Hopping Diffusion of Nanoparticles in Polymer Matrices.

Wepropose a hopping mechanism for diffusion of large nonstickynanoparticles subjected to topological constraints in both unentangledand entangled polymer solids (networks and gels) and entangled polymerliquids (melts and solutions). Probe particles with size larger thanthe mesh size axof unentangledpolymer networks or tube diameter aeof entangled polymer liquids are trapped by the network orentanglement cells. At long time scales, however, these particlescan diffuse by overcoming free energy barrier between neighboringconfinement cells. The terminal particle diffusion coefficient dominatedby this hopping diffusion is appreciable for particles with size moderatelylarger than the network mesh size axor tube diameter ae. Much larger particles in polymer solids will be permanentlytrapped by local network cells, whereas they can still move in polymerliquids by waiting for entanglement cells to rearrange on the relaxationtime scales of these liquids. Hopping diffusion in entangled polymerliquids and networks has a weaker dependence on particle size thanthat in unentangled networks as entanglements can slide along chainsunder polymer deformation. The proposed novel hopping model enablesunderstanding the motion of large nanoparticles in polymeric nanocompositesand the transport of nano drug carriers in complex biological gelssuch as mucus. [ABSTRACT FROM AUTHOR]