Electrokinetic behavior of two touching inhomogeneous biological cells and colloidal particles: Effects of multipolar interactions

We present a theory to investigate electrokinetic behavior, namely, electrorotation and dielectrophoresis under alternating current (ac) applied fields for a pair of touching inhomogeneous colloidal particles and biological cells. These inhomogeneous particles are treated as graded ones with physically motivated model dielectric and conductivity profiles. The mutual polarization interaction between the particles yields a change in their respective dipole moments, and hence in the ac electrokinetic spectra. The multipolar interactions between polarized particles are accurately captured by the multiple images method. In the point-dipole limit, our theory reproduces the known results. We find that the multipolar interactions as well as the spatial fluctuations inside the particles can affect the ac electrokinetic spectra significantly.

Figure 1

ER spectra for an isolated particle and two touching particles with $R∕2a=2.00,1.10,1.03$, respectively. Parameters: $c=-30{ϵ}_0$,$m=1.0$.

Figure 2

ER spectra for two touching particles. Upper panel for profile constants $m$ at $c=0$ and $c=-30{ϵ}_0$, respectively. Lower panel for various $c$ at $m=0$ and $m=1.0$, respectively. The spectrum is given as the imaginary part of the dipole factor. Parameter: $R∕2a=1.03$.

Figure 3

DEP spectra for two touching particles in the longitudinal field case. Upper panel for profile constants $m$ at $c=0$ and $c=-30{ϵ}_0$, respectively. Lower panel for various $c$ at $m=0$ and $m=1.0$, respectively. The spectrum is given as the real part of the dipole factor. Parameter: $R∕2a=1.03$.

Figure 4

Same as in Fig. 3, but in the transverse field case.

Figure 5

DEP spectra in the longitudinal field case (upper panel) and the transverse (lower panel), for an isolated particle, and two touching particles with separation ratio $R∕2a=2.00,1.10,1.03$, respectively. Parameters: $c=-30{ϵ}_0,m=1.0$.