Biomedical subjects

BJ Yoon

Publications and source records attributed to BJ Yoon.

6 recordsLinked to original sources

PubMed2000

Continuum Field Charging of Dielectric Spheroids.

Classical continuum theory for field charging is applied in an analysis of the ionic charging of spheroidal dielectrics. Assuming that the particle orientation is fixed during the charging process, the saturation charge and charging rate are determined as functions of the orientation and aspect ratio of spheroids. For spheroids of small dielectric constants the saturation charge becomes the largest when the electric field is directed perpendicular to the major axis of the spheroid. For an ensemble of randomly oriented spheroids the average saturation charge can be approximated as the arithmetic average of the saturation charges for the spheroid with the electric field directed along the three principal axes of the spheroid. In addition, the ensemble average of the dimensionless charging rate of randomly oriented spheroids of moderate axial ratio approximates the dimensionless charging rate of a sphere. Copyright 2000 Academic Press.

Journal Article↗

PubMed1999

Electrophoretic Motion of a Prolate Spheroid in Electro-osmotic Flow Developed in a Flat Cell.

Electrophoretic motion is analyzed for a neutrally buoyant, non-Brownian prolate spheroid suspended in an electro-osmotic flow developed in a flat microelectrophoresis cell. Neglecting the double-layer deformation, the trajectory and orientation of the spheroid is computed to assess the significance of particle motion in a lateral direction during an electrophoresis experiment. The double-layer thickness of the spheroid is arbitrary. In a closed microelectrophoresis system the electro-osmosis results in a parabolic flow field. During a short period of time (several seconds) the spheroid may deviate significantly in a lateral direction from a straight path parallel to the applied electric field. During a longer period of time (several minutes) the spheroid undergoes a sinuous motion in which it translates periodically back and forth across a straight path along the main flow direction. The spheroid may also translate along a closed trajectory. In all cases the orientation of the spheroid follows the equation for Jeffery orbit. Copyright 1999 Academic Press.

Journal Article↗

PubMed1998

Electrical Double-Layer Interactions of Regular Arrays of Spheres.

Electrostatic interactions are computed for three-dimensional regular arrays of spheres. Tetrahedral array of four spheres, octahedral array of six spheres, cubic array of eight spheres, and periodic arrays of spheres in body-centered cubic (BCC) and face-centered cubic (FCC) structures are considered. Based on the linearized Poisson-Boltzmann equation the electrostatic free energy is computed for both constant surface potential and constant surface charge conditions. Facilitating the complex geometry of the problem, the boundary element method is used. Test results for two-sphere interactions are in excellent agreement with existing exact solutions even at very small Debye length. The results for multisphere interactions are compared with those obtained by the pairwise additivity approximation. For BCC and FCC arrays comparison is made to the results from the pairwise additivity approximation and from the spherical cell model. At small Debye length the pairwise additivity approximation predicts the interactions reasonably well. At large Debye length, however, the cell model furnishes much better estimates. In addition, the electrostatic free energy difference between BCC and FCC structures at given particle concentration is found to be too small to assess any physical significance. Copyright 1998 Academic Press.

Journal Article↗

PubMed1997

Integral Eqution Approach for Solving the Nonlinear Poisson-Boltzmann Equation

A simple iterative method is devised for solving the nonlinear Poisson-Boltzmann equation. The method is based on the integral representation of the Poisson-Boltzmann equation and can be readily implemented for determining the potential and charge density around particles of various shapes. As an illustrative example the method is applied for computing the potential and surface charge density of the spherical double layer. Copyright 1997Academic Press

Journal Article↗

PubMed1997

Gravitational Settling in the Electrophoresis of Spheroids with Small Potentials in Quiescent Fluid

Electrophoretic motion is analyzed for non-neutrally buoyant, spheroidal particles settling in an unbounded fluid otherwise at rest. The double-layer thickness is arbitrary, and the surface potential of the spheroid is assumed to be small so that the deformation of the double-layer is neglected. Examples are presented for spheroids when the applied electric field is perpendicular to the gravity. The electrophoretic motions are determined for spheroids of arbitrary aspect ratios at arbitrary orientations. Depending on their orientations the gravitational drift can contribute up to 10% of the observed particle velocity in the direction of the electric field. The gravitational contribution is maximum when the angle between the axisymmetric axis of spheroids and the gravity is pi/4. However, for Brownian spheroids with a uniform orientation distribution the sedimentation effects are averaged out, thus there is no net gravitational drift in the direction of the applied electric field.

Journal Article↗

PubMed1997

Field Charging of Spherical Particles in Linear Electric Field

A simple expression is derived for the field charging rate of a spherical particle in a linear electric field. The analysis is based on the classical theory of unipolar field charging in the continuum regime. The rate expression is correct up to O(beta2), where beta is the dimensionless parameter which measures the variation of the applied electric field over the sphere.

Journal Article↗