Electrically Switchable Liquid Crystal Polymer Rod Actuators
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Electrically Switchable Liquid Crystal Polymer Rod Actuators Matthew Shafran, Konstantinos Sierros, Wade Huebsch, and Darran Cairns Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV, 26506 ABSTRACT Stimulus responsive liquid crystal nanorods, 60 μm in length and 200 nm in diameter, were fabricated by a template synthesis technique. The liquid crystal, RM 257, is a reactive monomer which polymerizes with the application of UV light. After polymerization the liquid crystal’s orientational order is permanently “frozen”. Therefore, the subsequent structures are temperature independent after curing. In this study the liquid crystal was confined in the pores of Anopore membranes before curing, which results in rod structures after photo-polymerization. After fabrication, the rods were observed under the application of both AC and DC electric fields. DC fields were noted by either up and down or translational movement of the rods. Application of AC fields resulted in random movement of the rods. INTRODUCTION Control of molecular order of structures is a powerful technique which gives the ability to tailor properties for specific applications such as electro-optical devices and electro-rheological fluids. One way to achieve this is through the use of reactive mesogens. Reactive mesogens also known as liquid crystal monomers, have polymerizable end groups [1]. Upon polymerization, the end groups form densely cross-linked structures where the molecular order is permanently “frozen” [1, 2]. Therefore reactive mesogens can be useful in externally activated systems. For example, Mol et al. have produced thermally responsive films with the aid of reactive mesogens [3]. The film response was controlled by temperature and director profile: twisted or splayed. Temperature controlled the amount of deflection while the director configuration controlled the type of bending. The twisted configuration demonstrated both bending and saddle shape deflection when heated and a splayed director exhibited curling when heated. Cairns et al. were able to fabricate a multitude of structures including spheres, rods, and tubes from reactive mesogens [4]. The spheres were produced by suspending the reactive mesogen in glycerol. The rods and tubes were formed with the use of Anopore membranes as templates and varying the concentration of reactive mesogen and chloroform and also through the use of surface treatments of the template. Cairns et al. were also able to fabricate and demonstrate responsive liquid crystal polymer spheres [5]. The solid polymer spheres where observed using polarized microscopy and showed rotation upon application of an electric field. The purpose of this work is to fabricate responsive, to externally applied electric fields, liquid crystal polymer rods and characterize and control their resulting movement in a fluidic environment. This research will be important for microfluidic and electro-rheological applications. In this study, polymer rods are fabricated by confining liquid crysta
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