Photocontrolled Manipulation of a Microscale Object: A Rotational or Translational Mechanism

Abstract

In this paper the photocontrolled manipulation of solid materials on the surface of a liquid crystalline thin film is described. Three different types of films namely cholesteric liquid crystal (ChLC), compensated nematic liquid crystal (NLC) and nematic LC were used. The rotational and translational manipulation of the microscale solid object was induced by irradiation of light and mode of manipulation (either translational or rotational) was changed by changing the isomer of the azobenzene compound used to make the film. Rotational motion of the object was observed on the ChLC and compensated NLC films containing chirally pure azobenzene compound. The direction of rotational motion was controlled either by changing the optical isomer of the chiral azobenzene or by changing the irradiating light (from ultraviolet to visible). When racemic mixture of the chiral azobenzene compound was used, a translational motion of the object was observed. Even though the direction of the translational motion can be controlled by controlling irradiation position, more facile and precise manipulation of the objects was possible by spatially controlled irradiation of Ar(+) laser and diode UV laser.

Light-induced Phase Transition of Lyotropic Liquid Crystals and Motion Behavior of Micron Objects via Photochemical Azobenzene Molecules

“…However, as shown in Fig.4 (b), when the Az-doped samples were irradiated with Ar+ laser, the samples lost their birefringence, so the phase transition from N to I state was induced. Similar experiment conducted in our previous work [6,7,12] explained the mechanism of phase transition by Ar+ laser irradiation in terms of order-disrupting molecules Az through conformational changes. That means the phase transition can be induced in an Az-doped-LLC system in which Ar+ laser exposure directly decreased the order of the mixture through trans-cis-trans cycle photoisomerization of Az moiety.…”

“…Similarly, the gradient in surface tension can also be used to control the motion of glass rods in Az-doped polyethylene glycol films, as found by Su Ma et al [10]. However, Lohn, et al described the micron objects can be assembled by thermos-induced phase transition [2], whose driving force is also accorded with our previous work [6][7]12].…”

“…Owing to the photo-isomerization behavior, much effort has been focused on the Az compounds to control phase transition of LCs as well as alignment of LCs for applications on optical displays and assembly technology, which have been studied by various external stimuli, such as gravitational field, external electric, magnetic fields, thermo, and light [1][2][3][4][5][6][7][8].…”

Photoresponsive Cholesteric Liquid Crystals

“…The glass rod rotated in the same direction as the cholesteric texture during the photoisomerization or thermal transition steps. A detailed study was also reported with the investigation of CLC-induced azobenzene dopants and fluorene-based overcrowded alkene dopants [65,68,140]. The authors pointed out that the rotational reorganization resulted from the conversion of the chiral molecular motor dopant to an isomer with a different HTP, leading to a change in the cholesteric pitch.…”

Optical and Physical Applications of Photocontrollable Materials: Azobenzene-Containing and Liquid Crystalline Polymers

“…More recently, research concerning the photocontrolled manipulation of microscale solid objects on the surface of a film of liquid crystal doped with a chiral azobenzene compound has been reported by Kurihara and coworkers [32,33]. Translational motion of a microscale object was observed in the racemic system (nematic liquid crystal doped with a racemic azobenzene compound or compensated nematic liquid crystal with cholesteric liquid crystal and chiral azobenzene compound) (Figure 2(b)).…”