Microstructure and dynamics of Janus particles in a phase separating medium

Abstract

The evolution of interactions and dynamics of Janus colloidal particles suspended in quasi-binary liquid mixtures undergoing phase separation is presented. The experimental system consisted of silica-nickel Janus particles dispersed in mixtures of 3-methylpyridine, water, and heavy water. Colloidal microstructure and dynamics were probed by ultra-small-angle X-ray scattering and ultra-small-angle X-ray photon correlation spectroscopy, respectively. The observed static and dynamic behaviors are significantly different from those found for Stöber silica colloids in this mixture. The Janus particles manifest a slow aggregation below the coexistence temperature and become strongly attractive upon phase separation of the solvent mixture. In the two-phase region, particles tend to display surfactant-like behavior with silica and nickel surfaces likely preferring water and 3-methylpyridine rich phases, respectively. While the onset of diffusiophoretic motion is evident in the dynamics, it is gradually suppressed by particle clustering at the investigated colloid volume fractions.

Phoretic dynamics of colloids in a phase separating critical liquid mixture

“…All these features can be exploited to modify the interactions and dynamics of colloids [17]. A wider range of tunability is achieved by using Janus colloids having faces with different wetting properties [18][19][20].…”

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…Figure 13 illustrates the observed anomalous dynamics and chain formation by peanut-shaped anisotropic magnetic particles in a magnetic field. Fast multispeckle XPCS has allowed the investigation of phoretic dynamics of colloids [112] and active motions of Janus colloids [113] in phase separating solvent mixtures. The availability of fast 2D detectors such as the Eiger-500k pixel detector has enabled multispeckle XPCS measurements in the sub-millisecond range [114].…”

Characterization of active matter in dense suspensions with heterodyne laser Doppler velocimetry

“…In particular, multiple scattering severely complicates acquisition of reliable information from the collected data in many optical approaches at large densities. Therefore, multi-speckle X-ray photon correlation spectroscopy (XPCS) has been applied which is able to return information on active motion fluctuations and passive diffusion simultaneously [31]. This, however, is instrumentally somewhat more demanding than cross-correlation techniques in conventional homodyne or heterodyne laser light scattering approaches [32,33].…”