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Ageing effect of plasma‐treated woolMaryam Naebe a , Ron Denning b , Mickey Huson b , Peter G. Cookson a & Xungai Wang aa Centre for Material and Fibre Innovation, Institute for Technology Research & Innovation ,Deakin University , Victoria 3217, Australiab CSIRO Materials Science and Engineering , Belmont, Victoria 3216, AustraliaPublished online: 16 Mar 2011.

To cite this article: Maryam Naebe , Ron Denning , Mickey Huson , Peter G. Cookson & Xungai Wang (2011) Ageing effect ofplasma‐treated wool, The Journal of The Textile Institute, 102:12, 1086-1093

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The Journal of The Textile Institute

Vol. 102, No. 12, December 2011, 1086–1093

ISSN 0040-5000 print/ISSN 1754-2340 onlineCopyright © 2011 The Textile InstituteDOI: 10.1080/00405000.2010.540088http://www.informaworld.com

Ageing effect of plasma-treated wool

Maryam Naebe

a

, Ron Denning

b

, Mickey Huson

b

, Peter G. Cookson

a

and Xungai Wang

a

*

a

Centre for Material and Fibre Innovation, Institute for Technology Research & Innovation, Deakin University, Victoria 3217, Australia;

b

CSIRO Materials Science and Engineering, Belmont, Victoria 3216, Australia

Taylor and Francis

(

Received 18 May 2010; final version received 10 November 2010

)

10.1080/00405000.2010.540088

Atmospheric pressure plasma treatment of wool fabric, with a relatively short exposure time, effectively removed thecovalently bonded lipid layer from the wool surface. The plasma-treated fabric showed increased wettability and thefibres showed greater roughness. X-ray photoelectron spectroscopy (XPS) analysis showed a much more hydrophilicsurface with significant increases in oxygen and nitrogen concentrations and a decrease in carbon concentration.Adhesion, as measured by scanning probe microscopy (SPM) force volume analysis, also increased, consistent withthe more hydrophilic surface leading to a greater meniscus force on the SPM probe. The ageing of fibres from theplasma-treated fabric was assessed over a period of 28 days. While no physical changes were observed, the chemicalnature of the surface changed significantly. XPS showed a decrease in the hydrophilic nature of the surface with time,consistent with the measured decrease in wettability. This change is proposed to be due to the reorientation ofproteolipid chains. SPM adhesion studies also showed the surface to be changing with time. After ageing for 28 days,the plasma-treated surface was relatively stable and still dramatically different from the untreated fibre, suggestingthat the oxidation of the surface and modification or removal of the lipid layer were permanent.

Keywords:

plasma; surface treatment; ageing; adhesion; hydrophilic/hydrophobic; wool

Introduction

The outermost layer of the wool fibre surface is coveredby an external thin membrane called the epicuticle,which is a thin band of proteinaceous material contain-ing a high concentration of the amino acid, cystine(Bradbury, 1973; Leeder & Bradbury, 1968) and asignificant proportion of bound lipid layer (Evans,Leeder, Rippon, & Rivett, 1985). A number of workershave studied the surface of wool fibre and a woolsurface model has been developed (Breakspear, Smith,& Luengo, 2005; Evans, Dennings, & Church, 2002;Huson et al., 2008; Leeder & Bradbury, 1968, 1971;McLaughlin & Pope, 1982; Negri, Cornell, & Rivett,1993a; Negri, Rankin, Nelson, & Rivett, 1996).

The model proposed by Evans et al. (1985)describes the epicuticle as an outermost fatty acidmonolayer (F-layer) and a protein matrix. The majorlipid component of the fatty layer was identified as amethyl-branched, 21-carbon fatty acid (Evans et al.,1985). Negri et al. (1993a) proposed a model in whichthe entire covalently bound lipid originated from theepicuticle. It was suggested that the intact lipidmembrane is attached to the protein through thioesterbonds (Negri et al., 1993a, 1993b); the thickness wasestimated to be about 2.8–3.0 nm (Negri et al., 1993a).

Scanning probe microscopy (SPM) results supportedNegri’s estimation (Crossley et al., 2000).

Time-of-flight secondary ion mass spectrometry(ToF-SIMS) analysis of untreated wool has identified afragment at 325 amu as 18-methyleicosanoic acid (18-MEA; C

21

H

41

O

2

) (Shao, Jones, Mitchell, Vickerman, &Carr, 1997; Volooj, Carr, Mitchell, & Vickerman, 2000;Ward et al., 1993). Negri et al. (1993a) described thislipid as oriented away from the fibre and thus forming ahydrophobic barrier at the surface of each cuticle cell.Negri’s model also explains the presence of a highproportion of carbon in the outer 3–5 nm of the cuticleas shown by X-ray photoelectron spectroscopy (XPS)(Carr, Leaver, & Hughes, 1986; Ward et al., 1993).

Recently, Huson et al. (2008) and Maxwell andHuson (2005) argued that the lipid is an integral part ofthe surface, rather than a discrete surface layer, and thatthe surface is capable of altering its structure inresponse to different environments. It was postulatedthat under dry conditions the surface of the keratinfibres is rich in lipid and is hydrophobic, while in highrelative humidity (RH) or water, it is rich in protein andhydrophilic (Maxwell & Huson, 2005).

It has been shown that the chemical treatment usingalkali, oxidants and reductants can change the surface of

*Corresponding author. Email: xwang@deakin.edu.au

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wool from hydrophobic to hydrophilic (Leeder, Rippon,& Rivett, 1985; Negri et al., 1993b; Shao et al., 1997).Treatments with alcoholic KOH remove the 18-MEAfrom the surface (Negri et al., 1996), while hydroxy-lamine treatment selectively removes 18-MEA withoutproducing any other chemical alteration to the fibre(Breakspear et al., 2005). In addition, it has been shownthat bleaching and permanent wave treatments with alka-line peroxide remove some 18-MEA from the surface ofhair fibre and oxidise cystine residue (Robbins, 1988).

Surface analysis of plasma-treated wool has shownthat plasma treatments modify the surface of the woolfibre (Dai, Elms, & George, 2001; Kan, Chan, & Yuen,2004; Molina, Espinos, Yubero, Erra, & Gonzalez-Elipe,2005; Molina, Jovan

[ccaron]

i

[cacute]

, Comelles, Bertran, & Erra, 2002;Naebe, Cookson, Rippon, Brady, et al., 2010; Naebe,Cookson, Rippon, & Wang, 2010; Ryu, Wakida, &Takagishi, 1991; Wakida et al., 1993). Regardless of thetreatment conditions used, the impact of plasma treatmentis attributed to several changes on the wool surface suchas partial or total removal of the fatty acid layer, formationof hydrophilic groups and an etching effect (Erra,Jovanèiæ, Molina, Jociæ, & Julia, 2002; Rakowski, 1997;Ryu, Wakida, Kawamura, Goto, & Takagishi, 1987).

Although a number of workers studied the surfacemorphology of wool fibres using SPM, their focus hasbeen on estimating the thickness of the surface lipidlayer and measuring the mechanical properties of thefibre surface (Crossley et al., 2000; Gibson et al., 2001;Maxwell & Huson, 2005). Few obtained the local phys-ical information such as roughness and adhesion. Inaddition, plasma treatment has been widely studied forits effect on the surface of the wool fibre, but the ageingeffect (changes on the plasma-treated wool fibre surfaceover time) has received little attention. The objective ofthis study is to investigate the effect of plasma treatmenton the wool fibre surface, and especially the effects ofageing for a period of 28 days after the treatment.

Experimental

Materials, plasma treatment, XPS and water uptake

The base fabric was a plain-weave pure wool fabric of222 g/m

2

manufactured from 20

µ

m fibre, and cleanedby soxhlet extraction as described previously (Naebe,Cookson, Rippon, Brady, et al., 2010). A plasma treat-ment with an exposure time of 30 sec was carried outusing an atmospheric plasma treatment system fromSigma Technologies International (Arizona, USA; APC2000), operated at ambient temperature with helium asthe plasma gas, as described previously (Naebe,Cookson, Rippon, Brady, et al., 2010).

XPS analysis was conducted using an Axis Ultraspectrometer (Kratos Analytical Ltd., UK) equipped

with a monochromatic X-ray source (Al K

α

,

h

ν

=1486.6 eV), operating at 150 W. Water uptake by thefabric was conducted by weighing a vertically clampedfabric sample immersed in water as described previ-ously (Naebe, Cookson, Rippon, Brady, et al., 2010) byweighing a vertically clamped fabric sample immersedin water. The equilibrium water uptake was defined asthe point where sample weight reached a constant valuefor 15 min. Samples were aged under standard condi-tions and tested for wettability after 3 h and after 1, 2,3, 7, 14, 21 and 28 days. A fresh sample was used foreach measurement.

Scanning probe microscopy

Yarns were withdrawn from the fabric, cleaned bySoxhlet extraction and then treated with plasma. Fibreswere removed from the plasma-treated yarn andmounted on a microscope slide using double-sidedadhesive tape. The experiments were carried out in airunder ambient conditions. A Digital Instrument Dimen-sion 3000 SPM was operated in contact mode using asilicon nitride probe with a nominal spring constant of0.58 N/m. Contaminants were removed from the tip bytreatment in a PSD-UV Ultra-Violet/Ozone Probe andSurface Decontamination unit manufactured by Novas-can Technologies (USA). During the measurements,humidity was monitored by a TESTO Model 610humidity and temperature meter.

Height and deflection images were captured simul-taneously using a scan rate of 1 Hz. Adhesion measure-ments were undertaken, using the force-volume mode,to collect a 16

×

16 array of force–distance curves overa 5

×

5

µ

m

2

area of the wool fibre surface. The adhesiondata were collected from five to seven areas on each oftwo fibres over a period of 28 days. Care was taken toreturn the probe to exactly the same area on the fibreeach time, as described previously (Maxwell & Huson,2005). Adhesion values are reported in nm of deflec-tion; however, an indication of the force can be obtainedby multiplying the value by the cantilever springconstant. Prior to examination of the samples, theposition-sensitive detector was calibrated by conductinga force measurement on a hard material (glass). Theroot-mean-squared (rms) roughness values (Rq) weredetermined from height images that had previouslybeen flattened (second order). To isolate the analysis tospecific areas and avoid unwanted peripheral features,roughness analyses were carried out using a box curserto analyse only selected portions of the image.

Scanning electron microscopy

Surface morphology of the samples was evaluated usinga Field Emission Scanning Electron Microscope

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(FE-SEM, Hitachi S4300 SE/N). Fabric samples weresputter-coated with gold using a Bal-tec SCD50 sputtercoater. The images were taken at a working distance of15 mm and an accelerating voltage of 1.2 kV.

Results and discussion

Surface change after treatment

Surface morphology

The SEM images for untreated and plasma-treatedfibres are shown in Figure 1. There was no apparentmorphological change to the surface or cuticle edge ofthe treated wool fibre. In contrast, SPM images showedsignificant microscopic changes on the fibre surface,consistent with an etching effect of the plasma treat-ment, as previously reported (Cai & Qiu, 2008; Canal,Molina, Bertran, & Erra, 2007). This can be due to thedifference between the two techniques in interpretingsubtle differences in height. SEM images were collectedin vacuum on surfaces coated with gold. In addition,changes in slope can result in an increase in electronreflection from the sample surface, producing a higher

intensity in the image. However, it can sometimes bedifficult to determine whether the feature is sloping upor down. On the other hand, AFM images werecollected in air on uncoated samples and yield directheight information, determining whether a feature is abump or pit is straightforward (Nessler, 1999). SPMimages of the untreated fibres show more longitudinalsurface striations compared to the plasma-treated fibre(Figure 2). The three-dimensional nature of the SPMimage was used to calculate changes in roughness andsurface area variations.

Figure 1. SEM images of wool fibres: (a) untreated, and (b) plasma-treated.Figure 2. SPM analysis of wool fibres (3D surface plot, 5

×

5

µ

m

2

): (a) untreated fibre, and (b) plasma-treated fibre.

Figure 1. SEM images of wool fibres: (a) untreated, and(b) plasma-treated.

Figure 2. SPM analysis of wool fibres (3D surface plot,5 × 5 µm2): (a) untreated fibre, and (b) plasma-treated fibre.

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An increase in roughness (Rq), which leads to anincrease in the surface area, of the plasma-treated fibrerelative to the untreated fibre can be seen in Figure 2.The Rq of the surface of the untreated fibre variedbetween 25 and 43 nm (with an average of 33.4 nm anda standard deviation of 6.3 nm) whereas that of theplasma-treated fibre varied from 70 to 93 nm (with anaverage of 85.2 nm and a standard deviation of 6.1 nm).An increase in the average roughness value of thetreated wool surface under different plasma conditionshas been reported previously (Klausen, Thomas, &Hocker, 1995; Phillips, 1995).

Surface hydrophilicity immediately after treatment

Water uptake is defined here as the total movement of aliquid through the fabric driven by a difference insurface energy between the fibre and the liquid andabsorption of the liquid by the fibre. The water uptakeof untreated fabric and the fabric that had been treatedwith plasma for 30 sec was evaluated as soon as possi-ble after treatment, usually within 4 h. With the treatedfabric, equilibrium uptake was achieved in less than1 min and it showed very high (>300%) initial wateruptake at equilibrium. The untreated fabric showed verylittle water uptake (0.03%) after 15 min of equilibration(Figure 3). A 30-sec plasma exposure time was judgedto be sufficient to produce a significant change insurface energy.

Figure 3. Equilibrium water uptake as a function of time: plasma-treated (

�

), and untreated (

▲

) (note the two different

y

-axis scales).

Surface analysis by XPS

Table 1 shows the surface composition of untreated andplasma-treated wool analysed by XPS. A significantincrease in oxygen and nitrogen concentration and adecrease in carbon concentration were observed for theplasma-treated fabric compared to the untreated fabric.The C/N ratio (an indicator of the level of covalentlybound surface lipid) for plasma-treated wool was

consistent with values determined by chemical analysisfor low-sulphur protein fractions (4.4) and wholeextract of wool (3.9) (Carr et al., 1986; Ward et al.,1993). A C/N ratio of 3.4 has also been reported for theepicuticle (King & Bradbury, 1968). High-resolutionXPS from a previous study (Naebe, Cookson, Rippon,Brady, et al., 2010) has shown that the plasma treatmentconditions used cause significant oxidation of theunderlying protein matrix, in particular the disulfidebonds, with the formation of cysteic acid residues.

A previous study (Naebe, Cookson, Rippon, Brady,et al., 2010) confirmed that plasma treatment under theconditions used in the present study removed the 18-MEA, the major component of the lipid layer, which iscovalently bound through thioester linkages to thesurface of the epicuticle (Negri et al., 1993a). Thisresulted in exposure of the underlying, hydrophilicprotein of the epicuticle, thereby increasing wettabilityof the wool.

Surface analysis by SPM

SPM adhesion studies showed significant variability onboth plasma-treated fibres and untreated control fibres,as assessed from measurements taken at different partsof each fibre. Nevertheless, the average adhesion on theplasma-treated fibre was significantly higher than thatof the untreated fibre. Table 2 shows the variation ofaverage adhesion values for six different areas on oneuntreated fibre and one plasma-treated fibre after 24 hof conditioning.

The higher adhesion on the plasma-treated samplewas consistent with the results on a micro-patternedmodel surface used by Huson et al. (2008), which showedthat adhesion on a hydrophilic carboxylic acid surfacewas stronger than that on a hydrophobic methyl surface.

The surface of the plasma-treated fibre was hydro-philic due to removal of the lipid layer. The resultanthigher water affinity increases the probability of a waterbridge forming between the probe tip and fibre speci-men, the increased meniscus force in turn causinggreater adhesion between the tip and the sample. In addi-tion, the higher water affinity is likely to affect the realarea of contact between the tip and sample (Bhushan &Jung, 2008), further increasing the adhesion.

Figure 3. Equilibrium water uptake as a function of time:plasma-treated (�), and untreated (▲) (note the two differenty-axis scales).

Table 1. Relative atomic concentration of untreated andplasma treated fabric.

ElementsCarbon

(C

1s

)Oxygen

(O

1s

)Nitrogen

(N

1s

)Sulphur

(S

2p

) C

1s

/N

1s

Binding energy (eV)

284.0 530.0 399.0 167.0

Untreated 73.8 13.8 9.9 2.4 7.5Plasma treated 54.2 26.9 15.3 2.6 3.5

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Unlike the results presented above, previous studieson hair (Bhushan & Chen, 2006; Breakspear et al.,2005; LaTorre & Bhushan, 2005, 2006) and wool(Huson et al., 2008) have shown that chemical treat-ment known to remove lipids from the surface generallyreduce adhesion. Huson et al. acknowledged that thisbehaviour was unusual and speculated that it could bedue to the surface being able to absorb moisture,thereby affecting the thickness of the adsorbed layer,and the possibility of ions or organic molecules leach-ing from the bulk of the fibre and contaminating theadsorbed layer.

It is also possible that in the plasma-treated fibresused in the present study, oxidation of the fibre surfacemight play a role in the increased adhesion. High-resolution XPS analysis showed significant oxidation ofsulphur to sulphonic acid as a consequence of theplasma treatment.

Surface change with ageing

Surface morphology

Changes in the surface morphology of the untreated andplasma-treated fibres were examined by SPM. Whilethe variation in roughness was observed between differ-ent areas of a sample, no significant changes in surfaceroughness were observed on untreated and plasma-treated fibres over a period of 28 days.

Surface hydrophiliciy changes with time

Untreated fabric and the fabric that had been treatedwith plasma for 30 sec were stored at 20

±

2

°

C and65

±

2% RH and tested over a period of 28 days. The rate

of water uptake was used to determine the changes inthe wetting properties of wool fabrics with ageing time.Figure 3 shows the percentage of water uptake at equi-librium versus ageing time. The untreated fabric took upvery little water and showed no change over the 28days. In contrast, the plasma-treated sample showedsignificantly higher initial water uptake, the equilibriumvalue decreasing significantly over the first three days,and subsequently more slowly. After 28 days, althoughthe plasma-treated fabric had lost some of its initialwettability, it was still considerably more hydrophilicthan the untreated fabric.

Surface analysis by XPS

Table 3 shows the surface composition of plasma-treatedwool analysed by XPS for different ageing times fromDay 1 to Day 28. An increase in carbon concentrationand a decrease in oxygen and nitrogen concentrationswere observed. The sulphur content remained almostconstant over the entire period. The relative atomicconcentration of carbon in the surface of the plasma-treated sample increased rapidly and then reached aconstant value (after approximately 14 days) that wassignificantly less than that of the untreated surface(73.8%). Nitrogen concentrations decreased to an almostconstant level over the same period. The C

1s

/N

1s

ratioremained unchanged (

∼

4.1) after 14 days of ageing.High-resolution XPS sulphur spectra from plasma-

treated wool samples after two, three and seven days ofageing are shown in Figure 4. The S2p spectra consistedof two peaks at 164 and 168 eV. The peak at 164.0 eVcorresponds to the presence of sulphur as a disulphidelinkage. The peak at higher bonding energy (168.0 eV)

Table 2. The average adhesion values of untreated and plasma-treated fibres from six different parts of the surface of each fibre.

Area

Sample 1 2 3 4 5 6 Mean STDEV

Untreated 83.3 37.1 81.2 37.8 84.2 76.3 66.7 22.8Plasma treated 127.3 146.7 135.8 146.1 156.2 121.8 133.8 13.0

Table 3. Surface analysis of plasma treated fabric over a period of one month.

Relative atomic concentration (%)

Storage time after plasma treatment (days)

Elements Binding energy (eV) 1 2 3 7 14 21 28

Carbon (C

1s

) 284.0 54.2 54.5 54.8 55.9 57.0 57.3 57.3Oxygen (O

1s

) 530.0 26.9 26.8 26.6 26.1 25.2 25.0 24.6Nitrogen (N

1s

) 399.0 15.3 15.1 15.1 14.6 13.8 13.9 13.9Sulphur (S

2P

) 167.0 2.6 2.6 2.5 2.5 2.6 2.6 2.6C

1s

/N

1s

3.5 3.6 3.6 3.8 4.1 4.1 4.1

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is attributed to the presence of oxidised sulphur species(S

6+

) in the protein matrix after plasma treatment (Brack,Lamb, Pham, & Turner, 1996; Molina et al., 2002).These oxidised species have been shown to be sulphonicacid (

−

SO

3

−

) (Bradley, Clackson, & Sykes, 1994; Shaoet al., 1997), and S–SO

3

H, (Shao et al., 1997).

Figure 4. High-resolution XPS sulphur spectra from plasma-treated wool after two, three and seven days of ageing.

The ratio of disulphide linkages to oxidised sulphurspecies (C–S/S-oxidised) recorded from S2p spectra ofthe plasma-treated fabrics after different ageing timeshas been summarised in Table 4. The ratio increasedsignificantly over the first seven days before remainingconstant, suggesting that while the total sulphur had notchanged (Table 3), the more oxidised sulphur specieshad migrated away from the surface of the plasma-treated sample.

The results suggest that the surface of plasma-treated wool fibre is mobile and changes as the fibre

ages. The increase in carbon content can be attributed tothe migration of the carbon from the bulk of the fibreonto the surface. This migration would explain thedecreased wettability (Figure 3). The results also showa decrease in the polarity of the surface and a decreasein oxygen (Table 1) and S

6+

(Figure 4). This can beattributed to the orientation of polar groups from thesurface to the bulk phase, resulting in rearrangement ofthe surface of the wool fibre.

Surface analysis by SPM

The effect of ageing plasma-treated fibres was studiedby SPM adhesion measurements and compared to anuntreated control fibre. Figure 5 shows the averageadhesion ratio of plasma-treated samples to untreatedsamples over a period of 28 days. This ratio increasedup to the ageing time of 14 days and then the valueremained relatively constant. After ageing for 28 days,the surface of plasma-treated samples showed threetimes more adhesion than that of the untreated fibre. Forpolymer surfaces, Everaert, Chatelier, Mei, andBusscher (1997) postulated that ageing or “hydrophobicrecovery” changes the hydrophilic nature of the surfacecreated by a plasma treatment to a relatively or fullyhydrophobic surface over time. In the present study,ageing did not change the hydrophilic surface of theplasma-treated wool to a completely hydrophobicsurface. This would suggest that the oxidation of thesurface and modification or removal of the lipid layerwere relatively permanent and rearrangement of thesurface would not return the fibre to its originalhydrophobic state.

Figure 5. Average adhesion ratio of plasma-treated to untreated fibre over a period of 28 days for all fibres and areas measured.

Rearrangement on the surface was relatively rapidimmediately after the plasma treatment, and slowedwith ageing time. The results agree with the modelproposed by Huson et al. (2008), suggesting that thedisordered lipid layer is capable of rearranging in

Figure 4. High-resolution XPS sulphur spectra from plasma-treated wool after two, three and seven days of ageing.

Table 4. Ratio of sulphur species of plasma treated fabricover a period of one month.

Storage time after plasma treatment (days)

1 2 3 7 14 21 28

C–S/S-oxidised 1.01 1.11 1.18 1.33 1.30 1.32 1.48

Figure 5. Average adhesion ratio of plasma-treated tountreated fibre over a period of 28 days for all fibres andareas measured.

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response to changes in the environment, but the changesin adhesion measured by SPM are difficult to explain.As the hydrophilic nature of the surface created by theplasma treatment changes to a more hydrophobicsurface over time, one would expect a reduction insurface adhesion. More work is needed to expand thecurrent understanding of the wool fibre surface toexplain this anomaly.

Conclusion

Atmospheric plasma treatment of wool fabric resultedin increased wettability of the fabric and fibres, withgreater roughness and adhesion as measured by SPManalysis. XPS suggested a much more hydrophilicsurface with a significant increase in oxygen andnitrogen concentrations and a decrease in carbonconcentration. These changes are consistent with theremoval of the covalently bound lipid from the surfaceof the fibre. The significant oxidation of the underlyingprotein matrix, in particular the disulfide bonds, withthe formation of cysteic acid residue was shown.

When the plasma-treated wool fibre was allowed toage, no changes were seen in the morphology of thesurface. However, wettability studies, as well as surfaceanalyses using SPM and XPS, showed that the chemicalnature of the surface was changing with time. Anincrease in carbon concentration and a decrease inoxygen and nitrogen concentrations were observed over14 days. After that period, the concentrations remainedrelatively constant. Although the sulphur content wasfairly stable over 28 days of ageing, the intensity ratioof disulphide linkages to oxidised sulphur species (C–S/S-oxidised) changed, showing that (with time) the moreoxidised sulphur species migrated away from thesurface of the plasma-treated sample. This increase inthe hydrophobic nature of the surface was consistentwith the decrease in wettability with time, but at oddswith the increased adhesion as measured by SPM. Afterageing for 28 days, the plasma-treated surface was rela-tively stable and still dramatically different from theuntreated fibre, suggesting that the oxidation of thesurface and modification or removal of the lipid layerwere permanent. In spite of rearrangement of thesurface, the treated fibre remained considerably morehydrophilic than the untreated fibre.

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