Boundary conditions in random sequential adsorption

The influence of different boundary conditions on the density of random packings of disks is studied. Packings are generated using the random sequential adsorption algorithm with three different types of boundary conditions: periodic, open, and wall. It is found that the finite size effects are smallest for periodic boundary conditions, as expected. On the other hand, in the case of open and wall boundaries it is possible to introduce an effective packing size and a constant correction term to significantly improve the packing densities.Comment: 9 pages, 7 figure

Adsorption of bacteriophage under various physiological conditions of the host

The first step in the growth of bacteriophage is the combination of phage with the susceptible bacterial host. The rate of this combination is, under simple conditions, proportional to both the bacterial concentration and to the phage concentration. Various aspects of this process have been studied quantitatively by previous workers (1, 2). Their results will be analyzed and discussed in the sections entitled "Residual free phage," and "Theory of adsorption rates." The main purpose of this paper was the study of a detail of the adsorption process that had not previously received attention, namely the dependence of the rate constant of adsorption on the physiological state of the bacterial host. Such a dependence must be anticipated for two reasons. First, it is known that the size of a bacterium changes very considerably depending on its phase of growth in a given culture medium, and an increased cell surface should lead to an increase of the adsorption rate on to a given number of bacteria. Second, for motile bacteria, like E. coli, the adsorption will be faster when the bacteria move about rapidly than when their motility is reduced by adverse physiological conditions. Our experiments show that the rate constant under optimal conditions is more than sixty times greater than under poor conditions

Competitive adsorption of p-hydroxybenzoic acid and phenol on activated carbon : experimental study and modelling.

The competitive adsorption of phenol and p-hydroxybenzoic acid (4HBA) has been investigated on activated carbon (AC) for a wide range of concentrations under unbuffered conditions. The results show a preferential adsorption of 4HBA which can be explained by the lower solubility of 4HBA and the electrostatic interactions between the AC and the ionic form of the molecule in this range of pH. The Langmuir isotherm is found suitable to describe the single-component adsorptions, indicating a monolayer adsorption in accordance with the microporous nature of the AC. Then the empirical extended Langmuir model and the predictive Ideal Adsorption Solution Theory model have been compared for competitive adsorption. When using parameter values optimized for single pollutants, both models show rather poor agreement with mixture data. However after fitting the extended Langmuir parameters with the whole data set, better results can be obtained, showing that there is some peculiar behaviour of the mixture under oxic conditions, probably tied to the effect of 4HBA on the irreversible adsorption of phenol

Critical adsorption on curved objects

A systematic fieldtheoretic description of critical adsorption on curved objects such as spherical or rodlike colloidal particles immersed in a fluid near criticality is presented. The temperature dependence of the corresponding order parameter profiles and of the excess adsorption are calculated explicitly. Critical adsorption on elongated rods is substantially more pronounced than on spherical particles. It turns out that, within the context of critical phenomena in confined geometries, critical adsorption on a microscopically thin `needle' represents a distinct universality class of its own. Under favorable conditions the results are relevant for the flocculation of colloidal particles.Comment: 52 pages, 10 figure

Critical adsorption of polyelectrolytes onto charged Janus nanospheres

Based on extensive Monte Carlo simulations and analytical considerations we study the electrostatically driven adsorption of flexible polyelectrolyte chains onto charged Janus nanospheres. These net-neutral colloids are composed of two equally but oppositely charged hemispheres. The critical binding conditions for polyelectrolyte chains are analysed as function of the radius of the Janus particle and its surface charge density, as well as the salt concentration in the ambient solution. Specifically for the adsorption of finite-length polyelectrolyte chains onto Janus nanoparticles, we demonstrate that the critical adsorption conditions drastically differ when the size of the Janus particle or the screening length of the electrolyte are varied. We compare the scaling laws obtained for the adsorption-desorption threshold to the known results for uniformly charged spherical particles, observing significant disparities. We also contrast the changes to the polyelectrolyte chain conformations and the binding energy distributions close to the adsorption-desorption transition for Janus nanoparticles to those for simple spherical particles. Finally, we discuss experimentally relevant physico-chemical systems for which our simulations results may become important. In particular, we observe similar trends with polyelectrolyte complexation with oppositely but heterogeneously charged proteins.Comment: 13 pages, 11 figures, RevTeX

Diffusive growth of a single droplet with three different boundary conditions

We study a single, motionless three-dimensional droplet growing by adsorption of diffusing monomers on a 2D substrate. The diffusing monomers are adsorbed at the aggregate perimeter of the droplet with different boundary conditions. Models with both an adsorption boundary condition and a radiation boundary condition, as well as a phenomenological model, are considered and solved in a quasistatic approximation. The latter two models allow particle detachment. In the short time limit, the droplet radius grows as a power of the time with exponents of 1/4, 1/2 and 3/4 for the models with adsorption, radiation and phenomenological boundary conditions, respectively. In the long time limit a universal growth rate as $[t/\ln(t)]^{1/3}$ is observed for the radius of the droplet for all models independent of the boundary conditions. This asymptotic behaviour was obtained by Krapivsky \cite{krapquasi} where a similarity variable approach was used to treat the growth of a droplet with an adsorption boundary condition based on a quasistatic approximation. Another boundary condition with a constant flux of monomers at the aggregate perimeter is also examined. The results exhibit a power law growth rate with an exponent of 1/3 for all times