Compression-driven migration of nanoparticles in semiflexible polymer brushes

•Migration behavior of NPs depends on NP size, chain stiffness and degree of compression.•Height of free-energy barrier and depth of free-energy well for NPs rely mainly on degree of compression and chain stiffness.•Micro-spatial distributions of binary NPs are controlled easily by compressing the surfaces.

The conformations of binary nanoparticles (NPs) in semiflexible polymer brushes under compression are investigated by molecular dynamics simulations, and a migration phenomenon of large NPs in semiflexible polymer brushes is observed in our simulation. For flexible polymer brushes, small NPs disperse freely within polymer brushes and large NPs tend to be located at the brush interface during the compression process. However, for semiflexible polymer brushes, both small and large NPs enter polymer brushes at the beginning of compression process. Most of large NPs can penetrate into polymer brushes and migrate towards the grafting surface, while most of small NPs are always located within polymer brushes during the compression process. The micro-spatial distributions of binary NPs are controlled easily by compressing the impenetrable surfaces through the external forces. There is a free-energy barrier located in the middle region between two impenetrable surfaces, and a free-energy well near the grafting surface in the free-energy landscape of a large NP within semiflexible polymer brushes. The height of free-energy barrier and the depth of free-energy well depend mainly on the compression degree of two impenetrable surfaces and also rely on the size of NPs as well as the interaction between polymer brushes and NPs. However, for flexible polymer brushes, there only exists a free-energy well near the polymer brush surface during the compression process. This investigation may stimulate experimental interest in novel nano-materials.

Graphical abstractPhase separation of binary NPs and migration behavior of large NPs in polymer brushes under compression are investigated by using molecular dynamics simulations. For flexible polymer brushes, small NPs disperse freely within polymer brushes and large NPs tend to be located at the brush interface during the compression process. For semiflexible polymer brushes, small NPs are located within polymer brushes, however, most of large NPs can penetrate into polymer brushes and migrate towards the grafting surface. In the free-energy landscape of NPs in semiflexible polymer brushes there are a free-energy barrier located in the middle region between two impenetrable surfaces, and a free-energy well near the grafting surface. The height of free-energy barrier and the depth of free-energy well depend mainly on the compression degree of two impenetrable surfaces and also rely on the size of NPs as well as the interactions between polymer brushes and NPs. However, for flexible polymer brushes, there only exists a free-energy well near the polymer brush surface during the compression process. The micro-spatial distributions of binary NPs are controlled easily by compressing the impenetrable surfaces through the external forces.Download high-res image (537KB)Download full-size image