Polymer Chain Swelling Induced by Dispersed Nanoparticles

The dimensions of individual deuterated polystyrene (d-PS) chains in a well-dispersed mixture of protonated polystyrene and chemically identical nanoparticles was determined by neutron scattering. A 10%–20% increase in the radius of gyration of d-PS was found when the nanoparticles are homogeneously dispersed in the polymer, an effect that occurs only when the radius of gyration of the polymer is larger than the nanoparticle radius. These results are reconciled with the existing literature.

Figure 1

(a) Neutron scattering intensity versus wave vector data for 2% 135 kD NP blended with 235 kD d-PS to provide scattering from the nanoparticles. The inset shows a Kratky plot of the same data. (b) Similar data for a larger nanoparticle, 1700 kD NP, blended with a smaller linear polymer, 21 kD d-PS.

Figure 2

(a) Intensity versus wave vector for 2% 65 kD d-PS blended with 98% 75 kD PS with SANS data compared to the Debye model with a constant incoherent background. (b) Intensity versus wave vector for 2% 65 kD d-PS blended with 98% 75 kD PS compared to 2% 65 kD d-PS blended with a 10% 25 kD NP—88% 75 kD PS mixture presented in a Guinier plot and associated analyses. (c) Kratky plot of $Q^{2}I$ versus $Q$ for 2% 65 kD d-PS blended with 75 kD PS containing 1%, 5%, and 10% 25 kD NP. The solid lines are $2I(0)/R_g{}^2$ determined with the Debye fits discussed in the text.

Figure 3

Radius of gyration of 65 kD d-PS (a) and 235 kD d-PS (b) for three nanoparticle molecular weights as a function of nanoparticle concentration. The 2% blends in (a) and (b) also contained 75 kD PS and 115 kD PS, respectively. The nanoparticles have radii: 2.0 nm (25 kD); 2.7 nm (52 kD); 3.6 nm (135 kD) if they collapse to the bulk density of polystyrene.