Deposition Of Colloidal Particles Research Articles

Deposition of latex particles at heterogeneous surfaces

Irreversible adsorption (deposition) of colloid particles at heterogeneous surfaces was studied experimentally. The substrate surfaces of desired heterogeneity were produced by covering mica surfaces by positively charged polystyrene latex particles. Then, deposition kinetics of negatively charged latex was studied under diffusion-controlled transport conditions. Particle distributions over surfaces and coverage were quantitatively evaluated using the direct microscope observation technique. Using this method, jamming coverage of colloid particles as a function of the heterogeneity degree (smaller particle coverage) was determined. These experimental data confirmed, in accordance with numerical simulations that the adsorption site multiplicity exerted a pronounced effect on the structure of adsorbed layers and the jamming coverage.

Assembly of Colloidal Particles by Evaporation on Surfaces with Patterned Hydrophobicity

Drops containing suspended particles are placed on surfaces of patterned wettability created using soft lithography; the drop diameter is large compared to the dimensions of the patterns on the substrate. As the three-phase contact line of the drop recedes, spontaneous dewetting of the hydrophobic domains and flow into the hydrophilic domains create discrete fluid elements with peripheries that can mimic the underlying surface topography. Suspended particles are carried with the fluid into the wetted regions and deposit there as the discrete fluid domains evaporate. If particle volume fractions are sufficiently high, the entire wetted domain can be covered with colloidal crystals. At lower volume fractions, flow within the evaporating fluid element can direct the deposition of colloidal particles at the peripheries of the domains. High-resolution arrays of particles were obtained with a variety of features depending upon the relative size of the wetting regions to the particles. When the wetting region is larger than the particles, three-dimensional and two-dimensional arrays of ordered particles mimicking the shape of the wetting pattern form, depending on the particle volume fraction. For lower volume fractions, one-dimensional (1-D) arrays along the wet/non-wet boundaries form. When the particle size is similar to the height of fluid on the wetted domain, zero-dimensional distributions of single particles centered in the wet regions can form for wetted squares or 1-D distributions (stripes) form along the axis of striped domains. Finally, when the wetting region is smaller than the particle size, the particles do not deposit within the features but are drawn backward with the receding drop. These results indicate that evaporation on surfaces of patterned wetting provides a highly parallelizable means of tailoring the geometry of particle distributions to create patterned media.

Use of MF and UF membranes for reclamation of glass industry wastewater containing colloidal clay and glass particles

Microfiltration (MF) or ultrafiltration (UF) can be a viable option for the separation of fine clay and glass particles in glass industry wastewater in order to recycle treated water (permeate) into the manufacturing process. The characteristics of treated water quality and membrane permeability were investigated using MF/UF equipment with different geometry and pore sizes at various operating conditions. Substantial particle removal was accomplished with the membranes having a pore size of less than 0.45 μm and so the quality of permeate was able to satisfy the requirements for reuse. During stirred flow and crossflow filtration runs, shear did have different effects on membrane permeability, which shed new light on an important issue that one result may not be extrapolated from the other. These phenomena could be attributed to the irreversibility of deposited particles with sticky nature as well as the difference of operational modes during MF/UF. To control irrecoverable losses of filterability due to colloidal particle deposition at the membrane surface, severe turbulent flow was required at the commencement of membrane operations. Particles’ movement over the membrane surface could be explained based on the distribution of their backtransport velocities at different shear conditions during crossflow filtration.

Prediction of Brownian particle deposition in porous media using the constricted tube model

The deposition of colloidal particles onto the collector surfaces of porous media is investigated using the Brownian dynamics simulation method. The pore structure in a filter bed was characterized by the constricted tube model. The effects of various shapes of the total interaction energy curves of DLVO theory and the effects of different particle diameters on the collection efficiencies of particles are examined. The simulation results show that the particle collection efficiency is strongly dependent on the geometry of the tube and on the shape of the total interaction energy curve. In a comparison with the available experimental measurements of the filter coefficient, it is found that the present model can give a smaller discrepancy than that of the convective diffusion model in the unfavorable deposition region.

Particle adsorption and deposition: role of electrostatic interactions

This work demonstrates how electrostatic interactions, described in terms of the classical DLVO theory, influence colloid particle deposition phenomena at solid/liquid interfaces. Electrostatic interactions governing particle adsorption in both non-polar and polar media (screened interactions) are discussed. Exact and approximate methods for calculating the interaction energy of spherical and non-spherical (anisotropic) particles are presented, including the Derjaguin method. Phenomenological transport equations governing particle deposition under the linear regime are discussed with the limiting analytical expressions for calculating initial flux. Non-linear adsorption regimes appearing for higher coverage of adsorbed particles are analysed. Various theoretical approaches are exposed, aimed at calculating blocking effects appearing due to the presence of adsorbed particles. The significant role of coupling between bulk transport and surface blocking is demonstrated. Experimental data obtained under well-defined transport conditions, such as diffusion and forced convection (impinging-jet cells), are reviewed. Various experimental techniques for detecting particles at interfaces are discussed, such as reflectometry, ellipsometry, streaming potential, atomic force microscopy, electron and optical microscopy, etc. The influence of ionic strength and flow rate on the initial particle deposition rate (limiting flux) is presented. The essential role of electrostatic interactions in particle deposition on heterogeneous surfaces is demonstrated. Experimental data pertinent to the high-coverage adsorption regime are also presented, especially the dependence of the maximum coverage of particles and proteins on the ionic strength. The influence of lateral electrostatic interactions on the structure of particle monolayers is elucidated, and the links between colloid and molecular systems are pointed out.

Characterisation and modelling of fouling in membrane bioreactors

A membrane bioreactor used for denitrification of a synthetic substrate was studied in term of membrane fouling. For standard pH and temperature conditions, subcritical conditions were defined to ensure the process stability. The stepwise method was used to determine the critical flux for the deposition of colloidal particles. Under standard physicochemical conditions, only a low and constant fouling resistance was observed if the permeate flux was maintained below the critical flux. The influence of physicochemical variations was then investigated by varying pH and temperature in the biological reactor. It was observed that, when the pH value was higher than a critical one, the membrane was rapidly fouled. This maximum admissible pH value decreased when the temperature increased. On analysing the reversible nature of fouling and the variations of ionic concentrations with the pH, the role of carbonate calcium precipitation was pointed out. By using classical filtration models, it was shown that the fouling mechanism could be the deposition of CaCO 3 particles formed in the bulk suspension by bulk crystallisation.

Effect of the coordination number of the pore-network on the transport and deposition of particles in porous media

Effect of the coordination number of the pore-network structure on the transport and deposition of colloidal particles in porous media was investigated. Applying with the orthogonal collocation principle and the pseudo-spectral method based on the Chebyshev polynomial, the complete solutions of the population balance equations describing the deposited particles, the suspended particles and the unblocked pore throats of porous media were obtained for the simple square network and the capillary tube network. It is shown that the network structure of porous media may significantly affect filtration rate, and therefore the effluent concentration and pressure drop. The filter with a capillary tube network structure owns higher filter coefficient than that of the filter with a simple square network structure. Theoretical predictions for different influent concentrations of particles, different flow rates and the case of blocking occurred in the filter bed are in agreement with the available experimental data.

Micropatterning Microscopic Charge Heterogeneity on Flat Surfaces for Studying the Interaction between Colloidal Particles and Heterogeneously Charged Surfaces

An effective technique for micropatterning microscopic chemical heterogeneity onto solid surfaces for studying colloid interaction with heterogeneously charged surfaces is presented. Charge heterogeneity is micropatterned onto glass surfaces by the chemical modification of specified surface regions with aminosilane. The deposition (adsorption) of colloidal particles onto the micropatterned glass surfaces, under well-controlled laminar flow conditions, is observed in real time using a stagnation point flow cell and an optical microscope with a CCD camera.

Effect of Gravity on Colloidal Deposition Studied by Atomic Force Microscopy

Atomic force microscopy (AFM) was used to study the effect of gravitational forces on the deposition of submicrometer colloidal particles onto solid surfaces to test the usual assumption that the contribution of gravity to the behavior of particles with diameters <1 μm is negligible. The effects of both particle size and density were examined using polystyrene sulfate latex, silica, and colloidal gold particles of several sizes ranging from 10 nm to 1 μm. The results show that significant differences are observed in the deposition of colloidal particles onto horizontal and vertical surfaces, under identical suspension conditions and exposure times, showing that gravitational forces can have a considerable effect. This effect was quantified by analysis of the AFM images. The experimental results are compared to calculations of the expected coverage and particle surface concentration assuming diffusion-limited adsorption and deposition by sedimentation. Gravity can be negligible for low-density particles with diameters considerably smaller than 1 μm. However, if the density of the colloidal particles is high, as in the case of colloidal gold, gravity can become a significant driving force for particle transport to the surface, even for particles with diameters much smaller than 100 nm.

Effect of hydrodynamic interactions on the irreversible deposition of colloidal particles: Deposition algorithm and simulations

A Stokesian dynamics constraint algorithm for the irreversible deposition of colloidal particles onto a surface is presented. This algorithm can also be used to simulate a variety of nondeposition phenomena and with any method for computing the hydrodynamic interactions among the particles. In particular, a multipole scheme we recently described for computing the mobility matrix of colloidal particles, with or without the presence of a wall, is used here in conjunction with the new deposition algorithm to perform Stokesian dynamics irreversible deposition simulations on a group of 75 colloidal particles. Deposition simulations are performed with and without the hydrodynamic effect of the wall (substrate) being included in the mobility matrix. The results of the simulations lead to important qualitative conclusions on the effect of hydrodynamic interactions on the deposition process, in particular the hydrodynamic effect of the wall. In addition, the simulations serve to illustrate the performance of the new deposition algorithm.

Photochemical deposition of colloidal Au-Ag particles on quartz

Colloidal Au-Ag films were produced on quartz by photoreduction of Au and Ag complexes dissolved inN,N-dimethylformamide. The formation kinetics and structure of the colloidal particles were studied.

Patterned colloidal deposition controlled by electrostatic and capillary forces.

We use substrates chemically micropatterned with anionic and cationic regions to govern the deposition of charged colloidal particles. The direct observation of the colloidal assembly suggests that this process includes two steps: an initial patterned attachment of colloids to the substrate and an additional ordering of the structure upon drying. The driving forces of the process, i.e. , screened electrostatic and lateral capillary interactions, are discussed. This approach makes it possible to fabricate complex, high-resolution two-dimensional arrays of colloidal particles.

Aggregation of pairs of particles on electrodes during electrophoretic deposition

During electrophoretic deposition (EPD) of colloidal particles, the particles that have been deposited on the electrode surface move laterally along the electrode and form larger clusters. Models based on fluid convection have been advanced to explain this phenomenon. The models fall into two categories: (1) electrokinetic — electroosmotic flow is generated by the interaction between the applied electric field and the charged double layer on the surface of each particle, and (2) polarization — flow is generated by nonuniform current densities on the electrode. The electrokinetic model predicts that the aggregation rate is proportional to the applied electric field E ∞ and the zeta potential of the particles, while the polarization model predicts that the rate goes as E ∞ 2 and is independent of the zeta potential. We report experimental data for the dynamics of interactions between two deposited particles in a steady electric field in the range 20–100 V/m. The particles were polystyrene latex and their size was between 2.5 and 10 μm diameter. The direction of the electric field was also changed, and two different concentrations of supporting electrolyte were used. The aggregation trajectories of sets of two deposited particles from an initial separation of about a particle diameter were recorded using optical microscopy, and the video frames were analyzed to compute separation vs. time for each set of particles. The data show that the relative velocity between the particles is proportional to the electric field and the zeta potential of the particles, and scale with the particle size as predicted by the electrokinetic theory.

Role of convection in particle deposition at solid surfaces

Recent theoretical and experimental data concerning colloid particle deposition from well-defined flows onto solid/liquid interfaces were reviewed. The macroscopic flow fields in the vicinity of the spherical and cylindrical collector (both isolated and forming a structured layer) were presented. Analogous solutions for the impinging-jet cells of (i) radial symmetry (radial impinging-jet cell RIJ) and (ii) plane symmetry (the slot impinging-jet cell SIJ) were also discussed. Similarities and differences between these flows are pointed out. The method of decomposing the macroscopic flows into local flows of simple geometry like shearing and stagnation flows was exposed. The microscopic flows are discussed in some detail, especially those connected with the motion of a spherical particle parallel and perpendicular to a solid wall. Using the local flow distributions the governing continuity equation is formulated, incorporating the convective transport in the bulk and the specific force dominated transport at the surface. Approximate analytical models aimed at decoupling these transfer steps are described, in particular the surface force boundary layer approximation (SFBLA). Limiting analytical solutions for the perfect sink boundary conditions were given. A procedure of extending the convective diffusion theory to non-linear adsorption regimes governed by the steric barrier due to adsorbed particles, was also presented. The role of the electro-hydrodynamic coupling leading to the hydrodynamic scattering effect in the blocking phenomena was discussed. The theoretical results are confronted with experimental data obtained in the well-defined systems, e.g. mostly in the RIJ and SIJ cells using monodisperse polystyrene latex colloids. A good agreement of theoretical and experimental data was found and most of the theoretical predictions were quantitatively confirmed, in particular the significance of the hydrodynamic scattering effect.

Deposition and detachment studies of fine particles by the packed column technique

The use of the packed column technique for the study of deposition of colloidal particles from dispersions in liquids onto collector beads is described. The technique also allows to investigate the removal of adhered particles, by rinsing the loaded column with solutions of different compositions. A number of examples are described illustrating the effects of various experimental conditions, including the surface and intrinsic properties of reactants, the nature and the ionic strength of the liquid phase, the effects of various additives, and of superimposed external magnetic fields, etc. The results are presented in terms of breakthrough curves and interpreted by means of three phenomenological parameters, which are related to interaction forces between colloidal particles and the collector. This approach makes it possible to distinguish between monolayer and multilayer depositions.

Effect of gravity on the deposition of colloidal particles on a planar surface

A steady state convective-diffusion equation is solved using a collocation method to find the concentration profile and flux of adsorbing particles near a particle adsorbed on the plane surface. At small values of the gravity number, NG=πd4Δρ/6kT, the concentration profile and flux vary slowly near the preadsorbed particle, while they are highly nonuniform at large values of NG. The effect of the position of the system boundary on the collocation calculation is discussed and it is shown how the concept of flux balance may be used to improve the accuracy of the results. Finally, we develop two fitting functions at high and low values of NG, respectively.

Analysis of Fine Bubble Attachment onto a Solid Surface within the Framework of Classical DLVO Theory

Fine bubble attachment onto a solid surface in an impinging jet flow was analyzed within the framework of DLVO theory. The effects of hydrodynamic convection, van der Waals (VDW) interaction, electrostatic double-layer (EDL) interaction, and gravitational force on bubble attachment rate (in terms of the Sherwood number) were examined in detail. The analyses showed that due to large Peclet number and gravity number for gas bubbles the behavior of the bubble attachment is significantly different from that of colloidal particle deposition in some aspects. Specifically, it was demonstrated that within a certain range of physicochemical conditions, gas bubbles can attach onto a solid surface despite the existence of repulsive VDW interaction force and the fact that the surfaces of both the bubble and the solid collector carry the same sign of electrostatic potentials. This is attributed to the role played by the short-range attractive asymmetric EDL interaction and the strong hydrodynamic and gravity forces, without any need for the so-called hydrophobic interaction force. In addition, it was also shown that the models derived for the impinging jet system can be used to evaluate transport of fine gas bubbles onto a large particle surface, suggesting that the information extracted from the impinging jet geometry can be applied to the analysis of flotation processes.

Extended random sequential adsorption model of irreversible deposition processes: from simulations to experiments.

An experimental study of the irreversible deposition of colloidal particles of various radii R on a solid surface is presented over a wide range of the Péclet number, Pe, or reduced radius R* (Pe = R*(4)). The experimental data are analyzed by means of a new generalized random sequential adsorption model that takes explicitly the diffusion of the particles during the deposition into account. It allows description of the continuous transition from a random sequential adsorption-like to a ballistic-like deposition behavior. It depends on three parameters: d(s), related to the diffusion of the particles before adhesion; n(s), related to the number of allowed adhesion trials of a particle; and R(e), representing the effective particle radius. The model allows accounting for all of the experimental observations relative to the radial distribution functions and the number density fluctuations over the whole coverage range and all investigated values of R*. In addition, it is found that d(s)/R is proportional to R*(-2) as expected for a diffusional process. Moreover, the parameters d(s) and n(s) appear to be connected through the empirical relation (d(s)/R)n(s)(2/3) = C, where C is found to be of the order of 50. This unique statistical model allows an accurate description of the irreversible deposition process, whatever the influence of gravity with respect to diffusion.

Colloidal Metal Deposition onto Functionalized Polystyrene Microspheres

Three different methods are described for uniformly anchoring metal colloids (Pt, Pd, and Au) onto the surface of polystyrene microspheres (PSMS). The first method we have employed is electrostatic deposition of preformed anionic colloidal particles onto a polycationic surface. In this method the functional groups on the surfaces of the microspheres (amine or carboxylic acid) are used to give the surface a net charge. These ionic spheres were then treated with polyelectrolytes of the opposite charge, which uniformly cover the surface. When the spheres have a net positive charge at the surface they show excellent adhesion of Au colloids. These metal-derivatized spheres can be prepared with electroactive viologen groups as well. In the second method investigated here, metal colloids are adsorbed to the surface of neutral functionalized PSMS. We report the synthesis and characterization of catalytically important noble monometallic colloids using various chemical and sonochemical methods. These metal colloid...

Brownian deposition kinetics of latex particles onto glass and polystyrene

There has been a large body of work on the deposition of colloidal particles onto many different kinds and shapes of surfaces. Nearly all work in the past has involved flowing systems in which a well-defined hydrodynamic layer exists at the collector surface with certain advantages and disadvantages. We have chosen a still system in which transport of particles to the collector surface occurs solely by diffusion. Both particles and surfaces were negatively charged, so that deposition was driven by dispersion forces. A photomicroscopic technique has been used to determine absolute values of initial rates of deposition. Three monodisperse polystyrene colloids of various particle sizes and surface charge densities were synthesized. Their zeta potentials were determined by microelectrophoresis in Ba(NO 3) 2 solutions. Collector surfaces were glass and glass coated with polystyrene. Their zeta potentials were determined from their streaming potentials in various concentrations of electrolyte. Direct determination of diffusion coefficients indicate that the particles behave normally. Initial deposition rates exhibit strong dependence on ionic strength, indicating large electrical double layer effects. Like the work of others, rates of deposition fell off with time, perhaps due to the presence of `hot spots', i.e. highly localized areas of greater reactivity. The most regular behavior occurred in deposition on polystyrene-coated glass, presumably because roughness and highly reactive sites on the glass surface were largely eliminated. Absolute rates were several times theoretical for fastest deposition. It is speculated that the hydrophobic effect plays a significant role in accelerating particles towards the collector. Plots of log (initial rate constant) vs. log (ionic strength) were linear and generally in the order anticipated by Reerink–Overbeek theory.