Proposal of mechanics of liquid crystals and development of liquid crystalline microactuators

Abstract

We propose a research field "mechanics of liquid crystals," in which liquid crystals are studied from a mechanical viewpoint. The unsteady behaviors of a liquid crystal between parallel plates under an electric field are investigated. The imposition of the electric field on the liquid crystal induces flows, whose profile and magnitude strongly depend on the twist angle of the director at the plates. A visualization experiment confirms the generation of flows. The mechanism of such generation can be explained by considering that the rotation of molecules generated by the imposition of the electric field induces a local velocity gradient. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2840673͔Since the discovery of the applicability of liquid crystals to display devices in the 1960s, many studies on liquid crystals have been carried out both fundamentally and practically. As a result, liquid crystal displays have established a strong position as a substitute for cathode ray tube displays. The manufacturing of such displays has grown into a large industry with a global scale and further development is expected. However, the technical development has reached a plateau except for a few trivial improvements.A research field, such as "mechanics of liquid crystals," should exist and various studies concerning liquid crystals should be performed from a mechanical viewpoint, because in mechanical engineering, solid mechanics and fluid mechanics are established in the fields of solid, and gas and liquid, respectively. However, there is no such research field, while there are some studies where a liquid crystal is regarded as a fluid. [1][2][3][4] Figure 1 shows the conceptual applications of liquid crystals; that is, we input some factors, such as electromagnetic field, flow, heat, and light, into liquid crystals and output different factors by utilizing the easy change in orientation state, which is the most representative feature of liquid crystals. An example of such applications is a liquid crystal display in which an electric field is input and a change in transmitted light is output. We can regard a liquid crystal as a medium of converting energy by combining input and output factors appropriately. The applications of liquid crystals are assumed to increase by changing the combination of input and output factors or by proposing other factors.Although it is well known that the imposition of a velocity gradient makes liquid crystalline molecules rotate and reorient to a different direction, its reverse phenomenon, such that the rotation of the molecules ͑by imposing, for example, an electric field͒ induces a velocity gradient, is not clearly understood. Since this phenomenon corresponds to the energy conversion from electrical to kinetic energies, to utilize such induced flow leads to development of microactuators. Some studies 5,6 were made for the generation of a flow, which was called "back flow;" however, in these studies, the mechanical applications of the back flow were not considered, although its effect ...

Molecular dynamics simulation of backflow generation in nematic liquid crystals

“…The profiles of the horizontal component of velocity u * confirm the transient "S-shaped" velocity profiles obtained in the calculation using continuum mechanics as reported in Ref. 1. Along with the change in molecular orientation, the magnitude of the velocity increases until a maximum value is 3.…”

“…[3][4][5] In more recent studies, the potential application of backflow for controlling the motion of an object has been addressed. 1,2 The backflow has been studied mainly in terms of the Ericksen-Leslie macroscopic continuum theory. [6][7][8] There are also different methods to study the effect of backflow such as the method used in Ref.…”

“…Recently, the potential development of a liquid-crystal-based microactuator or manipulator has been proposed. 1,2 The basic idea is to employ the flow induced by an electric field to control the motion of an object. The induced flow is known as backflow.…”

GPU-accelerated molecular dynamics simulation for study of liquid crystalline flows

“…The plot of bulk velocity at t * = 130 shows an S-shaped velocity profile. This confirms the generation of a bulk flow due to molecular reorientation, as demonstrated by a 2D molecular dynamics simulation [19] and simulation using macroscopic continuum approach [17] and observed in a visualization experiment [20].…”

“…The flow field changes the molecular orientation, and conversely, the change in molecular orientation generates a flow field known as backflow [15]. Recently, there has been an increasing interest in backflow owing to its potential applications to microactuators [16,17] and micromanipulators [18]. For the development of microactuators and micromanipulators, the understanding of the molecular-level mechanism of backflow is essential.…”