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Diffusion of Nanoparticles in Entangled Poly(vinyl alcohol) Solutions and Gels
journal contribution
posted on 2019-01-11, 20:13 authored by Kavindya K. Senanayake, Ehsan Akbari Fakhrabadi, Matthew W. Liberatore, Ashis MukhopadhyayWe studied the diffusion of gold
nanoparticles within entangled solutions and gels formed by high molecular
weight (Mw = 89000 g/mol) poly(vinyl alcohol)
(PVA) in water by using fluctuation correlation spectroscopy (FCS).
The nanoparticle size (2R) was varied between 5 and
30 nm, and the PVA volume fraction (ϕ) was chosen to be in the
entangled regime. We found that existing hydrodynamic and obstruction
models are inadequate to describe the size dependence of the particle
diffusion coefficient (D). For size ratios x = 2R/ae ≈
0.5–2.5, where ae is the entanglement
tube diameter in the solution, our results suggest a functional form
for D ∼ exp(−κx), where κ ≈ 1.4. This result qualitatively agrees with
the scaling theory prediction of hopping motion for particles within
entangled polymer solutions. For larger particles at higher volume
fractions, an additional sharp slowing down of the particle motion
was observed, which also exhibited an exponential dependence on the
size ratio, but with a much higher value of κ ≈ 7.5.
Such a rare hopping process can be explained qualitatively by recently
developed force-based nonlinear Langevin theory.