Journal of Colloid And Interface Science (v.293, #2)
Editorial Board (CO1).
Adsorption of some bivalent heavy metal ions from aqueous solutions by manganese nodule leached residues by Nigamananda Das; Ranajit Kumar Jana (253-262).
The leached residue, generated after selective extraction of Cu, Ni, and Co in sulfur dioxide-ammonia leaching of manganese nodules, was characterized and batch isothermal adsorption experiments were conducted at ambient temperature to evaluate the effectiveness of the water-washed leached residue for removal of different bivalent metal ions from aqueous synthetic solutions. The effects of pH, initial metal ion concentrations, amount of adsorbent, interfering ions, and heat treatment were also investigated. The uptake of metal ions increased with increasing pH. Under identical conditions the adsorption capacity increased in the order Cd2+ < Cu2+ < Pb2+. The adsorption kinetics was found to follow a first-order rate expression and the experimental equilibrium adsorption data fitted reasonably well to both Langmuir and Freundlich isotherm models. Various metal ions present in the leached residue were found to be released during adsorption of heavy metals, which decreased with increased pH and were practically negligible at pH ∼ 6.0. Desorption of adsorbed metal ions from metal-loaded leached residue and its regeneration ability were also studied. The results obtained could be useful for considering the leached manganese nodules residue as adsorbent for removal of heavy metal ions from contaminated water bodies.
Keywords: Adsorption; Heavy metals; Sea nodules; Desorption;
Mucin at solution/air and solid/solution interfaces by R. Maheshwari; Aruna Dhathathreyan (263-269).
In this paper the surface activity of protein mucin at solution/air interface has been studied. The experiments of the adsorbed protein at solution/air interface have been carried out with a range of protein concentrations at a defined pH. The adsorption of the protein to solid surfaces and the degree of hydrophobicity at solid/solution interface of mucin have been evaluated at different pH and in the presence of Hofmeister electrolyte. The results from these studies have been further substantiated by surface potential measurements of mucin covered surface on stainless steel. Quartz crystal microbalance (QCM) has been used to follow the protein adsorption kinetics from solution to solid surface. The results from these measurements show that the adsorption behavior has a remarkable dependence on the degree of maximum coverage and is almost independent of the ionic strength. Other characteristic features such as maximum adsorption values at the protein isoelectric point (IEP4.7) and low-affinity isotherms that showed surface saturation even under unfavorable electrostatic conditions have been observed. The amount of mucin adsorbed in the presence of electrolytes has been estimated using electron spectroscopy for chemical analysis (ESCA). The study clearly shows that there exists an inverse relationship between the hydrophobicity and surface tension of the protein and also on the hydrated radius of Hofmeister electrolyte used.In this paper the surface activity of protein mucin at solution/air interface has been studied. The adsorption of the protein to solid surfaces and the degree of hydrophobicity at solid/solution interface of mucin has been evaluated at different pH and in the presence of Hofmeister electrolyte. The study clearly shows that there exists an inverse relationship between the hydrophobicity and surface tension of the protein and also on the hydrated radius of Hofmeister electrolyte used.
Cadmium removal from aqueous solutions by hydroxy-8 quinoleine intercalated bentonite by A. Bentouami; M.S. Ouali (270-277).
An Algerian bentonite was purified and modified by intercalation of 8-hydroxyquinolinium ion. These materials were characterized by X-ray diffraction, infrared spectroscopy, and thermal analysis. Comparative batch experiments were performed using bentonite–oxine complex (B–oxine) and sodic bentonite (B-Na) for removing cadmium from aqueous solutions. Kinetics study results of cadmium removal with B-Na and B–oxine fit a pseudo-second-order model. The adsorption isotherm data follow the Langmuir equation in which parameters were calculated. B–oxine has a better cadmium removal capacity (61.35 mg/g) than B-Na (29.41 mg/g). Calculated thermodynamic parameters using the van't Hoff equation showed that the removal process is endothermic with B–oxine and exothermic with B-Na. A mechanism of ion exchange followed by complexation–precipitation is suggested for cadmium removal with B–oxine.
Keywords: Bentonite; 8-Hydroxyquinoleine; Cadmium; Complexation;
Oxidative coupling and the irreversible adsorption of phenol by graphite by Aluisio Cesar de Oliveira Pimenta; James E. Kilduff (278-289).
Uptake of phenol by graphite, and regeneration by methanol extraction, was measured to evaluate irreversible adsorption of phenols to carbon surfaces. The emphasis of this work was to identify the role of oxidative coupling, which has been invoked to explain irreversible phenol sorption by activated carbons. Graphite was chosen as a model carbon surface to eliminate potentially confounding effects of microporosity present in other types of carbonaceous sorbents. The isotherm data were well described by the Langmuir–Freundlich isotherm from pH 3 to 9. At pH 12, measured uptakes were higher than expected based on model predictions, suggesting the occurrence of an adsorption mechanism besides physisorption. One oxidative coupling product, 2,2′-dihydroxybiphenyl, was obtained exclusively after adsorption at pH values above 7, and appeared both in aqueous solution and in the methanol regenerant solution. The fraction of total uptake that was not recoverable by methanol extraction decreased with increasing phenol concentration in solution, suggesting preferential sorption by high-energy sites. However, absolute irreversible adsorption increased with phenol concentration in solution. Both fractional irreversible adsorption and 2,2′-dihydroxybiphenyl oxidative coupling product recovery as a function of pH and contact time demonstrated that irreversible sorption of phenol by graphite could not be explained by an oxidative coupling mechanism alone.Uptake of phenol by graphite, and regeneration by methanol extraction, was measured to evaluate and identify the role of oxidative coupling in irreversible adsorption of phenols to carbon surfaces.
Keywords: Graphite; Oxidative coupling; Irreversible adsorption; Phenol; Dihydroxybenzene;
Electro-optics of colloid–polyelectrolyte complexes: Counterion release from adsorbed macromolecules by Tsetska Radeva; Kamelia Kamburova (290-295).
Complexation between sodium carboxymethylcellulose (NaCMC) and ellipsoidal particles of oppositely charged β-FeOOH is studied using electric light scattering and electrophoresis. We focus on the complex behavior for overcharging of the particle surface. In this case, the fraction of condensed counterions on NaCMC is found to remain unchanged during polymer adsorption onto a weakly charged particle surface. Using the theory of Sens and Joanny, we evaluate the fraction of condensed counterions and compare it with results for nonadsorbed NaCMC. The polarization of condensed counterions along the chain of the adsorbed macromolecule is proved to create the electro-optical effect in suspensions stabilized by NaCMC adsorption.
Keywords: Polyelectrolyte adsorption; Counterion release; Colloid–polyelectrolyte complexation; Electrical polarizability; Electro-optics; Overcharging;
ATR-FTIR investigation on the complexation of myo-inositol hexaphosphate with aluminum hydroxide by Xiao-Hong Guan; Chii Shang; Jun Zhu; Guang-Hao Chen (296-302).
The adsorption isotherm of and the pH effect on the adsorption of myo-inositol hexaphosphate (myo-IP6) on amorphous aluminum hydroxide was investigated. It was found that the adsorption isotherm of myo-IP6 on aluminum hydroxide could be well fitted with the Freundlich isotherm. The amount of myo-IP6 adsorbed remained almost constant in the range of pH 4.0 to 7.0, but it decreased considerably as the initial pH was over 7. The adsorption of myo-IP6 resulted in an increase in the pH level due to the release of OH− ions, which suggested that the adsorption of myo-IP6 on aluminum hydroxide was caused by a ligand exchange reaction. ATR-FTIR analysis of myo-IP6 in solution and adsorbed on aluminum hydroxide at different pH were performed. The ATR-FTIR investigation indicated that myo-IP6 was adsorbed onto aluminum hydroxide by forming inner-sphere complexes and adsorption facilitated the deprotonation of phosphate groups. The asymmetric vibration of the P―O bond in Al―PO− 3 appearing at a lower frequency than that in the terminal HPO− 3 indicated that Al bound to the O atom not as strongly as the H atom did. The ATR-FTIR investigation and theoretical calculation (with the Gaussian 03 program) revealed that three of the six phosphate groups in myo-IP6 molecules were bound to aluminum hydroxide while the other three remained free when myo-IP6 was adsorbed on aluminum hydroxide.Calculated geometry of myo-inositol hexaphosphate complexed with aluminum hydroxide and the length of P–O in complexed phosphate group given in angstroms.
Keywords: Aluminum hydroxide; ATR-FTIR; Inner sphere complexes; Myo-inositol hexaphosphate; Organic phosphate;
Comparative modelling of mono- and dinitrophenols sorption on yellow bentonite from aqueous solutions by Z. Yaneva; B. Koumanova (303-311).
Equilibrium removal of three substituted nitrophenols, namely 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and 2,4-dinitrophenol (2,4-DNP), by adsorption on yellow bentonite was tested. The batch kinetic data are described by the pseudo-first order, pseudo-second order, and intraparticle diffusion models. Results show that chemisorption processes could be rate limiting in the sorption step. The adsorption equilibrium was modelled by the Langmuir and Freundlich equations. The Langmuir model better represents the equilibrium isotherm data for 2-NP, 4-NP, and 2,4-DNP uptake on yellow bentonite. 4-NP is adsorbed in larger amounts than the disubstituted nitrophenol. Uptake of nitrophenols increases in the order 2-NP < 2,4-DNP < 4-NP.
Keywords: Adsorption; Nitrophenols; Yellow bentonite; Kinetics modelling; Equilibrium;
A new surface structural approach to ion adsorption: Tracing the location of electrolyte ions by Rasoul Rahnemaie; Tjisse Hiemstra; Willem H. van Riemsdijk (312-321).
Electrolyte ions differ in size leading to the possibility that the distance of closest approach to a charged surface differs for different ions. So far, ions bound as outersphere complexes have been treated as point charges present at one or two electrostatic plane(s). However, in a multicomponent system, each electrolyte ion may have its own distance of approach and corresponding electrostatic plane with an ion-specific capacitance. It is preferable to make the capacitance of the compact part of the double layer a general characteristic of the solid–solution interface. A new surface structural approach is presented that may account for variation in size of electrolyte ions. In this approach, the location of the charge of the outersphere surface complexes is described using the concept of charge distribution in which the ion charge is allowed to be distributed over two electrostatic planes. It was shown that the concept can successfully describe the pH dependent proton binding and the shift in the isoelectric point (IEP) in the presence of variety of monovalent electrolyte ions, including Li+, Na+, K+, Cs+, Cl−, NO− 3, and ClO− 4 with a common set of parameters. The new concept also sheds more light on the degree of hydration of the ions when present as outersphere complexes. Interpretation of the charge distribution values obtained shows that Cl− ions are located relatively close to the surface. The large alkali ions K+, Cs+, and Rb+ are at the largest distance. Li+, Na+, NO− 3, and ClO− 4 are present at intermediate positions.
Keywords: Electrolyte ion; Diffuse double layer; Basic Stern; Three plane model; Adsorption; Iron oxide; Goethite; CD model; MUSIC model;
Mechanisms of ethyl(hydroxyethyl) cellulose–solid interaction: Influence of hydrophobic modification by Jing Wang; P. Somasundaran (322-332).
Hydroxyethyl cellulose and its hydrophobically modified derivatives are widely used in many industrial areas such as pharmaceuticals, cosmetics, textiles, paint and mineral industries. However, the interaction mechanisms of these biopolymers and solids have not been established. In this work, the interaction mechanism and conformation of hydrophobically modified ethyl(hydroxyethyl) cellulose (C14-EHEC) have been investigated using spectroscopic, AFM and allied techniques. Comparison was made with corresponding unmodified analogue in order to investigate the effects of the hydrophobic modification. Electrokinetic studies showed that polysaccharides adsorption decreased the negative zeta potential of talc but did not reverse the charge. EHEC adsorption on talc was not found to be affected significantly by changes in solution conditions such as pH and ionic strength, ruling out electrostatic force as the controlling factor. However, HM-EHEC adsorption was found to increase markedly with increase in ionic strength from 0.1 to 1 suggesting a role for the hydrophobic force in this adsorption process. Fluorescence spectroscopic studies conducted to investigate the role of hydrophobic bonding using pyrene probe showed no evidence of the formation of hydrophobic domains at talc–aqueous interface. Urea, a hydrogen bond breaker, reduced the adsorption of HM-EHEC on talc markedly. In FTIR study, the changes in the infrared bands, associated with the C―O stretch coupled to the C―C stretch and O―H deformation, were significant and therefore support strong hydrogen bonding of HM-EHEC on the solid surface. Moreover, Langmuir modeling of the adsorption isotherms suggests hydrogen bonding to be a major force for the adsorption of EHEC and C14-EHEC on solid since the adsorption free energies of these polymers were close to that for hydrogen bond formation. All of the above results suggest that the main driving force for EHEC adsorption on talc is hydrogen bonding rather than electrostatic interaction or hydrophobic force. For hydrophobically modified C14-EHEC, hydrophobic force plays a synergetic role in adsorption along with hydrogen bonding. From computer modeling and AFM imaging, it is proposed that C0-EHEC and C14-EHEC adsorb flat on talc with ethylene oxide side chains and hydrophobic groups protruding out from the surface into bulk water phase.The objective of this work was to clarify the mechanistic aspects of the interactions between EHEC/C14-EHEC and talc using a combination of spectroscopic, microscopic, electrostatic adsorption techniques and molecular modeling.
Keywords: Talc; EHEC; Hydrophobic modification; Polymer adsorption; Fluorescence; FTIR; AFM; Model; Zeta potential;
Adsorption behaviors of poly(amido amine) dendrimers with an azacrown core and long alkyl chain spacers on solid substrates by Masaki Ujihara; Toyoko Imae (333-341).
Adsorption behaviors of functional poly(amido amine) dendrimers with an azacrown core and long alkyl chain spacers were investigated on gold and self-assembled monolayer (SAM) by means of time course attenuated total reflection–surface enhanced infrared absorption and surface plasmon resonance spectroscopies. While 1.5th and 2.5th generation (G1.5 and G2.5) ester-terminated dendrimers were slightly adsorbed on all substrates examined, the adsorption of G2 amine-terminated dendrimer increased in the order dodecanethiol SAM < bare gold < 3-mercaptopropionic acid (MPA) SAM. The time course results also revealed that the G2 dendrimer displayed the steep increase of adsorption on the bare gold, followed by the slight progress of adsorption. G2 dendrimers adsorbed on MPA SAM involved their subsequent conformational rearrangement, while the adsorption equilibrium was quickly attained for G3 dendrimer on the MPA SAM. It was supported that G3 dendrimer was adsorbed with the perpendicularly extended structure on the MPA SAM substrate, and G2 dendrimer varied its conformation from the globular structure to the extended one perpendicular to the substrate.Siloxy focal dendron-protected TiO2 nanoparticles of 1–5 nm in size were prepared and their high ability as a photocatalyst was confirmed. Dendron behaved effectively as a reservoir of guest molecules beside as a protector.
Keywords: Dendrimer; Poly(amido amine) dendrimer; Azacrown; Adsorption; Solid substrate; Self-assembled monolayer; 3-Mercaptopropionic acid; Surface enhanced infrared absorption spectroscopy; Surface plasmon resonance spectroscopy;
Modeling spreading-pressure-dependent binary gas coadsorption equilibria using gravimetric data by D. Tondeur; F. Yu; K. Bonnot; L. Luo (342-352).
The present work proposes an approach to building nonideal coadsorption models in a thermodynamically consistent fashion, including the effects of pressure and spreading pressure, from simple gravimetric measurements. This is an “inverse problem” of parameter determination from appropriate and limited experimental data.The approach relies on the nonideal adsorbed solution theory, which includes activity coefficients and their dependence on spreading pressure, and on an original form of the excess Gibbs energy of mixing. A fully analytical development leads to explicit relations between the infinite dilution activity coefficients and three sets of independent information: the parameters of this excess Gibbs function, the limiting slopes of measured binary gravimetric curves at two different total pressures, and the properties of the single-component isotherms. From there, the four parameters of the model may be determined quasi-analytically and uniquely. The method is exemplified with the coadsorption of CO2 and CH4 on activated carbon, and a heterogeneous set of data. On one hand, the total adsorbed mass of the two components is measured at 1 bar by “incremental gravimetry.” On the other hand, data obtained from independent batch-type equilibration measurements at 2 bar allow a comparison of calculated and measured data for the individual component concentrations. It is emphasized, however, that only total adsorbed mass data are needed for application of the method.
Keywords: Adsorption; Coadsorption; Binary; Thermodynamics; Isotherms; Spreading-pressure-dependent; Gravimetry;
Surface characterisation of plasma-modified poly(ethylene terephthalate) by M. Carmen Almazán-Almazán; J.I. Paredes; M. Pérez-Mendoza; M. Domingo-García; F.J. López-Garzón; A. Martínez-Alonso; J.M.D. Tascón (353-363).
This paper reports the modifications produced by nitrogen and helium cold plasmas on the surface of PET. The changes have been studied by diffuse reflectance Fourier transform spectroscopy (DRIFTS), atomic force microscopy (AFM) and inverse gas–solid chromatography (IGSC). Nitrogen and oxygen atoms seem to appear on the surface of PET as a consequence of the exposure to the atmosphere after the treatments with plasmas. AFM shows that both plasmas altered in different extent the surface of PET as they break the polymer chains producing low molecular products which appear as bumps on the surface. The surface area and the porosity of PET does not change by plasma treatments even after 15 min. The dispersive component of the surface free energy, γ s d , decreases after long treatments with nitrogen plasma whereas it remains almost unchanged after long treatment with helium plasma.This paper reports the effect of nitrogen and helium plasma treatments on the surface of PET.
Keywords: Plasma treatments; Surface modifications; DRIFTS; AFM; Inverse gas–solid chromatography;
Modeling hydrophobic recovery of electrically discharged polydimethylsiloxane elastomers by Jongsoo Kim; Manoj K. Chaudhury; Michael J. Owen (364-375).
Theoretical models are proposed to account for the hydrophobic recovery kinetics of electrically discharged silicone elastomers, in which the effects of both the diffusion and adsorption of in situ produced low molecular weight (LMW) species are considered. A homogeneous solid diffusion model or a pore diffusion model well represents the surface restructuring of silicone elastomers exposed to partial electrical discharges. The computed diffusivity of the in situ produced LMW species through an inorganic, silica-like layer to the outermost part of the oxidized polymer is much smaller than that calculated from the absorption experiment of a silicone elastomer. At severe discharge intensity, no significant difference in the hydrophobic recovery is observed for extracted samples and those doped with free dimethylsiloxane fluid, whereas fluorinated siloxane fluid containing samples recover their hydrophobicity faster than the others. Modeling studies indicate that the faster recovery of the later samples may be due to the faster diffusion of the species produced from the fragmentation of the fluorinated siloxane fluid preexisting in the polymer during electrical discharge.
Keywords: Polydimethylsiloxane; Surface modification of PDMS; Corona discharge; Hydrophobic recovery modeling;
Strain hardening and fracture of heat-set fractal globular protein gels by Matthieu Pouzot; Taco Nicolai; Lazhar Benyahia; Dominique Durand (376-383).
Non-linear mechanical behavior at large shear deformation was been investigated for heat-set β-lactoglobulin gels at pH 7 and 0.1 M NaCl using both oscillatory shear and shear flow. These gels have a self-similar structure at length scales smaller than the correlation length of the gel with fractal dimension d f = 2 . Strain hardening is observed that can be well described using the model proposed by Gisler et al. [T.C. Gisler, R.C. Ball, D.A. Weitz, Phys. Rev. Let. 82 (1999) 1064] for fractal colloidal gels. The increase of the shear modulus normalized by the low strain value ( G 0 ) is independent of G 0 . For weak gels the elasticity increases up to a factor of ten, while for strong gels the increase is very small. At higher deformation irreversible fracture occurs, which leads eventually to macroscopic failure of the gel. For weak gels formed at low concentrations the deformation at failure is about 2, independent of the shear modulus. For strong gels fracture occurs at approximately constant stress ( 2 × 10 3 Pa ).Heat set globular protein gels show strain hardening followed by fracture. The strain hardening can be modelled by utilizing the fractal structure of the gels. Microscopic fracture precedes failure so that the minimum of the loss angle precedes the maximum of the storage modulus.
Aerosol size standards in the nanometer size range by Sven Ude; Juan Fernandez de la Mora; James N. Alexander; Daniel A. Saucy (384-393).
A technique for generating charged aerosols of polystyrene (pSty) with narrow size distributions has been developed. It is based on electrospraying commercial narrow mass standards of pSty dissolved in l-methyl-2-pyrrolidone (NMP) seeded with the newly synthesized salt dimethyl ammonium formate. This salt imparts a much larger electrical conductivity than previously known NMP electrolytes, leading to higher quality sprays with greatly reduced attachment of impurities. Controlling the solute concentration enables forming polystyrene particles containing from one up to more than ten single polystyrene molecules, whereby 4 mass standards with molecular weights from 9200 up to 96,000 g/mol yield particles covering densely the diameter range from 3 to 11 nm. Combined mobility and mass measurement with a differential mobility analyzer and a mass spectrometer in tandem are carried out with a pSty sample 9200 amu in molecular weight. They fix directly the mass versus mobility relation near 9200 amu, and indirectly for the other standards and their clusters. The apparent particle density resulting from mobility versus mass data agrees with the bulk density of the polymer, indicating that the particles are dense and spherical. Although these standards have been studied only in gaseous suspension, their injection in liquids such as water where pSty is insoluble should keep them spherical.
Keywords: Standard; Mass spectrometry; Electrical mobility; Spherical; Aerosol; Nanoparticle;
A systematic morphosynthesis of barium sulfate in the presence of phosphonate inhibitor by Fang Wang; Guiying Xu; Zhiqing Zhang; Shue Song; Shuli Dong (394-400).
A systematic study of the influence of various experimental parameters on the morphology and size of BaSO4 crystals after crystallization from water in the presence of diethylenetriamine penta (methylphosphonic acid) (DETPMP) was presented. Depending on the experimental conditions, there are various crystal morphologies including flowers, ellipsoids, spheres, or conjoined spheres. The results indicated that the experimental parameters, such as the concentration of the inhibitor, the pH of solution, the aging of the particle growth, and the ratio [Ba2+]/[SO2− 4], are important for the morphology and size of BaSO4. The morphogenesis of BaSO4 is controlled by the chelation of DETPMP with Ba2+ at the nucleation and the surface adsorption inhibition of crystal growth.A series of BaSO4 particles with various morphologies were obtained in the presence of DETPMP under different experimental parameters, such as C DETPMP , the pH, the aging time, and the ratio [Ba2+]/[ SO 4 2 − ].
Keywords: Morphology; Barium sulfate; Crystal growth; Inhibition;
Surface modification of magnetic nanoparticles capped by oleic acids: Characterization and colloidal stability in polar solvents by Sang-Yup Lee; Michael T. Harris (401-408).
The lyophobic surface of monodisperse magnetic nanoparticles capped by oleic acid was made to be more lyophilic by ozonolysis to increase the stability of the suspension in polar solvents like ethanol. The ozone oxidatively cleaved the double bond of oleic acid to form carbonyl and carboxyl groups on the surface of the nanoparticles. Additionally, interfacial ligand exchange of the capping molecules was applied to make the hydrophobic particle surface more hydrophilic. The magnetic particles showed enhanced miscibility and short-term stability in water after interfacial ligand exchange. The structure changes of the capping molecules on the nanoparticle surfaces were investigated using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). From these spectroscopy studies, the cleavage of the oleic acid and the formations of the carboxyl and carbonyl groups on the particle surface were confirmed. The shape and the magnetic properties of the nanoparticles were maintained after the surface modification. Ozonolysis is an effective method in modifying the lyophobic surface of the magnetic nanoparticles.
Keywords: Magnetic nanoparticle; Surface modification; Ozonolysis; Ligand exchange; Stability;
Room-temperature strategy for networked nonspherical gold nanostructures from Au(III)―[G-2]―CO2H dendrimer complex by Shuyan Gao; Hongjie Zhang; Xudong Liu; Xiaomei Wang; Liaohai Ge (409-413).
The present work describes a convenient approach to fabricate networked nonspherical gold nanostructures by using [G-2]―CO2H dendrimer and toluene as capping and bridging agents in a CH2Cl2 and H2O biphasic system. A controlled linear assembly is achieved without the use of any catalyst at room temperature. UV–vis spectrum, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD) analysis show that the product is well networked nanostructures with diameter of 4–10 nm and consists of coalesced face-centered cubic gold nanocrystals. Extended experiments reveal that both benzene and dimethylbenzene can also inhabit the gold ions to make them crosslinked, prolong the nucleation points and eventually facilitate the formation of the networks.
Keywords: Dendrimer; Gold; Networked; Nanostructures; Crystal growth;
Preparation of Cu–Ni alloy nanocrystallites in water-in-oil microemulsions by Jian Feng; Chao-Ping Zhang (414-420).
The well-mixed copper–nickel nanoparticles were prepared when the molar ratio of Cu2+ to Ni2+ was 1:1 by simultaneous reduction of CuSO4 and NiCl2 with hydrazine in the microemulsion of SDS/n-butanol/n-heptane/water at 70 °C, and was characterized by TEM, ED, TGA, EDS, and XRD. ED analysis and XRD patterns suggest the formation of the homogeneous alloy structure in the bimetallic nanoparticles. Average size of the sample calculated from the full width at medium height of peak 111 in the XRD patterns using Scherrer formula is 5.53 nm. TEM photographs show a narrow distribution of Cu–Ni nanoparticles that essentially are monodispersed and the mean diameter is 12 nm. The results indicate that the composition and size of alloy nanoparticles depend on the mole ratio of H2O to SDS, the method of addition of Cu2+ and Ni2+, and the mole ratio of Cu2+ and Ni2+ in the initial precursor solution.
Keywords: Copper–nickel alloy; Nanocrystallites; Microemulsion;
Effect of chelating functional polymer on the size of CdS nanocluster formation by Cheng-Chien Wang; An-Liu Chen; I-Han Chen (421-429).
Chelating poly(acrylates-co-2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) microspheres of diameter 250–310 nm were prepared by the soap-free emulsion polymerization method for varying amounts of GMA-IDA. Then CdS/copolymer composite was generated by chemical deposition on the surface of the copolymer microspheres. By XRD analysis it is found that the chelated CdS nanoparticles are a pure cubic zinc blende structure. The CdS/copolymer composite is examined by UV–vis absorbance, photoluminescence, and TEM observation. Average CdS nanoparticle size calculated from Henglein's empirical curve is in the range of 3.0–8.0 nm and varies according to the GMA-IDA molar ratio during polymerization, pH value during chelation, and postchelation annealing temperature. Higher ratio of chelating group, pH value, and annealing temperature produce larger CdS nanoparticles. As GMA-IDA ratio increases, photoluminescence exhibits a red shift from 510 to 520 nm, photoluminescence increases, and bandwidth decreases. Photoluminescence of the CdS nanoparticle becomes negligible when diameter exceeds 5 nm.The process of CdS formation on the surface of polymer microsphere.
Keywords: Nanoparticles; Hybrid particles; Chelating polymers; CdS; Semiconductors; Nanotemplates; Nanocomposites; Functional polymers;
Synthesis and self-assembled ring structures of Ni nanocrystals by Guangjun Cheng; Victor F. Puntes; Ting Guo (430-436).
Narrow size distribution Ni nanocrystals with average diameters from 5 to 13 nm (∼20% standard deviation) and a face-centered cubic (fcc) structure were synthesized via rapid thermo-decomposition in the presence of surfactants in solution. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize these nanocrystals. It was found that the solvent determined the rate of the decomposition of Ni precursors, while the surfactants controlled the size and shape of Ni nanocrystals. A three-step process was proposed to explain the synthesis. The purified Ni nanocrystals readily formed micrometer-sized ring structures on TEM grids after solvent evaporation (hexanes), and the magnetic field was found to increase the density of the rings.
Keywords: Nanocrystals; Nanocrystal synthesis; Magnetic materials; Self-assembly;
Effect of pH on photoluminescence enhancement in Pb-doped ZnS nanoparticles by Pramod H. Borse; W. Vogel; S.K. Kulkarni (437-442).
Narrowly dispersed Pb-doped zinc sulfide nanoparticles were synthesized at room temperature using a chemical method in which the nanoparticle surfaces were passivated using mercaptoethanol. The maximum intensity of the broad green luminescence (∼530 nm) from these nanoparticles was observed at an optimum dopant concentration of 0.104 Pb wt%. The emission intensity was found to depend on the synthesis pH conditions, thus yielding maximum intensity at 5.0 pH. Comparatively lower emission intensities were observed for the other pH values (2.5–9.0 pH range). This may be due to the pH-dependent Cl− (as well as Na+) incorporation into the ZnS matrix, which possibly helps in inducing required density of impurity (donor/co-activator) states in the energy gap of ZnS nanoparticles. X-ray diffraction analysis using Debye functional analysis showed that the particle size is 2.8 ± 0.3 nm .Excitation and emission spectra of Pb-doped particle with optimum concentration (Sample C) synthesized at various pH in the range of 2.5–9.0. Inset shows the variation of emission intensity with synthesis pH.
Keywords: Photoluminescence; Nanoparticles; ZnS; Pb doping; Donor; Acceptor;
Color properties of gold–silver alternate nanowires electrochemically grown in the pores of aluminum anodic oxidation film by Akihito Yasui; Mitsunobu Iwasaki; Tetsuro Kawahara; Hiroaki Tada; Seishiro Ito (443-448).
Repeated electrodeposition of gold and silver on anodized aluminum plate yielded Au–Ag alternate nanowires in the geometrically anisotropic pores of the anodic oxidation films with mean diameter 10 nm and depth 10 μm, respectively. The absorption maximum wavelengths in the visible region resulting from the transverse surface plasmon resonances of Au and Ag nanorods are invariant with their growth. Consequently, the color of the anodized aluminum was simply tuned in a wide range, which is impossible to attain in each monometallic system.Repeating electrodeposition of gold and silver on anodized aluminum plate has yielded Au–Ag alternate nanowires. The color of the film is simply tunable in a wide range.
Keywords: Nanowires; Nanorods; Gold; Silver; Alumina; Anodic oxidation; Surface plasmon; Colloids; Color materials; Catalysts;
Silica coating and photochemical properties of layered double hydroxide/ 4 , 4 ′ -diaminostilbene– 2 , 2 ′ -disulfonic acid nanocomposite by Ahmed Mohamed El-Toni; Shu Yin; Tsugio Sato (449-454).
Organic ultraviolet (UV) rays absorbents have been used as sunscreen materials, but they may pose a safety problem when used at high concentration. In order to prevent direct contact of organic UV rays absorbent to the human skin, a typical organic UV-absorbent, 4 , 4 ′ -diaminostilbene- 2 , 2 ′ -disulfonic acid (DASDSA), was intercalated into Zn2Al layered double hydroxide (Zn2Al-LDH) by coprecipitation reaction. However, deintercalation of DASDSA from Zn2Al-LDH, by the anion exchange reaction with carbonate ion, was observed. Therefore, Zn2Al-LDH/DASDSA was directly coated with silica by means of polymerization technique based on the Stöber method. Silica coating effectively depressed the deintercalation of DASDSA from Zn2Al-LDH. The amorphous silica was confirmed by XRD, SEM, TEM and FT-IR. The deintercalation behaviors as well as UV-shielding properties were investigated for coated particles.It is clear that coating with silica greatly suppressed the deintercalation of the DASDSA from the layer structure. The deintercalation percent decreased from 85% to less than 10% after silica coating. Deintercalation profiles of DASDSA from Zn2Al-LDH/DASDSA non-coated and coated with different amounts of silica in 0.02 mol dm−3 Na2CO3 aqueous solution at 50 °C. (a) Non-coated Zn2Al-LDH/DASDSA, (b), (c), (d) and (e) were coated with 5, 10, 15 and 20 wt% SiO2 using TEOS, whereas (f) and (g) were coated with 5.5 and 21.3 wt% SiO2 using Na2SiO3.
Keywords: Ultraviolet absorbent; Layered double hydroxide; Silica; Seeded polymerization; Coating; Deintercalation;
Existence of fluid layers in the corners of a capillary with non-uniform wettability by M.I.J. van Dijke; K.S. Sorbie (455-463).
Based on free energy variation we derive the criterion for displacement during water invasion of oil layers, sandwiched between water in corners and in the centre of a capillary with partly altered wettability. This displacement may arise in combination with a piston-like displacement in which the layers are formed, or, alternatively, these two displacements do not occur and a single piston-like displacement arises removing all oil from the pore cross-section at once. The free energy differentials associated with the three displacements determine exactly which displacement(s) happen during water invasion. Depending on the area and the (advancing) contact angle on the surface of altered wettability, as well as on the half-angles of the pore corners, layers may or may not exist. We compare the criterion for the displacement of oil layers with the existing geometrical criterion. The latter always allows a larger range of contact angles and pressure combination for which layers may exist than the presently derived criterion, hence the geometrical criterion is insufficient and is now superceded.
Keywords: Oil layer; Water invasion; Non-circular cross-section; Non-uniform wettability; Two-phase; Free energy; Capillary entry pressure;
Interfacial tension in phase-separated aqueous cationic/anionic surfactant mixtures by Yan-Qing Nan; Hong-Lai Liu; Ying Hu (464-474).
Interfacial tensions in two aqueous phase-separated cationic/anionic surfactant mixtures, CTAB/AS and 12-3-12/AS, without and with NaBr added were determined by the spinning drop method at 318.15 K. CTAB, 12-3-12 and AS are the abbreviations for cetyltrimethylammonium bromide, 1,3-propanediyl-bis(dodecyldimethylammonium bromide) and sodium dodecyl sulfonate, respectively. The interfacial tension σ was found to be in the range of 0.06 – 21 μN m −1 . Toward a better understanding of the influence of the concentration difference between the separated phases in aqueous two-phase systems (ATPS) to interfacial tension, compositions of equilibrium phases were determined by elemental analysis coupled with material balance and electroneutrality. The investigation indicates that the concentration differences of surfactant ions between the separated phases and the adsorption of surfactant ions at the interface are the decisive factors determining the magnitude of interfacial tension.Interfacial tensions in two aqueous phase-separated cationic/anionic surfactant mixtures were determined and the decisive factors for the magnitude of interfacial tension were discussed.
Keywords: Aqueous two-phase system; Interfacial tension; Cationic/anionic surfactant; Gemini surfactant; Phase composition;
Characterization of the flow of anisotropic colloidal particles using energy-dispersive X-ray diffraction by A.R. Rennie; S. Barè; J.K. Cockcroft; A.C. Jupe (475-482).
The technique of energy-dispersive X-ray diffraction to study the orientation of microscopic crystalline particles dispersed in a liquid has been described recently. This complements previous neutron diffraction studies by permitting measurements at higher spatial resolution. Work with synchrotron radiation and high-energy X-rays has allowed studies on liquid dispersions flowing in pipes with a thickness of about 1 cm and a spatial resolution of 100 μm. Kaolinite is often found as a dispersion of monocrystalline, microscopic plates. The crystallographic layer structure is commensurate with the particle shape: the 00l direction is normal to the plane of the plates. Measurements of diffraction of the flowing liquid dispersion in a pipe oriented in various directions to the incident beam can be used to deduce the average orientation and order parameters of the particles. The competing effects of alignment with walls and in flow fields were observed. Further work has measured the orientation near a bend in a pipe.The orientation distribution of a colloidal dispersion of kaolinite particles in complex flow fields is measured using synchrotron X-ray diffraction.
Keywords: Kaolinite; Flow alignment; Pipe flow; X-ray diffraction;
Flow behavior of periodical electroosmosis in microchannel for biochips by Xianming Wang; Jiankang Wu (483-488).
This paper presents an analytical solution for periodical electroosmotic flows in two-dimensional uniform microchannel based on Poisson–Boltzmann equations for electric double layer (EDL) and Navier–Stokes equation for incompressible viscous fluid. Analytical results indicate that the velocity of periodical electroosmosis strongly depends on Reynolds number Re = ω h 2 / ν , as well as on EDL properties and applied electric field. Slip velocity of EDL decreases as the Reynolds number increases. Electroosmotic velocity outside the EDL decreases, and lag phase angle of velocity increases as distance away from the channel wall increases. A wavelike velocity profile across the channel is found. An asymptotic solution for low Reynolds number is given in this paper. Periodical electroosmosis with low Reynolds has same velocity amplitude and a pluglike velocity profile as that of steady electroosmosis. Based on Debye–Hückel approximation, this paper also obtains a solution of periodical electroosmosis applicable to cases where the thickness of EDL is of the same order as half of channel width.This paper presents an analytical solution for periodical electroosmotic flows in two-dimensional uniform microchannel. Analytical results indicate that the velocity of periodical electroosmosis strongly depends on Reynolds number Re = ω h 2 / ν , as well as on EDL properties and applied electric field. A wavelike velocity profile across the microchannel is found, as shown in the following figure.
Keywords: Electric double layer; Periodical electroosmosis; Microchannel; Reynolds number;
Electrorheological properties of PMMA-b-PSt copolymer suspensions by Hasim Yilmaz; Mustafa Degirmenci; Halil Ibrahim Unal (489-495).
In this study, a block copolymer of methyl methacrylate (MMA) and styrene (St) synthesized by combined ultrasonic irradiation and reverse atom transfer radical polymerization (RATRP) processes was used. PMMA-b-PSt was partially hydrolyzed and converted to a lithium salt, PMMA-b-PSt-Li, before the electrorheological (ER) measurements carried out. Average particle diameter of PMMA-b-PSt-Li polymeric salt was determined by dynamic light scattering (DLS) as 22 μm. Suspensions of PMMA-b-PSt-Li polymeric salts were prepared in silicone oil. ER properties of PMMA-b-PSt-Li/silicone oil suspensions were studied as a function of electric field strength, dispersed phase concentration, shear rate, shear stress, temperature, frequency, and polar promoter. Further dielectric properties of PMMA-b-PSt-Li ionomer were also investigated.
Keywords: Electrorheological fluids; PMMA–PSt block copolymer; Ionomer; RATRP; Colloidal suspensions;
Experimental investigation of fluid drop spreading on heterogeneous and anisotropic porous media by Deepak Arora; Abhijit P. Deshpande; S.R. Chakravarthy (496-499).
Study of spreading phenomena on porous substrates is important from theoretical as well as applications point of view. An example of such applications is composite processing, where operations involve displacement of air/volatiles by polymeric fluids through porous media composed of fibers. In this work, dynamics of drop spreading was investigated on fibrous porous substrates used in composite processing. These porous media are heterogeneous and anisotropic. Spreading front of silicon oil drops was tracked on borosilicate glass, quartz, and two different kinds of glass fiber mats: woven fabric and unidirectional. For the woven fabric, spreading front was observed to progress in steps of increasing and decreasing rate. For the unidirectional mat, the spreading front progressed with decreasing rate. The dynamics of spreading were fitted to power law in order to compare results with other porous substrates.The dynamics of a fluid drop spreading on fibrous porous substrates (heterogeneous and anisotropic) through microscopic front tracking.
Keywords: Drop spreading; Capillary; Wetting; Fibrous porous media; Imbibition;
Solid–liquid interfacial energy as a tool to estimate shifts in isoelectric points of adsorbed proteins on solid surfaces by R. Maheshwari; R. Bhavani; A. Dhathathreyan (500-504).
This work reports the estimation of isoelectric points (pIs) of adsorbed amino acids and proteins on solid surfaces in the pH range between 3.5–11.0 from a measurement of solid/liquid interfacial energy. The values thus obtained are compared with the pIs determined in solution phase by other methods. Both glass and Teflon have been chosen as model solid surfaces. Close agreement between the reference pI values, obtained by the capillary isoelectric focusing and those obtained at solid/liquid interface is observed within an average difference of 0.04–0.08 pH unit when the pIs are above the pI of glass. For systems whose pIs are far away from that of glass (either in the acidic or highly alkaline range), a large shift in the isoelectric point is observed. In case of Teflon the pIs are closer to the reported values than at glass/liquid interface. This could be due to the fact that Teflon being a hydrophobic surface, its surface is dominated by dispersive forces, which may not be seriously affected by pH changes. The shift in the values at solid/liquid interface compared to that in solution have been examined using an ‘image charge approach.’This work reports the estimation of isoelectric points (pIs) of adsorbed amino acids and proteins on solid surfaces in the pH range 3.5–11.0 from a measurement of solid/liquid interfacial energy. Close agreement between the reference pI values obtained by the capillary isoelectric focusing and those obtained at solid/liquid interface is observed within an average difference of 0.04–0.08 pH unit when the pIs are above the pI of glass. For systems whose pIs are far away from that of glass (either in the acidic or highly alkaline range), a large shift in the isoelectric point is observed. In case of Teflon the pIs are closer to the reported values than at glass/liquid interface.
Keywords: Amino acids; Proteins; Isoelectric point; Adsorption;
Author Index for Volume 293 (505-506).