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 (Mw = 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/Do, where D is the diffusion coefficient in PAA solution and Do 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.
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