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Annales UMCS, Chemistry (v.63, #-1)
Is the world basic? Lessons from surface science by K. Mittal; F. M. Etzler; (pp. 1-16).
In this work the authors review various definitions of acids and bases. Furthermore, the application of these theories to surface and adhesion science is discussed. It is clear that application of various acid-base theories may not always lead to consistent conclusions on the acid-base character of surfaces. Possible reasons for the inconsistency include the nature of the scale, the choice of reference points, and the use of either poor or inconsistent statistical procedures in addition to experimental difficulties. The present authors recommend a future careful study and comparison of the various acid-base theories when applied to surface and adhesion science. The limited studies already preformed suggest this activity would be worthwhile.
Influence of the electrolyte concentration on interaction between silica particles by W. Wójcik; B. Jańczuk; R. Ogonowski; (pp. 17-30).
The destruction time of the sediment column structure was measured for different fractions of silica particles in NaCl and CaCl2 solutions whose concentrations were varied from 0.25 M to 2.0 M. A linear relationship between the reciprocal of the destruction time of the silica sediment column structure and average diameter of the silica fraction, the density and work of cohesion of the solutions was found. The determined values of the particle diameter, the cohesion work and density of the solution calculated from these linear dependences for the time equal to infinity (1/t = 0) were named critical. Using the above critical parameters the detachment force of one particle from another was calculated. For the system whose components had critical values the detachment force was found to be equal to the attachment force resulting from the interfacial interaction. On the basis of our earlier study and Derjaguin's approximation the radius of the contact plane and the attachment force between two silica particles were calculated. The detachment force decreased with increasing salt concentration, but the attachment force was nearly constant. It was found that for a given salt concentration the relationship of the reciprocal of the destruction time as a function of the difference between the detachment and attachment forces was also linear. It appeared that for the silica column structure having critical parameters the values of the difference between the detachment and attachment forces were negative. This means that in the calculation of the attachment force between silica particles in the studied solutions an additional interaction should be taken into account.
On the stability of magnetic colloids by M. T. López-López; G. R. Iglesias; J. D. G. Durán; F. González-Caballero; (pp. 31-46).
In this paper, the preparation of fluids belonging to ferrofluid (FF) and magnetorheological (MR) categories is described. Furthermore, the effect of different stabilizing additives (thixotropic agents, surfactants, magnetic nanoparticles) and carrier liquids on the sedimentation of these fluids is analyzed. These studies are conducted using: (i) optical and electromagnetic induction techniques for monitoring the stability of dilute and concentrated suspensions, respectively; (ii) contact angle and pendant drop measurements to explain the observed stability in different carriers. The results of these experiments are analyzed in detail and magnetic fluids with improved stability properties are prepared accordingly.
Biomedical applications of the Langmuir monolayer technique by K. Hąc-Wydro; P. Dynarowicz-Łątka; (pp. 47-60).
The modeling of natural membranes is a consequence of their complex structure. The paper describes different approaches used to model biomembranes, and emphasizes the advantages of applying the Langmuir monolayer technique in this aspect.
Equilibrium of counterion association in micellar systems: cetyltrimethylammoniumbromide by N. Kallay; T. Glušac; T. Preočanin; A. Čop; D. Kovačević; S. Žalac; (pp. 61-67).
Surface Complexation Model was applied for the analysis of counterion association in the micellar systems. The equilibrium in cetyltrimethylammoniumbromide (CtaBr) solution was examined. Thermodynamic equilibrium constant was calculated using experimental data obtained with ion-selective electrodes (silver/silver bromide and surfactant electrode).
Graphite flotation in the presence of sodium acetate by B. Grabowski; J. Drzymała; (pp. 68-72).
Graphite was subjected to flotation in the presence of increasing concentration of sodium acetate. A comparison of graphite flotation with the surface tension, both as a function of the sodium acetate concentration in the aqueous solution, revealed a similar pattern of both relations. It seems to confirm one of the theories of salt flotation claiming that for hydrophobic materials the change of flotation recovery with the salt concentration is mostly determined by the surface tension of the aqueous solution. It was found that graphite recovery increases when the surface tension of the solution and decreases as the surface tension decreases. At a low salt concentration this rule is not obeyed due to, very likely, the socalled Jones-Rey effect.
Surface characterization of clay particles via dielectric spectroscopy by M. L. Jiménez; A. V. Delgado; U. Kaatze; (pp. 73-86).
This work deals with the high frequency dielectric relaxation of clay (sodium montmorillonite, or NaMt) suspensions. By high frequency it is meant that the permittivity will be determined in the region where the Maxwell-Wagner-O'Konski relaxation takes place, roughly, the MHz frequency range. The applicability of dielectric determinations for the characterization of the electrical properties of these complex systems is demonstrated. In fact, standard electrophoresis measurements only allow to detect that the charge of the particles becomes slightly more negative upon increasing pH. Much more information is obtained from the high frequency electric permittivity for different concentrations of solids and pHs. From the characteristic frequencies of the relaxation it is possible to detect separate processes for parallel and perpendicular orientations of the clay platelets, modelled as oblate spheroids with a high aspect ratio. In addition, using a suitable model the surface conductivity of the clay particles can be estimated. Our data indicate that this quantity is minimum around pH 7, which is admitted as representative of the isoelectric point of the edges of the clay platelets. Data are also obtained on the amplitude (value of the relative permittivity at low frequency minus that at high frequency) of the relaxation, and it is found that it depends linearly on the volume fraction of solids, and that it is minimum at pH 5. These results are considered to be a manifestation of the fact that particle interactions do not affect the electric conduction inside the electric double layer, while the special behaviour at pH 5 is related to the existence of aggregates at pH 5, which increase the effective size of the particles and provoke a reduction of their effective conductivity.
Atmospheric oxidation of ascorbic acid in nonionic surfactant systems by J. Narkiewicz-Michałek; M. Szymula; K. A. Wilk; (pp. 87-93).
In our study we investigated the kinetics of atmospheric oxidation of ascorbic acid in the aqueous solutions of two non-ionic surfactants TRITON X-100 and commercial sugar ester C1616 (the most suitable emulsifier for food). For each surfactant the concentrations below and above the CMC were investigated. It was found that the micellar solutions of both surfactants showed faster oxidation rate than pure water. Less pronounced effects were observed with particular surfactant concentration change.
Energy & climate by E. Robens; H. M. El Nokraschy; A. Dąbrowski; (pp. 94-110).
Based on published reports a short survey is presented on climatic change. Considering world's increase in temperature the use of fossil energy should be replaced as far and as quickly as possible by alternatives. Actual methods for energy production are discussed. At present, only nuclear power plants and concentrating solar power plants are able to meet the large requirements. Regarding the limited resources of nuclear fuel, costs and problems of nuclear techniques urgently solar techniques should be developed for an extended application.
Biomodification of plastic surfaces and depression process by I. Polowczyk; Z. Sadowski; D. Smoczyńska; (pp. 111-121).
Plastics from the municipal waste must be recycled on a large scale. This contribution describes the initial work to determine the surface energy of plastic waste. Results of such investigations were correlated with both sedimentation and flotation data. The penetration rate of a liquid into the horizontal powder layer was measured; basing on the rate of liquid penetration, the effective radius of the porous bed was calculated. For modification of the surface of plastics, tannic acid, sodium lignin sulfonate and microbial broth from Pseudomonas aeruginosa growth were used. In order to determine the effect of these reagents on the surface energy of plastic powders, the penetration and flotation experiments were carried out. For polystyrene and polyethylene the estimated surface energy was 28.6 [mJ/m2] and 24.5 [mJ/m2], respectively. These results were correlated with the sediment height extreme of plastic powders in solvent pairs. The adsorption of tannic acid, sodium lignin sulfonate and biosurfactants from microbial filtrate caused an increase of the surface energy of plastic particles. For instance, the free energy of polyethylene particles was 34.9 [mJ/m2] after the sodium lignin sulfonate treatment, and 35.57 [mJ/m2] for the tannic acid adsorption. The natural flotation of plastic particles in the presence of modifying reagents was shown to be dependent on the concentration of these reagents.
Synthesis and characterization of a superhydrophobic surface from cyclic olefin copolymer by E. Doganci; H. Y. Erbil; (pp. 122-129).
Cyclic olefine copolymer (COC) which is an engineering plastic was tried to form a superhydrophobic surface by a phase separation process using solvent + non solvent mixtures. The cloud points of the COC + solvent + non-solvent mixtures were determined and evaluated by using Hansen 3-solubility parameter approach. It was determined that the amorphous COC polymer is not suitable to prepare a superhydrophobic surface when used alone. However, a superhdrophobic surface with a water contact angle of 158±2° was obtained when COC is mixed with crystalline polypropylene homopolymer. The water contact angle and surface morphology of the polymer coatings were examined.
Kinetics of multi-site-occupancy adsorption at the solid/solution interfaces. The absolute rate theory approach by W. Rudziński; W. Płaziński; (pp. 130-143).
The kinetic approach based on the absolute rate theory and the model of a two-site-occupancy adsorption has been proposed to describe the kinetics of sorption of solute at the solid/solution interfaces. The obtained general kinetic equation reduces to the popular empirical formulas (i.e. the Lagergren equation and the pseudo-second order equation) depending on the values of physical and technical parameters which characterize the adsorption system. here, for the case when the adsorption kinetics is governed by the rate of surface reactions. The features of this general equation are shown by presenting some simple model investigations, and its applicability is tested by presenting the analysis of some experimental data reported in literature.
Investigation of surface properties of lunar regolith - Part IV by E. Robens; A. Dąbrowski; E. Mendyk; J. Goworek; K. Skrzypiec; M. Drewniak; M. Dumańska-Słowik; W. Gac; R. Dobrowolski; S. Pasieczna-Patkowska; M. Huber; M. Iwan; K. J. Kurzydłowski; T. Płociński; J. Ryczkowski; Z. Rzączyńska; J. W. Sobczak; (pp. 144-168).
We investigated three lunar regolith powder samples from the Apollo missions. Apollo 11 and Apollo 12 samples come from lunar maria and Apollo 16 sample from a highland region. In the present paper we summarise in brief results of measurements using photoelectron spectroscopy (XPS), micro-Raman spectroscopy (RM), x-ray diffraction (XRD), x-ray fluorescence spectroscopy (XRF), temperature programmed reduction and oxidation (TPRO), thermogravimetry (TG), differential thermal analysis (DTA) and nitrogen adsorption. Parts of samples are visualised by means of scanning electron microscopy (SEM/EDX) and atomic force microscopy (AFM).
Some peculiarities in stability of nanodispersions by W. Nowicki; (pp. 169-179).
The stability of some classes of dispersion systems, extensively studied in modern material sciences and nanotechnology, is discussed in terms of the classical colloid chemistry laws. Some limitations of the technologies resulting from the specificity of the nanodispersed systems, utilized in nowadays applications, are pointed out.
Some problems of the optimization of the separation process in liquid chromatography by J. K. Różyło; I. Malinowska; (pp. 180-200).
One of the optimization theory worked out by Ościk has been used for some physicochemical studies and optimization of chromatographic process. On the basis of the theoretical equations a retention in binary mobile phases can be predicted with good agreement for a lot of chromatographic systems. The influence of the different properties of chromatographic systems can be determined by use of the discussed optimization theory.
The possibilities of the use of the theory for some physicochemical studies as determination of the hydrophobicity have been demonstrated too.
DPPC monolayers as simple models of biological membranes for studies of interactions with perfluorinated compounds by D. Matyszewska; R. Bilewicz; (pp. 201-210).
Langmuir monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) formed at the air-water interface were used as simple models of biological membranes to study interactions with two selected perfluorinated compounds: perfluorooctanoic acid (PFOA) and perfluorooctanesulphonic acid (PFOS). The presence of those common pollutants in the subphase led to the formation of more fluidic monolayer possessing different surface and barrier properties. The observed increase in the area per molecule in the Langmuir monolayer spread at the air-water interface was attributed to the incorporation of perfluorinated compounds into the layer. Moreover, perfluorooctanesulphonic acid was found to interact with DPPC monolayers transferred onto the electrode surface. Exposure of DPPC modified electrode to PFOS solution led to changes in electrode capacitance and in the efficiency of electron transfer rate observed for selected electroactive probes added to the solution.
Electrochemical study of corrosion of copper in 1-alkyl-3-methylimidazolium tetrafluoroborates by K. Marczewska-Boczkowska; M. Kosmulski; J. Olchowik; (pp. 211-222).
Copper is resistive to corrosion in dry and chloride-free 1-alkyl-3-methylimidazolium tetrafluoroborates at room temperature, and the corrosion rate decreases with the chain length of the substituent in imidazolium ring and increases with the temperature. The activation energies of corrosion are on the order of 50 kJ/mole. The corrosion in enhanced in the presence of traces of chlorides.
Influence of relative humidity on the wettability of silicon wafer surfaces by L. Hołysz; M. Mirosław; K. Terpiłowski; A. Szcześ; (pp. 223-239).
Investigation of wetting properties of the original silicon wafers and modified by oxidation was carried out by contact angles measurements of water at varying relative humidity (RH) of the atmosphere present in the measuring chamber. At three selected humidities (10, 30 and 50%) contact angles of diiodomethane and formamide were also determined for the original silicon wafer only. The topography of the tested surfaces was determined with the help of atomic force microscopy (AFM). Using the measured contact angles the total apparent surface free energy and its components of studied silicon wafers were determined using two models: the contact angle hysteresis (CAH) and Lifshitz-van der Waals acid-base (LWAB) approaches. In the former approach the advancing and receding contact angles are employed, and in the latter only the advancing angles. It was found that in the case of original silicon wafer the contact angels and surface free energy depend on the humidity only in the RH range from 10 to 40% with a minimum at 30% RH, and then they fluctuate around a mean value. For the oxidized silicon wafer the changes in the contact angles and the surface free energy depend on the relative humidity and change periodically with increasing RH. These changes can result from water adsorption on the hydrophilic silicon surface.
Spontaneous spreading of liquids on substrates with contrasting two types of substrates: that of liquids and that of solids
by J. Leja; (pp. 240-243).
Modeling of adsorption in pores with strongly heterogeneous walls. Computer simulations approach by B. Kuchta; L. Firlej; (pp. 244-256).
We discuss the state of art in computer simulation of adsorption in nanopores with strongly heterogeneous rough wall structures. As an example, we review the recent models used in simulations of MCM-41 adsorbent and discuss their capacity to reproduce experimental adsorption isotherms, in the whole range of relative pressures. The conclusions of previous studies are compared with our recent model of heterogeneous pores characterized by separately energetic or structural heterogeneity, or both of them. On this basis we identify the main factors responsible for the mechanism of adsorption and discuss their influence on the results of simulations of adsorption. Some possibilities of further improvements of the model are also suggested.
Enhancement of three-phase kinetic studies of complex reaction systems by semibatch reactor technology by T. Salmi; D. Yu. Murzin; P. Mäki-Arvela; J. Wärnå; K. Eränen; J.-P. Mikkola; A. Denecheau; K. Alho; (pp. 257-270).
A semibatch reactor concept was proposed for the determination of the kinetics in complex catalytic liquid and gas-liquid systems with reactions of highly varying rates. The method is based on continuous removal of liquid phase from the reactor, while the catalyst remains inside the reactor. The concept was demonstrated by catalytic hydrogenation of citral on Ni catalyst. The primary product (citronellal) is formed very rapidly, while the secondary (citronellol) and tertiary (3,7-dimethyloctanol) products appear much more slowly. With the proposed semibatch concept, the formation of the ultimate products was considerably accelerated and all of the rate parameters were successfully estimated by nonlinear regression analysis. The proposed approach can be extended to fixed beds with recycling as demonstrated by computer simulations.
The interaction of water vapor and hydrogen water mixtures with a polycrystalline uranium surface by E. Tiferet; M. H. Mintz; S. Zalkind; N. Shamir; (pp. 271-286).
The initial room-temperature interactions of water vapor with polycrystalline bulk annealed uranium surfaces were studied by combined measurements utilizing Direct Recoil Spectrometry (DRS) and X-ray Photoelectron Spectroscopy (XPS). It was found that the water goes through a complete dissociation into oxidic oxygen and two neutral H atoms throughout the whole exposure range. The process proceeds by two consecutive stages: (i) below about 80% monolayer coverage, the dissociation products chemisorb mainly on the remaining non-reacted metallic surface by a simple Langmuir-type process; (ii) Between about 80% and full coverage, three dimensional oxide islands (that start to form at 50-60% coverage) cover most of the surface and full dissociation continues on top of them, with part of the hydrogen staying on top of the oxide. It was also found that traces of about 2% water vapor are sufficient to inhibit hydrogen dissociation and chemisorption on uranium surfaces, under low pressure exposures, at room temperature. The efficiency of the inhibition increases with temperature in the range of 200 - 400 K. The inhibition effect is also influenced by the extent of residual strain of the sample, with increasing inhibition efficiencies exhibited by a less strained surface. O2, in contrast to H2O, is not an inhibitor to surface adsorption and dissociation of hydrogen. Three types of mechanisms are discussed in order to account for the above inhibition effect of water. It is concluded that the most probable mechanism involves the reversible adsorption of water molecules on hydrogen dissociation sites causing their "blocking".
Adsorption of dyes on mesoporous carbons by A. Deryło-Marczewska; A. W. Marczewski; Sz. Winter; (pp. 287-299).
Mesoporous carbonaceous materials were synthesized by applying the method of impregnation of mesoporous silica being the pore creating template. The isotherms of adsorption of methylene blue and methyl orange were measured from aqueous solutions. The kinetics of methylene blue adsorption was studied. The adsorption isotherms and kinetic dependence were discussed.