Microsphere Manipulation Using Ferroelectric Liquid Crystals

We propose a strategy for a micromanipulation method using SSFLC (surface stabilized ferroelectric liquid crystals). By adjusting the frequency of the applied ac electric field, the surface layers that cannot follow an applied ac electric field are constructed in SSFLC. In addition, by applying a sawtooth wave voltage, net flow along the smectic layer is generated. The flow direction is reversed by changing the polarity of the sawtooth wave. Consequently, the particles dispersed in SSFLC can be driven bidirectionally along the smectic layer. The particle velocity depends on the temperature, amplitude, and frequency of the applied voltage.

Figure 1

The principle of a micromanipulation method using SSFLC. The $z$ axis represents the layer normal and the rubbing direction. Bookshelf geometry is assumed.

Figure 2

Results of numerical calculation. (a) Applied sawtooth wave. (b) Time dependence of $c$ director distribution. The arrows represent the $c$ director. For simplification, a strong anchoring was applied to the boundary conditions. (c) Time dependence of flow velocity distribution. In these calculations, the following parameters were used: $\rho ={10}^3\mathrm{kg}/{\mathrm{m}}^3$, $P_s=+10\mu \mathrm{C}/{\mathrm{m}}^2$, $d=12\mu \mathrm{m}$.

Figure 3

Microphotographs of the particle motion. (a) The initial dispersion with no applied voltage. (b) The $-x$ directional motion. (c) The $+x$ directional motion. The microspheres were contingently adsorbed on the substrates. Therefore, the drift velocities were measured by selecting the arbitrary spheres not adsorbed on the substrates. However, these adsorptions were sometimes negated by the flow; (b) is a photograph for the flow applied for a time longer than (c).

Figure 4

Frequency dependence of the particle velocity.

Figure 5

Temperature dependence of the particle velocity. $T_C$ represents the Curie temperature for the $\mathrm{Sm}{C}^{*}\mathrm{\text{−}}\mathrm{Sm}A$ phase transition.

Figure 6

Amplitude dependence of the particle velocity.