Magnetic orientation of soft particles in a jammed solid

Abstract

Densely packed atoms, molecules, or small particles can get trapped in a jammed state thereby avoiding crystallization. The resulting amorphous structures display complex, spatially heterogeneous, trapping potentials in stark contrast to the uniform case of a crystal. Here we study active and passive rotational motion in a jammed colloidal dispersion of particles consisting of an anti-ferromagnetic core and a thermo-sensitive microgel soft shell. We determine the order parameter as a function of volume fraction from optical birefringence measurements. A simple model allows us to discriminate the orientation and relaxation of different subsets of particles according to their elastic trapping state.

Hindered nematic alignment of hematite spindles in poly(N-isopropylacrylamide) hydrogels: a small-angle X-ray scattering and rheology study

“…Despite the fact that the volume fraction of hematite spindles in the gels investigated here is insufficient to induce the formation of nematic order caused by excluded volume, due to the interaction of the spindles' magnetic moments, to a first approximation perpendicular to the spindle axis, a fieldinduced isotropic nematic phase transition can be observed: in a moderate external field, hematite spindles align with their long axes perpendicular to the field direction, as observed by small-angle X-ray scattering (SAXS) and optical birefringence (Mä rkert et al, 2011;Dagallier et al, 2010Dagallier et al, , 2012. In contrast with the studies of Roeder et al (2014, 2015) who used polyacrylamide grafted at the particle surface, in the present work the hematite spindles are not rigidly attached but are confined in the cavities of an inter-crosslinked polymer hydrogel network formed by pNIPAM.…”

High frequency viscoelasticity of soft particle glasses

“…1 f . Note that, in the jamming regime, the local elastic forces that trap the particles hinder their rotation, which accordingly is not considered in the simulations [44].…”

Preparation, properties, and applications of magnetic hematite microparticles

“…109 Again it is noteworthy that for the hematite spindles the influence of magnetic fields on the phase behaviour and particle alignment for different composite systems and at high concentrations has been explored in detail by several groups. [130][131][132][133][134][135][136][137]…”