how to get changing patterns on a textile surface by using

How to get changing patterns on a textile surface by using thermo chromic

pigments and an inherently conductive polymer

Laleh Maleki

Degree of master in science (one year) in Textile Technology

Borås Textile School

Sweden 2010

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How to get changing patterns on a textile surface by using thermo chromic pigments and an inherently conductive polymer

Laleh Maleki [email protected]

Examiner: PostDoc: Nils-‐Krister Persson

Supervisor: Maria Åkerfeldt

Högskolan I Borås

Swedish school of Textiles

Textilhögskolan 501 90 Borås

Phone: +46 33 435 40 00

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Acknowledgments:

First of all, I would like to thank my supervisors , Nils-‐krister Persson, Mari Åkerfeldt and Weronika Rehnby for providing me with the opportunity of working on this project.

I would also like to appreciate Catrin Tammjärv and Tariq Bashir for their kind support and assistance during all the experimental works.

And at the end, I express my special thanks to my mother for her unsparing support in every single step of my life.

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Abstract:

With regard to the recent interests in smart textiles, this research activity has been conducted with the aim of producing a pattern changing design on textiles. In order to fulfill the demands of such dynamic patterns a combination of conductive polymer and thermochromic pigments were used. The textile substrate was coated by conductive polymer dispersion (PEDOT: PSS ) and it was followed with printing thermochromic pigments on the surface of coating. The driving force of such thermochromic reaction has to be provided by the heat generated from conductive layer due to the current of electricity passing through the conductive layer.

These experiments were continued by changing the coating recipe in order to achieve the highest possible electrical resistance, which leads to the best initiation of thermochromic reactions.

Key words:

Thermochromic pigment, PEDOT:PSS, color changing effect

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1. Table of Contents 2. Introduction: ...................................................................................................................... 6 3. Background: ....................................................................................................................... 6 4. Aim:........................................................................................................................................ 7 5. Problem formulation:...................................................................................................... 8 6. Literature overview:........................................................................................................ 9

5-1. Thermochromism: ........................................................................................................................ 9 5-1-1. Thermochromic pigments: ....................................................................................................10

5-1-1-a. Liquid crystal type: ......................................................................................................................... 11 5-1-1-b. Leuco dyes: ....................................................................................................................................... 12

5-1-2. Light fastness the main weakness of thermochromic pigments: ..................................14 5-1-3. Application of Thermochromic dyes: .................................................................................15 5-2. Conductive polymers: ................................................................................................................16 5-2-1. General description: ...............................................................................................................16 5-2-2. Mechanism of electro-conductivity: ....................................................................................17 5-2-3. Poly(3,4-ethylenedioxythiophene): ......................................................................................18

5-2-3-a. In-situ Polymerization of PEDOT: ............................................................................................ 20 5-2-3-b. PEDOT:PSS-complex :................................................................................................................. 20

7. Methodology and experiments: .................................................................................24 8. Conclusion:........................................................................................................................31 9. Reference:..........................................................................................................................32

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2. Introduction:

During the last decade production of textiles with the ability of interaction with

surrounding environment has been under growing investigations. “Smart textiles” is a

relatively new section of modern textile and fashion industry, which includes many

different stimuli sensitive products. This field has opened up possibilities of design and

manufacturing various end products adapted to divers range of industries and applications.

In the recent years integration of electronics in textiles has been of a great interest among

smart textile researchers. This invention is observed as a bridge between textile

engineering and electronic engineering and has been functionalized in various applications

such as military, medical, leisure, sports, fashion, high-tech garments adapted to severe

environmental conditions and finally many industrial textiles. However, not all the

prototypes of electronic textiles and garments are user friendly. In many cases integration

of stiff and heavy conductors results in an awkward product. Therefore, in many

researches application of some alternatives with more adjustable properties has been

followed. Intrinsically Conductive Polymers (ICPs) is the best alternative for such

electronic components employed in textiles. Such polymers improve the flexibility and

ease of application in the end product yet they have some drawbacks. Instability over time

and affecting the substrate’s initial color are some of their common problems.

Combination of electronic textiles and pigments specifically thermochromic pigments can

result in products capable to compete with ordinary displays. Further applications of such

products are overload warning systems, toys, teaching materials, advertisement, magnetic

devices and so forth [3]. Therefore, thermochromism is another tool in order to improve

interaction, response and stimuli sensitivity of the ultimate smart textile.

3. Background:

This research project is one part of an ongoing research activity on different

conductive polymers employed in textile industry in order to design novel smart

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textiles. The overall scientific activity involves many master and PhD students at

Boras Textile and Engineering schools to study the possibility of functionalizing

intrinsically conductive polymers in everyday life. The study has been carried out on

different aspects of conductive polymers use such as; conductive coatings for smart

textiles, the possibility of spinning the conductive polymers and investigating the

achieved properties of conductive textiles by altering the influential parameters.

Interestingly enough, a number of industrial companies, which are active in the

production and development of functional smart textiles, express their interest in the

current research projects.

A combination of industrial sponsorship and scientific ambition is the driving force

behind merging the exceptional characteristics of thermochromic pigments with the

pure novelty of conductive polymers. Textile engineering and electronic science overlap

in the application of conductive polymers to design wearable electronics, textile displays

and other stimuli sensitive electronic textiles. The combination of thermochromic effect

and conductive coating in order to achieve the desired functionality of textile gadgets and

designing innovative ways of manufacturing such textiles in industrial production are the

concepts of conducting this project.

4. Aim:

The aim of this project is to achieve a printing pattern, which can change its expression as

a result of reacting to the external heat, and the pattern must be created by using

thermochromic pigments and an inherently conductive polymer(PEDOT). Targeting the

following details will continue the project:

-‐ Studying the possibility of mixing PEDOT and thermochromic pigment in one

paste

-‐ The possibility of using PEDOT as a component in the color recipe

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5. Problem formulation: -‐ Dispersing the pigments in printing paste: Practically the pigment must be

completely dispersed in the printing paste but, not always we achieve a

homogeneous paste and in some parts the color is darker and lighter in other parts.

-‐ Bluish substrate for printing: Clevious PH 1000 is originally dark blue and

depending on the coating formulation it changes the color of substrate to light blue

or in extreme conditions to dark blue. Unfortunately, this color is not vibrant

enough to be used as a component in printing recipe. Therefore, it would be very

difficult to obtain light colored patterns on such substrate.

-‐ Heterogeneous coating paste: The mixture of Clevious PH1000 and the employed

printing paste is not homogeneous. Accordingly, it has to be used immediately if

not, it would be separated.

-‐ Thermochromic pigments normally present very poor light fastness: This problem

will be discussed in more details in the “literature overview” section.

-‐ The possibility of connecting the final sample to current of electricity with the

most proper way: The most important part of this project is to apply the current of

electricity on samples, in this way the possibility of thermochromic effect will be

studied. In order to apply electricity on fabrics different methods have been used.

Electrode clips and concentric ring probe are the two most common methods of

measuring resistivity of conductive textiles. But the compatibility of these methods

to the samples must be studied.

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6. Literature overview:

5-1. Thermochromism: The ongoing development in science and technology introduces new products with

exceptional properties and abilities. During the recent years many researches have

expressed a considerable interest in stimuli sensitive materials and the design and

production of various environment-sensitive products. In the world of dyes and pigments,

dynamic pigments have fulfilled the need of a dynamic colored pattern and also brought

about many new design concepts in all the industries involved with the color world. In

Textile industry, chromic (dynamic) pigments have been used widely in fashion design

industry to create special and novel color changing designs. Nowadays, there is an

increasing attention towards the application of dynamic pigments in more applicable

textile products and paving the ways for producing functional textiles based on chromic

prints. Among all the different types of chromic pigments, thermochromic and

photochromic pigments are the predominant types of dynamic pigments that are used in

textile industry. Obviously, thermochromic pigments are of a great interest for this project.

Thermochromism is the ability of a material to change its color as a response to an

external heat. In other words, thermochromism can be given more accurately as the

following definition: “ Thermochromism is defined operationally as an easy noticeable

reversible color change in the temperature range limited by the boiling point of each

liquid, the boiling point of a solvent in the case of a solution or the melting point for

solids.” [1] The change in the color happens at a specific temperature, which is called “the

thermochromic transition temperature”. Since 1970 the mechanism of thermochromism

has been studied. According to the investigations thermochromism occurs base on

different mechanisms in which either of the following materials are used:

-‐ Organic compounds

-‐ Inorganic compounds

-‐ Polymers

-‐ Sole gels

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Thermochromism in organic compounds happens due to different mechanisms. Three

main mechanisms of thermochromism in organic compounds have been proven as below:

-‐ Variation in crystal structure (equilibrium between crystal structures)

-‐ Stereoisomers

-‐ Molecular rearrangement (equilibrium between two different species of the

material; acid-base, keto-enol, etc)

Inorganic thermochromic compounds:

Consisting of many metals and inorganic compounds with thermochromic

behavior in solid or solution phase, inorganic thermochromic compounds do not

fulfill the demands of textile industry. These materials normally exhibit their

thermochromic effect in solution and in vary high temperatures; therefore, they

are not suitable for textile applications.

5-1-1. Thermochromic pigments:

Thermochromic pigments have reached widespread use through different industries

including textile industry, military applications and plastic industry. In order to be

functional, thermochromic pigments are produced in microencapsulated form. However,

they are still problematic in some ways. In some cases low thermal stability and easy

extraction from the products, which results in toxicity have been reported.

Thermochromic dyes are typically produced in two types:

-‐ Liquid crystal type

-‐ Leuco type

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5-1-1-a. Liquid crystal type:

Liquid crystal thermochromic inks show a spectrum of color changes because they

selectively reflect specific wavelengths of light from their structure. This continuous color

change occurs due to the change in molecular arrangement of the liquid crystal in contact

with temperature. These thermochromic substances may consist of cholesteric liquid

crystals or mixtures of cholesteric and nematic1 liquid crystals.[3] Cholesteric liquid

crystals normally have a helical structure accordingly they are chiral. Molecules in each

layer of the helix do not have special order but the director in each layer twists with

respect to the above or below layer.1

The distance in which the director rotates 360°and returns to the initial direction is called

Pitch of the helix (Exhibited in the following picture).

Pitch is the most important characteristic of a cholesteric liquid crystal because it results in

selective reflection of the light with wavelengths equal to the pitch length. The sensitivity

of the pitch length to temperature results in chromic behavior

of cholesteric liquid crystal. In the proper temperature they

form a cholesteric liquid crystal; an intermediate phase

between the crystalline phase and the liquid phase. Change in

the temperature effectively results in thermal expansion of the

liquid crystal structure. Consequently, the visual color change

effect varies with the temperature owing to the changes in

layer spacing and pitches of the liquid crystal. The main

advantage of this group of dyes is their ability to exhibit a

finely colored image. [2] Whilst, according to many literatures their low color density and

being expensive are the major drawbacks of this product.

1Nematic liquid crystals exhibit no positional order while molecules tend to point the same direction

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5-1-1-b. Leuco dyes:

Leuco dyes; also known as molecular re-arrangement dyes, basically, show a single color

change due to a molecular re-arrangement in their chemical structure. Their color change

effect can be visualized as a reversible shift between two colors or a transition from

colored state to a colorless state. Keto-enol tautomerism or ring opening are the two

predominant mechanisms of molecular rearrangement. In general, tautomerism refers to

the interconversion of two organic isomers in an equilibrium state. Normally, this reaction

occurs based on the migration and relocation of hydrogen atoms (protons). One of the

most common types of tautomeric reaction is the conversion of ketone structure and to its

enol form.

The following picture illustrates equilibrium of ketone-enol tautomers:

Figure 1: Mechanism of keto-enol tautomerism / wikipedia pictures [25]

As it has been mentioned before, some practical thermochromic pigments are made upon

keto-enol rearrangement; In this case, change in the temperature induces the tautomerism

rearrangement, which leads to an increase in the conjugation and production of a new

chromophore[3] In general, Leuco dyes are functionally made of a combination of

chemicals.

In most cases the Leuco dye includes an electron donating color former, an electron

accepting color developer and a color change controlling agent [3] in other words, a Leuco

dye is made from an organic dye, an acidic activator and a non polar co-solvent medium.

The solvent is a solid with low melting point like ester or alcohol. At low temperatures

(lower than the melting point of the solvent) the color former and the developer are in

contact and the distinct color is visible. Upon heating (above the melting point of the

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solvent) separation of the color former and color developer avoids any electron interaction

and results in the colorless state. The general principle of thermochromism is

demonstrated in figure 2.

Figure 2: Principle of thermochromism

Some of the Leuco dyes are formed based on a combination of two dyes and a temperature

sensitive salt existing in an appropriate solvent. In principle, one dye is electron accepting

and the other one is electron donating. At high temperatures the salt dissociates and avoids

interaction between two dyes and the opposite effect happens at low temperatures. [4]

As it is mentioned before, some Leuco dyes exhibit a shift between two different colors

upon an ambient temperature. In such cases the dye is manufactured by combining a leuco

dye with a permanently colored dye. For instance, imagine that combining a red leuco dye

and a permanent yellow dye makes a thermochromic orange dye. At room temperature the

printed pattern is orange but by raising temperature the pattern switches to yellow.

Figurec3: Very Slowly Animating

Textiles: Shimmering Flower[5]

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5-1-2. Light fastness the main weakness of thermochromic pigments:

According to many researches thermochromic pigments present very poor light fastness.

The following table shows fastness properties of special type of thermochromic pigments,

according to the supplier.

Table2: Zenit AB pigments fastness properties

Perspiration Variotherm AQ

Conc. colors

Light

Acid Alkali

Chlorinated

water

Washing

40°

Gold orange 4 3 3-4 3-4 3-4

Fast Blue 1 2 2 2-3 3-4

Fast Black 2 3 3-4 3-4 3-4

Magneta 2-1 3 3-4 N/A 3-4

Brilliant Green 2-1 3 3-4 N/A 3-4

Pigments printed on cotton 300 gpk

Basically, the color former plays the main role in the resistance of thermochromic

pigment to fading. Therefore, different ways of stabilizing the color former have been

investigated. It has been proven that some UV absorbers like hydroxyarylbenzotriazoles

strongly influence the light fading of thermochromic pigment. Their capability of

behaving like an amphoteric counter-ion is the reason why they improve the light fastness.

zinc and nickel 5-(2-benzotriazolyl)-2, 4-dihydroxybenzoates, zinc and nickel 3-(2-

benzotriazolyl)-2-hydroxy-1-naphthoates, zinc and nickel 2, 4-dihydroxybenzophenone-3-

carboxylates and their derivatives are reportedly other types of stabilizers to improve light

fastness in Leuco dyes. [3]

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5-1-3. Application of Thermochromic dyes:

Thermochromic dyes have been widely used in textile applications, Specifically, they have

brought novelty into fashion industry. However, this is not the only field in which

thermochromic pigments are being used. Variety of non-textile applications and product

manufacturers are also consumers of thermochromic pigments. Thermometers,

temperature indicators and body monitoring devices can be counted among the non-textile

applications. During the recent years, smart textile section has opened new ways to

functionalize thermochromism. Specially designed T-shirts capable of showing wearer’s

body temperature is an example of such innovations. Very slowly shimmering flower [5]

is a textile base non-emissive display made from conductive and insulating yarns woven

together with Jacquard loom. Custom electronic components have been used to control

sending power to different areas of the textile. Ultimately, the fabric is printed with

thermochromic inks. Current of electricity through the conductive yarns provide the heat

required to initiate dynamic visual effect.

Figure4: Very slowly shimmering flower

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5-2. Conductive polymers:

During the recent years the possibility of integrating electronics in textiles has been under

ongoing investigations with respect to the developing area of smart textiles. Electronic and

textile industries overlap in the field of smart textiles and they have developed many new

common applications such as: military, medical, leisure, sport and technical/industrial

applications. [7] The aim is to create a smart wearable with the highest user-friendly

standard. Textiles might be equipped with electric-conductivity by different means; by

means of using conductive fibres like metal fibres or by coating the textile with metallic

salts, either of the mentioned methods have some drawbacks. In the prior, brittle and

heavy metallic fibres reduce the processability of fabrics and the latter loses the

conductivity after repeated laundering. The invention of intrinsically conductive polymers

ICPs is a turning point in creating conductive textiles. These conjugated plastics can be

coated on textile substrates with ordinary coating methods. In the following parts

conductive polymers and their applications will be discussed in more details.

5-2-1. General description:

The history of conductive polymers is back to 1970s when MacDiarmid, Heeger and

Shirakawa discovered that the conductivity of polyacetylene films could be changed over

several orders of magnitude by chemical doping. They were awarded Nobel Prize of

chemistry in 2000. [8] In the beginnings only laboratory scale investigations and

applications of conductive polymers were possible and it was due to the limitations of

conductive polymers like their poor stability and processability. In the last 10 years

continuous researches on alternative polymer backbones and copolymerization of present

conductive polymers yielded in more practical ICPs; of which polypyrroles, polyanilines,

and polythiophenes are the most commercialized examples. The conductivity of

polypyrroles and poly thiophenes is normally stable at room temperature and above for

many years.[9]

17

5-2-2. Mechanism of electro-conductivity:

The demand for smaller, more powerful, more flexible and capable of being fabricated

conductive materials in electronic devices gave rise to the functionalization of organic

conductors. Conductive polymers combine the electric properties of semiconductors with

the flexibility and ease of application in polymers. They also can provide similar electrical

properties with lower product cost.

The basic principle of electron transfer in conductive polymers is a system of conjugated

double bonds. In figure 4 the chemical structure of three different ICPs is illustrated:

Figure 5: chemical structure of some ICPs[8]

By noticing the chemical structures it can be easily observed that the molecule is made of

series of double bonds alternating with single bonds along the structure. Each double bond

consists of a π-bond and a σ-bond. But π-bonds are weak bonds and they can be easily

delocalized along the polymer chain. The delocalization of π bonds is the origin of

conduction electrons in conductive polymers.

Doping:

Adding electron donating or electron accepting dopants can vary the electric nature of the

original polymer. Through the doping process, electric conductivity of conductive

polymers can be changed from insulating state to conductive state owing to the fact that

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18

increasing the degree of doping increases the electric conductivity. The dopant molecules

are positioned between polymer chains and they donate or accept electron to or from the

polymer backbone. In this case the dopant molecules are attracted to the polymer by

Coulomb forces and they are not covalently bonded. Therefore, doping mechanism in

conjugated polymers is far away from the mechanism of doping in inorganic conductors.

[8]

It has been reported that the conductivity of conjugated systems can be i2ncreased by 10

orders of magnitude after doping [8], which makes them a resemble of metallic conductors

in behavior. Eventhough, they can be easily distinguished because of the change in their

conductivity as a result of low temperature. This phenomenon can be defined by spatially

localization of doping-induced conduction electrons at low temperatures. In such

condition only hoping transport is possible. This fact clarifies that the main reason of

conductivity in conjugated polymers is relative to the degree of structural and energetic

disorder. [8]

5-2-3. Poly(3,4-ethylenedioxythiophene):

Among all the members of conductive polymers Polythiophene has attracted a lot of

research interest in recent years. This polymer is an important member of conductive

polymers nowadays due to some of its exceptional properties including; solubility,

processability, and environmental stability, besides possessing excellent electrical

conductivity, electroluminescent property, and non-linear optical activity. [9] Poly(3,4-

ethylenedioxythiophene) abbreviated to PEDOT/PEDT has been widely used in technical

and commercial applications due to its outstanding properties. It plays a significant role in

antistatic and conductive coatings, electronic components and displays. [10] This polymer

presents very narrow bandgap2 resulting in extremely stable and very conductive cationic-

doped state. [10] This polymer can be employed in the form of in-situ PEDOT, which is

19

made by polymerization of EDT monomers or in the form of its derivatives. The chemical

structure of PEDOT is demonstrated in figure 6.

Figure 6: Chemical structure of PEDOT [11]

The mentioned properties are not the only characteristics of PEDOT. One of its

remarkable properties is observed when its conductivity changes upon changing the

environmental condition. Accordingly, Polythiophenes potentially are used as sensors like

humidity sensors or PH sensors.[10] Some of its specific properties are described below:

• Reversible doping:

PEDOT can be reversibly doped and undoped. Change in doping state of PEDOT

contributes to change in its color. PEDOT is normally light blue and transparent in

oxidized state while it is dark blue in neutral state. This visible change makes it a

suitable material for some optical properties.

• Exceptional stability:

Researches put its remarkable stability down to the electron-donating effect of the

oxygen atoms and its effective ring geometry. [12]

• High conductivity:

PEDOT presents very high degree of conductivity, which is attributed to its low

band-gap. It is believed that the effect of electron donor ethylene dioxy groups on

the energies of the frontier levels of the π systems [12] forms the low band-gap.

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20

5-2-3-a. In-situ Polymerization of PEDOT:

In-situ polymerization of PEDOT is of a great industrial importance. The properties of in-

situ polymerized PEDOT are affected by a variety of elements. Such factors during the

polymerization process alter the morphology, doping level, conductivity, crystallinity,

molecular weight and processability of the achieved polymer. The general mechanism of

polymerization for PEDOT is an oxidative polymerization but through a complicated

process. The polymerization process can be simplified in two steps:

1. Oxidative polymerisation of the monomer to the neutral polythiophene

2. Oxidative doping of the neutral polymer to the conductive polycation [10,13]

5-2-3-b. PEDOT:PSS-complex :

PEDOT in its original and neutral state is quite instable and insoluble in most

commonly used solvents. Therefore, in order to improve its processability and

coatability a derivative of the polymer is suggested. This derivative is produced by

oxidative polymerization of EDOT monomers in the presence of a template polymer.

The template is polystyrene sulfonic acid (PSS or PSSA) that is commercially available in

the form of water-soluble polymer and acts as an excellent dispersant for aqueous

PEDOT. Polymerization by using sodium peroxodisulfate as oxidant results in

PEDOT:PSS complex in its cationic and conductive form.[10] Chemical structure of

PEDOT and PSS is demonstrated in figure 7.

21

Figure 7: chemical structure of PEDOT:PSS in polymer film[8]

PSS with its higher molecular weight has two fundamental functions; the first is its charge

balancing counter ion nature, and the second is that it assists PEDOT segments to be

dispersed in water. Thus, PEDOT:PSS complex is not exactly water soluble, but it is a

stable aqueous dispersion, processable and deep blue. [13]

It is noteworthy that, according to different measurements PEDOT chains formed during

the oxidative polymerization are rather short, never exceeding 18 (6-18) repeating units,

which resembles a collection of oligomers.[13,8] Furthermore, considering Inganäs et al

demonstration PEDOT:PSS complex presents extremely high stability because PEDOT+

and PSS- ions could not be split by using standard capillary electrophoresis methods.

Various properties of PEDOT:PSS complex tailoring it to different applications relies on

its PSS-content and particle size. For instance, lower PSS-content results in higher

conductivity and enables antistatic and conductive applications. In contrast, for passive

matrix displays larger PSS-content and smaller particle size is favorable.[10] The

following table demonstrates the effect of PSS-content and particle size on the properties

of PEDOT:PSS complex:

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22

Table 2: Typical PEDOT:PSS grades and their properties.

PEDOT:PSS ratio

Solid content(%)

Electrical

conductivity

app(S/cm)

Typical application

1 : 2.5 plus 5% bw

DMSO 1.3 Up to 500 Conductive coating

1 : 2.5 1.3 10 Conductive coating

1 : 2.5 1.3 1 Antistatics

1 : 6 1.5 10-3 OLEDs

1 : 20 3 10-5 Pashive matrix displays

Some information regarding PEDOT:PSS coating:

In-situ polymerization of PEDOT on a substrate is completely different from dispersion

coating. In the former case the kinetic of polymerization by adding different components

is controllable. Clearly, properties of the achieved polymer depend on the polymerization

condition. In-situ polymerized PEDOT is suitable for applications with very high

conductivity demand. By this method electric conductivity of 500-700S/cm is

achievable.[10]

The situation is quite different when using PEDOT:PSS dispersions. In this case the

properties of the coating varies depending on the coating formulation. The addition of

binders, surfactants, wetting agents and even the thickness of the coating alter the resulting

conductivity. As an example, increasing the thickness of the coated film contributes to an

increase in conductivity, at the same time decreasing the transparency of the film.

Commercially available PEDOT:PSS dispersion H.C.Starck:

According to the increased consumption of PEDOT:PSS in numerous applications the

aqueous dispersion of PEDOT:PSS is commercially available under the trade name of

CLEVIOSTM. The supplier offers a variety of products appropriate for different

applications based on the particle size, solid content, additives and doping level of the

dispersion. These products are tailor-made for different applications from antistatic

23

coatings to conductive coatings and wide-ranging substrates through different

conventional coating methods. Furthermore, the product is accompanied with coating

formulation guide.

24

7. Methodology and experiments:

The experiments have been performed in many stages. And followed with a new set of

experiments presenting some variations.

Coating and printing of the samples:

Coating of the samples:

A group of samples was coated by using two different recipes of coating paste :

The coating method is manual knife coating.

The samples were dried at 100ºC for 4 minutes in the laboratory scale stenter.

(Intermediate drying)

Printing of the samples:

The printing paste ingredients:

Variotherm AQ Grön 5%

Or

Variotherm AQ Blå 5%

Or

Variotherm AQ Svart 5%

And

Paste 95%

After preparing the printing pastes the coated samples were hand-printed and cured at

150°C for 4 minutes.

Mixed paste:

Substituting the two stages of coating and printing with a simpler procedure and using a

Material Recipe 1 Recipe 2

Clevios PH 1000 20% 30%

Printing paste 80% 70%

25

mixed paste was the aim of the second series of experiments.

The mixed paste followed the below recipe:

Ingredients Mixed recipe

Clevios PH1000 20%

Variotherm AQ Grön/ Blå/ Svart 5%

Printing paste 75%

After hand-printing and drying achieved sample had observable pale shade. Therefore, in

order to reach similar shade with the previous samples, the amount of pigments in the

recipe was increased.

Variotherm AQ Grön/ Blå/ Svart 10%

The same curing condition used.

In order to help the electrical conductivity of the samples, the pattern of the printing

schablon was carefully chosen. Because, it is essential to have a continuous pattern and

facilitate the current of electricity. The following pictures show two examples of the

patterns which used during printing experiments:

An almost continuous pattern A not continuous pattern

Electrical experiments:

By using the ordinary electrical resistance measuring equipment in Boras engineering

school, different electrical voltages had been applied on the textile. The samples were

26

attached to the source of electricity with especial clip electrodes. The magnitude of

electrical resistance clearly demonstrated that current of electricity is passing through

the layer of coated polymer. But far away from our expectation, no visual color change

observed.

Although, no color change effect was observed, there were still some hopes of achieving

the goal by changing some simple parameters in the future studies:

First of all, the normal surface resistivity of Clevios PH 1000 must be calculated using

the following equations:

According to the supplier, Clevios PH 1000 has minimum conductivity of 900 S/cm

Figure 8: H.C.Starck technical information

Concerning this equation: conductivity σ=1/ρ [S/cm] the resistivity of polymer for its

minimum conductivity can be calculated:

900 [S/cm] = 1/ρ ⇒ ρ= 1.1*10-3

Thus the range of sheet resistance depending on film thickness can be calculated.

Assuming validity of this procedure and observing no color change initialized by heat

formation in coated polymer, it can be deducted that the amount of heat generated as a

result of electrical resistance is less than the required heat. Therefore, the experiments

pursued by:

27

1) Increasing the amount of Clevios PH 1000 in order to obtain more resistance and

more heat.

2) Replacing patterned schablons with open schablons to ensure electrical coverage

of the surface.

Printing with open schablon

Based on the above program, three different set of coating and printing samples were

prepared:

Clevios PH 1000 Variotherm AQ Grön/ Blå/ Svart

30% 10%

40% 10%

50% 10%

The resistance in films was measured afterward, using the same device. Following graphs

demonstrate resistance variation through the time for the above samples:

28

Graph1: Resistance

versus time for 30%

Clevios PH film

measured at Voltage:

150 v

Graph2: Resistance

versus time for 40%

Clevios PH measured

at voltage: 500 v

29

Graph3: Resistance

versus time for 50%

Clevios PH measured

at voltage: 10 v

As it is obvious from the results, increasing the amount of Clevios PH results in an

increase in conductivity accompanying by a decrease in resistance. Therefore, no color

change effect could be obtained. In order to have the color change effect the amount of

generated heat must be equal to 25-27° C (according to thermochromic pigments supplier)

in order to initiate thermochromism.

The below graphs illustrate Resistance versus time diagram for the same film but

measured in different voltages:

Graph4: Resistance

versus time for 50%

Clevios PH measured

at voltage: 10 v

30

Graph4: Resistance

versus time for 50%

Clevios PH measured

at voltage: 150 v

It can be concluded from the diagrams that an increasing in the voltage of measurement

resulted in an increase in the resistance. Eventhough, this phenomenon has been observed

by studying the graphs it cannot be regarded to the effect of voltage on the resistance. Due

to the fact that, conductors and semi-conductors might behave very differently in response

to electricity.

31

8. Conclusion:

Based upon the literature studies and practical works, it can be concluded that:

-‐ First of all, using PEDOT:PSS as a conductive film on textiles results in bluish

substrate which is not approval for all the final applications. Meanwhile, this color

is not vibrant and strong enough to be used as a component in the color recipe.

-‐ The properties of coating vary depending on different parameters and additives

influencing the ultimate paste.

-‐ The more concentration of PEDOT:PSS the more conductivity of textile and the

less resistance. Clearly, lower electrical resistance generates less heat and it cannot

start the color change effect.

-‐ It is possible to mix the printing and coating pastes, however, the mixed paste

does not belong the same properties. Mainly, the mixed paste made of the same

recipe as separated pastes has paler color. Consequently, the amount of pigment in

mixed recipe must be increased.

-‐ It is possible to connect such samples with electrical voltage by means of two

methods: attaching clips electrodes and using concentric ring probe.

Some notes regarding possible future researches:

In fact, this project can be continued to achieve the desired goal, which is initializing

color change effect based on PEDOT:PSS and thermochromic pigments combination.

Thus, it should be observed that a decrease in the amount of Clevios PH 1000 and

increasing the time of measurement might be appropriate solutions. Although,

increasing the time of measurement might cause generation of more heat and

consequently color change effect, this is inappropriate for the desired ultimate

function. Due to the fact that such products must be well adapted to the demands of

displays and advertisement markets. Which means that the thermochromic reaction

must be an immediate response to the current of electricity.

32

9. Reference:

[1] John C. Crano, Robert J. Guglielmetti, 2002.Physiochemical studies, biological applications, and thermochromism. New York : Kluwer Academic/Plenum Publishers

[2] H.R. Mattila, 2006. Intelligent textiles and clothing Boca Raton : CRC Press ; Cambridge : Woodhead Pub.

[3] S. Periyasamy, Gaurav Khanna. Thermochromic colors in textiles, www.fibre2fashion.com. Online available at: <http://www.fibre2fashion.com/industry-article/9/804/thermochromic-colors-in-textiles9.asp> accessed: May 2010

[4] S. Lam Po Tang, G. K. Stylios. 2005. An overview of smart technologies for clothing design and engineering. International Journal of Clothing Science and Technology, Vol. 18 No. 2, 2006 pp. 108-128

[5] Joanna Berzowska, 2005. Electronic Textiles: Wearable Computers, Reactive Fashion, and Soft Computation Textile, Volume 3, Issue 1, pp. 58–75

[6] Joanna Berzowska 2004 Very Slowly Animating Textiles: Shimmering Flower, accessed through google [February 2010] [7] M. Skrifvars, W. Rehnby, M. Gustafsson Coating of Textile Fabrics with Conductive Polymers for Smart Textile Applications, University college of Borås school of engineering and school of textile

[8] A. M. Nardes, 2007. On the conductivity of PEDOT:PSS thin films ,Technische Universiteit Eindhoven,

[9] Walid A. Daoud, John H. Xin, Yau S. Szeto, 2004. Polyethylenedioxythiophene coatings for humidity, temperature and strain sensing polyamide fibers. Sensors and Actuators B 109 (2005) 329–333. Available online at www.Sciencedirect.com

[10] Dr. Jill Simpson*, Dr. Stephan Kirchmeyer§, Dr. Knud Reuter 2005, Advances and applications of inherently conductive polymer technologies based on Poly(3,4-ethylenedioxythiophene). H.C.Starck

[11] L. Bert Groenendaal, F, Jonas, D. Freitag, H.Pielartzik, J.R. Reynolds Poly(3,4-ethylenedioxythiophene) and its derivatives: Past, Present and Future. Advanced Materials: 2000, 12, No. 7

[12] Y Wang, 2009. Research progress on a novel conductive polymer —poly(3,4- ethylenedioxythiophene) (PEDOT), College of Materials Science and Engineering, Shandong University of Science and Technology, China, IOP Publishing Ltd 2009 [13] Stephan Kirchmeyer, Knud Reuter, 2004. Scientific importance, properties and growing applications of poly(3,4-ethylenedioxythiophene), Journal of Materials Chemistry: 2005, 15, pg 2077-2088

33

[14] Han Kyun Kim, Mi Sun Kim, So Yeon Chun, Yun Heum Park, Characteristics of electrically conducting polymer-coated textiles, Mol. Cryst. Liq. Cryst., Vol 405, pp. 161-169, 2003, Korea

[15] CLEVIOS P formulation guide H.C.Starck, H.C. Starck Clevios GmbH, www.hcstarck.com (Accessed: April 2010)

[16] R.M. Christie, S. Robertson, S. Taylor, 2007, Design Concepts for a Temperature-sensitive Environment Using Thermochromic Color Change. Online available at: Color: Design and Creativity, Issue 1, 2007, (accessed: FEB 2010)

[17] William A. Maryniak, Toshio Uehara, Maciej A. Noras, 2003. Surface Resistivity and Surface Resistance Measurements Using a Concentric Ring Probe Technique. Trek application note, <Accessed: July 2010 on www.google.com> [18] S.M. Burkinshaw, J. Griffiths, A.D. Towns, 1998, Organic Thermochromic Pigments: A Mechanistic Study. Textile Technology Index, Library Databases Högskolan I Borås [19] N. Sekar, Samita S. Patil, 2006. Thermochromic dyes — Some new developments. Colourage; Nov2006, Vol. 53 Issue 11, p88-90. Accessed through Textile Technology Index, Library Databases Högskolan I Borås.

[20] Conductive Polymers. Asian Textile Journal; July 2002, Vol. 11 Issue 7, p35

[21] K. K. Gupta, A. K. Yadav, 2005. Development of Electrical Conductive Fabrics, Man-Made Textiles in India; Feb2005, Vol. 48 Issue 2, p44-51. Accessed through Textile Technology Index, Library Databases Högskolan I Borås. [22] Paras, Manoj Kumar, Varshneya, Geetika, 2008. Conductive Polymers for Smart Textiles. Man-Made Textiles in India; Nov2008, Vol. 51 Issue 11, p376-378. Accessed through Textile Technology Index, Library Databases Högskolan I Borås. [23] N. Sekar, Photochromic and Thermochromic Dyes and Their Applications. Colourage; July 1998, Vol. 45 Issue 7, p39. Accessed through Textile Technology Index, Library Databases Högskolan I Borås. [24] D. Van der Maas, M. Meagher, C Abegg, J. Huang. Thermochromic information surfaces. Ecole Polytechnique Fédérale de Lausanne, Switzerland [25] http://en.wikipedia.org/wiki/Keto-enol_tautomerism [26] http://www.chem.ufl.edu/~itl/4411L_f98/nmr/nmr.html [27] http://plc.cwru.edu/tutorial/enhanced/files/lc/phase/phase.htm

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