Journal of Colloid and Interface Science

Published by Elsevier
Online ISSN: 1095-7103
Publications
Article
Perikinetic coagulation experiments are reported which were performed under 1g and µg conditions during a flight in a sounding rocket, for dispersions of polystyrene, quartz, and amorphous silica particles. Coagulation rates for dispersions of polystyrene, quartz, and amorphous silica are found to increase significantly under µg conditions compared to 1g conditions. Another set of experiments was performed at 1g, 2g, 4g, and 7g, with different densities of the continuous phase; also a mixture of two different polystyrene latices was used. The most pronounced effect of gravity on coagulation rate is found for dispersions with a small density difference, on going from 1g to 2g. In this regime a significant decrease in coagulation rates is observed. For the latex mixture at pronounced density differences, gravity-induced coagulation was observed; however, the aggregates formed did not have a lasting contact. The rate constant calculated under µg conditions approaches the theoretical value of von Smoluchowski. By means of a video analysis of the perikinetic coagulation process, the formation of doublets was studied. The "interaction time" for two particles was found to be longer for the density-matched dispersion. Doublets of particles are easily disrupted, and at 1g, free convection currents were observed even at small temperature differences in the system. Copyright 1998 Academic Press.
 
Sketch of the electrical triple layer model at the clay basal surface in the case of a binary monovalent electrolyte, M represents the metal cations (e.g., Na + ) and A À the anions (e.g., Cl À ). OHP represents the outer Helmholtz plane (d-plane), which coincides here with the shear plane along which the zeta potential is defined. The bplane corresponds to the mean plane of the Stern layer while the 0-plane corresponds to the surface of the basal plane. x 1 : distance from 0-plane to b-plane. 
Water (top), Na (middle), and Cl (bottom) concentration profiles as a function of the distance from the clay surface. Red line: results obtained with SPC water force field. Blue line: results obtained with SPC/E water force field. Brown lines: coordinates of the most external oxygen atom of the structure. Green lines: coordinates of the most external oxygen atom + ionic radius of oxygen (taken at 1.4 Å). The center of the system corresponds to the middle of the interlayer. The resolution is 0.5 Å for large figures (mean of 5 ns trajectory) and 0.01 for inserts (mean of 1 ns trajectory). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 
Diffuse swarm composition from the triple layer model with (Na, red dashed line; Cl, blue dashed line) and comparison with MD results (Na, red full line; Cl, blue full line). Vertical dotted lines represent the position of the b and d-planes. The full black line is the water density as a function of the distance from the clay surface. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 
Article
Molecular dynamics (MD) simulations of a montmorillonite/water interface at the pore scale were carried out at 0.1molL(-1) NaCl concentration in order to constrain cation, anion, and water distribution and mobility influenced by the mineral surface. MD results enabled anion exclusion and cation condensation at the surface to be quantified. MD-derived values could then be compared with macroscopic model results obtained from the Modified Gouy-Chapman (MGC) theory. While the Na concentration profile is well reproduced in the diffuse layer, anion exclusion is overestimated by the MGC theory under our experimental conditions. We also showed that MD simulations can be used to constrain Basic Stern model parameters or, in combination with zeta potential measurements, can be used to constrain triple layer model (TLM) parameters by providing suitable values for the capacitance values. Na sorption intrinsic equilibrium constant values for clay basal surfaces are given accordingly.
 
Article
The electrosorption behavior of tetramethylthiourea (TMTU) on a mercury electrode from 1.0, 0.5, and 0.1 M NaClO(4) solutions containing 0.1 M tert-butanol (TB) is described by means of adsorption isotherm constants. The adsorption parameters for the double layer were calculated from a double-layer differential capacity measurement extrapolated to zero frequency. The values of the relative surface excess increase along with the concentration of NaClO(4). It seems that the adsorption of TMTU is determined by an interaction between adsorbed molecules. The presence of TB in the adsorption layer distinctly influences the parameters of the inner layer.
 
Article
The pH(pzc) values of several mechanical mixtures of amorphous hydrous oxides of iron (amorphous FeOOH) and manganese (delta-MnO2) have been determined using the solid addition method. While the pH(pzc) of delta-MnO2 remains almost unchanged, the corresponding value for amorphous FeOOH tends to increase with increased proportion of delta-MnO2 in the mixtures. The adsorption behavior of Co2+, Ni2+, Cu2+, and Zn2+ with respect to pH on a mechanical mixture of 70% delta-MnO2 and 30% amorphous FeOOH from 0.5 M NaCl and major ion sea water has been studied. Since delta-MnO2 is much more active adsorbent than amorphous FeOOH at pH below 6.5, the adsorption data on mixture have not only been normalized with respect to the mass of delta-MnO2 in the mixture, but also compared with adsorption data on delta-MnO2 alone. It is interesting to note that though each trace metal behaves in a different way from the other especially with respect to the nature of electrolyte medium, it is generally observed that the adsorption on the mixed oxide system is higher than that on delta-MnO2 alone under similar condition. It is also observed that adsorption in major ion sea water at a particular pH value is lower than in 0.5 M NaCl solution.
 
Article
Classical Monte Carlo (MC) simulations of D(2) molecules physisorbed on LiF(001) surfaces are reported and show a series of interesting commensurate structure forms, viz., p(2x2) -->p(8x2) -->p(4x2), with coverages Theta=0.5, 0.625, and 0.75, respectively, and are stable up to 8 K. These structures are consistent with recent helium atom scattering (HAS) results (the p(4x2) is not observed) in terms of coverage and stability, but disagree in terms of symmetry. The p(2x2) structure contains two D(2) molecules per unit cell, with each molecule lying parallel to the plane of the surface directly above every other cationic site. For the p(4x2) structure, there are two kinds of adsorption sites: a parallel site, as in the case of p(2x2), and a tilted site, where the D(2) molecules sit between cationic and anionic sites with the molecular axis directed toward the anionic site, with a tilt angle of theta approximately 63 degrees. Perturbation theory calculations show that the adsorbed D(2) molecules are azimuthally delocalized and hence the structures are indeed c-type. Our calculations also indicate that o-D(2) and helicoptering p-D(2) species prefer cationic sites, compared to cartwheeling p-D(2) species.
 
Article
The purpose of this work is the numerical resolution, in the case of anisotropic elasticity, of the problem of a misfit dislocation located between an infinite substrate and two-layer composite. This case is obtained where the period of a network of misfit dislocations is taken as much greater than the thickness of the two foils. As a result, in the vicinity of the dislocation, the limiting boundary conditions will be close to those of Volterra translation dislocation. The elastic fields of displacement and stress are calculated for various orientations of the burger's vector, by inversion of a 30 x 30 computed matrix. Before this calculation, we tested the precision of the results of the program by comparing the interfacial relative displacement obtained from it with the results of the analytical expression describing this same displacement. The composite NiSi2/Si/(001)GaAs the subject of several investigations, is treated as an example.
 
Article
The adsorption mechanism of water on the hydroxylated (001) plane of α-Al(2)O(3) was studied by measuring adsorption isotherms and GCMC simulations. The experimental adsorption isotherms for three α-Al(2)O(3) samples from different sources are typical type II, in which adsorption starts sharply at low pressures, suggesting a high affinity of water to the Al(2)O(3) surface. Water molecules are adsorbed in two registered forms (bilayer structure). In the first form, water is registered at the center of three surface hydroxyl groups by directing a proton of the water. In the second form, a water molecule is adsorbed by bridging two of the first-layer water molecules through hydrogen bonding, by which a hexagonal ring network is constructed over the hydroxylated surface. The network domains are spread over the surface, and their size decreases as the temperature increases. The simulated adsorption isotherms present a characteristic two-dimensional (2D) phase diagram including a 2D critical point at 365K, which is higher than that on the hydroxylated Cr(2)O(3) surface (319 K). This fact substantiates the high affinity of water molecules to the α-Al(2)O(3) surfaces, which enhances the adsorbability originating from higher heat of adsorption. The higher affinity of water molecules to the α-Al(2)O(3) (001) plane is ascribed to the high compatibility of the crystal plane to form a hexagonal ring network of (001) plane of ice Ih.
 
Article
Anatase TiO(2) nanosheets with exposed reactive {001} facets were prepared in the presence of HF. The photovoltaic properties of NaOH-washed anatase TiO(2) nanosheets with exposed {001} facets were investigated by assembling the TiO(2) as photoanodes in dye-sensitized solar cells (DSSCs). A decreased overall efficiency and increased recombination rate was observed in comparison with the H(2)O-washed counterpart by both dark current scan and open-circuit voltage decay scan, and XPS confirmed that the deleterious effect of sodium ions is responsible for this reduced efficiency in DSSCs.
 
Typical low-(A) and high-magnification (B) SEM images of sulfur doped anatase TiO 2 sheets; and TEM image (C), SAED patterns (D) and high resolution TEM image (E) of a sulfur doped single anatase TiO 2 sheet. The high resolution TEM image was recorded in the highlighted rectangular area in panel C near the edge of a TiO 2 crystal.
UV-visible absorption spectrum of sulfur doped anatase TiO 2 sheets obtained, and the inset in the right-up corner is the plot of transformed KubelkaMunk function versus the energy of light of the anatase TiO 2 sheets.
High resolution XPS spectra of F 1s, S 2p, Ti 2p and O 1s of sulfur doped anatase TiO 2 sheets.
Article
Extending the response range of wide-bandgap (3.2 eV) anatase TiO(2) photocatalysts into the visible light range can play an important role in promoting the practical applications of photocatalysts. Here, we report a route to prepare sulfur doped anatase TiO(2) single crystal sheets with a high percentage of {0 0 1} facets. The resultant TiO(2) sheets were investigated by a combination of experimental characterizations and electronic structure calculations. The synthesized sulfur doped anatase samples show an additional visible light absorption band from 400 nm to ca. 550 nm and some visible-light photocatalytic activity in *OH radical generation and photodecomposition of organic dyes. The Ti-S bond structure causes not only visible light absorption but also changes to an extent the surface structures of doped anatase TiO(2) sheets. Theoretically, localized 3p states of S formed in the bandgap are implicated for the visible light absorption of the sulfur doped anatase TiO(2).
 
Article
Density functional theory (DFT) calculations were applied to investigate the adsorption of water monomer, water clusters on NaNO(3)(001) surface. Single water molecule is more likely to locate on the bridge site with its H atom attracted by the O atom of nitrate ion and its O atom adjacent to Na(+). Mulliken population analysis shows that fewer electrons transfer from the Na atom of substrate to water molecule. A systematic study of water clusters adsorption at high coverages ranging from 0.5 monolayer (ML), 0.75ML, 1ML, 1.25ML, and 1.5ML on NaNO(3)(001) surface was also investigated, and the results indicate that for 1ML water adsorption on NaNO(3)(001) surface, a water chain is formed among four water molecules through hydrogen bonds. Interestingly, the water molecules are linked through hydrogen bonds to form a 14-membered macrocyclic water ring for 1.5ML adsorption on NaNO(3)(001) surface. Our estimated O-H symmetric stretching frequency (ν(O-H)) will have blueshift with decrease of water coverage, which is consistent with the tendency given by experiments.
 
Article
Noncontact atomic force microscopy (NC-AFM) has been used to investigate the morphological changes of a freshly cleaved (001) surface of barium sulfate (barite) etched with an aqueous solution of 0.1 M HCl at room temperature. Shallow triangular etch pits with a height of 3.6 Å were developed in atomically flat (001) terraces. The etching of the surface was found to proceed in a layer-by-layer dissolution process. Because the crystal structure of barite exhibits a two-fold screw axis parallel to the c axis, "alternating" etch pits were formed, with any two consecutive etch pits pointing opposite to each other. These etch pits became deeper and more elongated along the b axis with time. Copyright 1999 Academic Press.
 
Article
Chitosan, a naturally abundant biopolymer, has widely been studied for metal adsorption from various solutions, but the extension of chitosan as an adsorbent to remove organic substances from water and wastewater has seldom been explored. In this study, the adsorption of an azo dye, trisodium 2-hydroxy-1,1'-azonaphthalene-3,4',6-trisulfonate (1), from aqueous solution onto the various degrees of deacetylated chitosan has been investigated. Equilibrium studies have been carried out to determine the capacity of chitosan for dye. The experimental data were analyzed using two isotherm correlations, namely, Langmuir and Freundlich equations. The linear correlation coefficients were determined for each isotherm and the Langmuir provided the best fit. The experimental adsorption isotherms were perfectly reproduced in the simulated data obtained from numerical analysis on the basis of the Langmuir model and the isotherm constants. Adsorption of (1) onto the chitosan flakes was found to be strongly depending on degrees of deacetylation in chitosan and temperatures. Significant amounts of (1) were adsorbed by chitosan 8B (higher degree of deacetylated chitosan), but the adsorption capacity was reduced remarkably with increasing solution temperatures. Thermodynamic parameters such as change in free energy (DeltaG), enthalpy (DeltaH), and entropy (DeltaS) were also determined. In addition, kinetic study indicated that the adsorption process mechanisms were both transport- and attachment-limited.
 
Article
1-Hydroxyethane-(1,1-diphosphonic acid) (HEDP) is extensively used in many technical applications. This work, as a first stage, examines the adsorption of aqueous HEDP, Cu(II), and Zn(II) onto boehmite (gamma-AlOOH) as single solutes. These processes can be described by the formation of inner-sphere complexes by the surface complexation model with constant capacitance. Uncomplexed HEDP is adsorbed as a mononuclear complex over the entre pH range. Four mononuclear surface complexes with different protonation levels are required to obtain a good fit of the experimental data for the pH range studied. Cu(II)- and Zn(II)-HEDP complexes at equimolar concentrations are studied at high and low surface density. The results indicate that the presence of HEDP significantly promotes metal adsorption at low pH in defects of surface sites. However, metal adsorption exhibits the same trend in the absence and presence of HEDP when the surface sites are in excess. The constant capacitance model successfully describes the experimental data through a ligand-like adsorption complex at low pH. At high pH, the model predicts separate adsorption of divalent metal and HEDP onto different surface sites as the preferred adsorption form.
 
Typical breakthrough curves of HCFC-141b adsorption on activated carbon at various concentrations and 293 K (symbols: experimental data; solid lines: calculated from Eq. [4]).  
Arrhenius plots of rate constant (k) at various adsorbate concentrations of 399, 734, 1139, and 1954 ppmv for HCFC-141b adsorption on activated carbon. R 2 0.9648, 0.9351, 0.9849, and 0.9846, respectively.  
Article
Recovery of HCFC-141b, used as a major alternative solvent and foam-blowing agent for CFCs in industrial applications, has received great attention due to its gradual phase out. This paper describes an investigation of the adsorption breakthrough of HCFC-141b vapor on a commercial activated carbon. A simple theoretical model developed by Yoon and Nelson was applied to investigate the breakthrough behavior of HCFC-141b on an activated carbon column. The values of parameters k' (a rate constant) and tau (the time required for 50% adsorbate breakthrough) in the Yoon and Nelson model were determined at four different concentration levels (i.e., 399, 734, 1139, and 1954 ppmv) and five temperature ranges (i.e., 283, 293, 298, 303, and 313 K), respectively. These values were used to calculate the entire (0-100%) breakthrough curve (plot of percentage breakthrough versus time) regarding the adsorption of HCFC-141b on activated carbon columns. It was found that the calculated theoretical breakthrough curves are in high agreement with the corresponding experimental data. Also, the rate constant k' can be reasonably represented by the empirical Arrhenius equation. The results obtained are applicable for the scale-up design of adsorption columns in the HCFC adsorption on activated carbon adsorbent. Copyright 1999 Academic Press.
 
Article
A route for 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) immobilization on silica gel was established after reacting at the first stage the precursor silylant agent 3-trimethoxysilylpropylamine to the support. The pesticide was covalently bonded to available amine groups of the precursor, giving 1.03 mmol of amine per gram of silica. Infrared, (13)C, and (29)Si NMR spectra are in agreement with the proposed reaction between nitrogen of the amine group of the previously anchored silica to carbon on the para-position of the aromatic ring of the pesticide. The immobilization is clearly affected by the presence or absence of disprotonating agent, to give 12.50 and 68.40% reaction yield, respectively; these results were confirmed through elemental analysis. Copyright 2001 Academic Press.
 
Article
Amphiphilic fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide-acryloylmorpholine cooligomer/fluorescein nanocomposites afforded brilliant yellow-colored solutions in not only protic solvents such as methanol and ethanol but also protic-like solvents such as dichloromethane and 1,2-dichloroethane, respectively. However, the corresponding non-fluorinated cooligomer/fluorescein composites and parent fluorescein gave the colorless solutions under similar conditions. On the other hand, unexpectedly, such brilliant yellow-colored solutions provided by these fluorinated nanocomposites completely disappeared in aprotic solvents such as N,N-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran. Thus, these fluorinated fluorescein nanocomposites can exhibit a coloring-decoloring behavior through solvatochromic response.
 
Article
The adsorbability of 1,1,1,2-tetrafluoroethane (HFC134a), which has been the CFC12 replacement, onto tetrafluoromethane and tetrachloromethane plasma-treated activated carbon (FT-ACs and CT-ACs) was investigated. It is proved that the fluorine and the chlorine, which were produced by plasma treatment, were introduced into the pores having radii greater 7.5 A and with less than 7.5 A by plasma treatment, respectively. The adsorption site of HFC134a onto activated carbon may change with the quantities of fluorine or chlorine on the surface of the activated carbon. The amount of HFC134a adsorbed per unit specific surface area of FT-ACs and CT-ACs slightly increased a little compared to the untreated activated carbon (U-AC). The amount of fluoride ion eluted before the adsorption of HFC134a from the FT-ACs increased with the increasing plasma treatment time. That after the adsorption of HFC134a from only the activated carbon with the shortest plasma treatment time decreased. The amount of chloride ion eluted before the adsorption of HFC134a from the CT-ACs increased after 15 min of plasma treatment, but decreased with 30 min of plasma treatment. The chloride ion amount from the CT-ACs decreased after the adsorption of HCF134a. These results could be explained by the Langmuir constants a and Ws, which represent the adsorption equilibrium constant and the saturated amount of HFC134a adsorbed, respectively. The ratio of fluorine and chlorine species, the adsorption type, the layer interstitial type, and the covalent type, is different based on the plasma treatment time. It is concluded that the amount of HFC134a adsorbed onto the FT-ACs and CT-ACs did not depend upon the change of pore structure by the fluorine and chlorine.
 
Article
Surface properties of pristine and water-aged polymeric films made of alpha,omega-dihydroxypoly(dimethylsiloxane) (PDMS) cross-linked with (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (FTEOS17) or tetraethoxysilane (TEOS) were investigated. The FTEOS17-cured coatings showed stable advancing and receding contact angles over a period of 3 months of water exposure, compared to a 70 degrees decrease in receding contact angle for the TEOS-cured coatings. After immersion in water, hydroxyl groups were detected on the TEOS-cured coatings with attenuated total reflection infrared spectroscopy (ATR-FT/IR). Tapping-mode atomic force microscopy (TM-AFM) on pristine FTEOS17-cured coatings showed surfaces topologies ranging from smooth and featureless to topologically complex, depending on FTEOS17 concentration. The fluorinated coatings showed a stable surface morphology after water immersion, which we believe is due to the formation of a fluorinated siliceous phase that prevented the surface reconstruction, water penetration, and hydrolysis. The smooth pristine TEOS-cured coatings showed an increased roughness with cracks and erosion pits present on the surface after water immersion.
 
Article
To predict the selectivity of Yb(III)-PVC membrane, the semiempirical PM6/SPARKLE method was used to investigate the binding of Yb(III) and other cations to 1,10-phenanthroline-5,6-dione (PDO). The study has shown that the chelating ligand, PDO, is selectively coordinated to Yb(III) at two coordination sites involving the pyridylic nitrogen atoms in the interface of membrane/solution. The membrane was used as a potentiometric Yb sensor, based on PDO as an ionophore, sodium tetraphenyl borate (NaTBP) as a lipophilic ionic additive, and tributyl phosphate (TBP) as a plasticizer. The electrode had a good Nernstian response for Yb(III) ions over a wide concentration range from 5×10(-6) to 1×10(-2)M and a detection limit of 5.7×10(-7)M with a slope of 19.7±0.2mV/decade in a pH range of 4.0-12.0. The sensor had a very fast response time of less than 5s over the whole concentration range and can be used over a period of 6wk without any significant divergence in potentials.
 
Article
The adsorption of 2,2'-bipyridyl in binary mixtures of sodium kaolinite and hematite at pH 6.6 and of 1,10-phenanthroline in binary mixtures of sodium montmorillonite and hydroxy-Al montmorillonite at pH 7.5 was studied as a function of the equilibrium concentration and composition of the mixture. A model is presented for determining the partial specific adsorption of two adsorbents by each component of the mixture, based on the graphic method for determining partial quantities. The partial specific adsorption values obtained for binary mixtures of Na-kaolinite with hematite and Na-montmorillonite with hydroxy-Al montmorillonite are strongly influenced by the concentration of adsorbates and adsorbents in the mixtures.
 
Article
This paper describes the changes in the luminescent properties of the tris-(4,7-diphenyl-1,10-phenanthroline)(3)Cr(III), [Cr(dip)(3)](3+) complex in an aqueous solution of three polyelectrolytes containing cyclohexyl, phenyl or 1-naphthyl groups in the side chain. When the polyelectrolytes form hydrophobic microdomains the luminescence of [Cr(dip)(3)](3+) is affected. The luminescence increases in the presence of cyclohexyl groups in the side chains, but decreases in the presence of phenyl and naphthyl groups (in that order). This fact can be explained in terms of a reductive quenching mechanism between the complex and the aromatic groups. Indeed, experiments performed with the complex and the alcohols corresponding to the functional groups, i.e., cyclohexanol, phenol, and naphthol, also show the same behavior, confirming the interaction with the functional groups and not other components of the polyelectrolyte. The luminescent properties of the [Cr(dip)(3)](3+) complex allow the detection of hydrophobic microdomains arising from the host-guest interaction. Moreover, the complex is able to distinguish between a nonaromatic hydrophobic microdomain and an aromatic one.
 
Article
The process of 1,10-phenanthroline adsorption at pH 5 on Ca-montmorillonite, activated carbon, and silica gel mixtures was studied as a function of the equilibrium concentration and the composition of the mixture. A model is presented for determining adsorption of the main component (the variable in the system) of the mixture, based on the thermodynamic concept of apparent and partial quantities, in combination with an equation representing total adsorption of the other two adsorbents as a function of the weight fraction of one of them and introducing the concept of mean total adsorption. The partial specific adsorption of orthophenanthroline (OP) on Ca-montmorillonite is strongly influenced by the presence of activated carbon and silica gel. Owing to a phenomenon of cationic exchange, adsorption on the clay is higher at low proportions in the mixture, but the strong effect of carbon and silica gel becomes apparent at increasing amounts of clay in the mixture. The partial specific adsorption of orthophenanthroline on activated carbon and silica gel was determined using a total adsorption equation for the two adsorbents as a function of the weight fraction of one of them and shows behavior inverse to that of adsorption on clay.
 
Article
1,10-Phenanthroline (phen) and 1,10-phenanthroline-terminated ruthenium(II) complex [Ru-Lphen](2+) have been used to stabilize and functionalize gold nanoparticles (Au-NPs). The strong interaction between the nitrogen atoms of phen and the surface of Au-NPs allowed for the phase transfer of Au-NPs from toluene to aqueous phase containing [Ru-Lphen](2+). Reverse phase transfer of these Au-NPs from water to acetonitrile by substituting the Cl(-) counter anion by PF(-)(6) has also been demonstrated. Such facile post-functionalization, phase transfer and solvent transfer processes using metallic complexes bearing a terminal phenanthroline pendant group constitute a prerequisite for further studies of the electronic and optical properties of these NCs in various media.
 
Article
Surfactants form association complexes with cyclodextrins. In the present investigation we have used NMR-diffusometry and electrical conductivity to follow the interactions which take place between beta-cyclodextrin and a bolaform surfactant: dodecane 1,12-bis(trimethylammonium bromide). Both (1)H NMR self-diffusion and conductometry data indicate the formation of a 1:1 inclusion complex. Assuming this stoichiometry, it was possible to calculate the association constant; from the analysis of the self-diffusion coefficients of free beta-cyclodextrin and the bolaform surfactant an association constant K=3x10(3)M(-1) was obtained while the analysis of conductivity data gave a comparable value of K=2.5x10(3)M(-1).
 
Article
To better understand how grafted polymers interact with liposome membrane, a comparative study was conducted to investigate the influence of different chain length polyvinyl pyrrolidone-palmityl (PVP-p) conjugates on the thermotropic phase behavior of 1,2 dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) bilayer. Lipid-polymer dispersions were prepared by mixing DPPC and variable concentrations of PVP-p conjugates in chloroform. Hydration of lipids was performed at 50-55 degrees C after complete elimination of the organic solvent. Differential scanning calorimetry (DSC) was used to determine lipid miscibility and bilayer-polymer interactions. Particle size was determined by photon correlation spectroscopy. Increasing concentrations of 6 kDa PVP-p caused a shift of the main phase transition of DPPC at lower temperatures. At 9.1 mol% the DPPC phase pretransition (T(p)) is abolished. At 16.7 mol%, differential scanning calorimetry showed an endothermic phase transition at 24.9 degrees C. The enthalpy of this transition was twice as high compared to the main phase transition enthalpy of pure DPPC. Inclusion of more than 20 mol% of 6 kDa PVP-p resulted in a complete bilayer micellization. Qualitatively similar to the 6 kDa were the results obtained with the 12 kDa PVP-p conjugate. Increasing concentrations of 25 kDa PVP-p from 1 to 13 mol% resulted in a decrease of the main DPPC phase transition temperature. At 13 mol% the new molecular self-assembled structure as previously identified with the lower MW PVP-p conjugates also showed up at the DSC thermogram. However, in sharp contrast to the lower MW PVP-p conjugates, increasing the 25 kDa PVP-p content did not result in bilayer disruption; rather, it resulted in a bilayer stabilization. The consequences of the hydrophobically modified PVP interaction with the bilayer are considered negative with respect to the long-circulating properties of liposomes in the blood. Copyright 1999 Academic Press.
 
Article
In this work, Fe(3)O(4)-SiO(2)-poly(1,2-diaminobenzene) sub-micron particles (FSPs) with high saturated magnetization of ∼60-70emu/g were developed and utilized for the removal of As(III), Cu(II), and Cr(III) ions from aqueous solution. The isothermal results fitted well with the Freundlich model and the kinetic results fitted well with the two-site pseudo-second-order model, which indicated that multilayer adsorption of As(III), Cu(II), and Cr(III) ions on FSPs occurred at two sites with different energy of adsorption. The maximum adsorption capacities followed the order of As(III) (84±5mg/g, pH=6.0)>Cr(III) (77±3mg/g, pH=5.3)>Cu(II) (65±3mg/g, pH=6.0). And the chelating interaction was considered as the main adsorption mechanism. The as-prepared materials were chemically stable with low leaching of Fe (⩽1.7wt.%) and poly(1,2-diaminobenzene) (⩽4.9wt.%) in tap water, sea water, and acidic/basic solutions. These metal-loaded FSPs could be easily recovered from aqueous solutions using a permanent magnet within 20s. They could also be easily regenerated with acid. The present work indicates that the FSPs are promising for removal of heavy metal ions in field application.
 
Article
We have used pyrene fluorescence spectroscopy and isothermal titration calorimetry (ITC) to investigate the effect of hydrophobic-block length on values of the critical micelle concentration (cmc) for aqueous solutions of triblock poly(butylene oxide)-poly(ethylene oxide)-poly(butylene oxide) block copolymers (B(n)E(m)B(n), where m and n denote the respective block lengths) with hydrophobic block lengths in the range n=12-21. Combined with results from previous work on B(n)E(m)B(n) copolymers with shorter B blocks, plots of log(10)(cmc) (cmc in molar units and reduced to a common E-block length) against total number of B units (n(t)=n for diblock or n(t)=2n for triblock copolymers) display transitions in the slopes of the two plots, which indicate changes in the micellisation equilibrium. These occur at values of n(t)which can be assigned to the onset and completion of collapse of the hydrophobic B blocks, an effect not previously observed for reverse triblock copolymers. The results are compared with related data for diblock E(m)B(n) copolymers.
 
Article
A novel amphiphilic copolymer (γ-PGA-co-PLA-DPPE) containing poly(γ-glutamic acid) (γ-PGA), polylactide (PLA), and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) segments has been successfully synthesized. The chemical structures of the copolymers were characterized by Fourier-transform infrared spectroscopy (FT-IR), NMR ((1)H NMR, (13)C NMR, (31)P NMR), and thermogravimetric analysis (TGA). In order to estimate the feasibility as novel drug carriers, an anti-tumor model drug, doxorubicin hydrochloride salt (DOX) was encapsulated into the copolymers nanoparticles (NPs) by double emulsion and nanoprecipitation methods. The influence of processing factors on encapsulation efficiency and particle size using double emulsion and nanoprecipitation technique were studied. In addition, the DOX-loaded NPs exhibited pH-dependent drug release profiles in vitro. The cumulative release of DOX-loaded NPs was much faster at pH 5.0 than that at pH 7.4. In vitro cytotoxicity test of DOX-loaded NPs against Hela and C666-1 cells demonstrated that DOX-loaded NPs exhibited effectively time-delayed cytotoxicity. Confocal laser scanning microscopy (CLSM) showed that DOX-loaded NPs accumulated mostly in lysosomes instead of cell nucleus, in contrast to free DOX. Therefore, the copolymer nanoparticles were proved to be an available carrier for anti-tumor drug delivery.
 
Article
The behavior of the cationic hemicyanines trans-4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (HC) and 4,(4-(dihexadecylamino)styryl-N-methyl-pyridinium iodide (DIA) were studied in large unilamellar vesicles (LUV) of 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) using absorption, emission, depolarization and time resolved spectroscopies. Also, thorough spectroscopic studies were performed in homogeneous media to investigate the different interactions that the dyes can experience with its microenvironment. These results help us to comprehend the dye performance under different media and, consequently find interesting features of the DOPC membrane properties. The studies in homogeneous media analyzed by the Kamlet and Taft's solvatochromic comparison method demonstrate, for the first time, that the cationic hemycianines undergo specific interactions with the medium through the solvents ability to donate an electron pair as measured by the beta parameter. Thus, the absorption bands shifts bathochromically with beta while, the emission band shifts hypsochromically. In addition, for the relaxed hemicyanines the 00 energy, nu00, is invariant with the solvent properties. The results in LUV of DOPC show that, DIA undergoes a strong association with the vesicle bilayer while HC partitions between the water and the bilayer pseudophases. To monitor directly the microenvironment and dynamics around HC and DIA inside the DOPC bilayer, we use the wavelength-selective fluorescence approach, which is based on the red edge effect in fluorescence spectroscopy, in addition with the nu00 energy of the hemicyanines. The results show that the fluid state of the DOPC bilayer resembles the microenvironment of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) reverse micelles at W=[H2O]/[AOT] below 10 where there is no free water forming the water pool. Moreover, it is demonstrated for the first time, that the region of the bilayer close to the polar head of DOPC is a powerful electron donor environment.
 
Article
Differential scanning calorimetry (DSC), dynamic light scattering (DLS), and turbidity measurements have been used to study the effect of sodium decylsulfate, C10OS, on 1,2-dipalmitoylphosphatidylcholine, DPPC, vesicles. DSC measurements, performed soon after addition of C10OS solutions to DPPC vesicular dispersion, at several C10OS/DPPC molar ratios, showed the contemporary presence of maxima ascribable both to transitions of an unmodified DPPC membrane and to transitions related to membrane domains in which C10OS is also present. In all the considered samples only unilamellar vesicles are present as shown by DLS measurements carried out on aqueous DPPC and C10OS-DPPC systems. Also the aging of the samples confirmed the presence of SUV in the time scale of DSC measurements. On the basis of DSC results the pseudo-phase diagram of the system was drawn. This diagram does not represent a system in equilibrium, from a thermodynamic point of view, but only kinetically probable states. In fact the prolonged aging of the solutions used both for DSC and DLS scans highlight the disappearance of the unmodified DPPC membrane and its conversion into a mixed membrane. Turbidity measurements at 25 degrees C, performed as a function of surfactant composition, showed that C10OS initially contributes to increase the vesicles dimensions and allowed to calculate the saturation ratio C10OS/DPPC in the membrane. In contrast, at 45 degrees C the presence of surfactant gives origin immediately to smaller structures in comparison to vesicles, probably gel-state micelles.
 
Article
The nature of interactions between metal ions Ag(I), Hg(II), Cu(II) and chitosan derivative of 1,2-ethanedithiol, QTDT, was investigated by isothermal calorimetry using the membrane breaking technique. Simultaneous determination of thermal effects, Q(int), and amount of cation that interacts, n(int), are described. The experimental data have been interpreted in terms of the Langmuir equation to determine the maximum adsorption capacity to form a monolayer, N(mon), and the energy of interaction for a saturated monolayer per gram of QTDT, Q(mon). With N(mon) and Q(mon), the molar enthalpy of interaction for formation of a monolayer of anchored cations per gram of QTDT, Delta(mon)H(m), was determined. The Delta(mon)H(m) values for Ag(I), Hg(II), and Cu(II) were -60.56, -58.05, and -84.36 kJ mol(-1), respectively. Negative values of DeltaG show the spontaneity of the interaction processes. The least entropically favourable processes, i.e., those which present more negative DeltaS values, seem to be compensated by the more favourable enthalpic parameter.
 
Article
1,2-Dimethyl-3-hexadecylimidazolium bromide, which lacks an acidic proton at the C-2 imidazolium ring position, exhibits thermotropic SmA(2) phase behavior above its melting point of 90.3 degrees C and up to 232.1 degrees C. The corresponding layer spacing and the full width at half maximum from XRD patterns display a temperature dependence. In binary mixtures with water, over a concentration range of 40-75%, lyotropic liquid crystalline phases form between 0.5 and 25 degrees C. The molecules of the new ionic liquid (IL) in the binary mixtures show three different self-assembly processes, namely, formation of rod micelles, coexistence of rod micelles and a hexagonal phase, and a pure hexagonal phase. The distance between the two centers of adjacent columns of cylinder units remains nearly constant at 4.97+/-0.04nm when the IL content exceeds 70%, indicating that the cylinder units attain a dense and highly ordered packing.
 
Article
We report the effect of N-nitrosodiethylamine (NDA) on the interaction between bovine serum albumin (BSA) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine monolayers (DPPC) at the air-water interface. We prepared aqueous solutions of NDA/BSA complexes maintaining a constant concentration of BSA of 1.49 x 10(-9) M and using NDA concentrations to obtain 2000, 4000, 6000, 12,500, and 25,000 NDA/BSA molar ratios. The hysteresis area and the compressional modulus of the compression-expansion cycles performed at different times were dependent on the NDA concentration. The cycles performed demonstrate the stability of the new phase of DPPC/BSA and DPPC/NDA/BSA monolayers. This was achieved probably because the BSA concentration used was lower than the one needed for BSA to inhibit the return of DPPC molecules to the interface. Results of the compressional modulus at the onset of the new phase, obtained around 17 mN/m, 15 min and 1, 3, 5, and 12 h after DPPC deposition, indicated that the 3.0 x 10(-6) M NDA concentration produced a more rigid film, probably due to the higher alpha-helix content of BSA. AFM images were obtained for DPPC/BSA and two DPPC/NDA/BSA complexes. Our images show that 12,500 NDA/BSA molecules were mostly adsorbed in the liquid condensed phase. However, BSA molecules were distributed more homogeneously.
 
Article
Ternary mixtures of 1,2-dimethyl-3-hexadecylimidazolium bromide/1-decanol/water form two types of well-ordered lyotropic ionic liquid crystals, a hexagonal phase linked to the ionic liquid-water axis, and a lamellar phase located at the center of their phase diagram. The lamellar and hexagonal phases span a wide temperature range from 3 to 40 degrees C, depending on the composition. The spontaneous self-assembly of the mixtures arises from strong association between the hydroxyl groups of 1-decanol or water and the polar head-groups of the ionic liquid (head-group solvent), aromatic stacking interaction between the imidazolium rings and the hydrophobic effect.
 
Article
Copolymer E(17)B(12) (E denotes OCH(2)CH(2), B denotes OCH(2)CH(C(2)H(5)), and the subscripts denote number-average chain lengths) was prepared by sequential oxyanionic polymerization and characterized by GPC (for distribution width) and NMR spectroscopy (for absolute composition and chain length). Dynamic and static light scattering and rheometry were used to characterize micelles in dilute solution and demonstrate the formation of compact micelles at low temperatures and of elongated micelles at higher temperatures, the latter being accompanied by turbidity of the solution. Rheological methods applied across a range of concentrations and temperatures served to demonstrate the formation of worm-like micelles. Gels based on entangled worm-like micelles (some of them turbid) and on packed compact micelles were identified and their properties were explored.
 
Article
Interfacial tension has been used to study the adsorption at the water/1,2-dichloroethane interface of dicarbollylcobaltate(III) {(pi-(3)-1,2-B(9)C(2)H(11))(2)Co(III)(-)} of the monovalent and bivalent metals. At the limiting coverage, the area per dicarbollylcobaltate(III) anions in the monolayer found experimentally is equal to 95+/-8 Å(2). It can be assumed that the symmetry axis of the adsorbed anions is arranged parallel to the interface surface. By their effects on the surface activity of the dicarbollylcobaltate(III) anions, cations can be arranged in the following order: Mg(2+) approximately Ba(2+) approximately Pb(2+)>/=Li(+) approximately Na(+)>K(+)>NH(+)(4)>Rb(+)Tl(+) approximately Ag(+) approximately Cs(+). The parameters of Frumkin and the virial isotherms have been calculated. There is a rather strong repulsion among the adsorbed anions. To define the energy of the specific interaction between the anions and the adsorbed monolayer, the technique of E. Goddard et al. (J. Colloid Interface Sci. 24, 297 (1967)) was applied. Its application for two-phase systems permits us to define the parameters of the ion exchange reaction on the basis of measurements of interfacial tension. The ion exchange constants calculated by various methods have been compared. Copyright 2001 Academic Press.
 
Article
The aim of this study was the synthesis and physicochemical characterization of some nanosized hydroxides/oxides interesting in the field of ceramic materials with the aim of developing new materials for technological applications in the field of high-performance coatings. In particular, attention was focused on ZrO2nH2O, ZrO2, Zn(OH)2, ZnO, Al2O3nH2O, and Al2O3. The synthesis was carried out in 1,2-ethanediol at 150-160 degrees C or in water at 90 degrees C at a high degree of supersaturation in order to achieved nucleation rate much greater than the growth rate. The obtained ZrO2nH2O, Zn(OH)2, and Al2O3nH2O particles were peptized to eliminate possible agglomeration and then calcinated at a suitable temperature to allow the formation of the corresponding anhydrous oxides. The synthesized particles were characterized by scanning and transmission electron microscopy, X-ray diffractometry, and differential thermal analysis coupled with thermogravimetry and Fourier transform infrared spectroscopy. The study showed that all the products can be obtained in the nanostructured crystalline form; ZrO2 presented the interesting feature of different tetragonal/monoclinic ratios depending on the solvent used for the synthesis. Preliminary results on the potentialities of these ZrO2 particles as agents for ultrahard coatings on ceramic surfaces were encouraging and very promising.
 
Article
An evaluation of the physical interactions between gemini surfactants, DNA, and 1,2-dialkyl-sn-glycero-3-phosphoethanolamine helper lipid is presented in this work. Complexation between gemini surfactants and DNA was first investigated using surface tensiometry where the surface tension profiles obtained were found to be consistent with those typically observed for mixed surfactant-polymer systems; that is, there is a synergistic lowering of the surface tension, followed by a first (CAC) and second (CMC) break point in the plot. The surfactant alkyl tail length was observed to exhibit a significant effect on the CAC, thus demonstrating the importance of hydrophobic interactions during complexation between gemini surfactants and DNA. The second study presented is an investigation of the mixing interactions between gemini surfactants and DOPE using Clint's, Rubingh's, and Motomura's theories for mixed micellar formation. The mixing interactions between the 16-3-16/16-7-16/16-12-16/16-7NH-16 gemini surfactants and DOPE were observed to be antagonistic, where the strength of antagonism was found to be dependent upon the gemini surfactant spacer group and the solution composition.
 
Article
Mixed micelles of the phospholipid 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC) with sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) in aqueous solutions and the effects of interactions between the components were studied by fluorescence and NMR measurements. The regular solution theory (RST) was applied to analyze the experimental critical micelle concentration values determined from the fluorescence spectra of pyrene in the mixed micelles. Negative values for the interaction parameter (beta12) were obtained for both DHPC + SDS and DHPC + DTAB mixtures, with the value being more negative in the former case. The negative beta12 values for the two systems imply that the interaction between the phospholipid and the two ionic surfactants is attractive in nature, being more intense in the case of DHPC + SDS. The interaction parameter, beta12, varies with composition of the mixtures indicating changes in packing. The proton NMR shifts are quite different for the two systems and also vary with composition. An interpretation of these experimentally determined chemical shifts in terms of the degree of compactness attributed to electrostatic and steric interactions in the mixed micelle supports the conclusions derived from the fluorescence cmc experiments.
 
Article
Nanoparticles of octakis[3-(3-amino-1,2,4-triazole)propyl]octasilsesquioxane (ATZ-SSQ) were tested as ligands for transition-metal ions in aqueous solution with a special attention to sorption isotherms, ligand-metal interaction, and determination of metal ions in natural waters. The adsorption potential of the material ATZ-SSQ was compared with related [3(3-amino-1,2,4-triazole)propyl]silica gel (ATZ-SG). The adsorption was performed using a batchwise process and both organofunctionalized surfaces showed the ability to adsorb the metal ions from aqueous solution. The Langmuir model was used to simulate the sorption isotherms. The results suggest that the sorption of these metals on ATZ-SSQ and ATZ-SG occurs mainly by surface complexation. The equilibrium condition is reached at time lower than 3 min for ATZ-SSQ, while for ATZ-SG is only reached at time of 25 min. The maximum metal ion uptake values for ATZ-SSQ were higher than the corresponding values achieved with the ATZ-SG. In order to obtain more information on the ligand-metal interaction of the complexes on the surface of the ATZ-SSQ nanomaterial, ESR study with various degrees of copper loadings was carried out. The ATZ-SSQ was tested for the determination (in flow using a column technique) of the metal ions present in natural waters.
 
Article
Corrosion of copper in aerated synthetic sea water (3.5% NaCl) solutions and its inhibition by 3-amino-1,2,4-triazole (ATA) have been studied using electrochemical, gravimetric, and pH measurements, along with Raman spectroscopy. Electrochemical measurements indicated that the presence of ATA and the increase of its concentration suppress the corrosion process on the copper surface. This effect decreases cathodic, anodic, and corrosion (jcorr) currents and corrosion rates (Kcorr), while increasing polarization resistance (Rp), surface coverage (theta), and inhibition efficiency (IE%). Weight loss measurements indicated that the dissolution of copper and the accompanying change of pH decreased to a minimum even after 24 days immersion due to the presence of ATA and the increase of its concentration. Raman investigations revealed that the inhibition of copper corrosion is achieved by strong adsorption of ATA molecules onto the copper surface, preventing it from being corroded easily.
 
Article
New 1-acyl-1,2,4-triazoles (ATs) with different n-alkyl chain lengths from C2 to C18 were synthesized. ATs with long n-alkyl chains (C12 and larger) are non-charged amphiphilic molecules with a polar triazole head group. The Langmuir isotherms of ATs at the air-water interface with 12 (DoT-C12), 14 (MyT-C14), 16 (PaT-C16) and 18 (StT-C18) carbon atoms in their n-alkyl chains were studied using surface pressure-mean molecular area (pi-mmA) measurements. Characteristic for the Langmuir isotherms of PaT-C16 and StT-C-18 was the first sharp increase of the surface pressure at a mmA value of approximately 20A(2) marking a transition of the ATs from the gaseous state with n-alkyl chains already oriented perpendicular to the water surface to a condensed state. The collapse of the monolayers occurred between 20 and 36mNm(-1) with a typical 'spike' in the isotherms of MyT-C14, PaT-C16 and StT-C18 which can be assigned to the buckling and subsequent folding of the monolayer. After the collapse point a pseudo-plateau region of slightly increasing surface pressure appeared for all ATs from C12 to C18 indicating a trilayer formation by the roll-over mechanism for MyT-C14, PaT-C16 and StT-C18. Upon further compression the final collapse occurred at pi values between 59 and 67mNm(-1). From reversibility studies it was found that the Langmuir isotherms of the ATs were irreversible. The morphology of Langmuir-Blodgett films of ATs transferred onto silicon wafers was studied by atomic force microscopy.
 
Article
Two lipophilic ligands containing triazole and hydroxyl groups, N-alkyl(C(n)H(2n+1))-3,5-bis(hydroxymethyl)-1,2,4-triazole (n=10 and 12), were synthesized. Effects of their Cu(II) and Ni(II) complexes on the hydrolysis of p-nitrophenyl picolinate (PNPP) in cetyltrimethylammonium bromide (CTAB) micelles have been investigated kinetically, and some kinetic parameters of the reactions were obtained by employing the ternary complex kinetic model for metallomicellar catalysis. It was found that Cu(II) complexes of these triazole-based ligands showed more effective catalytic activity on the hydrolysis of PNPP than Ni(II) complexes. Also, the apparent first-order rate constants for product formation in the metallomicellar phase (k(N)(')), the association constants between the substrate and the binary complex (K(T)), and the association constants between the metal ion and the ligand (K(M)) increased with an increase in pH value, which may be attributed to an increase in the nucleophilicity of the hydroxyl groups in the ligand or the electrophilicity of the substrate at higher pH. In addition, at constant pH, k(N)(') and K(T) increased with an increase in the hydrocarbon chain length of the ligand, while K(M) decreased.
 
Article
Nonionic Triton X-100 micelles solubilize the otherwise water-insoluble (Z)-phenylhydrazones of some 5-substituted 3-benzoyl-1,2,4-oxadiazoles to an extent suitable for studying the occurrence of a general-base-catalyzed rearrangement in the presence of borate buffers (pH 9.6). The kinetic data, obtained at 40.0 degrees C over a wide range of surfactant concentrations, are found to conform to a reaction scheme which implies partitioning of the substrates and the base between water and the micellar pseudophase. Evidence that both the rate of the rearrangement reactions and the binding of the substrates to the micellar aggregates are primarily governed by the steric requirements of the 5-substituent group is obtained. Copyright 2001 Academic Press.
 
Article
Effects of 3-amino-1,2,4-triazole (ATA) on the inhibition of copper corrosion in 0.5 M HCl solutions have been studied using gravimetric, electrochemical, and Raman spectroscopy investigations. Weight-loss measurements after varied immersion periods revealed that the dissolution rate of copper decreased to a minimum, while the inhibition efficiency (zeta%) and consequently the degree of surface coverage (theta) increased with the presence of ATA and the increase of its concentration. Potentiodynamic polarization, chronoamperometric, and electrochemical impedance spectroscopy (EIS) measurements after 0, 24, and 48 h immersion of the copper electrode in the test solutions showed that the presence of ATA molecules significantly decreased cathodic, anodic, and corrosion (jcorr) currents and corrosion rates (Rcorr) and greatly increased polarization resistance (Rp), zeta%, and theta; this effect was increased on increasing the ATA content in the solution. Raman spectroscopy confirmed that ATA molecules strongly adsorbed onto the copper surface, blocking its active sites and preventing it from being corroded easily.
 
Article
Corrosion of copper in aerated acidic chloride pickling (0.5 M HCl) solutions and its inhibition by 3-amino-1,2,4-triazole-5-thiol (ATT) have been investigated using electrochemical techniques and weight-loss measurements, along with Raman spectroscopy. Electrochemical measurements for copper after varied immersion periods of 0, 24, and 48 h showed that the presence of ATT and the increase of its concentration significantly decrease cathodic, anodic, corrosion (j(Corr)) currents and corrosion rates (K(Corr)), as well as the dissolution currents at 300 mV vs Ag/AgCl, while increasing polarization resistance (Rp), degree of surface coverage (theta) and inhibition efficiency (IE%) to a great extent. Weight-loss measurements after different immersion periods of 6 to 48 h revealed that the dissolution of copper decreased to a minimum and the corresponding IE% increased with increasing ATT concentration. The detection of ATT molecules on the copper surface by Raman spectroscopy indicated that inhibition of copper corrosion is achieved by strong adsorption of ATT molecules onto the copper surface.
 
Article
In our continuing systematic studies concerning the synthesis, surface properties, and hydrolysis of chemodegradable, diastereomerically pure surface active 2,5-disubstituted 1,3-dioxane derivatives, two new groups of anionic surfactants, sodium cis- and trans-(2-n-undecyl-1,3-dioxan-5-yl)methyl sulfates and sodium cis- and trans-3-[(2-n-undecyl-1,3-dioxan-5-yl)oxy]propanesulfonates, were synthesized and investigated. Surface properties of these surfactants, i.e., surface excess concentration, Gamma, surface area demand per molecule, A, effectiveness of surface tension reduction, Pi, critical micelle concentration, CMC, and standard free energies of adsorption, DeltaGads0, and of micellization, DeltaGmic0, were determined. It was shown that the trans-isomers, in which the configuration of the polar group is equatorial, are more surface active than the cis-isomers with axial configuration of the polar group at the C-5 carbon atom of the 1,3-dioxane ring. The surfactants under study undergo easy hydrolysis reaction in DCl/D2O solution with cleavage of the 1,3-dioxane ring to nonsurface active intermediates. The trans-isomers are hydrolyzed faster than cis-isomers.
 
Article
The alkaline hydrolysis of carsalam (2H-1,3-benzoxazine-2,4(3H)-dione), denoted as I, and its N-substituted derivatives i.e., N-methyl-1,3-benzoxazine-2,4-dione (II) and N-benzoyl-1,3-benzoxazine-2,4-dione (III) was studied spectrophotometrically at physiological temperature. The rate of hydrolysis was found to be independent on the substrate concentration. In case of I, the reaction was fractional order with respect to [OH(-)] while for II and III, reaction obeyed the first order kinetics. Effect of cationic surfactants with varying hydrophobic chains (cetyltrimethylammonium bromide, CTAB, tetradecyltrimethylammonium bromide, TTAB and dodecyltrimethylammonium bromide, DTAB) and with different head-group (cetyl pyridinium chloride, CPC) and anionic surfactant (sodium dodecyl sulfate, SDS) was also seen on the rate of alkaline hydrolysis of the carsalam and its derivatives. Cationic surfactants first catalyzed the rate of hydrolysis at lower concentrations followed by the inhibition at higher concentrations. The length of the alkyl chain had remarkable effect on the catalytic efficiency of the surfactants. Similarly N-substitution on substrate also increased the catalysis by micelles. The anionic surfactant SDS inhibited the rate of hydrolysis at all of the concentrations studied. The catalysis by cationic micelles followed by inhibition was treated in terms of the pseudophase ion-exchange model, while for the inhibition by SDS micelles the Menger-Portnoy model was used to fit the data. The effect of salts (NaCl, NaBr and (CH(3))(4)NBr) was also seen on the hydrolysis of II and it was found that all salts inhibited the rate of reaction. The inhibition follows the trend NaCl<NaBr<(CH(3))(4)NBr.
 
Article
1,3- and 1,4-phenylenediamine were covalently attached to a self-assembled monolayer of 11-mercaptoundecanoic acid by formation of an amide bond. Bonding of the phenylenediamine isomers was confirmed by the presence of infrared features attributable to ring vibrational modes, the amide I vibration, and the amide II vibration in the reflection-absorption infrared spectrum of the modified interface. Reductive desorption peak potentials were shifted by 120 mV for the monolayer modified by 1,4-phenylenediamine and by 90 mV for the monolayer modified by 1,3-phenylenediamine relative to the desorption potential of the unmodified 11-mercaptoundecanoic acid monolayer. These potential shifts represent 23 and 17 kJ/mol stabilization of the monolayers modified by 1,4- and 1,3-phenylenediamine, respectively. Some of the additional stabilization energy is attributed to lateral hydrogen bonding between the amide groups and unreacted carboxylic acid groups in the monolayer. The difference between the stabilization energies for the interfaces modified with the different phenylenediamine isomers is attributed to structural differences between the isomeric monolayers influencing the molecular packing of the modified interface.
 
Top-cited authors
Vinod K Gupta
  • University of Johannesburg
Egon Matijevic
  • Clarkson University
Alok Mittal
  • Maulana Azad National Institute of Technology, Bhopal
Jyoti Mittal
  • Maulana Azad National Institute of Technology, Bhopal
Arti Malviya
  • Lakshmi Narain College of Technology