Fig. 6.

Electrostatic forces between the gold (Au) nanoparticles and the sample results in inaccurate rheology (light blue). Adding a poly(ethylene glycol) brush to the Au nanoparticles (Au PEGylated) can partially minimize electrostatic interactions, resulting in accurate measurements at intermediate frequencies (bold purple) and inaccurate measurements at high frequencies (light purple). Use of polystyrene nanoparticles with a poly(ethylene glycol) brush (PS PEGylated) results in accurate rheology over the full frequency range (bold pink). When particle size is significantly larger than the sample mesh size, particles of different sizes give similar rheological results.