GB2448676A - Electrochromic colour effects from polymer membranes having conductive coatings - Google Patents

Abstract

A polymeric membrane, such as a polyester film, is coated with a conductive metal film such as gold or silver. It is immersed in an aprotic solvent, such as dimethylformamide (DMF), and preferably also an organic electrolyte such as tetra-n-butylammonium. The immersed, metal coated polymeric membrane then undergoes an electrochromic colour change when electrically polarised. For example, gold and silver coated polymeric membranes undergo a colourless to vivid red colouration when the polarising potential is cycled between 0 and -4V. The colour change may be reversed upon reversal of the polarisation potential. The colour change, or reversal of such a colour change, may be effected by the application of a state state or a cyclic potential waveform.

Description

Electrochromjc Colour Effects

TECHNICAL FIELD

This invention relates to a newly discovered electronic or electrochemically induced colour change at a modified electrode surface. We have shown that suitable polymer modified electrodes may -when immersed within certain non-aqueous aprotic solvents, be induced to alter their absorbance properties in the UV / visible region of the electromagnetic spectrum, thereby giving rise to a colour change as perceived by the human eye.

This electrochsomic colour change may find application for signage, labelling, and information based technologies, or alternatively for enhancing the atheistic appearance of products for leisure and other applications.

A number of technologies are used for signage applications ranging from Light Emitting Diode (LED) approaches through to Plasma Technologies and Liquid Crystal Display (LCD) approaches; to date electrochromic approaches have failed to find commercial application due to a number of technical problems even though electrochromic approaches offer advantages in terms of lowered power consumption and ease of viewing angle when used within displays. This technology addresses some of the technical drawbacks associated with other electrochromic technologies.

TECHNiCAL FEATURES: In the present embodiment a thin (eg 5Onm thickness) polymer sheet or membrane of, for example, polyester, may be sputtered coated with a metal such as gold or silver to render one surface electrically as depicted within Fig 1.

Fig 1: Thm-pojymer Electrical

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Au or other metal coated to render surface electrically Microporous membrane to act as mechanical Gold and Silver coated microporous polyester membranes may be induced to undergo a vivid change in colour when the working electrode potential is cathodically polarised (either potentiostatically or via cyclic voltammetric approaches) beyond a certain threshold potential (eg -2.5V vs Ag reference) in an aprotic solvent such as dimethylfornamjde (DMF). This solvent may contain an organic electrolyte such as 0. IM tetra-n-butylammonjum perchiorate to facilitate electrical conduction across the electrolyte solution.

Electrochromjc effects of the type described here might lend themselves for exploitation within electronic displays and/or devices.

Gold and silver coated membranes of the type described within this embodiment undergo a colourless to vivid red colouration as received by the human eye when the polansing potential is cycled between 0 and -4V (vs a counter silver electrode).

The original membrane colour may be restored (known as electrochromjc bleaching') when the potential is reversed.

Claims (3)

1. That a polymer film (e.g. of polyester), membrane or other polymeric body when coated with a conductive film of layer (e.g. of gold or silver) -and when immersed within an aprotic solvent (such as dimethylformamide -DMF) and in the presence of a salt (such as tetra-n-butylammonjum perchlorate) may undergo an electrochromic colour change upon electrical (or electrochemical) polarisation.

2. That the electroclijomic colour change according to claim I, may be reversed upon either reversal of the polarisation -or relaxation or open circuit.

3. That the electrochromic colour effect according to claim I may be induced or reversed by a number of different electrochemjcal polarisation protocols -including for example polarisation by a steady state protocol, a ramped or cyclic waveform, pulsed potential waveform - or any other potential polansation procedure as * * *** appropriate. **e* I. * * * S * S.

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