Optimization of the optical properties of electrostrictive polyurethane for a smart lens
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Smart polymer material, such as electrostrictive polyurethane elastomer (PUE) with compliant electrodes (conductive polyyrrole PPy), is potentially useful as a small–scale, solid–state actuator technology in a changeable focal length lens in smart electroactive lens, (“EAL”). The limitation of the conventional lenses highlights the need to develop a new smart optical lens system that has the ability to change focal length according to the need of the wearer and to overcome the deficiency of using several conventional fixed focus length lenses. The basic principle of optical correction is to change the curvature and thickness of a lens, and so change the focal length. In this way, it would be possible to accommodate near and far distance visual tasks in one lens. Electrostrictive PUE with compliant electrodes has superior electromechanical coupling characteristics with application of an electric field and exhibit superior optical properties such as high index of refraction, transparent in the visible rang (400-700nm) and has adequate absorption of UV radiation (up to 380nm). It will be used as the smart material for an smart electroactive lens (EAL). In this thesis, both the optical and the electroactive properties of PUE film were investigated and developed for the proposed EAL. The governing equations for the dynamic performance of these characteristics were also derivative. In light of this, a new relationship was developed to provide a direct reading of the focal length, applied voltage, thickness and deflection. Attention was focused on the processing conditions which affect the film properties. These properties include optical transparency, electroactive response and Young’s modulus of elasticity. In this research, two techniques of producing PUE films were used, the first consists of moulding the PUE pellets under various pressure and temperature conditions while the second was based on producing films of various thickness by the solvent casting method using tetrahydrofuran (THF) as solvent followed by a 95°C annealing in vacuum for 30 min. Sample films of 50 mm diameter were rigidly attached to circular frames and tested under applied DC field in the range of 4-25 KV. The pellethane polyurethane elastomer (PellPUE polyether based polyurethane) film prepared by the first method has deformation response in the order of 0.8 mm; however, it was translucent. The PellPUE film prepared by the second method resulted in thinner film and reasonable electro-active response in the order of 0.3 mm. The transparency of the latter samples was excellent and closed the gap to produce a smart lens. The main goal of this project is to optimize the optical properties and the electroactive characteristic of smart PUE to suit different environmental conditions. This includes developing the dynamic response characteristics with the total transmitted light of the final composite films of over 83.4% in the visible range. PUE films with PPy electrode have demonstrated potential in developing smart lens materials.