Dispenser printed actively actuated colour-changing smart fabrics

Abstract

The thesis reports the development of all-printed actively actuated colour-changing fabrics for creative and smart fabric applications. The colour changing fabrics consist of thermochromic materials and track heaters dispenser printed on fabrics. Thermochromic materials change colour in response to a change in temperature and the heaters actuate the colour change function by controlling the temperature of the fabric.

Dispenser printing is a direct-write process where a material is additively deposited on digitally defined locations of the substrate. It is a novel process for printing active and functional materials on fabrics. State of the art thermochromic fabrics use heaters based on conductive yarns, printed circuit boards (PCBs), Peltier semiconductors, conductive coatings and commercial heating foils. These heater technologies have one or more of the four major limitations: inflexibility, limited design freedom, poor integration with fabrics and unreliability. The novel all-dispenser printed approach overcomes the limitations of existing methods by offering flexibility, complete design freedom, good integration with fabrics and reliability.

The thermochromic devices are fabricated on 65/35 blend polyester cotton which has a porous and high variation surface. The surface variation of the fabric is numerically characterised and its adverse effect on the electrical properties of printed conductors is experimentally demonstrated. Printing an interface layer on the fabric surface is used as a method of reducing the fabric surface variation. The four evaluated interface inks DuPont 5018, Electra EFV4/4965, Fabinks-IF-UV-1004 and FB-20 reduced the fabric surface variation by more than 95%. This improved the performance of the printed heaters and electrical interconnections on fabrics.

This thesis also presents design, modelling, fabrication and characterisation of track heaters. Track heaters are modelled in COMSOL Multiphysics software as a tool to determine the output of a heater design. It is used to derive design rules for printing track heaters. It is demonstrated that dispenser printed track heaters offer complete control of the shape and size of their heat profile. In addition to silver and carbon conductive inks, four custom conductive inks were formulated for printing heaters. The conductive inks achieved a broad range of printed resistivity from 2.43 x 10-7 Ω.m to 1.11 x 10-03 Ω.m. This allows the resistance of an application specific heater design to be varied to suit the requirements of an application.

Thermochromic ink development, formulation and characterisation using commercially available materials is discussed. A UV curable thermochromic ink which changed from an opaque black state to a colourless state was achieved. It produced black colour concentration of 90-100 % before colour change and a peak transmittance value of 34% after colour change. It was demonstrated that the optimum ink formulation can be altered to produce a range of colour changing effects such as multiple colour changes which increases the options for thermochromic fabric applications. Fabrication and characterisation of dispenser printed thermochromic devices is also detailed in this thesis.

Four demonstrator applications of the thermochromic devices on polyester cotton 65/35 fabric were achieved: a shutter display, a 7-segment display, a matrix display and a proximity controlled interactive thermochromic device. These demonstrators illustrated the freedom of design and versatility offered by the dispenser printed approach. These dispenser printed thermochromic devices can be used in creative applications to produce dynamic art, in smart fabric systems as actuators to communicate data and as non-emissive displays.

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Identifiers

ORCID for Michael Tudor: orcid.org/0000-0003-1179-9455

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