Structure of Polymer-Grafted Nanoparticle Melts

Abstract

The structure of neat melts of polymer-grafted nanoparticles (GNPs) is studied via coarse-grained molecular dynamics simulations. We systematically vary the degree of polymerization and grafting density at fixed nanoparticle (NP) radius and study in detail the shape and size of the GNP coronas. For sufficiently high grafting density, chain sections close to the NP core are extended and form a dry layer. Further away from the NP, there is an interpenetration layer, where the polymer coronas of neighboring GNPs overlap and the chain sections have almost unperturbed conformations. To better understand this partitioning, we develop a two-layer model, representing the grafted polymer around an NP by spherical dry and interpenetration layers. This model quantitatively predicts that the thicknesses of the two layers depend on one universal parameter, x, the degree of overcrowding of grafted chains relative to chains in the melt. Both simulations and theory show that the chain extension free energy is nonmonotonic with increasing chain length at a fixed grafting density, with a well-defined maximum. This maximum is indicative of the crossover from the dry layer-dominated to interpenetration layer-dominated regime, and it could have profound consequences on our understanding of a variety of anomalous transport properties of these GNPs. Our theoretical approach therefore provides a facile means for understanding and designing solvent-free GNP-based materials.

Structure and thermodynamics of grafted silica/polystyrene dilute nanocomposites investigated through self-consistent field theory

“…We mention at this point that the Alexander model, which we develop in our ESI, † is similar to the h dry region that Mydia et al 58 report in the context of their two-layer theoretical model for the description of nanoparticle brushes. In that work, 58 the authors state that in curved surfaces and for constant grafting density, the free energy associated with the stretching of grafted chains does not increase indefinitely with increasing length of grafted chains, but it rather saturates at a maximum value. This is well expected, since at some point the grafted chains cannot experience the presence of each other due to the curvature of the solid surface and therefore they become unperturbed.…”

“…13, we demonstrate a comparison between the stretching energy term obtained by the Alexander model (lines) and our SCFT model (markers); the latter is calculated either from: (a) A g conf given by eqn (30), or (b) A g stretch given by eqn ( 34) and (35). We mention at this point that the Alexander model, which we develop in our ESI, † is similar to the h dry region that Mydia et al 58 report in the context of their two-layer theoretical model for the description of nanoparticle brushes. In that work, 58 the authors state that in curved surfaces and for constant grafting density, the free energy associated with the stretching of grafted chains does not increase indefinitely with increasing length of grafted chains, but it rather saturates at a maximum value.…”

“…54,55 The brush thickness exhibits a rather complicated behavior across the transition regime from spherical nanoparticle to flat surface, which we try to describe through a scaling equation. Finally, the thermodynamics of these systems is examined in terms of the grand potential across the parameter space and a direct comparison with the Alexander model at fixed density 56,57 (which is similar to the dry part of the two-layer model) 58,59 is performed regarding the stretching free energy of grafted chains.…”

Interactions between Sterically Stabilized Nanoparticles: The Effects of Brush Bidispersity and Chain Stiffness

“…For example, brush coating technology is used for the alignment of one-dimension nanomaterials [ 19 ]. Accordingly, these materials have been actively studied both experimentally [ 20 , 21 , 22 ] and theoretically [ 15 , 21 , 23 , 24 , 25 ].…”

Static and dynamic properties of block copolymer based grafted nanoparticles across the non-ergodicity transition

“…Soft colloidal particles can be thought of as hybrids interpolating between polymers and hard spheres (HSs), 1 offering a plethora of possibilities for designing systems with tunable dynamic response. Examples of spherical soft colloidal systems are vesicles, dendrimers, 2 microgels, [3][4][5] block copolymer micelles, [6][7][8][9] polymer-grafted nanoparticles (PGNPs), [10][11][12][13][14] and star polymers. [15][16][17][18][19] Unlike hard-spheres, for which the phase diagram and associated dynamic properties have been exhaustively investigated, 20 the respective consequences of softness have not been fully explored.…”