Random sequential adsorption: An efficient tool for investigating the deposition of macromolecules and colloidal particles.

Random Sequential Adsorption (RSA) is one of the most efficient theoretical models used to investigate adsorption of macromolecules and particles, with a long-standing tradition in the field of colloid and interface science. In the first part of this paper, we demonstrate how the RSA model can be applied to interpret the experimental data and extract information about the density of the adsorption monolayer, the kinetics of its growth, and microstructural properties such as pair-correlation function and monolayer roughness. We briefly summarized the most important generalizations of the RSA model for monolayers and reviewed its extensions considering, e.

Roughness of surface decorated with randomly distributed pillars.

We have presented a quantitative analysis of roughness of planar surfaces decorated with randomly distributed, cylindrical pillars, disks, or cavities. We have described the roughness in terms of the surface power spectral density (PSD). First, we have derived a general equation for the PSD of such surfaces.

Wet formation and structural characterization of quasi-hexagonal monolayers.

We have presented a simple and efficient method for producing dense particle monolayers with controlled surface coverage. The method is based on particle sedimentation, manipulation of the particle-substrate electrostatic interaction, and gentle mechanical vibration of the system. It allows for obtaining quasi-hexagonal structures under wet conditions.

Modeling of LbL multilayers with controlled thickness, roughness, and specific surface area.

We present computer simulation results of the layer by layer self-assembling process of colloidal particles. We have generated five multilayer structures of monodisperse spherical particles according to a generalized model of random sequential adsorption of hard spheres. The multilayers, each created at a different single-layer surface coverage, are of similar thickness.

Novel numerical method for calculating initial flux of colloid particle adsorption through an energy barrier.

Using variable substitution, we present a general method for the numerical solution of stiff, ordinary, linear, homogeneous differential equations characteristic of colloid particle adsorption/deposition over an energy barrier. For the example of the radial impinging jet system, we demonstrate the application of this method of calculating the colloid concentration profile and initial particle flux in the presence of repulsive electrostatic interactions between the particle and adsorption surface. We show that our method works well in systems with energy barriers up to the order of hundreds of kT, at which point the adsorption flux vanishes.

Formation of multilayered structures in the layer by layer deposition of colloid particles.

Theoretical calculations of particle film formation in the layer by layer (LbL) self-assembling processes have been performed according to the generalized random sequential adsorption (RSA) scheme. The first (precursor) layer was generated using the standard RSA scheme pertinent to homogeneous surface. Formation of the consecutive layers (up to twenty) was simulated for two kinds of particles of equal size.

Adhesion of nonmotile Pseudomonas aeruginosa on "soft" polyelectrolyte layer in a radial stagnation point flow system: measurements and model predictions.

Prediction of bacterial deposition rates onto substrates in natural aquatic systems is quite challenging because of the inherent complexity of such systems. In this study, we compare experimental deposition kinetics of nonmotile bacteria (Pseudomonas aeruginosa) on an alginate-coated substrate in a radial stagnation point flow (RSPF) system to predictions based on DLVO theory. The "softness" of the surface layer of the bacteria and alginate-coated substrate was considered in the calculations of their electrokinetic surface properties, and the relevance of both the classical zeta potential and the outer surface potential as surrogates for surface potential was investigated.

Molecular dynamics study of small PNA molecules in lipid-water system.

We present the results of molecular dynamics simulations of small peptide nucleic acid (PNA) molecules, synthetic analogs of DNA, at a lipid bilayer in water. At neutral pH, without any salt, and in the NP(n)gammaT ensemble, two similar PNA molecules (6-mers) with the same nucleic base sequence and different terminal groups are investigated at the interface between water and a 1-palmitoyl-2-oleoylphosphatidylcholine lipid bilayer. The results of our simulations suggest that at low ionic strength of the solution, both PNA molecules adsorb at the lipid-water interface.

Colloid particle adsorption at random site (heterogeneous) surfaces.

Irreversible adsorption of colloid particles and globular proteins at heterogeneous surfaces was studied theoretically. The substrate surface was created by covering a uniform surface by coupling sites (active centers) of a desired coverage. In contrast to previous studies concerned with disks, in our simulations the centers were modeled by spheres having a size smaller than that of the adsorbing particles.

Prediction and measurement of the interparticle depletion interaction next to a flat wall.

A theoretical and experimental study was performed to investigate the depletion interaction between two colloidal particles next to a solid wall in a solution of nonadsorbing macromolecules. By calculating the change in free volume available to the macromolecules upon approach of the two particles, a relatively simple expression was developed for the interparticle depletion attraction in hard sphere systems as a function of the particle-particle and particle-plate spacing. Perhaps the most useful result obtained from this analysis was that the wall has no effect whenever the ratio of the particle radius to the macromolecule radius is greater than four.

Effect of depletion interactions on transport of colloidal particles in porous media.

The influence of depletion interactions on the transport of micrometer-sized, negatively charged polystyrene latex particles through porous media was studied by analysis of particle breakthrough curves as a response to short-pulse particle injections to the inlet of a packed column of glass beads. The column outlet latex particle concentration profiles and the total amount of particles exiting the column were determined as a function of the concentration of small, silica nanoparticles in the solution and the bulk flow rate. Because of similar charges, the silica particles do not adsorb to either the latex particles or glass beads and thus induce an attractive depletion force between the latex particles and glass bead collectors.

Surface clusters of colloid particles produced by deposition on sites.

The possibility of producing surface clusters of well-defined structure formed by colloid particles was analyzed theoretically and experimentally. Theoretical results were derived by performing Monte Carlo-type simulations according to the generalized random sequential adsorption (RSA) mechanism. In these simulations, the jamming coverage of particles adsorbing irreversibly on spherical sites was determined as a function of the particle-to-site size ratio lambda.

Application of the extended RSA models in studies of particle deposition at partially covered surfaces.

This paper reviews the application of the extended random sequential adsorption (RSA) approaches to the modeling of colloid-particle deposition (irreversible adsorption) on surfaces precovered with smaller particles. Hard (noninteracting) particle systems are discussed first. We report on the numerical simulations we performed to determine the available surface function, jamming coverage, and pair-correlation function of the larger particles.

Irreversible adsorption of particles at random-site surfaces.

Irreversible adsorption of negatively charged polystyrene latex particles (averaged diameter 0.9 microm) at heterogeneous surfaces was studied experimentally. The substrate bearing a controlled number of adsorption sites was produced by precovering mica sheets by positively charged polystyrene latex (averaged diameter of 0.

An approximate method for calculating depletion and structural interactions between colloidal particles.

An approximate method is evaluated for calculating the second virial coefficient in a dilute macromolecular solution bounded by two interfaces. The approximation is essentially the superposition of the coefficients calculated independently for each surface. To test this approach, the depletion interaction between two particles in a solution of nonadsorbing, spherical macromolecules is calculated in systems with either hard-wall or long-range electrostatic interactions.

Colloid Particle Adsorption on Partially Covered (Random) Surfaces.

The random sequential adsorption (RSA) approach was used to model irreversible adsorption of colloid particles at surfaces precovered with smaller particles having the same sign of surface charge. Numerical simulations were performed to determine the initial flux of larger particles as a function of surface coverage of smaller particles θ(s) at various size ratios lambda=a(l)/a(s). These numerical results were described by an analytical formula derived from scaled particle theory.