Potential of Mean Force between Bare or Grafted Silica/Polystyrene Surfaces from Self-Consistent Field Theory.

Aristotelis P Sgouros,Doros N Theodorou,Apostolos T Lakkas,Constantinos J Revelas

doi:10.3390/polym13081197

Aristotelis P Sgouros, Doros N Theodorou + Show 2 more

Open Access

https://doi.org/10.3390/polym13081197

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Journal: Polymers	Publication Date: Apr 7, 2021
Citations: 9	License type: CC BY 4.0

Affiliation: National Technical University of Athens

Abstract

We investigate single and opposing silica plates, either bare of grafted, in contact with vacuum or melt phases, using self-consistent field theory. Solid–polymer and solid–solid nonbonded interactions are described by means of a Hamaker potential, in conjunction with a ramp potential. The cohesive nonbonded interactions are described by the Sanchez-Lacombe or the Helfand free energy densities. We first build our thermodynamic reference by examining single surfaces, either bare or grafted, under various wetting conditions in terms of the corresponding contact angles, the macroscopic wetting functions (i.e., the work of cohesion, adhesion, spreading and immersion), the interfacial free energies and brush thickness. Subsequently, we derive the potential of mean force (PMF) of two approaching bare plates with melt between them, each time varying the wetting conditions. We then determine the PMF between two grafted silica plates separated by a molten polystyrene film. Allowing the grafting density and the molecular weight of grafted chains to vary between the two plates, we test how asymmetries existing in a real system could affect steric stabilization induced by the grafted chains. Additionally, we derive the PMF between two grafted surfaces in vacuum and determine how the equilibrium distance between the two grafted plates is influenced by their grafting density and the molecular weight of grafted chains. Finally, we provide design rules for the steric stabilization of opposing grafted surfaces (or fine nanoparticles) by taking account of the grafting density, the chain length of the grafted and matrix chains, and the asymmetry among the opposing surfaces.

Highlights

Grafting polymer chains on solid surfaces is a standard procedure for the steric stabilization of nanocomposite systems [1,2,3]
The temperature, T, of the system was always equal to 500 K and when matrix chains exist in the system, the calculations were performed under the grand canonical ensemble, which we find most suitable in such interfacial solid– polymer systems
The quantities extracted from these systems will be used as reference for the potential of mean force calculations involving two approaching silica surfaces, either grafted or bare

Summary

Introduction

Grafting polymer chains on solid surfaces is a standard procedure for the steric stabilization of nanocomposite systems [1,2,3]. Understanding the behavior of grafted polymer brushes requires a thorough investigation of the thermodynamics of the system under different conditions. In the case of two or more nanoparticles embedded inside a polymer melt, the challenge is to keep them separated by overcoming their tendency to form aggregates. One of the possible ways to get around this behavior is to graft polymer chains on the surface of the nanoparticles. Achieving a proper dispersion of nanoparticles inside the polymer melt is associated with a considerable enhancement of its properties [8,9,10,11,12]

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Discussion

Conclusion