Fluctuating Brownian stresslets and the intrinsic viscosity of colloidal suspensions.

The interplay between Brownian colloidal particles and their suspending fluid is well understood since Einstein's seminal work of 1905: the fluid consists of atoms whose thermal motion gives rise to the Brownian motion of the colloids, while the colloids increase the viscosity of the suspension under shear. An alternative route to the viscosity, by exploring the thermal stress fluctuations in a quiescent fluid in the Green-Kubo formalism, however, reveals a marked inconsistency with the viscosity under shear. We show that an additional stress term, accounting for Brownian fluctuating stresslets and coupled to the Brownian forces by a generalized fluctuation-dissipation theorem, is required for the description of the stress and viscosity of a colloidal suspension.

Intrinsic viscosities of non-spherical colloids by Brownian dynamics simulations.

A numerical study is presented on the intrinsic viscosities of sheared dilute suspensions of nonspherical Brownian colloidal particles. The simulations confirm theoretical predictions on the intrinsic viscosities of highly oblate and highly prolate spheroids in the limits of weak and strong Brownian noise (i.e.

Efficient Brownian Dynamics of rigid colloids in linear flow fields based on the grand mobility matrix.

We present an efficient general method to simulate in the Stokesian limit the coupled translational and rotational dynamics of arbitrarily shaped colloids subject to external potential forces and torques, linear flow fields, and Brownian motion. The colloid's surface is represented by a collection of spherical primary particles. The hydrodynamic interactions between these particles, here approximated at the Rotne-Prager-Yamakawa level, are evaluated only once to generate the body's (11 × 11) grand mobility matrix.

Size- and composition-dependent radio frequency magnetic permeability of iron oxide nanocrystals.

We investigate the size- and composition-dependent ac magnetic permeability of superparamagnetic iron oxide nanocrystals for radio frequency (RF) applications. The nanocrystals are obtained through high-temperature decomposition synthesis, and their stoichiometry is determined by Mössbauer spectroscopy. Two sets of oxides are studied: (a) as-synthesized magnetite-rich and (b) aged maghemite nanocrystals.