Journal of Colloid And Interface Science (v.319, #1)
Adsorption of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and related compounds onto montmorillonite clay
by Nagi Greesh; Patrice C. Hartmann; Valeska Cloete; Ronald D. Sanderson (pp. 2-11).
Sodium montmorillonite clay (Na-MMT) was modified using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). The objective of this study was to determine which chemical group is the ‘driving force’ leading to the adsorption of AMPS inside the clay galleries. AMPS has been reported to be a good candidate as a clay modifier for the preparation of polymer–clay nanocomposites by in situ free radical polymerization in emulsion. However, the way in which AMPS interacts with the surface of MMT has not yet been studied. The type of interaction between organic modifiers and clay plays a determining role in the successful preparation of polymer–clay nanocomposite materials. The adsorption ability of three other organic compounds similar to AMPS, namely sodium 1-allyloxy-2-hydroxypropyl sulfonate (Cops), N-isopropylacrylamide (NIPA) and methacryloyloxyundecan-1-yl sulfate (MET), was also evaluated. These selected compounds also have functional groups potentially able to interact with the clay surface (i.e., a sulfonate group, an amido group, or a sulfate group, respectively). Results of FT-IR, TGA and SAXS analyses showed that AMPS, NIPA, Cops and MET all interacted with clay, but to various extents.
Keywords: AMPS; Organic modifier; Clay; Montmorillonite; Adsorption
Polanyi-based models for the adsorption of naphthalene from aqueous solutions onto nonpolar polymeric adsorbents
by Chao Long; Aimin Li; Haisuo Wu; Fuqiang Liu; Quanxing Zhang (pp. 12-18).
In this research, naphthalene was adopted as the representative model compound of PAHs, and static adsorption of naphthalene from aqueous solution onto three commercial polymeric adsorbents with different pore structure was investigated. Nonlinear isotherms models, i.e., Freundlich, Langmuir, and Polanyi–Dubinin–Manes (PDM) models were tested to fit experimental data, and the experimental data were found to fit well by the PDM model. Through both isotherm modeling and constructing “characteristic curve,” Polanyi theory was useful to describe the adsorption process of naphthalene by polymeric adsorbents, providing evidence that a micropore filling phenomenon was involved during the adsorption process. In addition, a good linear correlation was obtained between the naphthalene adsorption capacities and the micropore volume of adsorbents (Vmicro), whereas no linear relationship was found between the naphthalene adsorption capacities and the specific surface area of adsorbents. Based on the PDM model, the micropore volumes of adsorbents was introduced to normalize the equilibrium adsorbed volume (qv), plots ofqv/Vmicro vs adsorption potential density for naphthalene on three different polymeric adsorbents were collapsed to a single correlation curve, which would be of great benefit to predict the adsorption capacity of adsorbent for the purpose of adsorption engineering design.Equilibrium volume adsorbed (qv) of naphthalene on three polymeric adsorbents was normalized using the micropore volume of adsorbents (Vmicro), plots ofqv/Vmicro vs adsorption potential density produced a single correlation curve.
Keywords: Polymeric adsorbents; Polycyclic aromatic hydrocarbons; Adsorption; Polanyi potential theory
Layered double hydroxide intercalated with p-methylbenzoate and p-bromobenzoate: Molecular simulations and XRD analysis
by Petr Kovář; Klára Melánová; Vítězslav Zima; Ludvík Beneš; Pavla Čapková (pp. 19-24).
Samples of Mg4Al2 layered double hydroxide (LDH) intercalated with p-methylbenzoate and p-bromobenzoate anions were prepared by reconstruction of calcined LDH. The interlayer arrangement of guests was investigated by molecular modeling combined with X-ray powder diffraction and thermogravimetry. Molecular modeling was carried out in a Cerius2 modeling environment. In both structures the guest anions adopt a nearly perpendicular arrangement of their long axis with respect to the host layers and they are anchored to the OH groups of the layers through COO− groups via electrostatic interactions. Molecular modeling revealed that both structures of the intercalates exhibit a certain disorder of guest anions in the interlayer space. In the case of LDH– p-methylbenzoate intercalate the anions tend to be situated in disordered rows, and the LDH– p-bromobenzoate intercalate exhibits a total disorientation of guest anions. A good agreement between calculated and measured X-ray diffraction patterns and between experimental and calculated basal spacings was obtained. In the LDH– p-methylbenzoate intercalatedexp=16.96Å anddcalc=16.97Å, and in the case of LDH– p-bromobenzoate intercalatedexp=17.19Å anddcalc=17.40Å.
Keywords: Layered double hydroxide; p; -Bromobenzoate; p-; Methylbenzoate; Molecular simulations; X-ray diffraction
Coprecipitation of gold(III) complex ions with manganese(II) hydroxide and their stoichiometric reduction to atomic gold (Au(0)): Analysis by Mössbauer spectroscopy and XPS
by Mamiko Yamashita; Hironori Ohashi; Yasuhiro Kobayashi; Yoshihiro Okaue; Tsutomu Kurisaki; Hisanobu Wakita; Takushi Yokoyama (pp. 25-29).
To elucidate the formation process of precursor of gold-supported manganese dioxide (MnO2), the coprecipitation behavior of [AuCl4− n(OH) n]− (n=0–4) (Au(III)) complex ions with manganese(II) hydroxide (Mn(OH)2) and the change in their chemical state were examined. The Au(III) complex ions were rapidly and effectively coprecipitated with Mn(OH)2 at pH 9. According to the Mössbauer spectra for gold (Au) coprecipitated with Mn(OH)2, below an Au content of 60 wt% in the coprecipitates, all of the coprecipitated Au existed in the atomic state (Au(0)), while, above an Au content of 65 wt%, part of the gold existed in the Au(III) state, and the proportion increased with increasing coprecipitated Au content. Based on the results of X-ray photoelectron spectroscopy, Mn(II) in Mn(OH)2 converted to Mn(IV) in conjunction with coprecipitation of Au(III) complex ions. These results indicate that the rapid stoichiometric reduction of Au(III) to Au(0) is caused by electron transfer from Mn(II) in Mn(OH)2 to the Au(III) complex ion through an MnOAu bond.After the coprecipitation of [AuCl n(OH)4− n]− with Mn(OH)2, the stoichiometric reduction of Au(III) to Au(0) is rapidly caused by electron transfer from Mn(II) to Au(III) complex ion through the MnOAu bond.
Keywords: Au(III) complex ion; Coprecipitation; Mn(OH); 2; Reduction; Atomic Au; Oxidation; MnO; 2; Environmental catalyst; 197; Au Mössbauer spectra; XPS
Adsorption of basic fuchsin using waste materials—bottom ash and deoiled soya—as adsorbents
by V.K. Gupta; Alok Mittal; Vibha Gajbe; Jyoti Mittal (pp. 30-39).
Basic fuchsin, a triaminotriphenylmethane dye, was removed by adsorption utilizing two waste materials—“bottom ash,” a power plant waste material, and “deoiled soya,” an agriculture waste product. The adsorbents were characterized through IR spectroscopy and differential thermal analysis (DTA). Batch adsorption experiments were carried out by measuring effects of pH, adsorbate concentration, sieve size, amount of adsorbent, contact time, temperature, etc. The results have been verified on the basis of Langmuir and Freundlich adsorption isotherm models and data obtained have been applied to calculate thermodynamic parameters. Specific rate constants for the processes were calculated by kinetic measurements and a pseudo-second-order adsorption kinetics was observed in each case. To identify whether the ongoing process is particle diffusion or film diffusion, the treatment given by Boyd and Reichenberg was employed. To assess the practical utility of the adsorbent, the aqueous adsorbate samples were eluted through fixed-bed columns of respective adsorbents. Attempts were also made to recover the adsorbed dyes by passing suitable solvent through the columns.Effect of pH on the percentage adsorption of basic fuchsin on bottom ash and deoiled soya.
Keywords: Basic fuchsin; Bottom ash; Deoiled soya; Adsorption; Kinetics
Structural characterization of U(VI) surface complexes on kaolinite in the presence of humic acid using EXAFS spectroscopy
by Adéla Křepelová; Tobias Reich; Susanne Sachs; Jakob Drebert; Gert Bernhard (pp. 40-47).
To determine the influence of humic acid (HA), pH, and presence of atmospheric CO2 on the sorption of U(VI) onto kaolinite, the structure of the surface complexes was studied by U LIII-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The best fits to the experimental EXAFS data were obtained by including two uranium coordination shells with two axial (Oax) and five equatorial (Oeq) oxygen atoms at1.77±0.02 and2.34±0.02Å, respectively, and two coordination shells with one Al/Si atom each at 3.1 and 3.3 Å. As in the case of the binary system U(VI)-kaolinite, uranium forms inner-sphere surface complexes by edge sharing with aluminum octahedra and/or silicon tetrahedra. HA and atmospheric CO2 as well as pH had no influence on the EXAFS structural parameters in the pH range of 5–8. Despite the presence of HA, U(VI) prefers to sorb directly onto kaolinite and not to HA that is bound to the clay surface. X-ray photoelectron spectroscopy (XPS) measurements of kaolinite particles that had been exposed to HA suspensions showed that significant parts of the kaolinite surface are not covered by HA.Raw U LIII-edgek3-weighted EXAFS data (left) and corresponding Fourier transforms (right) for U(VI) sorbed onto kaolinite under different experimental conditions.
Keywords: Uranium(VI); Kaolinite; Humic acid; Sorption; EXAFS; XPS; Surface complexes
Adsorption behavior of anionic polyelectrolyte for chemical mechanical polishing (CMP)
by Sarah Kim; Jae-Hyun So; Dong-Jun Lee; Seung-Man Yang (pp. 48-52).
In this work, we investigated the adsorption characteristics of anionic polyelectrolytes, which are used in shallow trench isolation chemical mechanical polishing with ceria abrasives. Specifically, the adsorption isotherms and chain conformation of anionic polyelectrolytes were studied in order to elucidate the difference in removal rates of silicon dioxide (SiO2) and silicon nitride (Si3N4) layers and the high selectivity characteristics of ceria slurry. Adsorption isotherms, FT-IR spectroscopy and contact angle measurements revealed that the anionic polyelectrolyte additives had much better adsorption affinities for the Si3N4 surface than for the SiO2 surface. Moreover, blanket wafer polishing results were successfully correlated with the adsorption isotherms of polyelectrolytes on the oxide particle suspensions.The selectivity of STI CMP is optimized by investigating adsorption behavior of anionic polyelectrolyte.
Keywords: Anionic polyelectrolyte; STI CMP; Adsorption behavior; Removal rate; Selectivity
Surface-modified carbon black for As(V) removal
by Dipu Borah; Shigeo Satokawa; Shigeru Kato; Toshinori Kojima (pp. 53-62).
This paper reports the results of the adsorption performance of As(V) removal by a commercial carbon black and its H2SO4-modified form in a single-ion situation. The influence of different process parameters and the physicochemical principles involved were studied in detail. Acid modification caused morphological changes in the virgin carbon black as evidenced by BET surface area measurements and SEM study. FTIR spectra showed the introduction of sulfonic acid group in the parent carbon due to H2SO4 treatment. TGA analysis revealed higher weight loss characteristics of the modified carbon, demonstrating the creation of functional groups. The point of zero charge (pHpzc) of the modified carbon black is highly acidic (3.5) compared to commercial carbon black (6.4). It directly infers the generation of acidic functional moieties in the carbon black. The adsorption experiments were carried out following batch equilibrium techniques. The kinetics and thermodynamics of adsorption were investigated to unveil the mechanism and nature of the adsorption process, respectively. The kinetic parameters of different models were calculated and discussed. The kinetics of adsorption can be expressed by a pseudo-second-order model and intraparticle diffusion was not the rate-determining step. Dependence of pH on adsorption showed maximum metal uptake in the range of 4–5 and inferred surface complexion as the principal mechanism of adsorption. The equilibrium adsorption data were modeled using Freundlich, Langmuir, and Dubinin–Kaganer–Radushkevich (DKR) isotherm equations and the corresponding isotherm parameters were calculated and discussed in detail.The removal of As(V) from aqueous medium was studied by using a commercial and its H2SO4-modified carbon black in a single-ion situation following a batch equilibrium technique.
Keywords: Carbon black; Modification; pH; pzc; As(V) adsorption; Kinetics; Thermodynamics; Isotherms
An AFM, XPS and wettability study of the surface heterogeneity of PS/PMMA-r-PMAA demixed thin films
by Emilienne M. Zuyderhoff; Caroline M. Dekeyser; Paul G. Rouxhet; Christine C. Dupont-Gillain (pp. 63-71).
A series of homopolymer/random copolymer blends was used to produce heterogeneous surfaces by demixing in thin films. The chosen homopolymer is polystyrene (PS) and the random copolymer is poly(methyl methacrylate)-r-poly(methacrylic acid) (PMMA-r-PMAA), whose acidic functions could be used as reactive sites in view of further surface functionalization. The proportion of each polymer at the interface was deduced from X-ray photoelectron spectroscopy (XPS) data using, on the one hand, the O/C ratio, and on the other hand, decomposition of the carbon peak of the blends in two components corresponding to the carbon peaks of PS and PMMA-r-PMAA. Combining the information from XPS with atomic force microscopy (AFM) images, water contact angle measurements and PS selective dissolution, it appears that the surfaces obtained from blends with a high PS content (90/10 to 70/30) display pits with a bottom made of PMMA-r-PMAA, randomly distributed in a PS matrix. On the other hand, the surfaces obtained from blends with a low PS content (30/70 to 10/90) display randomly distributed PS islands surrounded by a PMMA-r-PMAA matrix. The characteristics of the heterogeneous films are thought to be governed by the higher affinity of PMMA-r-PMAA for the solvent (dioxane), which leads to the elevation of the PS phase compared to the PMMA-r-PMAA phase, and to surface enrichment in PMMA-r-PMAA.
Keywords: PS; PMMA-r-PMAA; XPS; AFM; Demixed film; Polymer blend; Selective dissolution; Wettability
Chirality and helix stability of polyglutamic acid enantiomers
by Eleftheria K. Kodona; Charalambos Alexopoulos; Eugenia Panou-Pomonis; Philippos J. Pomonis (pp. 72-80).
In this work the chirality and the relative thermal stability of ordered micellar aggregates of poly-l- and poly-d-glutamic acids with the cationic surfactant C14TAB is examined. The complexed mesophases poly-l-Glu/C14TAB and poly-d-Glu/C14TAB were characterized by circular dichroism (CD) in the temperature range 10–70 °C for their chirality and thermal stability as well as by X-ray diffraction (XRD) for the micellar ordered structure. Low angle XRD analysis showed that both micellar aggregates poly-l-Glu/C14TAB and poly-d-Glu/C14TAB are hexagonally packed in a MCM-41 fashion with an intermicellar distance identical and equal to3.55±0.10nm. The CD spectra indicated that both complexes poly-l-Glu/C14TAB and poly-d-Glu/C14TAB possess a mainly α-helix structure and are exact mirror images to each other. The same mirror images and a mainly α-helix configuration were also observed by CD for the free poly-l- and poly-d-glutamic acids at room temperature. As the temperature increases from 10 up to 70 °C the α-helix of the poly-l-glutamic acid is gradually transformed to a mixture containing increased amounts of the 310-helix while the α-helix structure of the poly-d-glutamic acid is constantly degenerated. In contrast the α-helices of the corresponding complexes poly-l-Glu/C14TAB and poly-d-Glu/C14TAB are degenerated upon heating without appreciable increase of the 310-helices as an intermediate configuration. This difference in helix conservation is attributed to increase protection of thel-enantiomers, compared tod-enantiomers, which might be related to the survival ofl-aminoacids in the living world.Depiction of the chiral micellar aggregates developed in the systems P-l-Glu/C14TAB and P-d-Glu/C14TAB packed in hexagonal lattices of similar size3.55±0.10nm (a,b-axes).
Keywords: Ordered micellar aggregates; Poly-; l; -glutamic acid; Poly-; d; -glutamic acid; C; 14; TAB; Thermal stability; Chirality
Uptake of amitriptyline and nortriptyline with liposomes, proteins, and serum: Implications for drug detoxification
by Brett Howell; Anuj Chauhan (pp. 81-93).
Liposomes composed of DOPG and DMPC were studied for their ability to sequester amitriptyline and nortriptyline under physiological conditions. The liposomes reduced the free drug concentration in protein mixtures and in human serum, but the drug uptake efficiency of liposomes was reduced in the presence of plasma proteins, perhaps due to adsorption of proteins on the liposomes. The reduction was significantly more for the pure DOPG liposomes. The 50:50 DMPC:DOPG liposomes (0.72 mg lipid/mL) reduced the free amitriptyline concentration by 50–60% in the presence of 7% proteins (4% albumin (w/w), 2% fibrinogen (w/w), 1% globulins (w/w)). In human serum, the free drug reduction was 35–70% with the same 50:50 liposomes (0.72 mg lipid/mL). The liposomal systems were equally efficient at sequestering nortriptyline, which is a major metabolite of amitriptyline. The drug binding to liposomes in the presence of serum proteins is also quick and reversible and the likely mechanism of drug sequestration is adsorption of drug on the surface of liposomes. Accordingly, the drug uptake increases with increased charge and lipid loading. Even though the serum proteins reduced the effectiveness of the liposomes at sequestering the drug, the 50:50 DMPC:DOPG liposomes may be effective at treating amitriptyline overdose patients.In this paper, we study the uptake of amitriptyline in aqueous solutions by liposomes consisting of a neutral lipid 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and a negatively charged lipid 1,2-dioleoyl- sn-glycero-3-[phospho- rac-(1-glycerol)] (DOPG). The 50:50 DMPC:DOPG liposomes at 0.72 mg lipid/mL loading reduce the free drug concentration in serum by about 30–40% at physiologically relevant concentrations.
Keywords: Liposomes; Overdose; Amitriptyline; DMPC; DOPG; Protein; Albumin; Fibrinogen; Globulin; Isotherms
In situ growth of nanogold on quartz crystal microbalance and its application in the interaction between heparin and antithrombin III
by Qundan Zhang; Yanyan Huang; Rui Zhao; Guoquan Liu; Yi Chen (pp. 94-99).
A novel biosensor for detecting antithrombin III (AT III) was constructed based on in situ growth of nanogold on the gold electrode of quartz crystal microbalance (QCM). The growth process of nanogold was monitored by QCM in real time. Heparin was used as the affinity ligand and immobilized onto the nanogold modified gold electrode. A flow injection analysis–quartz crystal microbalance (FIA-QCM) system was used to investigate the relationship between nanogold growth and the AT III response. Along with the nanogold particle growth within initial 5 min, the amount of heparin immobilized onto the nanogold modified electrode increased quickly. Correspondingly, the frequency response to AT III binding increased rapidly at the same time. After that, both the immobilized amount of heparin and the sensor response to AT III decreased gradually. Compared with the directly immobilized large nanogold particles, the in situ grown particles with the same size occupy more sensor surface, resulting in higher frequency shifts to AT III in the interaction study between heparin and AT III. The obtained constants of AT III binding to immobilized heparin arekass=(1.65±0.12)×103L/mols,kdiss=(2.63±0.18)×10−21/s andKA=(6.27±0.42)×104L/mol.In situ growth of nanogold on quartz crystal microbalance was realized for enhancing the sensor response and applied to determine the interaction between heparin and antithrombin III.
Keywords: In situ growth; Nanogold; Quartz crystal microbalance; Heparin; Antithrombin III
Using phospholipid Langmuir and Langmuir–Blodgett films as matrix for urease immobilization
by Luciano Caseli; Frank N. Crespilho; Thatyane M. Nobre; Maria Elisabete D. Zaniquelli; Valtencir Zucolotto; Osvaldo N. Oliveira Jr. (pp. 100-108).
The immobilization of enzymes in organized two-dimensional matrices is a key requirement for many biotechnological applications. In this paper, we used the Langmuir–Blodgett (LB) technique to obtain controlled architectures of urease immobilized in solid supports, whose physicochemical properties were investigated in detail. Urease molecules were adsorbed at the air–water interface and incorporated into Langmuir monolayers of the phospholipid dipalmitoyl phosphatidyl glycerol (DPPG). Incorporation of urease made DPPG monolayers more flexible and caused the reduction of the equilibrium and dynamic elasticity of the film. Urease and DPPG–urease mixed monolayers could be transferred onto solid substrates, forming LB films. A close packing arrangement of urease was obtained, especially in the mixed LB films, which was inferred with nanogravimetry and electrochemistry measurements. From the blocking effect of the LB films deposited onto indium tin oxide (ITO) substrates, the electrochemical properties of the LB films pointed to a charge transport controlled by the lipid architecture.
Keywords: Langmuir–Blodgett films; Monolayers; Urease; Biosensor; Air–water interface
Effect of Na4O7P2 on Cu powder preparation from Cu2O–water slurry system
by J.G. Ahn; T.H. Hoang; D.J. Kim; M.S. Kim; C.O. Kim; H.S. Chung (pp. 109-114).
A unique approach is presented for preparing highly dispersed ultrafine copper particles from cuprous oxide slurry using a wet chemical reaction with hydrazine (N2H4) as a reductant along with an appropriate addition of sodium pyrophosphate (Na4O7P2) as a surfactant. It was found that very thin oxidized surfaces on the copper particles are formed during the reaction in the solution and subsequently sodium pyrophosphate plays an important role in the zeta potential of the particles, affecting their dispersion and growth significantly. The copper particles at low zeta potential easily aggregate and grow to bigger ones, whereas they at high zeta potential keep away each other and grew individually to ultrafine size. Additionally, a model for the copper particles growth in accordance with dispersion is proposed.
Keywords: Ultrafine copper powders; Slurry; Dispersion; Sodium pyrophosphate; Zeta potential
Novel ionic liquid assisted synthesis of SnO2 microspheres
by Wen-Sheng Dong; Meng-Yuan Li; Chunling Liu; Fengqiang Lin; Zhaotie Liu (pp. 115-122).
Tin oxide (SnO2) microspheres with an average 2.5 μm in diameters have been successfully synthesized through a rapid hydrothermal process heating by microwave in the presence of an ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate. X-ray diffraction, scanning electron microscopy and transmission electron microscopy are used to characterize the morphology and crystalline structure of the microspheres. The as-synthesized SnO2 microspheres exhibit a tetragonal rutile structure. The mechanism of the microspheres formation is proposed.Tin oxide (SnO2) microspheres with an average 2.5 μm in diameters have been successfully synthesized through a rapid hydrothermal process heating by microwave in the presence of an ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate.
Keywords: Tin oxide; Ionic liquids; Microwave; Microspheres
Ga2O3 and GaN nanocrystalline film: Reverse micelle assisted solvothermal synthesis and characterization
by Godhuli Sinha; Dibyendu Ganguli; Subhadra Chaudhuri (pp. 123-129).
Gallium oxide ( β-Ga2O3) nanoparticles were successfully deposited on quartz glass substrates using sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/ n-hexane/ethylene glycol monomethyl ether (EGME) reverse micelle-mediated solvothermal process with different w values. The mean diameter of Ga2O3 particles was ∼2–3 nm and found to be approximately independent of w values of the reverse micelles. However, when the Ga2O3 nanocrystalline films were nitrided at 900 °C under flowing NH3 atmosphere for 1 h, the mean diameter of the resulted gallium nitride (wurtzite-GaN) nanoparticles varied from 3–9 nm. Both nanocrystalline films of Ga2O3 and GaN were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, UV–vis spectroscopy and photoluminescence in order to study their chemical and physical properties explicitly.Ga2O3 nanoparticles (∼2–3 nm) are deposited on quartz substrates by non-aqueous reverse micelle mediated solvothermal process with different w values and converted to GaN nanoparticles by annealing them at 900 °C in NH3 atmosphere. Both Ga2O3 and GaN nanoparticles show strong luminescence properties.
Keywords: Ga; 2; O; 3; and GaN nanocrystalline films; Nanoparticles; Non-aqueous reverse micelle
Effect of polycrystalline structure of TiO2 particles on the light scattering efficiency
by Kimberly Nelson; Yulin Deng (pp. 130-139).
The opacifying power of synthesized polycrystalline TiO2 particles in a cellulose matrix was found experimentally and theoretically to be superior to that of a commercial rutile pigment, depending on crystal structure of the synthesized particles. The crystal structure of the particles was varied by calcination of amorphous titania nanoparticles at different temperatures and was characterized using SEM, TEM, and XRD. Polycrystalline anatase pigments had less opacifying power than commercial rutile, while polycrystalline pigments containing a one-to-one mixture of anatase and rutile had similar opacifying power as the commercial pigment if they have a similar overall particle size. The polycrystalline rutile pigments composed of a linear linkage of several individual rutile crystals gave 6% more opacity than the commercial rutile pigment. Theoretical light scattering calculations using the T-matrix method showed the light scattering efficiency of linearly arranged polycrystalline rutile particles to depend on number and size of crystals composing the particle. It is suggested that the efficiency of rutile pigments can be increased dramatically by controlling both the primary crystal size and the overall particle size. It is believed that the greater than expected light scattering efficiency of the biphasic pigment results from reflection and refraction of light at the grain boundaries between crystals of different phase, which have different refractive indices.The experiments and theoretical analysis indicate that both primary crystal size and overall particle size need to be optimized in order to obtain the best light scattering efficiency.
Keywords: Titanium dioxide; Light scattering; Opacity; Pigment; Polycrystalline
A one-step aqueous synthetic route to extremely small CdSe nanoparticles
by Xianfeng Chen; John L. Hutchison; Peter J. Dobson; Gareth Wakefield (pp. 140-143).
By employing Na2Se as a selenium source, we demonstrate that extremely small (∼1 nm) mercapto acid-stabilized CdSe nanoparticles can be conveniently prepared in water. The as-prepared nanoparticles start to show dominant near band-gap photoluminescence in the blue spectral range and show high photoluminescence in the green spectral range.Extremely small (∼1 nm) mercapto acid-stabilized CdSe nanoparticles with near band-gap photoluminescence in the blue spectral range were synthesized through a one-step aqueous route.
Keywords: CdSe; Nanoparticles; Photoluminescence; Mercapto acid
Colloidal aspects relating to direct incorporation of TiO2 nanoparticles into mesoporous spheres by an aerosol-assisted process
by Petr O. Vasiliev; Bertrand Faure; Jovice Boon Sing Ng; Lennart Bergström (pp. 144-151).
Titania nanoparticles have been incorporated into spherical mesoporous silica powders by an aerosol-assisted synthesis process from both aqueous and ethanol-based precursor dispersions. Transmission electron microscopy (TEM) showed that the titania nanoparticles exist as single particles or small aggregates within the mesoporous carrier particles and analysis of the nitrogen adsorption isotherms proved that the pore blocking of the particles is small. Particle size and zeta potential measurements showed that the addition of tetraethoxysiloxane (TEOS), and also hexadecyl trimethyl ammonium bromide (C16TAB) induced flocculation of the TiO2 nanoparticles. The higher yield and narrower size distribution of the composite powder produced from ethanol-based dispersions compared to the aqueous dispersions could be related to a smaller degree of aggregation, indicated by rheological measurements.
Keywords: Colloid; Titania; Mesoporous; Nanoparticle; Aerosol-assisted; Functionalization; Rheology
Viscoelastic properties of polystyrene and poly(methyl methacrylate) dispersions sterically stabilized by hydrophobically modified inulin (polyfructose) polymeric surfactant
by Jérémie Nestor; Marc Obiols-Rabasa; Jordi Esquena; Conxita Solans; Bart Levecke; Karl Booten; Tharwat F. Tadros (pp. 152-159).
Recently, steric repulsive forces induced by a new graft copolymer surfactant, which is based in inulin (polyfructose), have been described. Previous investigations by atomic force microscopy between solid surfaces covered with adsorbed surfactant indicated strong repulsive forces even at high electrolyte concentration, due to the steric repulsion produced by the surfactant hydration. In the present paper, the colloidal stabilization provided by this surfactant is studied by rheology. The measurements were carried out on sterically stabilized polystyrene (PS) and poly(methyl methacrylate) (PMMA) containing adsorbed surfactant (INUTEC®SP1). Steady-state shear stress as a function of shear rate curves was established at various latex volume fractions. The viscosity volume fraction curves were compared with those calculated using the Doughtry–Krieger equation for hard sphere dispersions. From the experimentalηr–ϕ curves the effective volume fraction of the latex dispersions could be calculated and this was used to determine the adsorbed layer thickness Δ. The value obtained was 9.6 nm, which is in good agreement with that obtained using atomic force microscopy (AFM). Viscoelastic measurements of the various latex dispersions were carried out as a function of applied stress (to obtain the linear viscoelastic region) and frequency. The results showed a change from predominantly viscous to predominantly elastic response at a critical volume fraction (ϕc). The effective critical volume fraction,ϕeff, was calculated using the adsorbed layer thickness ( Δ) obtained from steady-state measurements. For PS latex dispersionsϕeff was found to be equal to 0.24 whereas for PMMAϕeff=0.12. These results indicated a much softer interaction between the latex dispersions containing hydrated polyfructose loops and tails when compared with latices containing poly(ethylene oxide) (PEO) layers. The difference could be attributed to the stronger hydration of the polyfructose loops and tails when compared with PEO. This clearly shows the much stronger steric interaction between particles stabilized using hydrophobically modified inulin.
Keywords: Latex particles; Inulin polymeric surfactant; Rheology; Steric repulsions
Control of particle cluster dispersion using responsive polymeric additives
by L. Bava; D.L. Feke; I. Manas-Zloczower; S.J. Rowan (pp. 160-168).
The dispersion behavior of clusters of hydrophilic and hydrophobic silica treated with a thermoresponsive polymer has been investigated. The influence of the thermoresponsive interfacial chemistry was assessed by performing dispersion studies in poly(dimethylsiloxane) (PDMS) at 25 and 68 °C for agglomerates of powders incorporating poly( N-isopropyl acrylamide) (PNIPAM), a thermoresponsive polymer, and water. While the dispersion of clusters of hydrophilic silica was found to be temperature independent, dispersion of hydrophobic silica exhibited a temperature dependency. The response of the polymer upon temperature variation brings about modifications in the interparticle interactions of the PNIPAM-treated powders thus leading to changes in the cluster cohesivity. The dependence of the cluster cohesivity on temperature was evidenced through changes in the dispersion mechanism and kinetics of the treated silica clusters at both tested temperatures. In addition, optical microscopy of silica suspensions with and without PNIPAM at 25 and 60 °C, illustrated the effect of the polymer presence and configuration on the particle–particle interaction forces. While micrographs of the particles at 25 °C show less evidence of particle aggregation, the micrographs at 60 °C illustrate an increase in aggregation suggesting an enhancement in the attractive forces between particles.Silica clusters which incorporate a thermoresponsive polymeric additive show hydrodynamic dispersion modes and rates that are sensitive to temperature.
Keywords: Responsive polymers; Dispersion; Cluster cohesivity
Advantages and limitations of the synchrotron based transmission X-ray microscopy in the study of the clay aggregate structure in aqueous suspensions
by Marek S. Zbik; Ray L. Frost; Yen-Fang Song (pp. 169-174).
This paper reports new application of new transmission X-ray microscopy powered by a synchrotron source for the study of aqueous based clay suspensions. This paper delineates the advantages and limitations of this method. The tested transmission X-ray microscopy (TXM) technique has shown good agreement with the cryo-stage SEM technique. The spacial resolution of this TXM technique is 60 nm and clay particles with diameter below 500 nm are clearly visible and their pseudohexagonal symmetry is recognizable in detail. It is clearly demonstrated the methodology of implementing TXM to study aqueous based clay suspensions that are close to ∼60 nm tomographic resolution. The technique enables us to study discrete structure of clay suspensions in water and within aggregates. This has never been previously possible. Larger crystals, more compact aggregates and less colloidal fraction present in kaolinite from Georgia has impact on faster settling and gelling in denser suspension than for Birdwood kaolinite in which colloidal particles create gel-like networking in less dense aqueous suspension.It is clearly demonstrated the methodology of implementing TXM to study aqueous based clay suspensions that are close to 60 nm tomographic resolution. This has never been previously possible.
Keywords: Transmission X-ray microscopy (TXM); Scanning electron microscopy (SEM); Synchrotron radiation; Kaolinite; Minerals; Interface segregation
Thermoresponsive polymer-stabilized silver nanoparticles
by Limin Guo; Jingjing Nie; Binyang Du; Zhangquan Peng; Bernd Tesche; Karl Kleinermanns (pp. 175-181).
Silver nanoparticles (Ag NPs) stabilized by a thermoresponsive polymer, poly( N-isopropylacrylamide) (PNIPAM), have been synthesized by the reduction of silver ions with NaBH4 in aqueous solutions. The obtained Ag NPs are very stable at room temperature due to the extended coil conformation of the PNIPAM chain at temperatures below its volume phase transition temperature (∼32 °C). At higher temperatures (such as 45 °C) above the phase transition of PNIPAM, only minute aggregation between Ag NPs was observed, showing that the collapsed PNIPAM chains still retain the ability to stabilize Ag NPs. The PNIPAM-stabilized Ag NPs were then characterized as a function of the thermal phase transition of PNIPAM by UV–vis spectroscopy, dynamic light scattering, transmission electron microscopy, and cyclic voltammeter. Consistent results were obtained showing that the phase transition of PNIPAM has some effect on the optical properties of Ag NPs. Switchable electrochemical response of the PNIPAM-stabilized Ag NPs triggered by temperature change was observed.Thermo-responsive poly( N-isopropylacrylamide) (PNIPAM)-stabilized Ag nanoparticles (Ag NPs) were successfully synthesized by simply reducing the silver salt in the PNIPAM aqueous solution. The PNIPAM-stabilized Ag NPs show tunable optical properties, which is fully reversible dependence on the phase transition of PNIPAM. The Ag NPs only show electrochemically active when the PNIPAM chains collapse. These unique properties render PNIPAM-stabilized Ag NPs as potential electrode coating materials, of which the electrochemical properties could be switched by the environmental temperature.
Keywords: Silver nanoparticles; Thermoresponsive polymer; Optical property; Electrochemistry
The strength of liquid bridges in random granular materials
by Zdeněk Grof; Christopher J. Lawrence; František Štěpánek (pp. 182-192).
The strength of capillary bridges in randomly packed granular media was analyzed by means of computer simulations. A novel simulation method, based on the tracking of moving interfaces, has been implemented and used for determining the equilibrium shape of capillary bridges in a granular medium under a range of liquid saturations and solid-phase geometry. The net force acting on each grain due to the capillary bridges was evaluated, as well as the aggregate force acting between two wet granular media during their separation in the normal directions. The simulation results are consistent with previous experimental observations and reveal interesting phenomena such as the existence of a maximum in the tensile strength of a wet granular medium as function of liquid saturation.
Keywords: Capillary force; Wetting; Pendular and funicular regime; Modeling; Tensile strength; Surface tension; Contact angle
Preparation of Ru-doped SnO2-supported Pt catalysts and their electrocatalytic properties for methanol oxidation
by H.L. Pang; X.H. Zhang; X.X. Zhong; B. Liu; X.G. Wei; Y.F. Kuang; J.H. Chen (pp. 193-198).
Ru-doped SnO2 nanoparticles were prepared by chemical precipitation and calcinations at 823 K. Due to high stability in diluted acidic solution, Ru-doped SnO2 nanoparticles were selected as the catalyst support and second catalyst for methanol electrooxidation. The micrograph, elemental composition, and structure of the Ru-doped SnO2 nanoparticles were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction, respectively. The electrocatalytic properties of the Ru-doped SnO2-supported Pt catalyst (Pt/Ru-doped SnO2) for methanol oxidation have been investigated by cyclic voltammetry. Under the same loading mass of Pt, the Pt/Ru-doped SnO2 catalyst shows better electrocatalytic performance than the Pt/SnO2 catalyst and the best atomic ratio of Ru to Sn in Ru-doped SnO2 is 1/75. Additionally, the Pt/Ru-doped SnO2 catalyst possesses good long-term cycle stability.The Pt/Ru-doped SnO2 catalyst shows better electrocatalytic performance for methanol electrooxidation than the Pt/SnO2 catalyst and the best atomic ratio of Ru to Sn in Ru-doped SnO2 is 1/75.
Keywords: Ru-doped SnO; 2; nanoparticles; Electrocatalyst; Methanol oxidation; Electrochemical properties
Immobilization of iron tetrasulfophthalocyanine on functionalized MCM-48 and MCM-41 mesoporous silicas: Catalysts for oxidation of styrene
by Mahtab Pirouzmand; Mostafa M. Amini; Nasser Safari (pp. 199-205).
Iron tetrasulfophthalocyanine (FePcS) has been anchored on the surface of functionalized MCM-48 and MCM-41 silicas by means of chemical bonding to aminosilane groups. The prepared materials, FePcS/NH2-MCM-48 and FePcS/NH2-MCM-41, were characterized by diffuse reflectance UV–vis and infrared (IR) spectroscopies, low-angle X-ray diffraction (XRD), and surface area analysis (BET). The tendencies of FePcS absorption on functionalized MCM-48 and MCM-41 were measured by UV–vis spectroscopy. The functionalized MCM-48 showed a larger amine to silica ratio than the functionalized MCM-41. Low-angle X-ray diffraction analysis showed that, by anchoring iron tetrasulfophthalocyanine into functionalized MCM-48 and MCM-41, the intensity of main reflection decreased. The catalytic activities of the supported iron tetrasulfophthalocyanine were examined by the oxidation of styrene in the presence of tert-butyl hydroperoxide. The FePcS/NH2-MCM-48 showed higher activity and durability in the liquid-phase oxidation of styrene under mild condition compared with the FePcS/NH2-MCM-41 and unsupported catalyst.Iron tetrasulfophthalocyanine (FePcS) has been anchored on the surface of functionalized MCM-48 and MCM-41 silicas by means of chemical bonding to aminosilane groups.
Keywords: MCM-48; MCM-41; Iron tetrasulfophthalocyanine; Styrene
The dependence of hematite site-occupancy standard state triple-layer model parameters on inner-layer capacitance
by Yu Sik Hwang; John J. Lenhart (pp. 206-213).
Potentiometric acid–base titration data for three hematite samples that differed on the basis of specific surface area (17.4, 33, 83 m2/g for hematite A, B, and C, respectively) was analyzed using the triple-layer model (TLM). The sensitivity of the TLM fits of the data to the choice of site density (Ns) was evaluated from 1.5 to 22 sites/nm2. In general, little dependence in the quality of fit was determined, irrespective of the value ofNs. Values of the electrolyte adsorption equilibrium constants (logKcation0 andlogKanion0) steadily increased with decreasingNs. These constants are consistent with the commonly used 1.0 M standard state and when converted into comparable constants consistent with the site-occupancy standard state (logKcationθ andlogKanionθ) a single value for each respective constant was determined. Values of the inner-layer capacitance (C1) were varied during these optimizations and increased with decreasingNs, particularly below 5 sites/nm2. The optimizedC1 values exhibited an apparent inverse relationship with specific surface area (i.e.,C1 for hematiteA>C1 for hematiteB>C1 for hematite C). The magnitude of change inC1 with respect toNs depended upon the magnitude ofC1 for each hematite as the higher theC1 value, the greater was the change with respect toNs. These results suggest when the site-occupancy standard state parameters are used to predict constants at different site density values without re-regression of titration data that variations inC1 should be accounted for, particularly for low specific surface area samples that have a highC1.New site-occupancy equilibrium constants are independent of site density as long as variations inC1 are taken into account, particularly for low specific surface area samples with highC1 values.
Keywords: Hematite; Surface complexation model; TLM parameters; Site density; Inner-layer capacitance; Specific surface area; FITEQL; Site-occupancy standard state
Time resolved alteration process of oxide glasses
by Luc Girard; Mehdi Arab; Olivier Spalla (pp. 214-225).
Dissolution of oxide glasses by water has been studied by small angles X-ray scattering. It is shown that the altered residual surface layer due to dissolution and recondensation of Si atoms is a porous material with nanometer size pores. Based on five elements oxide glass (18NaO2–17B2O3–4CaO– yZrO2–(61−y)SiO2 withy=0, 1, 2, 4 and 8) the experiment highlights a strong influence of insoluble element on both the kinetic of alteration and the structure of the altered layer. It is shown that above 2% Zr content, the fraction of porous volume and the surface of exchange in the altered layer pass through a maximum value in the first hours of alteration corresponding to an overshoot of Si lixiviation without recondensation as the saturation limit is not reached. When the saturation limit is reached the porous volume fraction is just below the fraction of volume occupied primarily by the sodium and the boron.
Keywords: Alteration; SAXS; Oxide glasses; Lixiviation; Altered layer; Porous; Silica gel; Nanosized; Scattering; Percolation; Glass; Interfacial process
Diffusion of ions in unsaturated porous materials
by A. Revil; D. Jougnot (pp. 226-235).
In a salinity gradient, the diffusion of ions through the connected porosity of a porous and charged material is influenced by the charged nature of the interface between the pore water and the solid. This influence is exerted through the generation of a macroscopic electrical field termed the diffusion or membrane potential. This electrical field depends on the excess of counterions located in the pore space counterbalancing the charge density of the surface of the solid. In unsaturated porous materials, we have to consider (1) the effect of the charged nature of the air/water interface, (2) the increase of the counterion density as the counterions are packed in a smaller volume when the saturation of the nonwetting phase (air) increases, and (3) the influence of the water saturation upon the tortuosity of the water phase. The volume average of the Nernst–Planck equation is used to determine the constitutive equations for the coupled diffusion flux and current density of a multicomponent electrolyte in unsaturated conditions. We assume that water is the wetting phase for the solid phase. We neglect the electro-osmotic flow in the coupled constitutive equations and the deformation of the medium (the medium is assumed to be both isotropic and rigid). This model explains well the observed tendency of strong decreases of the apparent diffusion coefficient of ions with the decrease of the saturation of the water phase under steady-state conditions. This decrease is mainly due to the influence of the saturation upon the tortuosity of the water phase.Modeling of the effect of the saturation of the water phase upon the diffusivity of sodium chloride in a clay-rock (between full saturation and critical water saturation,swc).
Keywords: Diffusion potential; Diffusion; Unsaturated porous media; Diffusivity; Ion transport; Clay; Charged porous media; Porous media
Prediction of permeate flux during osmotic pressure-controlled electric field-enhanced cross-flow ultrafiltration
by Biswajit Sarkar; Sunando DasGupta; Sirshendu De (pp. 236-246).
Electric field-enhanced cross-flow ultrafiltration has been carried out to separate protein, bovine serum albumin, from aqueous solution using a 30,000 molecular weight cutoff membrane. A theoretical model is developed to predict permeate flux under a laminar flow regime including the effects of external d.c. electric field and suction through the membrane for osmotic pressure-controlled ultrafiltration. The governing equations of the concentration profile in the developing mass transfer boundary layer in a rectangular channel are solved using a similarity solution method. The effect of d.c. electric field on the variation of membrane surface concentration and permeate flux along the length of the channel is quantified using this model. The expression of Sherwood number relation for estimation of mass transfer coefficient is derived. The analysis revealed that there is a significant effect of electric field on the mass transfer coefficient. A detailed parametric study has been carried out to observe the effect of feed concentration, electric field, cross-flow velocity, and pressure on the permeate flux. For 1 kg/m3 BSA solution, by applying a d.c. electric field of 1000 V/m, the permeate flux increases from 42 to 98 L/m2 h compared to that with zero electric field. The experimental results are successfully compared with the model predicted results.Variation of average permeate flux with electric field is shown in the adjacent figure. Model predicts closely the experimental data.
Keywords: Membranes; Ultrafiltration; Electrophoresis; Laminar flow; Osmotic pressure
Effects of calcination temperature on the pore size and wall crystalline structure of mesoporous alumina
by Zhong-Xi Sun; Ting-Ting Zheng; Qi-Bing Bo; Miao Du; Willis Forsling (pp. 247-251).
In this paper, mesoporous alumina with different pore sizes and wall crystalline structures was synthesized at calcination temperatures over 550 °C. The characterization of the samples calcined at 550, 800, 1100, and 1300 °C, respectively, was performed using TEM, XRD, FTIR, TG/DTA, and N2 adsorption/desorption techniques. The correlation between pore size and wall crystalline structure on calcination temperature was systematically investigated.XRD results of as-synthesized mesostructured alumina (A) and MA after calcination at 550 °C (B), 800 °C (C), 1100 °C (D), and 1300 °C (E) confirm the formation of MA with different crystalline structures.
Keywords: Mesoporous alumina; Calcination temperature; Pore size; PEG
An improved process for separation of proteins using modified chitosan–silica cross-linked charged ultrafilter membranes under coupled driving forces: Isoelectric separation of proteins
by Arunima Saxena; Bijay P. Tripathi; Vinod K. Shahi (pp. 252-262).
Functionalized chitosan namely as N-methylene phosphonic chitosan (PC) and quaternized chitosan (QC) silica composite charged ultrafilter membranes were prepared by acid catalyzed sol–gel method in the aqueous media and gelated in methanol for tailoring their pore structure. These membranes were employed for developing a simple membrane process for pH sensitive protein fractionation under coupled driving forces (pressure and electric gradient). Protein transmission (selectivity) and membrane throughput across both membranes were studied using binary mixture of protein under different gradients at pH points: 2.0, 4.8, 10.7, and 13.0. It was concluded that separation from the binary mixture of BSA–LYS, separation LYS at pH 4.8 (p I of BSA) using negatively charged PC–Si membrane or separation BSA at pH 10.7 (p I of LYS) using positively charged QC–Si membrane, was possible with high selectivity. Also in all cases, due to coupling of driving forces, filtrate flux and selectivity were enhanced by several folds. Furthermore, applied electric gradient progressively increased the separation factor values, which was close to 10 for PC–Si and 15 for QC–Si membranes. Relatively high separation value of individual protein from binary mixture and filtrate velocity suggests the practical usefulness of this novel process and biopolymer membranes.Diagram of the cell for protein separation under coupled driving force using charged ultrafilter membrane.
Keywords: Protein separation; Charged ultrafilter membrane; Bioseparation; Modified chitosan–silica composite
Viscous coalescence of expanding low-viscosity drops; the dueling drops experiment
by Marcos Borrell; L. Gary Leal (pp. 263-269).
A new experimental device was designed and developed for the systematic study of the interaction of two, very small low viscosity expanding drops that were pushed out of the ends of two aligned opposing capillaries into a polymeric liquid. The idea of this experiment is to mimic the interactions of two expanding bubbles during the formation of polymeric foams; for convenience, we call this device the dueling drops experiment. In the current setup, we are able to grow drops (50–200 μm maximum diameter) at a controlled flow rate (down to 0.1 μl/day). Optical observation of the pair of growing drops was achieved by the use of an optical zoom lens system for a side view, and a “long-range” microscope for a top view, thus ensuring complete alignment of the capillaries and partial observation of the thin-film. Measurements are reported for the drainage time between the apparent initial contact of the drops and film rupture. A simple scaling theory was developed based on the drainage of two approaching flat disk-like interfaces, the radius of which expands throughout the interaction as the volume of the drop increases.A qualitative sketch of one side of “dueling drop” device, which consists of two opposing capillaries.
Keywords: Coalescence; Drops; Thin-film
Self-assembled film based on carboxymethyl- β-cyclodextrin and diazoresin and its binding properties for methylene blue
by Junge Zhi; Xuling Tian; Wei Zhao; Jinbo Shen; Bin Tong; Yuping Dong (pp. 270-276).
Polyelectrolyte-layered films containing β-cyclodextrin ( β-CD) were fabricated by a layer-by-layer deposition of carboxymethyl- β-cyclodextrin (CM- β-CD) as a polyanion and cationic photosensitive diazoresin (DR) on a solid surface. Under UV irradiation, following the decomposition of diazonium group between the adjacent interfaces of the multilayers, the ionic bonds of the self-assembly film convert to covalent bonds and the film become stable toward many common organic solvent. When a high-ionic-strength buffer is employed as a bathing solution, the film is thicker than that deposited from water solution. And the deposition increases with the increase of the carboxymethylated degree of CM- β-CD. The CM- β-CD/DR film can bind methylene blue (MB), and the durability of MB-adsorbing films to reductive glucose indicates that MB molecules not only diffuse into the film, but also load to the cavity of β-CD through a host–guest complexation assisted by electrostatic interactions. The binding quantity of MB increases linearly with increasing the number of bilayers, and is influenced obviously by the pH value of MB aqueous solution. MB molecules can desorb from the 12-bilayer MB-absorbing CM- β-CD/DR films when being immersed in water/ethanol mixture, and the released quantity of MB increases a little with increasing the concentration of water when it is below 30%, while decreases evidently over 30%.The UV–vis spectra of MB-adsorbing CM- β-CD(7.4)/DR film before and after being immersed in reductive glucose solution.
Keywords: Self-assembled multilayer films; Carboxymethyl-; β; -cyclodextrin; Diazoresin; Binding and desorption properties; Methylene blue dye
Structural characterization and properties of an azopolymer arranged in Langmuir and Langmuir–Blodgett films
by Marta Haro; Ignacio Gascón; Ricardo Aroca; M. Carmen López; Félix M. Royo (pp. 277-286).
The fabrication of Langmuir and Langmuir–Blodgett (LB) films of an acid-azopolymer (PAzCOOH) is reported. Several techniques were used in their characterization: surface pressure ( π) and surface potential (Δ V) isotherms, UV–vis reflection spectroscopy, and Brewster angle microscopy (BAM) for the Langmuir films and contact angle measurements, UV–vis, fluorescence, IR and Raman spectroscopy and scanning electronic microscopy (SEM) for the LB films. Our study reveals that lateral chains of the polymer situate preferentially onto the water surface with the acid group in contact with the water, where aggregates are scarcely formed. Therefore, the lateral chains of PAzCOOH can be treated as individual monomers to determine structural properties of the fabricated Langmuir and LB films. Monomeric treatment has been used to interpret UV–vis reflection spectroscopy, and a monomer model has been performed to represent lateral chains using density functional theory at B3LYP 6-31G(d,p) level of theory to assign the observed vibrational spectra.The ability to form well-arranged Langmuir and Langmuir–Blodgett films of an azopolymer is reported. Lateral chains are situated in contact with water and, consequently, monomeric analysis can be applied.
Keywords: Azopolymer; Langmuir–Blodgett film; Langmuir monolayer; Reflection spectroscopy; In-plane dichroism; SERS; Raman; Gaussian; Photodegradation
Determination of interfacial tension between two immiscible polymers with and without surfactants at the interface
by Y.T. Hu (pp. 287-294).
A second-order drop deformation method for inferring interfacial tension between two immiscible polymers is proposed and shown to improve the accuracy of tension estimate appreciably. A small step-strain method, which uses a strong flow (capillary number >1) and short flow time∼O(0.1s), is successfully developed to avoid complications caused by the surfactants for surfactant-laden drops. This method is demonstrated to give good tension estimates for a range of viscosity ratios and surface coverage.
Keywords: Drop deformation; Drop retraction; Interfacial tension; Surfactants
Temperature and compression rate independent domain shape in Langmuir monolayers of di- n-dodecyl hydrogen phosphate at the air–water interface
by Md. Mufazzal Hossain; Ken-ichi Iimura; Teiji Kato (pp. 295-301).
Thermodynamic and morphological properties of Langmuir monolayers of di- n-dodecyl hydrogen phosphate (DDP) have been studied by film balance and Brewster angle microscopy (BAM) over a wide range of temperature between 5 and 40 °C. Fromπ–A isotherms, a generalized phase diagram consisting of gas (G), liquid expanded (LE) and liquid condensed (LC) phases is constructed for the DDP monolayers. The BAM images show the formation of gas bubble in the bright background of LE phase during G–LE phase transitions and fingering LC domains during LE–LC phase transitions. The shapes of these domains are independent of temperature, showing a sharp contrast to the temperature-dependent monolayer morphologies of amphiphilic systems where the shape of the LC domains changes either from compact circular to fingering or from irregular or spiral to compact patterns with increasing temperature. In addition, the domains do not show any change in their shapes with decreasing the compression rate. Since the two-alkyl chains are directly attached by covalent bonds to the phosphate group, the rearrangement of the molecules needs to move the whole molecules including the hydration sphere. The difficulty related to such a movement of the molecules causes the fingering domains, which are independent of external variables. Although the domains are formed in a fingering shape, the equilibrium shape can be attained by about 120 min at 15 °C indicating a rather slow relaxation rate.Temperature and compression rate independent domains in DDP monolayers.
Keywords: Langmuir monolayers; Phase transition; Brewster angle microscopy; Di-; n; -dodecyl hydrogen phosphate; Triple point
Layer-by-layer fabrication of broad-band superhydrophobic antireflection coatings in near-infrared region
by Lianbin Zhang; Yang Li; Junqi Sun; Jiacong Shen (pp. 302-308).
Broad-band superhydrophobic antireflective (AR) coatings in near infrared (NIR) region were readily fabricated on silicon or quartz substrates by a layer-by-layer (LbL) assembly technique. First, a porous poly(diallyldimethylammonium chloride) (PDDA)/SiO2 nanoparticle multilayer coating with AR property was prepared by LbL deposition of PDDA and 200 nm SiO2 nanoparticles. PDDA was then alternately assembled with sodium silicate on the PDDA/SiO2 nanoparticle coating to prepare a two-level hierarchical surface. Superhydrophobic AR coating with a water contact angle of 154° was finally obtained after chemical vapor deposition of a layer of fluoroalkylsilane on the hierarchical surface. Quartz substrate with the as-fabricated superhydrophobic AR coating has a maximal transmittance above 98% of incidence light in the NIR region, which is increased by five percent compared with bare quartz substrate. Simultaneously, the superhydrophobic property endows the AR coating with water-repellent ability. Such superhydrophobic AR coatings can effectively avoid the disturbance of water vapor on their AR property and are expected to be applicable under humid environments.Broad-band superhydrophobic antireflective (AR) coatings in near infrared (NIR) region were readily fabricated on silicon or quartz substrates by a layer-by-layer (LbL) assembly technique.
Keywords: Antireflection; Superhydrophobic; Layer-by-layer assembly; Multilayer films; SiO; 2; nanoparticles
Shape of menisci in terrestrial dewetted Bridgman growth
by Liliana Braescu / (pp. 309-315).
Dewetted Bridgman is a crystal growth technique in which the crystal is detached from the crucible wall by a liquid free surface at the level of the solid–liquid interface, called liquid meniscus, which creates a gap between the crystal and the ampoule. Dewetting phenomenon was first obtained spontaneously in spatial experiments during the Bridgman solidification, and opened the possibility of reproducing experiments on the earth—obtained by applying a gas pressure differenceΔP=Pcold–Phot between the cold and the hot sides of the sample. In order to understand the process which leads to a crystal with a constant radius on the ground, analytical and numerical studies of axisymmetric meniscus shapes are made and the dependence of the meniscus shape on the pressure difference is established. For this aim, starting from the Young–Laplace equation of a capillary surface in equilibrium in the presence of gas pressure, a mathematical model able to describe the meniscus surfacez=z(r) and the angleθ=θ(r) between the tangent to the meniscus and the horizontal axis is presented. On the basis of this model, inequalities of the pressure intervals for which dewetting is feasible are established. Numerical results are performed for InSb crystals.The inequalities which define pressure differenceΔP=Pcold–Phot intervals for which detached solidification is feasible are determined.
Keywords: Dewetting; Contact angle; Growth angle; Menisci; Taylor approximation; Numerical simulation
Equilibrium partition of polycyclic aromatic hydrocarbons in cloud point extraction with a silicone surfactant
by Bingjia Yao; Li Yang (pp. 316-321).
In the cloud point extraction (CPE) process with PEG/PPG-18/18 dimethicone, the flexible chain structure of the silicone surfactant efficiently decreased the water content remaining in the surfactant-rich phase, compared with conventional nonionic surfactants, represented by Triton X-114. Meanwhile, the phase volume ratio of surfactant-rich phase to aqueous phase obtained in the silicone surfactant CPE system was found to be maintained at a low value with increasing surfactant concentration; whereas a rapid increase tendency was commonly observed in that of other nonionic surfactants. Based on these advantages, the equilibrium partition of three polycyclic aromatic hydrocarbons (PAHs), anthracene, phenanthrene and pyrene, was studied in the CPE process with PEG/PPG-18/18 dimethicone. Equilibrium parameters, including preconcentration factor, distribution coefficient and recovery, were determined, and the performance was compared with that of another related CPE research, where Tergitol 15-S-7 was used. Due to the low surfactant-rich phase volume, higher concentrations of the three PAHs in the surfactant-rich phase, and the resulting higher preconcentration factors and distribution coefficients were able to be achieved at the same time. Moreover, the great performance was able to be maintained even at a high surfactant concentration or PAHs initial concentration.PEG/PPG-18/18 dimethicone offered a much lower water content in the surfactant-rich phase and a sustained phase volume ratio in cloud point extractions of PAHs.
Keywords: Polycyclic aromatic hydrocarbons; Phase equilibrium; Cloud point extraction; Surfactant; Separations; Scale-up; Water treatment
Synthesis of nanocrystalline calcium phosphate in microemulsion—effect of nature of surfactants
by Sujata Singh; Pallavi Bhardwaj; V. Singh; S. Aggarwal; U.K. Mandal (pp. 322-329).
Nanosized calcium phosphate (CP) powders have been synthesized by an inverse microemulsion system using kerosene as the oil phase, a cationic surfactant Aliquat 336, a non-ionic surfactant Tween 20 and their mixture and aqueous solutions of calcium nitrate tetrahydrate and biammonium hydrogen phosphate as the water phase. It has been found that the nature of surfactants played an important role to regulate the size and morphologies of the calcium phosphate nanoparticles. The cationic surfactant Aliquat 336 has been found to regulate the nucleation and crystal growth. The synthesized powders have been comprehensively characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Our results show that the brushite (DCPD) is the major phase comprising the calcium phosphate nanoparticles. In mixed surfactants mediated system a morphological controlled highly crystalline particles have been synthesized. Further, the role of Aliquat 336 has been established and a plausible synthetic mechanism has been proposed.TEM images demonstrating the effect of surfactant on the formation of nanocrystalline calcium phosphate (CP) in microemulsion in presence of (a) non-ionic surfactant, (b) ionic surfactant and (c) mixed surfactant.
Keywords: Microemulsion; Calcium phosphate; Nanocrystalline; Surfactant
Polyelectrolyte–surfactant complexes with long range order
by Isabel E. Pacios; Björn Lindman; Krister Thuresson (pp. 330-337).
Mixtures of carboxymethyl cellulose (CMC) or hydrophobically modified CMC with an oppositely charged surfactant (benzyldimethyltetradecylammonium chloride) in water were prepared. When the global polymer concentration is 0.18% by weight and the surfactant content is high enough, a precipitate with hexagonal order is formed. The precipitate composition shows practically constancy in its water content and a slight diminution in polymer concentration when the global surfactant content is varied between 0.9 and 23 wt%. The lattice parameter in this phase decreases when the polymer/surfactant ratio in the phase increases; this variation is faster with CMC than with the hydrophobically modified CMC. In this way electrostatic and hydrophobic interactions are far from being additive. From the extrapolation to infinite dilution, the global interaction seems to depend on the substitution degree in the polymer. Additionally, the comparison between the radius at the polar–apolar interface in the cylinders and the lattice parameter as a function of polymer/surfactant ratio in the hexagonal phase is compatible with some of the alkyl chains belonging to the hydrophobically modified CMC being present in the aqueous zone.
Keywords: Carboxymethyl cellulose; Hydrophobic modified carboxymethyl cellulose; Polyelectrolyte–surfactant complexes; Hexagonal mesophase
Salt-induced viscoelastic wormlike micelles formed in surface active ionic liquid aqueous solution
by Bin Dong; Jin Zhang; Liqiang Zheng; Suqing Wang; Xinwei Li; Tohru Inoue (pp. 338-343).
The growth and structure of the aqueous micellar solutions of a surface active ionic liquid, 1-hexadecyl-3-methylimidazolium bromide (C16mimBr), in the presence of an organic salt sodium tosylate (NaTos), were investigated by rheological measurements and freeze-fracture transmission electron microscopy at room temperature (298 K). As in some conventional ionic surfactant/salt aqueous systems, wormlike micelles and network structures could be formed in the C16mimBr/NaTos aqueous solutions, according to measurements of the zero-shear viscosity, the entanglement length, the average contour length, as well as application of the Cox–Merz empirical rule and Cole–Cole plots. FF-TEM images further confirmed that wormlike micelles were formed in these aqueous solutions. The wormlike micelles presented here would expand potential applications of ionic liquids in home care products, oilfield stimulation fluids, and nanobiotechnology.Salt-induced viscoelastic wormlike micelles formed in surface active ionic liquid aqueous solutions were investigated.
Keywords: Surface active ionic liquid; Wormlike micelles; Rheology; Viscoelasticity; FF-TEM
Translational motion of a spherical particle near a planar liquid–fluid interface
by Yandong Gao; Dongqing Li (pp. 344-352).
The translational electrophoretic motion of a colloidal spherical particle parallel to a planar liquid–fluid interface is analyzed by using the reciprocal theorem developed by Yariv and Brenner [E. Yariv, H. Brenner, J. Fluid Mech. 484 (2003) 85]. Based on the thin electric double layers assumption, analytical solutions of the forces acting on the particle are obtained, and the influence of the liquid–fluid interface on the electrophoretic velocity of the particle is studied. It is found that the speed of the particle's electrokinetic motion will increase as the separation distance between the particle and the interface decreases. This enhancement of electrophoretic mobility becomes more significant when the viscosity of the fluid phase becomes larger.Schematic of the electrokinetic motion of a particle near a liquid–fluid interface.
Keywords: Electrophoretic motion; Boundary effects; Colloidal particle; Fluid–fluid interface
Easily prepared high-quantum-yield CdS quantum dots in water using hyperbranched polyethylenimine as modifier
by Jie Mao; J.N. Jun-Na Yao; L.N. Li-Na Wang; Wei-Sheng Liu (pp. 353-356).
Some research has reported interaction between polyamidoamine dendrimers or polyethylenimine and quantum dots causing a quantum yield decrease of quantum dots. In this work, however, polyethylenimines of different molecular weight that were used to modify CdS quantum dots gave rise to the enhancement of CdS quantum yield to nearly 100%. Herein, we present the synthesis of a kind of easily prepared high-quantum-yield CdS quantum dot in aqueous solution and the study of the interaction between CdS and polyethylenimine.The quantum yield of prepared CdS quantum dots is enhanced through PEI modification from 30 up to 95%. It is an impressive effect. The prevalent strategy of growing a shell on top of nanocrystal core for enhancement of quantum yield has a highest reported enhancement of 85%. Which method is better needs to be reconsidered.
Keywords: CdS; Polyethylenimines (PEI); Photoluminescence enhancement; Quantum yield
Investigation on the assembled structure–property correlation of supramolecular hydrogel formed from low-molecular-weight gelator
by Yujiang Wang; Liming Tang; Jian Yu (pp. 357-364).
The investigation on structure–property correlation is important for understanding the gelating mechanism of supramolecular hydrogels. In this paper, a low-molecular-weight hydrogelator (termed as gelator 1) prepared from 1,2,4,5-benzene tetracarboxylic acid (BTA) and 4-hydroxy pyridine (PHP) was able to gel water effectively. The influence of environmental stimulation, such as cooling speed and ultrasonic treatment, on the structure of the assembling fibers and the macroscopic properties of the gels was investigated via multiple techniques. The results indicated that the fiber size decreased as increasing the cooling speed and the smallest fibers were obtained under ultrasonic treatment. As the fibers became smaller, the gel with higherTgel, lower bonded water content and higher dynamic modulus was obtained. Therefore it is possible to control the gel performances via the environmental stimulation. The relationship between the assembled structure and properties is helpful for understanding the gel formation mechanism and makes the gels suitable for different applications.
Keywords: Supramolecular hydrogel; Low-molecular-weight gelator; Hydrogen bond
A study of atmospheric-pressure CHF3/Ar plasma treatment on dielectric characteristics of polyimide films
by Soo-Jin Park; Eun-Jung Lee; Byung-Joo Kim (pp. 365-369).
In this work, the influence of atmospheric-pressure CHF3/Ar plasma treatment on surface dielectric properties of polyimide films was investigated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements. The dielectric characteristics of the films were studied using a dielectric spectrometer. From the results, it was found that the plasma treatment introduced fluorine functional groups onto the polyimide surfaces. F1s/C1s ratios of the polyimides were enhanced with the increase of plasma treatment time. Consequently, the fluorine groups led to a decrease of the surface free energy and dielectric constant of the polyimide films, which can largely be attributed to the decrease of the deformation polarizability or London dispersive component of surface free energy of the solid surface studied.The dielectric constant was calculated according to the usual parallel plate capacitor formula. The dielectric-constant room-temperature dependence of the dielectric constants of the polyimide films on frequency is shown in the figure. It can be seen that the dielectric constant slightly decreased slightly with increasing inputted frequency when the temperature was kept constant.
Keywords: Polyimide film; Atmospheric-pressure CHF; 3; /Ar plasma; Fluorine; Deformation; Polarizability
Design and synthesis of ordered mesoporous silica materials with high degree of silica condensation at high temperature from a mixture of polymer surfactant with small organic ammonium
by Chunyu Wang; Yunchen Du; Defeng Li; Xiangyu Guan; Fei Li; Feng-Shou Xiao (pp. 370-373).
Thermal stability on a mixture of triblock polymer (P123) and fluorocarbon surfactant (FC-4) in acidic media for synthesis of ordered mesoporous materials has been carefully investigated by NMR spectroscopy at various treated temperatures (RT–180 °C) and the templating mechanism of the mixture on high-temperature synthesis has been proposed. Accordingly, we have designed fluorocarbon-free templates for syntheses of ordered mesoporous silica materials at high temperatures. As expected, ordered mesoporous silica materials with high degree of silica condensation are synthesized at high temperatures from these designed templates.The proposed procedure on synthesis of ordered mesoporous silica materials with high degree of silica condensation from mixture of triblock polymer (P123) and small organic ammonium templates at high temperature.
Keywords: NMR spectroscopy; Mesoporous materials; High degree of silica condensation; Polymer surfactant; Organic ammonium; Fluorocarbon surfactant
Adsorption of ions onto amorphous silica: Ion exchange model
by Sergey Pivovarov (pp. 374-376).
Single site ion exchange model was applied for description of the published data on adsorption of sodium, calcium, cadmium, and zinc onto amorphous silica. The following equilibria were detected (25 °C; X—adsorption site;TotX=6μmol/m2):2X + Na+ + OH− ⇔ XNa+ + XOH−, log K° = 5.1,3X + Me2+ + 2OH− ⇔ XMe2+ + 2XOH−, log K° = 11.6 (Ca), 11.7 (Cd),2X + Me2+ + 2OH− ⇔ XMeOH+ + XOH−, log K° = 14.1 (Cd), 15.5 (Zn).Model simulations of base titration curves (left; data from Karlsson et al. [Aquat. Geochem. 7 (2001) 13]) and calcium adsorption (right; data from Janusz et al. [J. Colloid Interface Sci. 266 (2003) 259]).
Keywords: Silica; Sodium; Calcium; Zinc; Cadmium; Adsorption; Ionic exchange
Rapid synthesis of highly ordered Si-MCM-41
by Xianbin Liu; Hui Sun; Yanhui Yang (pp. 377-380).
A very short-time synthesis of highly ordered MCM-41 molecular sieve was formulated by using cetyltrimethylammonium bromide (CTAB) as the template and silica gel from SiliCycle as the silica source. The physical properties of MCM-41 samples were characterized by X-ray diffraction (XRD), nitrogen physisorption, and transmission electron microscopy (TEM). The MCM-41 sample prepared in this study exhibited well defined long-range order and good hydrothermal stability. It was demonstrated that reducing the time of self-assembly step to 2 h during the synthesis had no unfavorable effect on the quality of MCM-41 materials.We described in this paper a facile method for the rapid synthesis of high-quality mesoporous Si-MCM-41 in a very short preparation time of 2 h.
Keywords: Si-MCM-41; Rapid synthesis; Nitrogen physisorption; TEM; XRD
Development of porosity in carbons from yeast grains by activation with alkali metal carbonates
by Y. Urabe; T. Ishikura; K. Kaneko (pp. 381-383).
Cellular structured activated carbon samples were prepared with the aid of alkali carbonates X2CO3 (X = Li, Na, K, Rb, or Cs) from dry bread yeast with a milling procedure. The resultant carbon possesses a very large adsorption amount even for supercritical methane. The activation with Cs2CO3 gave the greatest surface area of 2420 m2 g−1 from the subtracting pore effect method. The activation efficiency of X2CO3 (X = Li, Na, K, Rb, and Cs) was associated with the order of Gibbs free energy of X2O (X = Li, Na, K, Rb, and Cs) which should play an important role in the gasification. The carbon activated with Rb2CO3 gave the greatest adsorption amount of supercritical methane of 90 mg g−1 at 0.9 MPa at 303 K.Novel carbon of micropores and macropores was prepared from dry bread yeast of ordered cellular structures with the aid of a series of alkali carbonates. The activated carbon produced with Rb2CO3 gave the greatest adsorptivity for supercritical methane. Figure: Adsorption isotherms of CH4 on activated carbon samples at 303 K (●, Li-AC; ■, Na-AC; ▴, K-AC; □, Rb-AC; ○, Cs-AC).
Keywords: Alkali carbonate; Nanoporous carbon; Methane adsorption