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Even though silica nanoparticles and their monolayers find a broad field of applications, only a few studies providing a quantitative description of silica nanoparticle deposition at solid/liquid interfaces have been reported in the literature. Given the deficit of reliable experimental data, the goal of this work is to acquire thorough physicochemical characteristics of amorphous silica nanoparticle deposition. Silica nanoparticle monolayers of controlled coverage were formed on macroion (PAH)-modified mica. The size of the particles determined by dynamic light scattering (DLS), atomic force microscopy (AFM) and scanning electron microscopy (SEM) was equal to 28 nm. The electrophoretic mobility and the zeta potential of the particles were also determined as a function of ionic strength and pH. Using a well-defined suspension, systematic studies of particle deposition kinetics were carried out. The coverage of the self-assembled particle monolayers was determined by AFM and SEM imaging. Particle deposition was carried out under diffusion controlled transport conditions. For long deposition times, the saturation coverage was attained, systematically increasing with ionic strength up to 0.48 for I = 0.15 M NaCl. The deposition kinetic runs were adequately interpreted using the random sequential adsorption (RSA) model. This model was also used to determine the specific density of silica particles that confirmed their porous structure. In addition, the particle desorption kinetics was studied using AFM and SEM methods. It was confirmed that silica nanoparticle desorption was negligible within the time period of 60 hours. Our experimental data proved, therefore, that it is feasible to produce uniform and stable silica particle monolayers of desired coverage in the self-assembly processes, controlled by the bulk suspension concentration and the ionic strength. Such monolayers may find practical applications as substrates for selective protein and nanoparticle deposition, or various catalytic applications.

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Monodisperse silver nanoparticle sols were synthesized via chemical reduction processes in aqueous environment without using polymeric stabilizing agents or surfactants. The sols obtained using various reducing agents; inorganic cell permeabilizers and organic phenolic compounds; inter alia gallic acid (GA) and tannin (TA) were thoroughly characterized by various physicochemical methods such as TEM, SEM, AFM, DLS and micro-electrophoresis. The antibacterial activity of the sols against two E. coli strains was characterized via the determination of the Minimum Bactericidal Concentration (MBC). All sols exhibited a pronounced bactericidal effect against the standard K12 strain, especially the GA and TA sols showing MBC concentration as low as 1-5 mg L(-1). In the case of the antibiotic resistant strain the highest activity (MBC of 10 mg L(-1)) was observed for the sol synthesized using sodium hypophosphate and sodium tripolyphosphate. Additionally, interactions of silver nanoparticles with bacteria cell were studied using TEM and AFM imaging. It was shown that the silver particles attach to the bacteria surface inducing disintegration, which enables their penetration inside the bacteria. Our measurements confirmed that the surface chemistry of silver nanoparticles can play a decisive role.

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Physicochemical characteristics of tannic acid (tannin) suspensions comprising its stability for a wide range of ionic strength and pH were thoroughly investigated using UV-vis spectrophotometry, dynamic light scattering and microelectrophoretic measurements. These studies allowed to determine the hydrodynamic diameter of the tannic acid that was 1.63 nm for the pH range 3.5-5.5. For pH above 6.0 the hydrodynamic diameter significantly decreased as a result of the tannin hydrolysis. The electrophoretic mobility measurements confirmed that tannic acid is negatively charged for these values of pH and ionic strength 10(-4)-10(-2) M. Therefore, in order to promote adsorption of tannin molecules on negatively charged mica, the poly(allylamine hydrochloride) (PAH) supporting monolayers were first adsorbed under diffusion transport conditions. The coverage of polyelectrolyte monolayers was regulated by changing bulk concentration of PAH and the adsorption time. The electrokinetic characteristics of bare and PAH-covered mica were determined using the streaming potential measurements. The zeta potential of these PAH monolayers was highly positive, equal to 46 mV for ionic strength of 10(-2) M. The kinetics of tannin adsorption on these PAH supporting monolayers was evaluated by the in situ the streaming potential measurements. The zeta potential of PAH monolayers abruptly decreases with the adsorption of tannin molecules that was quantitatively interpreted in terms of the three-dimensional electrokinetic model. The acid-base characteristics of tannin monolayers were acquired via the streaming potential measurements for a broad range of pH. The obtained results indicate that it is possible to control adsorption of tannin on positively charged surfaces in order to designed new multilayer structures of desirable electrokinetic properties and stability.

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Recent developments in the electrokinetic determination of particle, polyelectrolyte and protein deposition at solid/electrolyte interfaces, are reviewed. In the first section basic theoretical results are discussed enabling a quantitative interpretation of the streaming current/potential and microelectrophoretic measurements. Experimental results are presented, pertinent to electrokinetic characteristics of simple (homogeneous) surfaces such as mica, silica and various polymeric surfaces used in protein studies. The influence of the ionic strength, background electrolyte composition and pH is discussed, and the effective (electrokientic) charge of these interfaces is evaluated. In the next section, experimental data obtained by streaming potential measurements for colloid particle mono- and bilayers are presented and interpreted successfully in terms of available theoretical approaches. These results, obtained for model systems of monodisperse colloid particles are used as reference data for discussion of more complicated experiments performed for polyelectrolyte and protein covered surfaces. Results are discussed, obtained for cationic polyelectrolytes (PEI, PAH) and fibrinogen adsorbing on mica, interpreted quantitatively in terms of the theoretical approach postulating a heterogeneous 3D charge distribution. The Gouy-Chapman model, based on the continuous charge distribution proved inadequate. Interesting experimental data are also discussed, obtained by electrophoretic methods in the case of protein adsorption on colloid latex particles. In the last section, supplementary results on particle deposition on heterogeneous surfaces produced by controlled protein adsorption are discussed. Quantitative relationships between the amount of adsorbed protein, zeta potential of the interface and the particle coverage are specified. Possibility of evaluating the heterogeneity of protein charge distribution is pointed out. The anomalous deposition of colloid particles on protein molecules bearing the same sign of zeta potential, which contradicts classical DLVO theory, is interpreted in terms of the fluctuation theory. It is concluded that theoretical and experimental results obtained for model colloid systems and flat interfaces can be effectively used for interpretation of protein adsorption phenomena, studied by electrophoresis. In this way the universality of electrokinetic phenomena is underlined.

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Colloid particle deposition was applied to characterize fibrinogen (Fb) monolayers on mica, which were produced by controlled adsorption under diffusion transport. By adjusting the time of adsorption and the bulk Fb concentration, monolayers of desired surface concentration were obtained. The surface concentration of Fb was determined directly by AFM enumeration of single molecules adsorbed over the substrate surface. It was proven that Fb adsorbed irreversibly on mica both at pH 3.5 and at pH 7.4 with the rate governed by bulk transport. The electrokinetic properties of Fb monolayers produced in this way were studied using the streaming potential method. The dependence of the apparent zeta potential of Fb monolayers was determined as a function of the coverage. It was shown that for pH 3.5 the initial negative zeta potential of the mica substrate was converted to positive for Fb coverage exceeding 0.16. On the other hand, for pH 7.4, the zeta potential of a Fb-covered mica remained negative for the entire coverage range. The charge distribution in Fb monolayers was additionally studied using the colloid deposition method, in which negatively and positively charged polystyrene latex particles (ca. 800 nm in diameter) were used. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed. Results of these experiments were quantitatively interpreted in terms of the fluctuation theory assuming that adsorption sites consisted of two and three Fb molecules, for pH 3.5 and 7.4, respectively. These results suggested that for pH 7.4, the distribution of charge on Fb molecules was heterogeneous, characterized by the presence of positive patches, whereas the average zeta potential was negative, equal to -19 mV. The utility of the colloid deposition method for studying Fb monolayers was further demonstrated in deposition experiments involving positive latex particles. It was shown that for a rather broad range of fibrinogen coverage, both the positive and the negative latex particles can adsorb on surfaces covered by Fb, which behaved, therefore, as superadsorbing surfaces. It was also concluded that the colloid deposition method can be used to determine the Fb bulk concentration for the range inaccessible for other methods.

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Recent developments in the electrokinetic determination of particle, protein and polyelectrolyte monolayers at solid/electrolyte interfaces, are reviewed. Illustrative theoretical results characterizing particle transport to interfaces are presented, especially analytical formulae for the limiting flux under various deposition regimes and expressions for diffusion coefficients of various particle shapes. Then, blocking effects appearing for higher surface coverage of particles are characterized in terms of the random sequential adsorption model. These theoretical predictions are used for interpretation of experimental results obtained for colloid particles and proteins under convection and diffusion transport conditions. The kinetics of particle deposition and the structure of monolayers are analyzed quantitatively in terms of the generalized random sequential adsorption (RSA) model, considering the coupling of the bulk and surface transport steps. Experimental results are also discussed, showing the dependence of the jamming coverage of monolayers on the ionic strength of particle suspensions. In the next section, theoretical and experimental results pertaining to electrokinetics of particle covered surfaces are presented. Theoretical models are discussed, enabling a quantitative evaluation of the streaming current and the streaming potential as a function of particle coverage and their surface properties (zeta potential). Experimental data related to electrokinetic characteristics of particle monolayers, mostly streaming potential measurements, are presented and interpreted in terms of the above theoretical approaches. These results, obtained for model systems of monodisperse colloid particles are used as reference data for discussion of experiments performed for polyelectrolyte and protein covered surfaces. The utility of the electrokinetic measurements for a precise, in situ determination of particle and protein monolayers at various interfaces is pointed out.

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Theoretical and experimental results pertinent to irreversible adsorption (deposition) of particles at heterogeneous and patterned surfaces were reviewed. Three main deposition regimes are distinguished: (i) the quasi continuous surface regime, (ii) the random site surface (RSS) regime and (iii) the patterned surface regime. Theoretical results obtained for the RSS and the patterned surface regime were presented, in particular the topology of particle monolayers, the jamming (maximum) coverage, the averaged number of particles adsorbed and particle distribution density over various surface patterns. Special attention was focused on rectangular surface features (stripes). These results were obtained using the random sequential adsorption (RSA) approach, whose range of validity is assessed using the limiting analytical solutions. These theoretical predictions were used for interpretation of experimental results obtained mostly for monodisperse latex particles adsorbing on random site surfaces created by controlled colloid particle or polyelectrolyte adsorption. The structure of monolayers was analyzed adsorption probability as a function of site coverage and the jamming coverage limit for various particle to site size ratio. Finally, recent results were discussed, obtained for surface features of regular shape like circles and rectangles. It was concluded that these experimental data confirmed the validity of the RSA model for describing particle deposition at heterogeneous and patterned surfaces. It was also concluded that theoretical and experimental results obtained for model colloid systems can be effectively used as useful reference states for analyzing protein and macromolecule adsorption at heterogeneous surfaces.

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In this work, the structure of poly(acrylic acid) (PAA) molecules in electrolyte solutions obtained from molecular dynamic simulations was compared with experimental data derived from dynamic light scattering (PCS), dynamic viscosity, and electrophoretic measurements. Simulations and measurements were carried out for polymer having a molecular weight of 12 kD for various ionic strengths of the supporting electrolyte (NaCl). The effect of the ionization degree of the polymer, regulated by the change in the pH of the solution in the range 4-9 units, was also studied systematically. It was predicted from theoretical simulations that, for low electrolyte concentration (10(-3) M) and pH = 9 (full nominal ionization of PAA), the molecule assumed the shape of a flexible rod having the effective length L(ef) = 21 nm, compared to the contour length L(ext) = 41 nm predicted for a fully extended polymer chain. For an electrolyte concentration of 0.15 M, it was predicted that L(ef) = 10.5 nm. For a lower ionization degree, a significant folding of the molecule was predicted, which assumed the shape of a sphere having the radius of 2 nm. These theoretical predictions were compared with PCS experimental measurements of the diffusion coefficient of the molecule, which allowed one to calculate its hydrodynamic radius R(H). It was found that R(H) varied between 6.6 nm for low ionic strength (pH = 9) and 5.8 nm for higher ionic strength (pH = 4). The R(H) values for pH = 9 were in a good agreement with theoretical predictions of particle shape, approximated by prolate spheroids, bent to various forms. On the other hand, a significant deviation from the theoretical shape predictions occurring at pH = 4 was interpreted in terms of the chain hydration effect neglected in simulations. To obtain additional shape information, the dynamic viscosity of polyelectrolyte solutions was measured using a capillary viscometer. It was found that, after considering the correction for hydration, the experimental results were in a good agreement with the Brenner's viscosity theory for prolate spheroid suspensions. The effective lengths derived from viscosity measurements using this theory were in good agreement with values predicted from the molecular dynamic simulations.

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Adsorption of a cationic polyelectrolyte, polyallylamine hydrochloride (PAH), having a molecular weight of 70,000 on mica was characterized by the streaming potential method and by deposition of negative polystyrene latex particles. Formation of PAH layers was followed by determining the apparent zeta potential of surface zeta as function of bulk PAH concentration. The zeta potential was calculated from the streaming potential measured in the parallel-plate channel formed by two mica plates precovered by the polyelectrolyte. The experimental data were expressed as the dependence of the reduced zeta potential zeta/zeta0 on the PAH coverage Theta(PAH), calculated using the convective diffusion theory. It was found that for the ionic strength of 10(-2) M, the dependence of zeta/zeta0 on Theta(PAH) can be reflected by the theoretical model formulated previously for surfaces covered by colloid particles. The electrokinetic measurements were complemented by particle deposition experiments on PAH-covered mica surfaces. A direct correlation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For ThetaPAH > 0.3 the initial deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. The initial deposition rates for surfaces modified by PAH were compared with previous experimental and theoretical results obtained for heterogeneous surfaces formed by preadsorption of colloid particles. It was revealed that negative latex deposition occurred at surfaces exhibiting negative apparent zeta potential, which explained the anomalous deposition of particles observed in previous works. It was suggested that the combined electrokinetic and particle deposition methods can be used for detecting adsorbed polyelectrolytes at surfaces for coverage range of a percent. This enables one to measure bulk polyelectrolyte concentrations at the level of 0.05 ppm.

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Polyelectrolyte multilayer adsorption on mica was studied by the streaming potential method in the parallel-plate channel setup. The technique was calibrated by performing model measurements of streaming potential by using monodisperse latex particles. Two types of polyelectrolytes were used in our studies: poly(allylamine) hydrochloride (PAH), of a cationic type, and poly(sodium 4-styrenesulfonate) (PSS) of an anionic type, both having molecular weight of 70,000. The bulk characteristics of polymers were determined by measuring the specific density, diffusion coefficient for various ionic strengths, and zeta potential. These measurements as well as molecular dynamic simulations of chain shape and configurations suggested that the molecules assume an extended, wormlike shape in the bulk. Accordingly, the diffusion coefficient was interpreted in terms of a simple hydrodynamic model pertinent to flexible rods. These data allowed a proper interpretation of polyelectrolyte multilayer adsorption from NaCl solutions of various concentrations or from 10(-3) M Tris buffer. After completing a bilayer, periodic variations in the apparent zeta potential between positive and negative values were observed for multilayers terminated by PAH and PSS, respectively. These limiting zeta potential values correlated quite well with the zeta potential of the polymers in the bulk. The stability of polyelectrolyte films against prolonged washing (reaching 26 h) also was determined using the streaming potential method. It was demonstrated that the PSS layer was considerably more resistant to washing, compared to the PAH layer. It was concluded that the experimental data were consistent with the model postulating particle-like adsorption of polyelectrolytes with little chain interpenetration. It also was concluded that due to high sensitivity, the electrokinetic method applied can be effectively used for quantitative studies of polyelectrolyte adsorption, desorption, and reconformation.

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A theoretical model was developed for describing localized adsorption kinetics of proteins and colloid particles at solid/liquid interfaces. In contrast to previous approaches the adsorption and desorption rate constants as well as the surface blocking function were evaluated explicitly without using empirical parameters. It was also predicted that irreversible adsorption kinetics can unequivocally be characterized in terms of the adsorption rate constant k(a) and the maximum (jamming) coverage Theta(mx) known for various particle shapes from previous Monte-Carlo simulations. The dimensionless constant k(a) was shown to be inversely proportional to the concentration of particles which is usually very low for protein and colloid adsorption measurements. From the theoretical model it was also deduced that in this case the asymptotic adsorption law for large dimensionless time tau can be expressed as Theta(mx)-Theta approximately 1/tau(1/(n-1)) (where n=3 for spheres, n=4 for side-on adsorption of spheroids, n=5 for randomly oriented spheroid adsorption). It was also shown that this limiting adsorption regime occurs for proteins at surface coverage Theta(l) very close to the jamming value Theta(mx), becoming therefore difficult to detect due to limited experimental accuracy. These analytical predictions were found to be in agreement with numerical calculations performed by using the finite-difference scheme, valid for an arbitrary range of adsorption time. Moreover, it was demonstrated that these numerical results adequately reflected the experimental results of Johnson and Lenhoff who determined the kinetics of colloid particle adsorption using atomic force microscopy. Previously used approaches assuming that particle adsorption flux is reduced by the factor B(Theta) were found to be inadequate. It was also demonstrated that due to the similarity of underlying parameters the results obtained for colloid systems can be exploited as well-defined reference data for estimating the adsorption kinetics of proteins. Copyright 2000 Academic Press.

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A detailed description of flow distribution in the slot impinging jet cell (SIJ) is presented. Numerical solutions of the governing Navier-Stokes equation showed that for Re < 30 the flow resembles closely the one occurring near a cylinder placed in a uniform flow. It was also shown that for tangential distances x/d < 0.25 the flow configuration in the vicinity of the solid can be approximated by the plane-parallel stagnation flow with the perpendicular velocity component independent of this distance. This flow field was used for deriving the mass transfer equation, which was then numerically solved to obtain the initial flux (adsorption rate) for various transport conditions. These theoretical predictions were verified experimentally using polystyrene latex particles of the size 1 and 1.48 µm. A good agreement between predicted and measured initial flux values was found for a broad range of Reynolds number and ionic strength of the particle suspension. This confirmed that the SIJ cell surface was uniformly accessible for particles at distances x/d < 0.5. At larger distances a systematic deviation from uniform deposition rates was observed, becoming important for higher coverages and Re. This effect was attributed to the hydrodynamic scattering of adsorbing particles on particles already attached to the surface. This phenomenon was quantitatively accounted for by the Brownian dynamics type simulations. Copyright 1999 Academic Press.

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A numerical scheme for solving the nonlinear Poisson-Boltzmann equation for the sphere/sphere and plane/sphere geometries has been developed. The method is based on an alternating direction overrelaxation procedure using the Newton-Raphson iteration to solve the nonlinear equation stemming from finite-difference discretization. The novelty of the algorithm consists in using the grid transforming functions that allow a more uniform distribution of mesh points in the vicinity of the particle. The method was used to perform extensive calculations for opposite surface potentials of the interface and the particle immersed in a symmetric electrolyte solution. The electric potential distribution (within and outside the sphere) was calculated, as well as the force and energy of interaction (from the integral of the force over separation distance), for the constant potential, the constant charge, and the mixed cases. The energy profiles calculated for various kappaa were compared with the analytical approximations derived using the Hogg-Healy-Fuerstenau method and the linear superposition approach (LSA). These calculations enabled us to conclude that the LSA can be used as a good estimate of interaction energy for a broad range of kappaa values at distances greater than kappa-1, i.e., for problems pertinent to colloid particle adsorption.

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Random sequential adsorption (RSA) of polydisperse mixtures of hard and interacting spherical particles was analyzed. Theoretical results were derived by performing numerical MC simulations both for Gaussian and for continuous distributions of particle sizes characterized by standard deviations below 20%. Adsorption kinetics of these mixtures was determined for a broad range of times showing that for tau < 5 the influence of polydispersity was rather minor for both Gauss and continuous particle size distributions. More significant deviations were predicted for the asymptotic adsorption regime close to jamming. In the case of continuous distributions this limiting kinetics could be described by the power law dependence thetainfinity - theta approximately tau-1/3 in accordance with the predictions of G. Tarjus and J. Talbot (1991, J. Phys. Math Gen. 24, L913). The jamming concentration thetainfinity for hard (noninteracting) particles was found to increase proportionally to sigma;. It was also shown that the polydispersity of particle mixtures can exert an effect on the structure of the adsorption layer (characterized in terms of the pair correlation function). The broadening of this function was confirmed experimentally by using colloid suspensions of spherical particles (polystyrene latex) characterized by sigma; = 6-10%.

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The adsorption kinetics of negatively charged polystyrene latex at mica surface precovered with smaller sized (submicrometer) latex particles was investigated experimentally. The direct microscope observation method combined with the impinging jet technique was used in this study. Experimental results were presented concerning the initial flux and adsorption kinetics of larger particles at surfaces partially covered with smaller sized latex particles. The experimental results were interpreted in terms of the Monte Carlo simulations performed using the random sequential adsorption (RSA) model. Limiting analytical solutions for predicting the initial flux and adsorption kinetics were also formulated. It was found that the experimental results were in good agreement with theoretical predictions (derived for hard particle interaction potential). This confirmed the hypothesis that small colloid particles present in low concentration at surfaces considerably diminish adsorption rates of larger particles. Copyright 1997 Academic Press. Copyright 1997Academic Press

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The work is a continuation of studies of accidents at work at the Belchatów Industrial District. Analysed have been indirect factors causing accidents at work. Those factors were found to cause accidents much more often than the direct ones. They are particularly significant for young workers. The season, month, day of month, consecutive working hour and climate did not significantly affect the frequency of accidents.

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Health effects of accidents at work at the Belchatów Industrial District have been investigated. Most injuries due to accidents have been bruises, wounds and bone fractures of upper and lower limbs. Much less frequent, as compared to other industrial plants, are injuries of head, chest and abdomen. The causes of those injuries have been discussed. In addition, the activities of occupational health services have been analysed.

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The work has been aimed at an analysis of accidents at work occurring throughout 1981-1982 at the Belchatów Industrial District. The most common causes of accidents at work have been direct factors resulting mainly from workers' inadvertence or recklessness, improper performance of occupational tasks, lack of appropriate tools, and settlement of private affairs at work. The incidence of accidents at work might be reduced by compliance with safety-and-hygiene-of-work rules, better supervision, work organization and efficient working tools.

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