Innovative Tuneable Optical Devices Based on Smart Electroactive Elastomers

PhD ThesisElectroactive polymers that deform in response to electrical stimulation have been a significant area of interest under development over the last decade. Recently, so-called dielectric elastomer actuators (DEAs), which consist of a dielectric elastomer membrane sandwiched between two compliant electrodes, have been shown as a promising technology for the development of new adaptive optical devices. This thesis presents research into tuneable optical transparency devices using DEA technology, which are capable of reversibly controlling light transmittance by electrically changing the surface topography using transparent electrodes. The deformable poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) conducting polymer is selected as the optimal transparent conductor amongst a diversity of electronic materials, owing to its high transparency, environmental stability and surface wrinkling reversibility. In this work, the concept to make the surface transparency electrically tuneable to both higher and lower values within the same device is presented. This concept is applicable to any soft insulating membrane, by coating both of its surfaces with a circular transparent stretchable conductor, surrounded by a stretchable annular conductor. The two conductors are used as independently addressable electrodes to generate a dielectric elastomer-based actuation of the membrane, so as to electrically control its surface topography. The optical transmittance can thus be modulated within a broad range between 25% and 83%. Furthermore, another concept to achieve the electrically-induced directional control of light diffusion on soft elastomer membranes is demonstrated. The uniaxial pre-strain of elastomer membranes contributes to the alignment of surface wrinkles upon 4 electrical activation to directionally scatter light. This concept provides a dual function that can not only electrically spread light in a desired direction but also tune the optical transmittance within an even broader range between 4% and 75%. Those tuneable optical devices using dielectric elastomer actuation have shown thin structures, low specific weight and acoustically silent operation. They could be potentially useful in electrically operated smart windows, controllable light diffusers and directional beam spreaders with light shaping