A new perspective on correlated polyelectrolyte adsorption: Positioning, conformation, and patterns

Adsorption of polyelectrolytes and polyelectrolytes-surfactant mixtures at surfaces: a physico-chemical approach to a cosmetic challenge

The use of polymer and polymer - surfactant mixtures for designing and developing textile and personal care cosmetic formulations is associated with various physico-chemical aspects, e.g. detergency and conditioning in the case of hair or wool, that determine their correct performances in preserving and improving the appearance and properties of the surface where they are applied. In this work, special attention is paid to the systems combining polycations and negatively charged surfactants. The paper introduces the hair surface and presents a comprehensive review of the adsorption properties of these systems at solid-water interfaces mimicking the negative charge and surface energy of hair. These model surfaces include mixtures of thiols that confer various charge densities to the surface. The kinetics and factors that govern the adsorption are discussed from the angle of those used in shampoos and conditioners developed by the cosmetic industry. Finally, systems able to adsorb onto negatively charged surfaces regardless of the anionic character are presented, opening new ways of depositing conditioning polymers onto keratin substrates such as hair.

Temperature-sensitive nanogels in the presence of salt: explicit coarse-grained simulations

In this work, coarse-grained simulations of two charged thermo-shrinking nanogels (with degrees of ionization of 0.125 and 0.250) in the presence of 1:1 and 3:1 electrolytes have been explicitly performed through the bead-spring model of polyelectrolyte. In a first set of simulations, salt concentrations for 1:1 and 3:1 electrolytes ranged from 1 to 100 mM and from 0.167 to 16.7 mM, respectively, whereas temperature remained fixed at a value for which hydrophobic forces were negligible in our case (288 K). The sizes of swollen nanogels are smaller when trivalent cations are present, but they do not change significantly in the range of concentrations of 3:1 electrolyte studied here. It should be also stressed that trivalent cations neutralize the nanogel charge more efficiently. According to these results the electrostatic repulsion plays an important role. In a second set of simulations, the temperature varied from 288 to 333 K to study the effect of salt on the thermal response when hydrophobic forces are not negligible. For the nanogels with the lowest degree of ionization, the behavior of the radius with increasing the temperature can be described by a sigmoid function, which shifts towards lower temperatures in the presence of salt. This shift is more clearly observed for trivalent cations, even at low concentrations. For the nanogels with the highest degree of ionization, the effect of additional electrolyte is also noticeable. In this case, hydrophobic forces are not the only responsible for their shrinkage in the presence of trivalent cations. The surface electrostatic potential and the concentration of salt cations inside the nanogel have been computed from simulations and a modified Poisson-Boltzmann (PB) cell model. The thermosensitivity in size have certain influence on the sensitivity of these properties to temperature changes. The rich behavior of the surface electrostatic potential and the uptake of salt cations are successfully predicted by the modified PB cell model proposed (at least qualitatively). Particularly, the model is able to predict how the retention of salt cations depends on their charge and the ionic valence when nanogels shrink.

Inverted critical adsorption of polyelectrolytes in confinement

What are the fundamental laws for the adsorption of charged polymers onto oppositely charged surfaces, for convex, planar, and concave geometries? This question is at the heart of surface coating applications, various complex formation phenomena, as well as in the context of cellular and viral biophysics. It has been a long-standing challenge in theoretical polymer physics; for realistic systems the quantitative understanding is however often achievable only by computer simulations. In this study, we present the findings of such extensive Monte-Carlo in silico experiments for polymer-surface adsorption in confined domains. We study the inverted critical adsorption of finite-length polyelectrolytes in three fundamental geometries: planar slit, cylindrical pore, and spherical cavity. The scaling relations extracted from simulations for the critical surface charge density σc-defining the adsorption-desorption transition-are in excellent agreement with our analytical calculations based on the ground-state analysis of the Edwards equation. In particular, we confirm the magnitude and scaling of σc for the concave interfaces versus the Debye screening length 1/κ and the extent of confinement a for these three interfaces for small κa values. For large κa the critical adsorption condition approaches the known planar limit. The transition between the two regimes takes place when the radius of surface curvature or half of the slit thickness a is of the order of 1/κ. We also rationalize how σc(κ) dependence gets modified for semi-flexible versus flexible chains under external confinement. We examine the implications of the chain length for critical adsorption-the effect often hard to tackle theoretically-putting an emphasis on polymers inside attractive spherical cavities. The applications of our findings to some biological systems are discussed, for instance the adsorption of nucleic acids onto the inner surfaces of cylindrical and spherical viral capsids.

Critical adsorption of polyelectrolytes onto charged Janus nanospheres

The conditions of critical polyelectrolyte adsorption onto spherical charged Janus nano-particles are exploited by Monte-Carlo computer simulations and theoretically.