(402d) Nanoscale Viscosity Measurements Using Magnetic Nanoparticles

Magnetic nanoparticles with diameters of up to 20 nm typically consist of single crystalline domains with an embedded magnetic moment. So-called thermally blocked magnetic nanoparticles behave as colloidal nanoscale permanent magnets which respond to imposed magnetic fields by aligning their magnetic moment through rigid body rotation of the particle. Such response is retarded by the viscous drag of the surrounding medium, thus it is possible that nano-scale rheological information may be obtained through the response of magnetic nanoparticles to magnetic fields. We will illustrate this possibility through a combination of the underlying theory and experimental demonstrations of: (1) comparisons of gelation temperatures obtained through nano- and macro-scale viscosity measurements; (2) quantitative comparisons of the temperature dependent nano- and macro-scale viscosity of mineral oils; and (3) quantitative comparisons between the nano- and macro-scale viscosity for linear poly(ethylene glycol) as a function of molecular weight.