Effect of the solvent quality on the structural rearrangement of spherical brushes: coarse-grained models

Abstract

A coarse-grained model for flexible polymers end-grafted to repulsive spherical nanoparticles is studied for various polymer lengths, grafting densities, and nanoparticle sizes by molecular dynamics simulations, considering variable solvent quality in the framework of an implicit solvent treatment. Below the theta point, the tuning of the temperature strongly influences the coverage of the nanoparticle surface by collapsed single chains or clusters of several chains. The shape and size of the aggregates depend on the number of monomers and surface density of the polymers. Specifically we analyzed the effect of the solvent quality on the density profiles and radius of gyration of the single molecule. The stretching of the chains parallel to the surface, required for the cluster formation, leads to a slightly non-monotonic temperature variation of the polymer linear dimensions at intermediate chain lengths. For theta conditions, however, the chains are still stretched in the radial direction. In particular for long chains a crossover to the star polymer limit occurs that is studied in detail with self-consistent field theory. At a theoretical level we extended our study exploring the case of a spherical brush embedded in a polymer melt. For different choices of the Flory-Huggins parameter between free and grafted chains, the amount of monomers of the free chains adsorbed on the nanoparticle surface is predicted via self-consistent field calculations.

Polymer brushes on flat and curved surfaces: How computer simulations can help to test theories and to interpret experiments

“…This latter conclusion also applies when one considers polymer brushes where chains are grafted to cylinders76, 217–223 or spheres66 under poor solvent conditions. Particularly delicate is also the extension to binary polymer brushes in cylindrical geometry, where the quasi‐one‐dimensional character of the system provides additional fluctuation mechanisms to destroy the long‐range mesophase order that mean field‐type treatments predict 219–223.…”

“…We first consider a spherical polymer brush where chains are grafted to a sphere of radius R 60–66. Note that in this case the total number f = 4π R 2 σ of grafted chain is finite, and if the size of a single chain R e exceeds R , the situation is reminiscent of a star polymer 166–169.…”

“…A related mesophase formation is possible when brushes are formed from end‐grafted block copolymers 21–25. Another important aspect concerns the geometry of the substrate surface on which the chains are anchoring: the most frequently studied cases are planar substrates1–9, 26–59 albeit it is also possible to graft these polymers on the surface of spherical colloids60–66 or nanoparticles. Also grafting at the surface of cylindrical rods is of interest67–76 as well as on the inner surface of hollow cylinders 77–86.…”

Flory-Huggins parameter χ, from binary mixtures of Lennard-Jones particles to block copolymer melts

“…[25][26][27] Particle-based descriptions preserve the molecular structure of the initial polymer to a much higher degree and can provide insights into the microscopic properties of the system. The downside of bead-spring models compared to SCFT calculations, however, is that the free energy is not directly accessible, making additional (and potentially) expensive calculations necessary to access such quantities.…”

Structure of Polymer Layers Grafted to Nanoparticles in Silica–Polystyrene Nanocomposites

“…[26][27][28][29] An attempt to overcome the restrictions posed by the saddle-point approximation was made by Sides et al 30 The coordinates of all particles in the system were explicitly retained as degrees of freedom. It was crucial to update simultaneously the coordinates and the chemical potential field variables.…”