Molecular modeling of intermolecular and intramolecular excluded volume interactions for polymers at interfaces

A hybrid modeling approach is proposed for inhomogeneous polymer solutions. The method is illustrated for the depletion problem with polymer chains up to N=103 segments in semidilute solutions and good solvent conditions. In a three-dimensional volume, a set of freely jointed chains is considered for which the translational degrees of freedom are sampled using a coarse grained Monte Carlo simulation and the conformational degrees of freedom of the chains are computed using a modified self-consistent field theory. As a result, both intramolecular and intermolecular excluded volume effects are accounted for, not only for chains near the surface, but in the bulk as well. Results are consistent with computer simulations and scaling considerations. More specifically, the depletion thickness, which is a measure for the bulk correlation length, scales as d~J-0.75 and converges to the mean field result in the concentrated regim

Self-organization of polymers in bulk and at interfaces

Fully atomistic analysis of polymeric systems is computationally very demanding because the time and length scales involved span over several orders of magnitude. At the same time many properties of polymers are universal in the sense that they do not depend on the chemical nature of the comprising monomers. This makes coarse-grained methods, such as self-consistent field (SCF) modeling, an ideal tool for studying them. In this thesis we employ SCF modeling to study intra- and intermolecular self-organization organization of polymers and ordering of polymers near interfaces. Where possible, the results are compared to experiments and predictions of analytical theories

Coarse-grained hybrid simulation of liposomes

Soft Matter Chemistr

Formation and structure of ionomer complexes from grafted polyelectrolytes

We discuss the structure and formation of Ionomer Complexes formed upon mixing a grafted block copolymer (poly(acrylic acid)-b-poly(acrylate methoxy poly(ethylene oxide)), PAA21-b-PAPEO14) with a linear polyelectrolyte (poly(N-methyl 2-vinyl pyridinium iodide), P2MVPI), called grafted block ionomer complexes (GBICs), and a chemically identical grafted copolymer (poly(acrylic acid)-co-poly(acrylate methoxy poly(ethylene oxide)), PAA28-co-PAPEO22) with a linear polyelectrolyte, called grafted ionomer complexes (GICs). Light scattering measurements show that GBICs are much bigger (~70–100 nm) and GICs are much smaller or comparable in size (6–22 nm) to regular complex coacervate core micelles (C3Ms). The mechanism of GICs formation is different from the formation of regular C3Ms and GBICs, and their size depends on the length of the homopolyelectrolyte. The sizes of GBICs and GICs slightly decrease with temperature increasing from 20 to 65 °C. This effect is stronger for GBICs than for GICs, is reversible for GICs and GBIC-PAPEO14/P2MVPI228, and shows some hysteresis for GBIC-PAPEO14/P2MVPI43. Self-consistent field (SCF) calculations for assembly of a grafted block copolymer (having clearly separated charged and grafted blocks) with an oppositely charged linear polyelectrolyte of length comparable to the charged copolymer block predict formation of relatively small spherical micelles (~6 nm), with a composition close to complete charge neutralization. The formation of micellar assemblies is suppressed if charged and grafted monomers are evenly distributed along the backbone, i.e., in case of a grafted copolymer. The very large difference between the sizes found experimentally for GBICs and the sizes predicted from SCF calculations supports the view that there is some secondary association mechanism. A possible mechanism is discussed

New ends to the tale of tails: adsorption of comb polymers and the effect on colloid stability

In this paper we consider the classical problem of homopolymer adsorption at the solid–liquid interface and discuss its implications for colloidal stability. More specifically, our focus is on comb-like homopolymers in the strong adsorption limit. A self-consistent field analysis shows that for relatively long side chains but still much longer backbones, the adsorbed layer is dominated by the side chains near the surface, whereas at larger distances the layer has features that belong to the backbone. As a rule, homopolymer adsorption promotes flocculation of colloids. This is attributed to the long polymer chains that form bridges between the colloidal particles. However, the free ends of the chains do not participate in the bridging and thus contribute with a small repulsive term to the mainly attractive pair interaction. For comb polymers, the free ends of the side chains amplify the repulsion dramatically. As a result, in contrast to linear adsorbed homopolymers, comb polymers typically prevent flocculatio

Modeling of triblock terpolymer micelles with a segregated corona

We report on self-consistent field predictions for the formation of spherical micelles by ANBMCN triblock terpolymers in a selective solvent, that is, a good solvent for the AN and CN blocks and a poor solvent for the middle BM block. Above some threshold value for the repulsion between the A and C monomers, we find micelles with a laterally segregated corona, that is, Janus micelles. We consider the thermodynamic stability, the size, and the size fluctuations of these micelles. The transition between the homogeneous and the segregated states is smooth not only because of the finite size of the system, but also due to the compositional symmetry within the triblock terpolymer. It is found that the aggregation number decreases with increasing repulsion between A and C below the transition point and increases above the transition point. The formation of the interface is triggered by the high polymer density near the core. The interface between the A and C rich regions occupies a constant angle in spherical coordinates. This means that it widens in the radial direction. In these micelles, the lateral segregation gives a new fluctuation mode to the micelles; as the lateral segregation is coupled to the aggregation number, we anticipate a rich behavior in experimental systems

Analysis of the longitudinal structure of a collapsed molecular bottle brush using a self-consistent field approach

The two-gradient self-consistent field Scheutjens-Fleer (SCF-SF) approach is employed for study of conformational transition occurring in molecular bottle brushes upon decrease in the solvent strength for grafted chains. In particular, the solvent strength was varied from theta to poor solvent conditions. It was found that at moderately poor solvent strength the bottle brush collapses, keeping cylindrically uniform shape. Further decrease in the solvent strength leads to appearance of longitudinal undulations in the collapsed cylindrical structure. This result of our SCF modeling is in agreement with earlier predictions of scaling theory concerning longitudinal instability of uniform cylindrical structure of the collapsed brush. In particular, predicted by scaling theory dependence for the period of the structure on the degree of polymerization of grafted chains (~n1/2) and independence of the transition temperature of the molecular weight are in good agreement with results of our SCF modelin

Demonstrating The Entity Registry System : Implementing 5-Star Linked Data Without the Web

Abstract. Linked Data applications often assume that connectivity to data repositories and entity resolution services are always available. This may not be a valid assumption in many cases. Indeed, there are about 4.5 billion people in the world who have no or limited Web access. Many data-driven applications may have a critical impact on the life of those people, but are inaccessible to those populations due to the architecture of today’s data registries. In this paper, we propose and evaluate a new open-source system that can be used as a general-purpose entity registry suitable for deployment in poorly-connected or ad-hoc environments.