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Clusters in sedimentation equilibrium for an experimental hard-sphere-plus-dipolar Brownian colloidal system.

Newman HD, Yethiraj A - Sci Rep (2015)

Bottom Line: Care is taken to ensure that both the dimensionless gravitational energy, which is equivalent to a Peclet number Peg, and dipolar strength Λ are of order unity.In the presence of an external electric field, anisotropic chain-chain clusters form; this cluster formation manifests itself with the appearance of a plateau in the diffusion coefficient when the dimensionless dipolar strength Λ ~ 1.The structure and dynamics of this chain-chain cluster state is examined for a monodisperse system for two particle sizes.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Physical Oceanography, Memorial University, St. John's, NL, A1B 3X7, Canada.

ABSTRACT
In this work, we use structure and dynamics in sedimentation equilibrium, in the presence of gravity, to examine, via confocal microscopy, a Brownian colloidal system in the presence of an external electric field. The zero field equation of state (EOS) is hard sphere without any re-scaling of particle size, and the hydrodynamic corrections to the long-time self-diffusion coefficient are quantitatively consistent with the expected value for hard spheres. Care is taken to ensure that both the dimensionless gravitational energy, which is equivalent to a Peclet number Peg, and dipolar strength Λ are of order unity. In the presence of an external electric field, anisotropic chain-chain clusters form; this cluster formation manifests itself with the appearance of a plateau in the diffusion coefficient when the dimensionless dipolar strength Λ ~ 1. The structure and dynamics of this chain-chain cluster state is examined for a monodisperse system for two particle sizes.

No MeSH data available.


Effect of an electric field in the presence of gravity.Left panel: 0.8 μm diameter PMMA colloids in 70:30 decalin/TCE. Snapshots (–) at four selected fields are shown (gravity to the left, and  increasing to the right). Above a critical field, E > 1000 V/mm, there are well-formed chains. The left hand corner of each image is the substrate, and  increases to the right. Middle panel: 1.0 μm diameter PMMA colloids in 60:40 decalin/TCE. Snapshots (–) at 4 selected fields (with comparable dipolar strengths Λ). Right panel: The binary mixture has the thickest columns of chains.
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f1: Effect of an electric field in the presence of gravity.Left panel: 0.8 μm diameter PMMA colloids in 70:30 decalin/TCE. Snapshots (–) at four selected fields are shown (gravity to the left, and increasing to the right). Above a critical field, E > 1000 V/mm, there are well-formed chains. The left hand corner of each image is the substrate, and increases to the right. Middle panel: 1.0 μm diameter PMMA colloids in 60:40 decalin/TCE. Snapshots (–) at 4 selected fields (with comparable dipolar strengths Λ). Right panel: The binary mixture has the thickest columns of chains.

Mentions: Experiments were carried out for two monodisperse colloidal systems with 0.8 and 1 μm-diameter spheres, as well as a bidisperse system, at several values of a uniaxial AC electric field (see Methods). Snapshots of colloidal sediments at zero field and some selected field strengths are shown in Fig. 1. The alternating electric field is along z, i.e. parallel and anti-parallel to the direction of gravity (which points to the left). Figure 1 (left panel) shows 4 x-z particle profiles for the 0.8 μm diameter PMMA colloids in 70:30 decalin/TCE. As the field increases from zero to 1667 V/mm, the sediment goes from fluid-like to fully-formed chains. The middle panel in Fig. 1 shows comparable profiles for 1.0 μm diameter PMMA colloids in 60:40 decalin/TCE. The field strengths chosen are ones for comparable values of the dipolar strength


Clusters in sedimentation equilibrium for an experimental hard-sphere-plus-dipolar Brownian colloidal system.

Newman HD, Yethiraj A - Sci Rep (2015)

Effect of an electric field in the presence of gravity.Left panel: 0.8 μm diameter PMMA colloids in 70:30 decalin/TCE. Snapshots (–) at four selected fields are shown (gravity to the left, and  increasing to the right). Above a critical field, E > 1000 V/mm, there are well-formed chains. The left hand corner of each image is the substrate, and  increases to the right. Middle panel: 1.0 μm diameter PMMA colloids in 60:40 decalin/TCE. Snapshots (–) at 4 selected fields (with comparable dipolar strengths Λ). Right panel: The binary mixture has the thickest columns of chains.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4555105&req=5

f1: Effect of an electric field in the presence of gravity.Left panel: 0.8 μm diameter PMMA colloids in 70:30 decalin/TCE. Snapshots (–) at four selected fields are shown (gravity to the left, and increasing to the right). Above a critical field, E > 1000 V/mm, there are well-formed chains. The left hand corner of each image is the substrate, and increases to the right. Middle panel: 1.0 μm diameter PMMA colloids in 60:40 decalin/TCE. Snapshots (–) at 4 selected fields (with comparable dipolar strengths Λ). Right panel: The binary mixture has the thickest columns of chains.
Mentions: Experiments were carried out for two monodisperse colloidal systems with 0.8 and 1 μm-diameter spheres, as well as a bidisperse system, at several values of a uniaxial AC electric field (see Methods). Snapshots of colloidal sediments at zero field and some selected field strengths are shown in Fig. 1. The alternating electric field is along z, i.e. parallel and anti-parallel to the direction of gravity (which points to the left). Figure 1 (left panel) shows 4 x-z particle profiles for the 0.8 μm diameter PMMA colloids in 70:30 decalin/TCE. As the field increases from zero to 1667 V/mm, the sediment goes from fluid-like to fully-formed chains. The middle panel in Fig. 1 shows comparable profiles for 1.0 μm diameter PMMA colloids in 60:40 decalin/TCE. The field strengths chosen are ones for comparable values of the dipolar strength

Bottom Line: Care is taken to ensure that both the dimensionless gravitational energy, which is equivalent to a Peclet number Peg, and dipolar strength Λ are of order unity.In the presence of an external electric field, anisotropic chain-chain clusters form; this cluster formation manifests itself with the appearance of a plateau in the diffusion coefficient when the dimensionless dipolar strength Λ ~ 1.The structure and dynamics of this chain-chain cluster state is examined for a monodisperse system for two particle sizes.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Physical Oceanography, Memorial University, St. John's, NL, A1B 3X7, Canada.

ABSTRACT
In this work, we use structure and dynamics in sedimentation equilibrium, in the presence of gravity, to examine, via confocal microscopy, a Brownian colloidal system in the presence of an external electric field. The zero field equation of state (EOS) is hard sphere without any re-scaling of particle size, and the hydrodynamic corrections to the long-time self-diffusion coefficient are quantitatively consistent with the expected value for hard spheres. Care is taken to ensure that both the dimensionless gravitational energy, which is equivalent to a Peclet number Peg, and dipolar strength Λ are of order unity. In the presence of an external electric field, anisotropic chain-chain clusters form; this cluster formation manifests itself with the appearance of a plateau in the diffusion coefficient when the dimensionless dipolar strength Λ ~ 1. The structure and dynamics of this chain-chain cluster state is examined for a monodisperse system for two particle sizes.

No MeSH data available.