Diffusion of nanoparticles within a semidilute polyelectrolyte solution

Abstract

We studied the diffusion of charged gold nanoparticles within a semidilute solution of weakly charged polyelectrolyte, polyacrylic acid (PAA) of high molecular weight (M_w = 10⁶ g mol⁻¹) by using fluorescence correlation spectroscopy (FCS). Nanoparticle size (d) was varied between 5 nm to 40 nm and PAA volume fraction (ϕ) in water ranged from about 8ϕ* to 33ϕ*, where ϕ* is the overlap volume fraction. The reduced diffusion coefficient – defined as −D/D_o, where D is the diffusion coefficient in PAA solution and D_o is that in neat water – has a weak dependence on the particle size. D follows a power law of the form ∼ϕ^−0.5, which can be explained by a mean-field hydrodynamic theory in porous medium. Additional, rheology measurements showed a zero shear rate viscosity and shear thinning, which are typical of high molecular weight polyelectrolytes.