-65, IO-280, IO-310, and IO-420, respectively. The first-order kinetic constants k for BPA degradation under UV illumination in the presence of oxalate with the optimal initial concentration are ranked as IO-280>IO-310>IO-65>IO-420. The experiments demonstrated that the optimal pH value should be in the range of 3–4. Furthermore, the dependence of BPA degradation should be also attributable to the formation of the dissolved Fe–oxalate in the solution and the adsorbed Fe–oxalate on the surface of iron oxides, and also the formation of hydrogen peroxide.
Keywords: Bisphenol A; Iron oxides; Oxalic acid; Photodegradation
In situ Raman monitoring triazole formation from self-assembled monolayers of 1,4-diethynylbenzene on Ag and Au surfaces via “click” cyclization
by Bum Keun Yoo; Sang-Woo Joo (pp. 491-496).
We prepared acetylenyl-terminated aromatic self-assembled monolayers (SAMs) of 1,4-diethynylbenzene on silver and gold. After the fabrication of pendent acetylenyl SAMs, the formation of triazoles was performed via Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition “click” chemistry. A density functional theory (DFT) calculation of Raman frequencies showed good agreement with our experimental data to provide evidence of the formation of the triazole molecule. Our results indicated that “click” chemistry could be successfully applied to simple aromatic SAMs proximate (<1nm) to roughened gold surfaces. The reaction process could be monitored in real time by measuring intensity changes of the ν(CC)free band in surface-enhanced Raman scattering (SERS) spectra.
Keywords: 1,4-Diethynylbenzene; Self-assembled monolayers; Ag; Au; Click chemistry; SERS
Enhancement of photocatalytic activity of P25 TiO2 by vanadium-ion implantation under visible light irradiation
by Jinkai Zhou; Masato Takeuchi; Ajay K. Ray; Masakazu Anpo; X.S. Zhao (pp. 497-501).
An ion-implantation method was used to prepare V-ion-implanted P25 TiO2 photocatalysts. Their photocatalytic activity for the degradation of formic acid under visible light irradiation (λ>450 nm) was investigated. Upon implantation of V ions into the lattice of P25 TiO2, the photoactivity was remarkably enhanced. HRTEM images showed that the implanted V ions existed in the form of VO2(T) in the lattice of P25 TiO2. The intensity of photoluminescence (PL) spectra of V-ion-implanted P25 TiO2 decreased with the increase of the amount of implanted V ions, indicating the decrease of electron–hole pair recombination. It was also observed that the lower the PL intensity of V-ion-implanted P25 TiO2, the higher the photoactivity.V ions implanted into the lattice of TiO2 as VO2(T).
Keywords: Vanadium-ion implantation; Visible light irradiation; Photocatalytic activity
An investigation of the surface-enhanced Raman scattering effect from new substrates of several kinds of nanowire arrays
by Lisheng Zhang; Pengxiang Zhang; Yan Fang (pp. 502-506).
Silver, titanium, nickel, and aluminum nanowire arrays with diameters from 90 to 110 nm were prepared on AAO templates by laser molecular beam epitaxy. On the several kinds of nanowire arrays, high-quality surface-enhanced Raman scattering (SERS) spectra of probe molecules of the red dye Sudan II (C18H16N2O) were obtained. In particular, the SERS spectrum of Sudan II on an aluminum nanowire array is reported for the first time.Silver, titanium, nickel, and aluminum nanowire arrays with diameters from 90 to 110 nm were prepared on AAO templates by laser molecular beam epitaxy (LMBE). On the several kinds of nanowires arrays, high quality surface enhanced Raman scattering (SERS) spectra of probe molecules red dye Sudan II (C18H16N2O) were obtained. Especially, the SERS spectrum of Sudan II on an aluminum nanowire array was reported for the first time.
Keywords: SERS; LMBE; Nanowires arrays
Preparation and self-assembly of carboxylic acid-functionalized silica
by Yanqing An; Miao Chen; Qunji Xue; Weimin Liu (pp. 507-513).
A simple method for the fabrication of silica nanoparticle film based on the covalent-bonding interaction between carboxylic acid-functionalized silica nanoparticles (SiO2–COOH) and amino-terminated silicon wafer was developed. Prior to assembly, silica nanoparticles with an average diameter 80 nm were prepared using the Stöber method, amino-functionalized silica nanoparticles (SiO2–NH2) were prepared by a silanization with 3-aminopropyltriethoxysilane (APTES), while carboxylic acid-functionalized silica nanoparticles (SiO2–COOH) were prepared by a ring opening linker elongation reaction of the amine functions with succinic anhydride, at the same time, amino-terminated silicon wafer (Si–NH2) was obtained by self-assembling 3-aminopropyltriethoxysilane, then one layer relative close-packed carboxylic acid-functionalized silica nanoparticles (SiO2–COOH) was arranged on silicon wafer through amidation reaction under DCC coupling agent.Synthesis carboxylic acid functional silica nanoparticle, then self-assembly on amine-terminated silicon wafer through amidation.
Keywords: Surface functionalization; Covalent assembly; Amidation; Carboxylic acid-functionalized silica nanoparticles
Synthesis, characterization, and visible light activity of new nanoparticle photocatalysts based on silver, carbon, and sulfur-doped TiO2
by Dambar B. Hamal; Kenneth J. Klabunde (pp. 514-522).
New nanoparticle photocatalysts based on silver, carbon, and sulfur-doped TiO2 having only the homogeneous anatase crystalline phase and high surface area were successfully synthesized by a modified sol–gel route. The catalysts were characterized by EDX, XRD, BET, UV–vis, IR, and Raman spectroscopy. The effects of the experimental parameters on the visible light reactivity of the catalysts were evaluated for the photodegradation of gaseous acetaldehyde as a model indoor pollutant. The activity results show that the silver(I) ion, Ag+, doping significantly promotes the visible light reactivities of carbon and sulfur-doped TiO2 catalysts without any phase transformation from anatase to rutile. Moreover, Ag/(C, S)–TiO2 photocatalysts degrade acetaldehyde 10 times faster in visible light and 3 times faster in UV light illuminations than the accredited photocatalyst P25–TiO2. The commendable visible photoactivities of Ag/(C, S)–TiO2 new nanoparticle photocatalysts are predominantly attributable to an improvement in anatase crystallinity, high surface area, low band gap and nature of precursor materials used.New nanoparticle photocatalysts based on silver, carbon, and sulfur-doped titania (Ag/(C, S)–TiO2) degrade efficiently gaseous acetaldehyde under (a) visible and (b) UV light.
Keywords: Ag; +; -doped TiO; 2; Visible light activity; Titania; Doping; C-doped TiO; 2; Nanoparticles; Acetaldehyde; Photocatalysts; S-doped TiO; 2
Electrochemical behavior and luminescent properties of a multilayer film containing mixed-addenda polyoxometalates K10H3[Eu(SiMo9W2O39)2] and tris(2,2′-bipyridine)ruthenium(II)
by Tao Dong; Huiyuan Ma; Wei Zhang; Lihong Gong; Fuping Wang; Chunxiang Li (pp. 523-529).
Inorganic–organic composite films containing the mixed-addenda heteropolytungsto-molybdate K10H3[Eu(SiMo9W2O39)2]⋅ xH2O (abbreviated as EuSiMo9W2) and tris(2,2′-bipyridine)ruthenium(II) Ru(bpy)2+3 (abbreviated as Ru(bpy)3) were fabricated by the layer-by-layer self-assembly method. UV–vis spectroscopy shows that the absorbance values at characteristic peaks increase linearly with the number of EuSiMo9W2/Ru(bpy)3 bilayers, suggesting that the deposition process is linear and highly reproducible from layer to layer. The composition of the multilayer film was measured by X-ray photoelectron spectra. Atomic force microscopy presented a correspondingly uniform surface morphology and a homogeneity of the multilayer films. The film exhibited photoluminescence arising from thed–π∗ metal-to-ligand transition of Ru2+, and5D0 metastable state to terminate levels in the7FJ (J=0–4) ground-state multiplet transitions of Eu3+. The film also exhibited catalytic activities toward the reduction of IO−3, H2O2, BrO−3, NO−2 and the oxidation of C2O2−4. It may provide a novel material as bifunctional electrocatalysts and fluorescence probes in biochemistry, luminescence sensors, electroluminescent optical devices, and so on.An inorganic–organic composite film containing the mixed-addenda heteropolytungsto-molybdate K10H3[Eu(SiMo9W2O39)2]⋅ xH2O and tris(2,2′-bipyridine)ruthenium(II) Ru(bpy)2+3 was fabricated by the layer-by-layer self-assembly method. The film exhibited photoluminescence arising fromd–π∗ metal-to-ligand transition of Ru2+, and5D0 metastable state to terminate levels in the7FJ (J=0–4) ground-state multiplet transitions of Eu3+. The film also exhibited catalytic activities towards the reduction of IO−3, H2O2, BrO−3, NO−2 and the oxidation of C2O2−4.
Keywords: Layer-by-layer; Thin film; Polyoxometalate; Electrocatalysis
Cleavage of phosphate diesters mediated by Zn(II) complex in Gemini surfactant micelles
by Weidong Jiang; Bin Xu; Qi Lin; Jianzhang Li; Haiyan Fu; Xiancheng Zeng; Hua Chen (pp. 530-536).
The cleavage of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) catalyzed by the Zn(II)–biap (biap:N,N-bis(2-ethyl-5-methylimidazole-4-ylmethyl)aminopropane) complex has been investigated spectrophotometrically in a micellar solution of cationic Gemini surfactant 16-2-16 [bis(hexadecyldimethylammonium)ethane bromide] and CTAB (hexadecyltrimethylammonium bromide) at25±0.1°C. The experimental results reveal that a higher rate of acceleration (about 2016-fold) of HPNP cleavage promoted by the Zn(II)–biap complex has been observed in the 16-2-16 micellar solution in comparison with the background rate (k0) of HPNP spontaneous cleavage at 25 °C. Reaction rates of HPNP cleavage in CTAB micellar solutions are only about 40% of that in Gemini 16-2-16 micelles under comparable conditions. In addition, the cleavage rates of HPNP in Gemini micelles and in CTAB micelles are respectively 29.5 times and 12 times faster than that in aqueous buffer. Especially, a “sandwich absorptive mode” has been proposed to explain the acceleration of HPNP cleavage in a cationic micellar solution.Metal-promoted cleavage of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP) in Gemini 16-2-16 micelles has firstly been evaluated. A 29.5- and 2.5-fold kinetic advantages in Gemini 16-2-16 micelles have respectively been observed in comparison with in pure buffer and CTAB micelles.
Keywords: HPNP cleavage; Catalysis; Surface absorption; Gemini 16-2-16 micelles; Zinc(II) complex
Solid acid catalysts from clays: Preparation of mesoporous catalysts by chemical activation of metakaolin under acid conditions
by M. Lenarda; L. Storaro; A. Talon; E. Moretti; P. Riello (pp. 537-543).
Natural kaolin was treated at 850 or 950 °C in air flow to give respectively the metakaolin samples MK8 and MK9. The obtained materials were successively treated at 90 °C with a 1 M solution of H2SO4, for various time lengths. The acid treatment of MK8 was found to give a high surface area microporous material with good catalytic properties related to the high density of acid sites, while MK9 gave an ordered mesoporous material with a low density of acid sites. The materials were characterized by several techniques, X-ray powder diffraction, thermogravimetric analysis, N2 physisorption, scanning electron microscopy, and temperature-programmed desorption of ammonia. The 1-butene isomerization was used as test reaction to evaluate the acidity of the samples.Natural kaolin was treated at 850 or 950 °C to give respectively the metakaolin samples MK8 and MK9. The obtained materials were successively treated at 90 °C with a 1 M solution of H2SO4, for various time lengths. The acid treatment of MK8 was found to give a high surface area microporous material with good catalytic properties related to the high density of acid sites, while MK9 gave an ordered mesoporous material with a low density of acid sites.
Keywords: Metakaolin; Acid treatment; Acid catalyst; Microporosity; Mesoporosity
Surface arsenic speciation of a drinking-water treatment residual using X-ray absorption spectroscopy
by Konstantinos C. Makris; Dibyendu Sarkar; Jason G. Parsons; Rupali Datta; Jorge L. Gardea-Torresdey (pp. 544-550).
Drinking-water treatment residuals (WTRs) present a low-cost geosorbent for As-contaminated waters and soils. Previous work has demonstrated the high affinity of WTRs for As, but data pertaining to the stability of sorbed As is missing. Sorption/desorption and X-ray absorption spectroscopy (XAS), both XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) studies, were combined to determine the stability of As sorbed by an Fe-based WTR. Arsenic(V) and As(III) sorption kinetics were biphasic in nature, sorbing>90% of the initial added As (15,000 mg kg−1) after 48 h of reaction. Subsequent desorption experiments with a high P load (7500 mg kg−1) showed negligible As desorption for both As species, approximately<3.5% of sorbed As; the small amount of desorbed As was attributed to the abundance of sorption sites. XANES data showed that sorption kinetics for either As(III) or As(V) initially added to solution had no effect on the sorbed As oxidation state. EXAFS spectroscopy suggested that As added either as As(III) or as As(V) formed inner-sphere mononuclear, bidentate complexes, suggesting the stability of the sorbed As, which was further corroborated by the minimum As desorption from the Fe-WTR.Arsenic K-edge EXAFS of As(V) (graph A) and As(III) (graph B) sorbed by the Fe-based drinking-water treatment residual showed inner-sphere mononuclear, bidentate complexes, suggesting the stability of the sorbed As.
Keywords: Residuals; Drinking water; Stability; Arsenic (As); XANES; EXAFS; Remediation
Thermodynamic studies of bovine lung surfactant extract mixing with cholesterol and its palmitate derivative
by A.K. Panda; K. Nag; R.R. Harbottle; F. Possmayer; N.O. Petersen (pp. 551-555).
Langmuir film behavior of bovine lipid extract surfactant (BLES), mixed with cholesterol (CHOL) and cholesterol palmitate (CHOLP), has been studied by surface pressure ( π)–area ( A) measurements. Associative interactions, observed for both systems, were less favored at lower BLES content. The presence of unsaturated phospholipids and surfactant proteins in BLES favored the association. Miscibility of BLES was better with CHOLP than with CHOL at all compositions, indicating more compact packing of the BLES–CHOLP than of the BLES–CHOL system. The most stable mixtures were found at 30–40 mol% CHOL and at low π and at 20–25 mol% CHOLP but at higher π. These results suggest that BLES–CHOL miscibility is better at low π and low CHOL concentrations, while BLES–CHOLP miscibility is better at high π and high CHOLP concentrations.Aex/Aid as a function of composition for mixed monolayers of BLES/CHOL and BLES/CHOLP at 296 K.
Keywords: BLES; Cholesterol; Cholesterol palmitate; Excess area; Miscibility; Surface pressure
Microemulsion breakdown by pervaporation technique: Effect of the alkyl chain length of n-alkanol, a cosurfactant of the microemulsion
by Saâd Moulay; Amel Zafour Hadj-Ziane; Jean-Paul Canselier (pp. 556-561).
Two sets of microemulsions, cyclohexane- and water-rich ones, were prepared with the following n-alkanols as cosurfactants: n-propanol, n-butanol, n-pentanol, and n-hexanol. The results showed the influence of the alkyl chain length of the n-alkanol on the permselectivity properties of the pervaporation technique in the breakdown of the microemulsions. The variations of the total flux rate J and the enrichment factor β were in parallel with the effect of the cosurfactant on the swelling extent of the PDMS membrane.
Keywords: n; -Alkanol; Microemulsion; PDMS membrane; Pervaporation
Mesoscopic simulations of phase distribution effects on the effective thermal conductivity of microgranular porous media
by Moran Wang; Ning Pan; Jinku Wang; Shiyi Chen (pp. 562-570).
This paper analyzes the phase distribution effects on the effective thermal conductivity (ETC) of multi-phase microgranular porous media using mesoscopic statistics based numerical methods. A multi-parameter random generation-growth method, quartet structure generation set (QSGS), is developed for replicating microstructures of multi-phase granular porous media based on the macroscopic statistical information, such as the volume fractions and the phase interactions. The phase distribution characteristics and the interphase connections are controlled by adjusting the related parameters. Then the energy transport equations through porous media are solved by a lattice Boltzmann method developed by us with multi-phase conjugate heat transfer considered. The results indicate that a smaller average particle size could lead to a larger effective thermal conductivity of two-phase porous media for a certain porosity. For the anisotropic media, if the larger directional growth probability is along the direction of temperature gradient, the effective thermal conductivity in the parallel direction is enhanced as a result, and that in the vertical direction will be weakened. For multi-phase porous media, the degree of phase conglomeration is determined by the phase interactions. A larger liquid–liquid interaction leads to a higher degree of liquid phase conglomeration and therefore a larger effective thermal conductivity of the porous media.We present a numerical tool to model the effective thermal conductivity of multi-phase porous media and analyze the phase distribution effects on the effective thermal conductivity of microporous media.
Keywords: Effective thermal conductivity; Microporous media; Phase distribution; Anisotropy
DC conductivity, cationic exchange capacity, and specific surface area related to chemical composition of pore lining chlorites
by François Henn; Claudine Durand; Adrian Cerepi; Etienne Brosse; J.C. Giuntini (pp. 571-578).
Low resistivity in argillaceous sandstone reservoirs may be attributed either to the effect of microporosity, or to specific effects due to intrinsic clays' conducting properties or to other conducting minerals. In order to distinguish these effects, cation exchange capacity, specific surface areas, and dc conductivity of various pore lining chlorite-bearing sandstones from different hydrocarbon reservoir measurements are investigated. Cation exchange capacity and specific surface area are measured on whole rocks as well as on size-separated fractions. Both sets of values are low, in agreement with the structural and textural observations. The conductivity of these chlorites, measured in air conditions and after dehydration, is investigated by means of complex impedance spectroscopy on size-separated fractions as a function of temperature and compared to that of reference clays. The results show a large influence of moisture, applied electric field frequency, and temperature on the electrical properties. The magnitude of the dehydrated clays' conductivity is such that its influence on the conductivity of argillaceous sandstone is lower than that related to the presence of water or brine by several orders of magnitude. The dc conductivity and the related activation energy of the dehydrated samples appear to be related to the chemical composition of the clays. More specifically, a clear correlation occurs with the electrical charges of the clay network, that is to say with the location, i.e., tetrahedral or octahedral sites, of the substituting trivalent elements.This work emphasises that the low resistivity measured in argillaceous sandstone reservoirs cannot be correlated to the intrinsic, i.e., dehydrated conductivity of clays, as shown from the conductivity analysis of a series of reference clays and chlorites extracted from argillaceous sandstone reservoirs. On the other hand, it is shown that a correlation exists between the intrinsic clay conductivity and the localisation of the substituting trivalent cations into the clay structure.
Keywords: Clays; Sandstones; Conductivity; Specific surface area; Cationic exchange capacity
Prediction of solid–water–hydrocarbon contact angle
by Alireza Bahramian; Ali Danesh (pp. 579-586).
The reliability of a recently developed solid–vapour and solid–liquid interfacial tension models has been investigated by applying them to predict liquid–vapour and liquid–liquid interfacial tension values. The impact of the geometrical molecular packing and the molecular orientations near the surface on the predicted values are discussed. The mutual solubility data are shown to be adequate for calculation of the interaction parameters in the solid–liquid model and a new equation, using this information, is developed for prediction of water–hydrocarbon interfacial tension. The model has been applied to recent data on water–methane– n-decane and water–methane–cyclohexane– n-decane interfacial tensions at elevated temperature and pressure and its reliability demonstrated. It is shown that the solid–liquid interfacial tension model is solely adequate for predicting the contact angle by applying it to mercury–water–benzene and stearic acid–water– n-decane systems.It is shown that the solid–liquid interfacial tension model along with the solubility data is solely adequate for predicting the contact angle.
Keywords: Contact angle; Interfacial tension; Solid–fluid interface; Water–hydrocarbon
Interfacial behavior of common food contact polymer additives
by W.M. Heiserman; S.Z. Can; R.A. Walker; T.H. Begley; W. Limm (pp. 587-594).
Irganox 1076 (IN1076) and Irganox 1010 (IN1010), phenol containing species often used as antioxidant additives in food packaging polymers have both hydrophilic and hydrophobic functional groups. Consequently these additives are likely to absorb to surfaces where their free energy is minimized. Experiments described in this work examine the two-dimensional phase behavior and vibrational structure of IN1076 and IN1010 films adsorbed to the air/water interface. Surface pressure isotherms show that repeated compression of these films leads to continued irreversible loss of molecules and that on a per molecule basis, this loss is more pronounced for IN1076 than for IN1010. Differences in the surface properties of these two antioxidant additives are interpreted based on differences in molecular structure. Surface specific vibrational measurements of these organic films show very little conformational order, implying that even when closely packed, both antioxidant species have little affinity for forming highly organized domains. These findings have important ramifications for mechanisms that reduce antioxidant activity in polymers as well as descriptions of antioxidant blooming on polymer surfaces.Successive compressions of organic films formed at the air/water interface from Irganox 1076, a common antioxidant additive in polymers, show irreversible loss of material.
Keywords: Irganox 1076; Irganox 1010; Phenol; Air–water interface; Isothermal compression; Surface pressure; Vibrational sum frequency spectroscopy (VSFS); Aggregation; Organization; Surfactants; Antioxidant additives; Food packaging material
Electric field induced instabilities in thin confined bilayers
by Dipankar Bandyopadhyay; Ashutosh Sharma (pp. 595-608).
A long wave nonlinear theory and simulations on the electric field induced instability of a thin (<1000 nm thick) viscous bilayer resting on a solid substrate are presented. The instabilities in these systems are initiated by one of the two basic short time modes of deformation at the twin interfaces—in-phase bending or out of phase squeezing. Linear stability analysis (LSA) is carried out to identify the conditions for these modes. It is shown that these modes can be switched and the relative amplitudes of deformation at the interfaces can be profoundly altered by varying the thicknesses, viscosities, interfacial tensions and dielectric constants of the films. Nonlinear simulations are presented to support the results obtained from the LSA. In addition, simulations show a number of interesting interfacial morphologies including: (a) embedded upper layer in the array of lower layer columns, (b) columns of the upper layer grown towards the substrate and sheathed by the lower layer liquid, (c) lower layer columns sheathed by the upper layer liquid leading to concentric core–shell columns, (d) droplets of upper liquid on the largely undisturbed lower layer, (e) symmetry breaking traveling waves at the interfaces, and (f) evolution of two different wavelengths at the two interfaces of a bilayer. The effects of viscous and the capillary resistances on the evolution of instability and morphology are also discussed.Electric field induced interfacial morphologies at the bilayer interfaces.
Keywords: Thin film; Bilayer; Electric field instability; Interfacial dynamics
Simulation of droplet formation and coalescence using lattice Boltzmann-based single-phase model
by Xiu Qing Xing; David Lee Butler; Sum Huan Ng; Zhenfeng Wang; Steven Danyluk; Chun Yang (pp. 609-618).
A lattice Boltzmann method-based single-phase free surface model is developed to study the interfacial dynamics of coalescence, droplet formation and detachment phenomena related to surface tension and wetting effects. Compared with the conventional multiphase models, the lattice Boltzmann-based single-phase model has a higher computational efficiency since it is not necessary to simulate the motion of the gas phase. A perturbation, which is given in the same fashion as the perturbation step in Gunstensen's color model, is added to the distribution functions of the interface cells for incorporating the surface tension into the single-phase model. The assignment of different mass gradients along the fluid–wall interface is used to model the wetting properties of the solid surface. Implementations of the model are demonstrated for simulating the processes of the droplet coalescence, the droplet formation and detachment from ceiling and from nozzles with different shapes and different wall wetting properties.Implementation of the model demonstrates the simulation of the droplet formation process and the detachment from the ceiling with different wall wetting properties.
Keywords: Lattice Boltzmann; Surface tension; Wetting; Droplet coalescence; Droplet formation
Influence of surface treatments on micropore structure and hydrogen adsorption behavior of nanoporous carbons
by Byung-Joo Kim; Soo-Jin Park (pp. 619-621).
The scope of this work was to control the pore sizes of porous carbons by various surface treatments and to investigate the relation between pore structures and hydrogen adsorption capacity. The effects of various surface treatments (i.e., gas-phase ozone, anodic oxidation, fluorination, and oxygen plasma) on the micropore structures of porous carbons were investigated by N2/77 K isothermal adsorption. The hydrogen adsorption capacity was measured by H2 isothermal adsorption at 77 K. In the result, the specific surface area and micropore volume of all of the treated samples were slightly decreased due to the micropore filling or pore collapsing behaviors. It was also found that in F2-treated carbons the center of the pore size distribution was shifted to left side, meaning that the average size of the micropores decreased. The F2- and plasma-treated samples showed higher hydrogen storage capacities than did the other samples, the F2-treated one being the best, indicating that the micropore size of the porous carbons played a key role in the hydrogen adsorption at 77 K.The figure shows the hydrogen adsorption capacity of each sample treated. It is very interesting that the F-ACFs and P-ACFs showed higher capacities than that of the V-ACFs, whereas the O-ACFs and A-ACFs showed lower capacities, the F-ACFs showing the best hydrogen adsorption.
Keywords: Micropore structure; Surface treatment; Nanoporous carbon; Hydrogen adsorption
Effective adsorption energy distribution function as a new mean-field characteristic of surface heterogeneity in adsorption systems with lateral interactions
by Piotr Zarzycki (pp. 622-627).
Recent papers [W. Piasecki, Langmuir 22 (2006) 6761; P. Zarzycki, Langmuir 22 (2006) 11234; P. Zarzycki, J. Colloid Interface Sci. 306 (2007) 328] showed that the distinction between surface heterogeneity and effects of electrostatic interactions becomes problematic for metal oxide/electrolyte systems. This observation suggests that both mentioned factors can be combined into one (“effective” energy). Hence, the effective adsorption energy distribution function (EAEDF) with the Langmuir isotherm can be used in the framework of integral adsorption isotherm (IAI) instead of the classical adsorption energy distribution function (AEDF) with the Fowler–Guggenheim isotherm. The histogram method was used to obtain the effective distributions from the grand canonical Monte Carlo simulations of H+ ion adsorption. The new approach (IAI/EAEDF) gives a much better description of the heterogeneous metal oxide/electrolyte interface than IAI/AEDF. Moreover, reduced quantities are introduced in order to compare different metal oxide/electrolyte systems in a convenient way.
Keywords: Mean-field approximation; Dynamic surface heterogeneity; Monte Carlo simulation; Effective adsorption energy distribution function
by Arthur Hubbard (pp. 628-628).