Electrochromic reverse-mode PDLCs as smart windows

The reduction of energy consumption is according to the EU Parliament one of the most important actions to reduce the use of fossil fuels and the emission of carbon dioxide to contrast climate changes. Smart windows, and in particular PDLCs, are an easy way to increase the energy efficiency of buildings and promote energy saving. They have found application as large area surfaces able to change on-demand their transmittance in a continuous manner from an opaque to a transparent state in many fields such as interior design, architecture, and automotive. In this work, we report the preparation and characterisation of a reverse mode PDLC, in which the nematic mixture of a liquid crystal and an ionic liquid allows the on-demand modification of both the transmittance and colour of the device. The transparent and uncoloured OFF state, which is the suggested state from a safety and energy saving point of view, can be modulated into an opaque and/or coloured state by the application of an AC and/or DC electric field. A smart PDLC film was fabricated and its electro-optical and electrochromic properties were investigated. Four different and tuneable states were obtained: (a) a transparent and colour-less state (both AC and DC electric field off), (b) an opaque and colour-less state (AC electric field on and DC electric field off), (c) a transparent and coloured state (AC electric field off and DC electric field on), and (d) an opaque and coloured state (both AC and DC electric field on).