Adsorption of ions on surfaces modified with brushes of polyampholytes

Ising density functional theory for weak polyelectrolytes with strong coupling of ionization and intrachain correlations

We report a theoretical framework for weak polyelectrolytes by combining the polymer density functional theory with the Ising model for charge regulation. The so-called Ising density functional theory provides an accurate description of the effects of polymer conformation on the ionization of individual segments and is able to account for both the intra- and interchain correlations due to the excluded-volume effects, chain connectivity, and electrostatic interactions. Theoretical predictions of the titration behavior and microscopic structure of ionizable polymers are found to be in excellent agreement with the experiment.

Towards the description of adsorption of water in slit-like pores with walls covered by molecular brushes

The density profiles, adsorption isotherms, and phase behavior of a water model in a slit-like pore with walls modified by pre-adsorbed tethered chain molecules have been studied in the framework of a density functional theory. Each chain is bonded to the surface by its terminal segment, and the surface density of grafted chains is the same for each wall. The model for water taken from the work of Clark et al. [Mol. Phys. 104, 3561 (2006)] reproduces successfully a bulk equation of state. The mean field approach has been used to describe the effects of attractive interactions. The chemical association effects are taken into account by using the first-order thermodynamic perturbation theory of Wertheim. We have found that the presence of molecular brushes on the pore walls has important consequences for the adsorption and phase behavior of confined water. If the brush segments do not attract water molecules strongly, the vapor-liquid coexistence envelope shrinks upon increasing brush density, but the critical temperature is weakly affected. Alteration from capillary condensation to evaporation is observed with changes in the brush density, number of segments of tethered chains, and/or chemical identity of segments. The crossover temperature is affected by all these factors. Moreover, we have shown that affinity of water to segments of tethers is an important factor determining adsorption of water vapor and the entire phase diagram.

Self-assembly of hairy disks in two dimensions - insights from molecular simulations

We report the results of large scale molecular dynamics simulations conducted for sparsely grafted disks in two-dimensional systems. The main goal of this work is to show how the ligand mobility influences the self-assembly of particles decorated with short chains. We also analyze the impact of the chain length on the structure of dense phases. A crossover between the systems controlled by the core-core or by the segment-segment interactions is discussed. We prove that the ligand mobility determines the structure of the system. The particles with fixed tethers are found to order into different structures, an amorphous phase, hexagonal or honeycomb lattices, and a "spaghetti"-like phase containing single strings of cores, depending on the length of attached chains. The disks with mobile monomers assemble into a hexagonal structure, while the particles with longer mobile chains attached to them form a lamellar phase consisting of double strings of cores.