Chromic Textiles: from molecular design to textile design

School of Textiles & Design, Heriot-Watt University Scotland UK

Prof. R M Christie

Dyes

•  For traditional applications •  Require a uniform, reproducible,

stable colour •  A change in colour, eg., due to

exposure to light, heat, was a defect •  There are niche applications for colour

change materials, especially if •  controllable •  reversible

Chromic materials

•  Dyes and pigments that react to environmental conditions and stimuli, by changing colour.

Colourless Dye

ColouredDye

Coloured Dye

apply 'stimulus'

remove 'stimulus'

or

Chromic materials

•  Photochromism light •  Thermochromism heat •  Ionochromism ions (eg., pH) •  Electrochromism electrical •  Solvatochromism solvents •  Piezochromism, Tribochromism mechanical •  Gasochromism,Vapochromism gases •  Chronochromism, time •  Biochromism biological sources

Chromism Stimulus

Challenges of chromic materials for textiles

•  limited in scope and availability •  relatively expensive. •  not developed specifically for textiles •  cannot necessarily be used in the same way as traditional

dyes and pigments •  limited access to technical expertise, information and

support. •  limited stability in certain environments •  associated with novelty / gimmicks

Our approach to chromic textiles

•  Developing a methodology for objective

assessment of the colour change properties •  Optimisation of application methodology for

textiles •  Computer-aided molecular design and

synthesis of chromic materials specifically for textile applications

Photochromism

•  Develop colour in UV light (e.g., sunlight) •  Revert to colourless when the light source is

removed •  Spectacles which become sunglasses

A Bdark

UV light

Applications of Photochromic Dyes

Application and evaluation of commercially available

photochromics on textiles

Commercial photochromic dyes screen-printed at 0.05% concentration – exposed to UV.

Photochromic printed textiles - washfastness and lightfastness

Effect of HALS Additives on Lightfastness

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12 14 16

Exposure Time / hrsΔ

E/Δ

Eo

No Additive1% HALS

Effect of Repeated Washings on Colorability

0

5

10

15

20

25

BeforeWashing

1st Wash 2nd Wash 3rd Wash 4th Wash

Number of washes

ΔE

bet

wee

n B

ackg

rou

nd

an

d D

evel

op

ed

Co

lou

r

Cotton

Polyester

Molecular design and synthesis of photochromics for textiles

•  Provides solubility in water •  Provides affinity for the fibres •  Dyes fabric (wool, silk, nylon) as an acid dye to give a colourless

fabric which acquires a blue colour on irradiation •  Useful for digital (inkjet) printing

NaO3S

Photochromic dye

•  EC Framework 6 Integrated Project •  Digital Fast Patterned Microdisposal of

Fluids for Multifunctional Protective Textiles

•  (Inkjet printing of functionality) •  Around 30 partners

Inkjet printed photochromic cotton

Before exposure After UV exposure

0

0.2

0.4

0.6

0.8

400 450 500 550 600 650 700Wavelength (nm)

K/S

Cotton

Cotton after UV irradiation

Cotton (Urea preteated )

Cotton (Urea pretreated) after UVirradiation

Coloured to coloured photochromics, by design

•  Computer-aided molecular modelling allows

•  Prediction of photochromism •  Prediction of original colour •  Prediction of colour after irradiation

PhotochromeChromophore

Modelled structures of compound 1 and its ring-opened forms 2a-2d

1 2a 2b

2c 2d

00.10.20.30.4

0.50.60.70.8

300 400 500 600 700NM

A

Withoutirradiation 5minirradiaton 10minutes

20minutes 30minutes 40minutes

55minutes 65minutes 80minutes

120minutes 140minutes

Photochromic textiles UV exposure

Thermochromism •  Colour change activated

by temperature change

Thermochromic Liquid Crystals

pitchlength

temperature

pitch length

Spectrum of colours produced by interference Requires a black background

Assessment of liquid crystal thermochromics printed on textiles

5

10

15

20

400 450 500 550 600 650 700Wavelength, nm

% R

efle

ctan

ce

27oC

27.4oC28oC29oC

31oC35oC41oC

-20

-15

-10

-5

0

5

10

15

-20 -15 -10 -5 0 5 10 15a*

-b*

28oC30oC

35oC

40oC

b*

-a*

25

30

35

40

45

50

55

10 15 20 25 30 35 40 45 50Temperature, oC

Ligh

tnes

s, L

*TCP1004

TCP1005

TCP1001

TCP1006

Variable temperature colour measurement

Heat- sink technology applied directly to thermochromic fabric.

Acknowledgements

•  David Bryant •  Reduwan Shah •  Ayesha Rasheed •  Anna Little •  Mohanad Aldib •  Wassim Ibrahim

•  Sara Robertson •  Sarah Taylor •  John Fletcher •  Luca Rossini •  Marie Ledendal