Synthetic Metals 150 (2005) 139–143

Development of a cooling fabric from conducting polymercoated fibres: Proof of concept

Eric Hu, Akif Kaynak∗, Yuncang LiSchool of Engineering and Technology, Deakin University, Victoria 3217, Australia

Received 16 December 2004; accepted 28 January 2005Available online 17 March 2005

Abstract

It is supposed that there should be a thermal electric effect if a dc current is applied across two dissimilar conducting polymers, similarto so called “Peltier effect” in metals or semiconductors. However, this hypothesis has not been tested on conducting polymers and usingthese materials to make cooling fabrics has never been attempted before. Polypyrrole coated fabrics were used to test the hypothesis in thispreliminary study. Seebeck and the Peltier effects were proven to exist. However, thermoelectricity effect between two conducting polymerc ◦ steadyd ooling fabrici©

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tAodoomtmbcitsc

ntacteseightonal

the

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lmstical

theucetiesaves a-oly-pro-and

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oated fabric samples was only about 10�V/ C. Cooling effect by conductive polymer powder was achieved but performance was unue to electrical degradation of the conducting polymer. Nevertheless, the concept was demonstrated and the development of a c

s possible.2005 Elsevier B.V. All rights reserved.

eywords:Cooling effect; Peltier effect; Conducting polymers; Textiles

. Introduction

The clothing industry has been involved in research on tex-ile materials that offered greater comfort and functionality.

cooling effect would be one of the most desired attributesf clothing. New fabric technologies have recently intro-uced garments that provide a cooling effect without relyingn external cooling sources. A portable cooling system isften incorporated into a garment and includes a heat transferedium to absorb heat from the body. Typically, these ma-

erials can be grouped into three general categories: granularaterials, phase change materials and water-retaining fibre-ased materials. These systems can be further classified asirculating or passive[1]. The former includes a fluid circulat-

ng through tubes stitched into the garment and upon contacthe fluid removes the body heat. This set up requires a powerupply, a pump, and a heat sink to absorb the heat from the cir-ulating liquid. The latter use special materials incorporated

∗ Corresponding author. Tel.: +61 3 5227 2909; fax: +61 3 5227 2539.E-mail address:akaynak@deakin.edu.au (A. Kaynak).

into the garment to absorb heat from the body through coand do not require interaction of the wearer. Both of thsystems are generally bulky and not suitable for lightweapplications. Moreover, additional weight causes additimetabolic heat generation due to extra work done bywearer.

Conducting polymers have attracted a great dearesearch interest due to wide-ranging modulation ofelectrical properties and responsiveness to external stsuch as temperature and chemicals[2–4]. But chemicallyor electrochemically synthesized conducting polymer fihave poor mechanical properties, which hinder their pracapplications. This limitation is overcome by allowingpolymerisation to take place on textile surfaces to prodconductive fabrics with excellent mechanical proper[5–7]. Potential of such fabrics in heating applications hbeen reported[8–10]. Furthermore, novel fibres that act asemiconductor (n- or p-type material)[11,12]could be produced by coating the surface of fibres with conducting pmers. Using these conductive fibres, new fabrics could beduced, that will demonstrate the so called “Peltier effect”

379-6779/$ – see front matter © 2005 Elsevier B.V. All rights reserved.oi:10.1016/j.synthmet.2005.01.018

140 E. Hu et al. / Synthetic Metals 150 (2005) 139–143

achieve the cooling effect like the traditional semi-conductorcooler. This paper presents the preliminary investigationson the proposed cooling fabric by working on the Peltiereffect.

2. Experimental and results

2.1. The Seebeck effect

In the world of thermoelectric technology, there are threethermoelectric effects, the Seebeck effect, Peltier effectand Thomson effect. The Seebeck effect occurs betweenjunctions of any two members of the thermoelectric series.In the presence of a temperature difference between thejunctions a small current flows around the circuit. ThePeltier effect occurs whenever electrical current flowsthrough two dissimilar conductors; depending on thedirection of current flow, the junction of the two conductorswill either absorb or release heat. The Peltier effect isthe reverse of the Seebeck effect and a typical junctionphenomenon.

Experimentally, it is easier to prove the Seebeck effect thanPeltier effect as the applied temperature is controlled in theformer and the resulting potential difference is measured. Ift eltiere e thee weref

t inc ntal

Table 1Results showing the existence of Seebeck effect

Sample �T (◦C) �V (mV) R (�)

1 55 0.022 53002 55 0.058 587

�T: the temperature difference between hot and cold side;�V: the thermo-electricity produced at�T; R: the resistance of fabric.

bench rig was set up. Two different fabrics (A and B)were connected as shown inFig. 1. Conductive fabric Awas prepared by immersing the textile in an aqueous solu-tion containing 2.4 mg/ml pyrrole and 14 mg/ml Ferric chlo-ride. The reaction was conducted at 4◦C for 4 h. Then,the conductive fabric is rinsed with water and dried at80◦C for 6 h. Conductive fabric B was prepared by ox-idizing the fabric by immersing into a 10 g/l ferric chlo-ride solution followed by exposure to monomer (pyrrole)vapour to obtain a semiconducting coating of polypyrroleon the fabric. A temperature difference is applied to thetwo junctions of conductive fabrics A and B. The poten-tial difference was measured by a Fluke 189/FVF multime-ter.

The low temperature plate (ice water, about 5◦C) was con-nected to the positive and the high temperature (hot water) tothe negative terminal of the voltmeter (Fig. 1). The thermo-electricity was observed and the result is shown inTable 1. Ifthe cold and the hot sides are reversed, thermoelectricity willbe negative.

The thermoelectricity was also observed in conductivepolymer fabric (part A) in contact with aluminium as partB. The result are shown inFig. 2with further data inTable 2.

et-up f

he Seeback effect exists in the conductive fabric, the Pffect should also be observed. So, experiments to provxistence of the Seeback effect on conductive fabricsollowed by the Peltier effect tests.

In order to prove the existence of Seebeck effeconducting polymer coated fabrics, a simple experime

Fig. 1. Experimental s

or testing Seeback effect.

E. Hu et al. / Synthetic Metals 150 (2005) 139–143 141

Fig. 2. Thermoelectricity effect between conducting polymer coated fabric(A) and aluminium (B).

Table 2Thermoelectricity comparison

Material Thermoelectricity (�V/◦C)

Metal ∼10Semiconductor 100–1000Conductive polymer fabric ∼10Fabric and metal ∼150

2.2. Peltier effect

Results demonstrate that the Seebeck effect exists betweentwo conductive polymer fabrics. However, Peltier effect is thekey for the cooling effect. A rig was built (Fig. 3) to test thePeltier effect. A fan blew air through top side and kept theheat exchange equilibrium between both sides. An electricalpotential (12 V) was applied between the metal plates caus-ing an electrical current to flow between the plates throughthe conducting polymer layer. In this process the charge car-riers overcome the potential difference between metal andconductive polymer to achieve the cooling effect (Peltier ef-fect) on the bottom side inFig. 3. Bulk polymerised polypyr-role (p-doped) particles were used as the conducting polymermaterial in this experiment as the layers required to be wellseparated to minimise heat transfer effects between the metalplates. The bulk polymerised particles compress to yield ahighly conductive layer and also enable a good separationbetween the layers. In the experimental set-up, shown inFig. 3, the heat should be absorbed from the downside and

Fig. 4. (a) Polypyrrole powder and (b) scanning electron microscopy imageof polypyrrole powder.

released to topside; the polymer has higher potential than themetal. A thermocouple and a thermal camera were both usedto measure temperatures on both sides to prove the coolingeffect.

Polypyrrole (PPy) (p-doped) conducting polymer par-ticles were prepared from 10% ferric chloride 6H2O2,2% anthraquinone sulphuric acid and 5% pyrrole[7]. An-thraquinone sulphuric acid, pyrrole and ferric chloride wereslowly added into a beaker. Polymerisation takes place in thesolution and often referred to as bulk polymerisation. The so-lution was continuously stirred for about 3 h before filteringto get the black conducting polypyrrole powder (Fig. 4a). The

t-up for proving the Peltier effect.

Fig. 3. Experimental se

142 E. Hu et al. / Synthetic Metals 150 (2005) 139–143

Fig. 5. Peltier effect experiments. (a) Temperature and current vs. time and (b) resistance and current vs. time for polypyrrole.

nodular morphology of polypyrrole particles can be seen inthe scanning electron microscopy image inFig. 4b. The con-ductivity of the powder was about 100 S/cm.

Results from the Peltier test rig (Fig. 5a) indicate thata slightly lower temperature was observed in the lowerplate, which proved the existence of the Peltier effect in thematerial. However, the temperature difference between twosides gradually diminished during the experiment while theelectrical resistance across the polymer increased with time.This may be attributed to the accelerated rate of degradationof the conducting polymer due to the applied potentialbetween the plates. The increased resistance resulted inreduction of the current as the conducting polymer degraded(Fig. 5b). Another factor that contributed to the smaller tem-perature difference was the poor thermal insulation betweenthe two sides so that heat from the hot side heated up thecold side.

Theoretically, the magnitude of the cooling effect in thePeltier rig depends on the electrical potential difference be-tween the conducting polymer and metal. When a chargecarrier (i.e. positive electron, the “hole”) moves from metal(lower electrical potential) to the polymer (higher potential),the amount of heat absorbed depends on the potential differ-ence between the polymer and metal layer. This mechanismis shown inFig. 6. At the same time, the passage of chargecarriers through the polymer layer (with electrical resistance)

l.

creates ohmic heat, which is conducted to the other side (i.e.low temperature side). In other words, two opposite heat flowsexist between polymer and metal in this experimental setting,one is from metal to polymer due to the passage of “holes”that results in the lower (than polymer) temperature of metal,i.e. the cooling effect, the other is heat conduction from poly-mer to metal due to the temperature difference between them.To improve the cooling effect, theoretically, the first heat flowmust be increased by increasing the potential difference be-tween the two materials used and the second must be reducedby better insulation. In our case, the potential difference be-tween metal and polypyrrole (p-doped) powder was not largeenough to produce a significant cooling effect (i.e. the firstheat flow). The potential of metal is between that of p- andn-type semiconductors (or polymers). A junction formed be-tween an n- and p-doped polypyrrole would be ideal for thistest, if an n-doped polymer sample could be made. Betterinsulation can be achieved by improving design of the exper-imental settings.

3. Conclusion

This preliminary study demonstrated that both the See-beck and Peltier effects can be achieved by using conductingp lingf r, ap yetb e tot c-t Thec uctorm thed onr ablee cuso mep atured callyu

Fig. 6. Peltier effect between a p-type semiconductor and a meta

olymer materials, so that it is possible to make a cooabric from conducting polymer coated fibres. Howeveractically useful cooling effect has not been achievedy using the current conducting polypyrrole fibres du

heir electrical instability, insufficient dissimilarity in elerical properties and the un-ideal set up of testing rig.urrent polymers used are more like a p-type semi-condaterials. Therefore, further research should focus onevelopment of n-type conducting polymer fibres andendering the conducting polymers more electrically stspecially under high temperatures. Future work will fon synthesising conducting polymers, which will overcoroblems encountered in achieving a satisfactory temperifference and to achieve a more significant and practiseful cooling effect.

E. Hu et al. / Synthetic Metals 150 (2005) 139–143 143

Acknowledgements

The authors acknowledge Dr. Tong Lin for providing testsamples and Ms. Eva Hakansson for helping to prepare theconducting polymer powders.

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