Electrochromic Gels for Smart Windows (ChromGels)

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It has been shown that large office buildings waste 20-40% of their energy on air-conditioning to cool down the building as a result of the sun. This is highly inefficient and has an impact on the environment. One way that has been proposed to tackle this problem is the use of Smart Windows. These windows are comprised of chromic materials that change to a dark colour upon the application an external stimulus. The change in colour results in high energy UV light that heats up the building being filtered out, thus reducing the need for air-conditioning. It is predicted that these technologies will save 20% on their energy bills, as the buildings will not heat up as much from the sunlight. However, so far this transparent-to-dark colour has been difficult to achieve. Suitable materials for Smart Glass that can change colour can be metal-based, organic-based or a hybrid of the two. Metal-based chromics are already used in displays and diagnostic tests. However, precious metals (Au and Ag) used in these high-end technologies is a rapidly running out resource, and are often difficult and dangerous to mine, and their use relies on countries cooperating well with each other. The processing of metals such as Cd, Lb, U and Cs has huge environmental consequences and the disposal of them leads to toxic and nuclear waste which has devastating effects on the workers, neighbouring villages and wildlife. Any metals that can be replaced with organic alternatives have a huge benefit to health, the economy and the environment. Organic materials are generally easier to process and can be synthesised on a larger scale. We have found a molecule based on a functionalised naphthalene diimide that when self-assembled in water shows great promise to be used in such applications. From proof of principle data we have collected, the assembled material can undergo a reversible transparent to black transition by applying a small voltage to the sample. This transition is quick and can be cycled at least 100 times without loss of colour intensity or response time. However, this system needs optimising to be able to fulfil industry standards, for example stability over 1000 cycles, reducing the speed of response of both transitions and the uniformity of colour across the device. We aim to do this with this proposal to make the organic alternative to metal systems competitive to use in the Smart Window technology.