Local pulses of electrical potential can induce long-range transient excitations in self-aligned molecular films

Abstract

Natural liquids can contain self-aligned molecules (such as liquid crystals and biological membranes) which give them unique properties of anisotropic diffusion, coupling between the molecular orientation and flow, etc. Here, we describe the observation of new phenomena in those materials: long-distance transport and molecular orientation waves that are induced by pulses of spatially localized electrical potential. As a result, the morphological properties of the material are significantly altered well beyond the reach of the electrical field. The local dielectric torque-induced reduction of the effective molecular volume and corresponding pressure gradients are in the origin of these phenomena. Our observations are made for electric fields that are an order of magnitude smaller than those present in biological membranes. Thus, this discovery may have important impact on the understanding of the operation of these membranes and on the dynamics of action potential propagation in neural cells. The corresponding possible influence of observed excitation mechanisms on the ionic gates and the role of myelin sheath are discussed.

Electrically Induced Hydrodynamic Effect in Nematics Caused by Volume Reduction

“…This reorientation, in turn, can cause hydrodynamic flow; so-called backflow effects can be observed. As already explained by the authors in [17], this effect can support the observed material transport only at the early stage of the process since the characteristic relaxation time of the process is much shorter than the relaxation time of the director.…”

“…A pressure gradient, which in this case is caused by the local dielectric torque-induced reduction of the effective molecular volume, will result in a flow of the NLC. The authors in [17] observed the LC reorientation near the boundaries between two parts of the LC cell. This reorientation, in turn, can cause hydrodynamic flow; so-called backflow effects can be observed.…”

“…As mentioned, here we discuss nematic LC, in which the molecules are oriented predominantly in one direction, the unit vector of which is called the director n. A cell is considered, such as that described in [17], which contains a homeotropically aligned nematic liquid crystal (Figure 1). The normal to the cell's walls is along the z-axis, while the x-axis is located in the cell plane.…”

“…Different mechanisms of hydrodynamical flow in nematic liquid crystal (NLC) (Rayleigh-Bernard mechanism [14], thermocapillary (Marangoni) mechanism [15], backflow effect [16], and direct volume expansion mechanism [9]) have been extensively studied both theoretically and experimentally. In this work, the electric field-induced hydrodynamical motions are of particular interest, considering their promising applications in microfluidics, MEMS, and so on [17][18][19][20]. Here we will theoretically investigate the dynamics of the field-induced hydrodynamic flow caused by the effective volume reduction mechanism [17] in homeotropically aligned nematics.…”

“…In this work, the electric field-induced hydrodynamical motions are of particular interest, considering their promising applications in microfluidics, MEMS, and so on [17][18][19][20]. Here we will theoretically investigate the dynamics of the field-induced hydrodynamic flow caused by the effective volume reduction mechanism [17] in homeotropically aligned nematics. The mechanism involves the following: the applied electric field reduces the effective molecular volume in the applied zone, generating pressure gradients that result in a Poiseuille flow [21].…”