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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
Degree of master in science (one year) in Textile Technology Borås Textile School Sweden 2010 How to get changing patterns on a textile surface by using thermo chromic
pigments and an inherently conductive polymer
Laleh Maleki x090228@student.hb.se 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
2 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. 3 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 4 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 5 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 6 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
7 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.
8 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
9 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
10 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 11 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
12 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]
13 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
Variotherm
AQ Light
Conc. colors
Perspiration
Chlorinated Washing
Acid
Alkali
water
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-(2benzotriazolyl)-2-hydroxy-1-naphthoates, zinc and nickel 2, 4-dihydroxybenzophenone-3carboxylates and their derivatives are reportedly other types of stabilizers to improve light
fastness in Leuco dyes. [3]
14 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
15 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]
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[8]
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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(3,4ethylenedioxythiophene) 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 cationicdoped state. [10] This polymer can be employed in the form of in-situ PEDOT, which is
18 ��
��
��
��
��
��
��
� ��
��
��
��
��
��
��
made
of EDT
in the form
��
��monomers
�� or��
�� of
��
��by polymerization
��
��
structure of ��
PEDOT
is demonstrated in figure 6.
��
��
��
��
��
� ��
��
its derivatives. The chemical
��
��
��
��
�� Figure
��
�� structure
��
��
6: Chemical
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.
19 5-2-3-a. In-situ Polymerization of PEDOT:
In-situ polymerization of PEDOT is of a great industrial importance. The properties of insitu 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.
20 *,1./0,-! KAFFL! +&-! 6)! &(()(I! &-(! /20*! ')*.1/*! 0-! &-! &M.),.*! (0*7)'*0,-! ,?!
ABCD>EAFFI! :2)')! ABCD>! 0*! 0/*! ,J0(09)(! */&/)#! B&+2! 72)-81! '0-@! ,?! /2)! AFF!
4,-,4)'!2&*!,-)!&+0(0+!FDNO!K*.1?,-&/)L!@',.7I!*))!30@.')!P#N#!
!
!""#
!$%&'#
"
30@.')! P#NE! Q)?/E! +&'/,,-! ')7')*)-/0-@! /2)! /,7! 50):! ,?! /2)! 4,'72,1,@8! ,?! &! /20-!
Figure 7: chemical
structure
of PEDOT:PSS
film[8]
?014! ,?! ABCD>EAFF! 7&'/0+1)*I! *.'',.-()(!
68! &!
/20-!
AFFG'0+2!in polymer
*.'?&+)!
1&8)'#!
ABCD>! +2&0-*! &')! (0*71&8)(! &*! *2,'/! 6&'*#! R0@2/E! +2)40+&1! */'.+/.')! ,?! /2)!
*7)+0)*!7')*)-/!0-!/2)!?014!K')7',(.+)(!?',4!$#!$!()!S,T!&%(#34!;UV=L#!
PSS with its higher molecular weight has two fundamental functions; the first is its charge
!
balancing counter ion nature, and the second is that it assists PEDOT segments to be
dispersed in water. Thus, PEDOT:PSS complex is not exactly water soluble, but it is a
!"#"!"
stable aqueous dispersion,
processable and deep blue. [13]
"#!$#!%&'()*!
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:
21 Table 2: Typical PEDOT:PSS grades and their properties.
Electrical
PEDOT:PSS ratio
Solid content(%)
conductivity
Typical application
app(S/cm)
1 : 2.5 plus 5% bw
1.3
Up to 500
Conductive coating
1 : 2.5
1.3
10
Conductive coating
1 : 2.5
1.3
1
DMSO
1:6
1 : 20
1.5
3
Antistatics
10
-3
OLEDs
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
22 coatings to conductive coatings and wide-ranging substrates through different
conventional coating methods. Furthermore, the product is accompanied with coating
formulation guide.
23 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 :
Material
Recipe 1
Recipe 2
Clevios PH 1000
20%
30%
Printing paste
80%
70%
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
24 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
25 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:
26 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:
27 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
28 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
29 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.
30 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.
31 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-colorsin-textiles9.asp> accessed: May 2010
[4] S. Lam Po Tang, G. K. Stylios. 2005. An overview of smart technologies for clothing design
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[5] Joanna Berzowska, 2005. Electronic Textiles: Wearable Computers, Reactive Fashion, and
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[6] Joanna Berzowska 2004 Very Slowly Animating Textiles: Shimmering Flower, accessed
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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
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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(3,4ethylenedioxythiophene). H.C.Starck
[11] L. Bert Groenendaal, F, Jonas, D. Freitag, H.Pielartzik, J.R. Reynolds Poly(3,4ethylenedioxythiophene) and its derivatives: Past, Present and Future. Advanced Materials: 2000,
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[12] Y Wang, 2009. Research progress on a novel conductive polymer —poly(3,4ethylenedioxythiophene) (PEDOT), College of Materials Science and Engineering, Shandong
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2077-2088
32 [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
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[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
33