Two-dimensional crystallization of microspheres by a coplanar AC electric field.

Langmuir : the ACS journal of surfaces and colloids · 2004 · Unclear · Insufficient evidence

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UnclearInsufficient evidencePaper 3661

Study snapshot

PublicationLangmuir : the ACS journal of surfaces and colloids · 2004

Study typeengineering

Reported directionUnclear

Evidence ratingInsufficient

Abstract

The particle-field and particle-particle interactions induced by alternating electric fields can be conveniently used for on-chip assembly of colloidal crystals. Two coplanar electrodes with a millimeter-sized gap between them are used here to assemble two-dimensional crystals from suspensions of either latex or silica microspheres. When an AC voltage is applied, the particles accumulate and crystallize on the surface between the electrodes. Light diffraction and microscopic observations demonstrate that the hexagonal crystal is always oriented with one axis along the direction of the field. The particles disassemble when the field is turned off, and the process can be repeated many times. The diffraction patterns from all consecutively formed crystals are identical. This assembly is driven by forces that depend on the electric field gradient, and a model is proposed involving a combination of dielectrophoresis and induced dipole chaining. The organization of large two-dimensional crystals allows characterization of the electrostatic interactions in the particle ensembles. The process can be controlled via the field strength, the frequency, and the viscosity of the liquid media. It could be used to make rudimentary optical switches or to separate mixtures of particles of different sizes.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeengineering

Effect directionunclear

PopulationNot supplied

Sample sizeNot supplied

ExposureNot supplied

Evidence strengthInsufficientConfidence: 74% · Peer reviewed: yes

Main findings

Applying an AC voltage across two coplanar electrodes caused latex or silica microspheres to accumulate and form two-dimensional hexagonal crystals on the surface between the electrodes. Diffraction and microscopy indicated the hexagonal crystal was oriented with one axis along the field direction, and crystals disassembled when the field was turned off; consecutively formed crystals produced identical diffraction patterns. The authors propose the assembly is driven by electric-field-gradient-dependent forces involving dielectrophoresis and induced dipole chaining, and note control via field strength, frequency, and liquid viscosity.

Outcomes measured

Two-dimensional crystallization/assembly of latex or silica microspheres between electrodes
Crystal orientation relative to applied field
Reversibility/repeatability of assembly upon field on/off
Light diffraction and microscopic characterization of formed crystals

Limitations

No numerical exposure parameters (field strength, frequency) provided in the abstract
No quantitative performance metrics or statistical analysis described in the abstract
Sample size/number of experiments not reported in the abstract

View raw extracted JSON

{
  "study_type": "engineering",
  "exposure": {
    "band": null,
    "source": "coplanar AC electric field (two coplanar electrodes with millimeter-sized gap)",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "Two-dimensional crystallization/assembly of latex or silica microspheres between electrodes",
    "Crystal orientation relative to applied field",
    "Reversibility/repeatability of assembly upon field on/off",
    "Light diffraction and microscopic characterization of formed crystals"
  ],
  "main_findings": "Applying an AC voltage across two coplanar electrodes caused latex or silica microspheres to accumulate and form two-dimensional hexagonal crystals on the surface between the electrodes. Diffraction and microscopy indicated the hexagonal crystal was oriented with one axis along the field direction, and crystals disassembled when the field was turned off; consecutively formed crystals produced identical diffraction patterns. The authors propose the assembly is driven by electric-field-gradient-dependent forces involving dielectrophoresis and induced dipole chaining, and note control via field strength, frequency, and liquid viscosity.",
  "effect_direction": "unclear",
  "limitations": [
    "No numerical exposure parameters (field strength, frequency) provided in the abstract",
    "No quantitative performance metrics or statistical analysis described in the abstract",
    "Sample size/number of experiments not reported in the abstract"
  ],
  "evidence_strength": "insufficient",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "alternating electric field",
    "AC voltage",
    "coplanar electrodes",
    "dielectrophoresis",
    "induced dipole chaining",
    "colloidal crystals",
    "microspheres",
    "latex",
    "silica",
    "two-dimensional crystallization",
    "on-chip assembly",
    "light diffraction"
  ],
  "suggested_hubs": []
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1021/la035812y
PubMed: 15835659

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