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Applied Surface Science 290 (2014) 381– 387

Contents lists available at ScienceDirect

Applied Surface Science

j ourna l ho me page: www.elsev ier .com/ locate /apsusc

urface modification of polycarbonate and polyethylene naphtalateoils by UV-ozone treatment and �Plasma printing

.O.F. Verkuijlena, M.H.A. van Dongena,∗, A.A.E. Stevensb, J. van Geldropa, J.P.C. Bernardsa

Expertise Centre Thin Films & Functional Materials, Fontys University of Applied Sciences, 5600 AH Eindhoven, The NetherlandsInnoPhysicsB.V., 5627 JM Eindhoven, The Netherlands

r t i c l e i n f o

rticle history:eceived 18 July 2013eceived in revised form 11 October 2013ccepted 17 November 2013vailable online 23 November 2013

eywords:ielectric barrier dischargeV-ozonePlasma printing

a b s t r a c t

In this study, we investigated the effect of UV-ozone and �Plasma printing on surface modificationof polycarbonate (PC) and polyethylene naphthalate (PEN). The effects on the wetting behaviour wasstudied, in terms of surface energy and chemical modification of the treated substrate, by analysis ofattenuated total reflectance-Fourier transform infrared spectrometry (ATR-FTIR) and X-ray photoelectronspectroscopy (XPS). Both UV-ozone and �Plasma printing are effective ways to modify the wettability ofboth polymer substrates, substantially increasing the wetting envelope after a short treatment period.This increase is primarily due to an increase of the polar part of the surface energy. This is confirmedby ATR-FTIR and XPS, which show the formation of oxygen containing groups as well as a decrease inthe aromatic C C bonds on the surface of the substrate due to the treatment. For both types of surface

urface modificationurface energyttenuated total reflectance-Fourier

ransform infrared spectrometry (AT-FTIR)-ray photoelectron spectroscopy (XPS)etting

treatment, prolonged exposure showed no further increase in wettability, although continuous change inchemical composition of the surface was measured. This effect is more evident for UV-ozone treatment,as a larger increase in O/C ratio of the surface was measured as compared to �Plasma printing. It canbe concluded that �Plasma printing results in a more chemically selective modification as compared toUV-ozone. In the case that chemical selectivity and treatment time are considered important, �Plasmaprinting is favourable over UV-ozone.

. Introduction

Organic and printed electronics, like organic LEDs, solar cells,ensors and RFIDs, are an expanding market with a large variety ofpplications. Advantages of plastic electronic devices are, amongthers, the relative low cost as a consequence of high throughputnd the flexibility in choice of polymer films. Devices can be pro-uced by various printing techniques, such as inkjet printing orcreen printing, using liquid functional inks [1–3]. A major chal-enge in the production of organic printed electronics is to controlhe wettability and adhesion of the functional inks on the substrate,specially on polymer substrate. It is well known that polymersave a low surface energy in the range of 20–40 mN/m. As most

unctional inks for printed electronics are either solvent or waterased with typical surface tensions in the range of 30–70 mN/m,he wetting of these inks on polymer films is often poor [4]. An

ndication of the wetting properties of a substrate for a particularnk can be obtained by the use of the wetting envelope. The wet-ing envelope uses the dispersive and polar parts of the surface

∗ Corresponding author at: Rachelsmolen 1, 5612 MA Eindhoven, Theetherlands. Tel.: +31 8550 70925.

E-mail address: mha.vandongen@fontys.nl (M.H.A. van Dongen).

169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.apsusc.2013.11.089

© 2013 Elsevier B.V. All rights reserved.

energy from the substrate to predict whether a particular liquid,with known dispersive and polar part of the surface tension, willwet the substrate completely. As the polar part of the surface energyof polymer films is very small due to a lack of polar groups onthe surface, the wetting envelope will be small. This results inpoor wetting, even if the total surface energy of the substrate andsurface tension of the liquid are equal. The wetting envelope canbe substantially improved by increasing the electronegativity ofthe substrate by adding polar groups on the surface of the sub-strate, thus increasing the polar part of the surface energy of thesubstrate. Two commonly used methods of increasing the polarpart of the surface energy, and therefore widening the wettingenvelope of a substrate, are UV-ozone treatment and dielectric bar-rier discharge (DBD) plasma treatment. Both methods are used toimprove the wetting of functional inks on substrates [5–7]. In thisinvestigation, we will compare the surface modification of poly-carbonate (PC) and polyethylene naphthalate (PEN) by UV-ozoneand �Plasma printing, a special type of atmospheric DBD plasmatreatment. To investigate the relationship between the change insurface energy and the change in chemical composition of the sub-

strate for both methods, the composition of the substrate is alsoanalysed by X-ray photoelectron spectroscopy (XPS) and atten-uated total reflectance-Fourier transform infrared spectrometry(ATR-FTIR) [8–11].

382 R.O.F. Verkuijlen et al. / Applied Surfa

Fod

ictomDpsihtcpstutcaoitspdntbp

2

2

(uwTrtppTpos(

ig. 1. A representation of the �Plasma printing principle consisting of an arrayf needle electrodes and a conducting substrate table (a). When decreasing the gapistance plasma ignites and the dielectric is treated (image courtesy of Innophysics).

UV-ozone treatment is widely used as an effective surface clean-ng method to remove a variety of contaminants on a substrate. Theleaning is mainly a result of a photosensitized oxidation of the con-aminants, removing them from the substrate. A negative side effectf the cleaning of polymer substrates is the oxidation of the poly-er itself, damaging the material [12,13]. Atmospheric pressureBD plasma treatment, with for example air as plasma gas, addsolar groups to the substrate surface. This enlarges both the totalurface energy and the wetting envelope of the substrate, signif-cantly improving the wetting behaviour [14,15]. Various studiesave shown that oxygen incorporation in the surface occurs dueo plasma treatment [16–18]. In this investigation, we use a spe-ific type of atmospheric DBD plasma treatment, called �Plasmarinting. The major difference between normal atmospheric pres-ure DBD plasma and �Plasma printing is the ability to locally treathe substrate and to allow patterned surface activation without these of a mask. Potentially, this could be interesting in the deposi-ion of functional inks for printed electronics, where tracks of e.g.onductive materials need to be positioned close to each other. Cre-ting gradients in surface energy could enhance the printing qualityf the functional inks [19–23]. �Plasma printing is comparable tonkjet print technology. However, instead of printing ink droplets,he surface is exposed dot-wise to atmospheric DBD plasma. Achematic representation of the �Plasma printing principle is dis-layed in Fig. 1. The substrate table acts as one electrode with aielectric barrier and a print head equipped with an array of 24eedle shaped electrodes comprise the DBD reactor. In between theable and needles, a substrate is placed that serves as the dielectricarrier. Huiskamp et al. described the technology behind �Plasmarinting in detail [20].

. Experimental

.1. Preparation of the samples

In this study polycarbonate (PC) and polyethylene naphthalatePEN) (Goodfellow UK, 125 �m thick) substrates were modifiedsing UV-ozone and �Plasma printing. The UV-ozone treatmentsere carried out using a commercial UV-ozone cleaner (UVOCS

10X10) which generates UV emissions in the 254 and 185 nmange to obtain ozone and atomic oxygen. Both PC and PEN werereated within a range of 1–60 min of UV-ozone exposure. �Plasmarinting was carried out using a Roth & Rau Pixdro LP50 inkjetrinter equipped with an InnoPhysics POD24 �Plasma print head.he plasma was generated at ambient pressure in air using 5 kV

eak tot peak and a gap distance between needles and substratef 300 �m. Rectangles of 30 × 60 mm2 were printed on PC and PENubstrates. Each rectangle was printed at the print head native DPIdots per inch) of 181 at a print head movement speed of 50 mm/s.

ce Science 290 (2014) 381– 387

This corresponds to approx. 17 ms of actual plasma exposure witha maximum energy density of 40 mJ/cm2 after a single treatment ofthe rectangle. Both polymers were treated within a range of 1–500plasma treatments.

3. Analysis of the samples

3.1. Wetting envelope and surface energy

To assess the polar and dispersive parts of the substrate surfacefree energy, �P

S and �DS respectively, the method of Owens, Wendt,

Rabel and Kaelble (OWRK) was used [24]. This method uses a linearequation, y = mx + b, in which the slope m and intercept b corre-spond to the square root of the polar and dispersive components ofthe substrate surface free energy respectively as shown in Eq. (1):

(1 + cos �

) �PL + �D

L

2√

�DL︸ ︷︷ ︸

y

=√

�PS︸︷︷︸

m

√�P

L

�DL

+√

�DS︸ ︷︷ ︸

b

(1)

The unknown polar and dispersive parts of the substrate surfacefree energy, �P

S and �DS respectively, can be determined by measur-

ing the contact angle for typically two or more test liquids withknown polar

(�P

L

)and dispersive part

(�D

L

)of the liquid surface

free energy. The wetting envelope is a special representation of Eq.(1), in which a plot is made for a substrate with known polar anddispersive part of the surface energy. Plotting Eq. (1) for a contactangle equal to 0 degrees, i.e. total wetting, as a function of the liq-uid polar and dispersive surface energies, an envelope can be drawnto predict the wetting behaviour of a liquid on the substrate. Liq-uids with a polar and dispersive part of the liquid surface energybeing enclosed in the envelope will wet completely. Liquids out-side the wetting envelope will only wet partially. To determine thepolar and dispersive parts of the solid surface energy and wettingenvelope of the substrates, contact angle measurements were per-formed using deionized water and diiodomethane (Sigma–Aldrich,purity 99%) as test liquids. The dispersive and polar part of the liq-uid surface energies for deionized water and diiodomethane weretaken from Ström et al. [25]. Ten droplets of 5 �l, alternating deion-ized water and diiodomethane were positioned 7 mm apart onthe substrate. The contact angle was measured with a DataphysicsOCA30 contact angle measurement device. The contact angle pro-file was extracted from the images using Young–Laplace fitting.All ten measurements per sample were used to calculate the solidsurface energies and wetting envelope with an accuracy of 2 mN/m.

3.2. Attenuated total reflectance-Fourier transform infraredspectrometry

Attenuated total reflectance-Fourier transform infrared spec-trometry (ATR-FTIR) measurements were carried out on a ThermoAvator 330 spectrometer equipped with a Golden Gate SingleReflection Diamond ATR. The angle of incidence of the diamondcrystal was 45◦. The spectra were collected with a resolution of4 cm–1 and averaged over 32 scans for wavenumbers from 4000to 600 cm–1. To clarify the surface modification by the treatmentspectral subtraction was used. The spectrum of an untreated PCor PEN substrate was measured and used as a reference. Morent

et al. [26] showed ATR-FTIR can be used for the detection ofsurface oxidation caused by plasma treatment even though thepenetration depth is relatively deep compared to the modificationdepth.

R.O.F. Verkuijlen et al. / Applied Surface Science 290 (2014) 381– 387 383

Fig. 2. Wetting envelopes for UV-ozone treated PC (a) and PEN (b) as a function of treatment time and �Plasma treated PC (c) and PEN (d) as a function of number oft gy (m

3

putspoceXe

4

4

attss(kcsotFamf

reatments. The axis shows the polar and dispersive parts of the liquid surface ener

.3. X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) measurements wereerformed on a Thermo Scientific K-Alpha KA1066 spectrometersing a monochromatic Al K� X-ray source (h� = 1486.6 eV). Pho-oelectrons were collected at a take-off angle of 60◦. An X-raypot 400 �m in diametre was used in the analysis. The sam-les were neutralized using a flood gun to correct for differentialr non-uniform charging. All spectra were corrected for sampleharging using the C 1s peak in adventitious carbon (bindingnergy = 284.0 eV) as an internal reference [27]. High-resolutionPS scans were performed for the O 1s and C 1s regions at passnergy of 50 eV.

. Results and discussion

.1. Wetting and surface energy

As introduced above, UV-ozone treatment and �Plasma printingre both methods to improve the wetting behaviour of a liquid ono the surface of a substrate. The wetting envelope is a fast methodo predict the wetting behaviour of the liquids on the treated sub-trates. In Fig. 2, the wetting envelopes for both PC and PEN arehown after either UV-ozone treatment (a,b) or �Plasma printingc,d). If the polar

(�P

L

)and dispersive part

(�D

L

)of a liquid are

nown and falls within the wetting envelope, the liquid will wetompletely. If not, only partial wetting will take place. As can beeen, the wetting envelope increases rapidly for both methods afternly a short treatment. This indicates a large improvement in wet-ing for a wide range of liquids compared to untreated PC and PEN.

or the UV-ozone treated samples, the wetting envelope maximizesfter approx. 10 min for PC and 5 min for PEN. For the plasma treat-ent, the maximum wetting envelope is reached after 2 treatments

or PC and 3–4 treatments for PEN.

arkers are added for clarity).

For a better understanding of the wetting properties, the surfaceenergy of the substrate is measured as a function of the treatmenttime. This is shown in Fig. 3 for both UV-ozone and �Plasma treatedPC and PEN. As can be seen, for all experiments an increase in totalsurface energy was observed.

The UV-ozone treated substrates show an increase from40 ± 2 mN/m to 68 ± 2 mN/m for PC and 45 ± 2 mN/m to65 ± 2 mN/m for PEN. The maximum surface energies are reachedafter approx. 10 min for PC and 5 min for PEN. The increase intotal surface energy can be fully attributed to an increase in thepolar part of the surface energy, which increases from 0 mN/m toapprox. 40 ± 2 mN/m for both PC and PEN. The dispersive part forboth polymers decreases by approx.15 ± 2 mN/m. The �Plasmatreated substrates show a similar trend, as for both polymersthe total surface energy increases with increasing number oftreatments (Fig. 3c and d). However, this increase is much faster,already reaching its maximum after 2 treatments with approx.55 ± 2 mN/m for PC and 60 ± 2 mN/m for PEN. This is slightlyless compared to the UV-ozone treatment, resulting in a smallerwetting envelope (Fig. 2). The increase in total surface energy canalso be fully attributed to the increase in the polar part of thesurface energy. For PC and PEN, the increases measured, in thepolar parts of the surface energies equal approx. 25 ± 2 mN/m and28 ± 2 mN/m respectively. For both polymers a similar decrease ofapprox. 15 ± 2 mN/m in the dispersive part of the surface energy ismeasured. This is comparable to the UV-ozone treatment.

Summarized, when comparing UV-ozone and �Plasma treatedPC and PEN, a strong increase in the wetting envelope for bothmethods is found. However, the wetting on both polymers shows tobe more susceptible for �Plasma treatment, reaching the maximum

wetting envelope much faster. The increase in wetting envelope canbe attributed to an increase in the polar part and a smaller decreaseof the dispersive part of the surface energy, resulting in an overalllarger surface energy.

384 R.O.F. Verkuijlen et al. / Applied Surface Science 290 (2014) 381– 387

F ne trea

4

togaiFPamdiTpa

buct

TC

ig. 3. Total, polar and dispersive part of the surface energy (�S, �PS , �D

S ) for UV-ozond PEN (d) as a function of number of treatments.

.2. ATR-FTIR analysis

For atmospheric DBD plasma experiments in air, it is known thathe increase of the polar surface energy is caused by incorporationf oxygen-containing functionalities into the polymer. These oxy-en containing groups provide more interaction between substratend test fluids, increasing the wetting envelope [28]. To confirm thencorporation of oxygen by UV-ozone and �Plasma treatment, ATR-TIR measurements were performed on both untreated and treatedC and PEN films. Although a strong increase in wetting is obtainedfter short treatment times by either UV-ozone or �Plasma treat-ent, the chemical modification of the surface is too small to be

etermined by ATR-FTIR due to the large penetration depth ofnfrared light in PC and PEN compared to the modification depth.herefore, in the case of �Plasma printing, 500 treatments wereerformed to obtain a sufficiently intensive modification measur-ble with ATR-FTIR.

Fig. 4 shows the ATR-FTIR spectra for both PC (a) and PEN (b),

efore and after 500 �plasma treatments. The spectrum of thentreated polymers can be attributed to specific bonds within thehemical structure of the material. The characteristic bands forhe most interesting bonds are listed in Table 1 for both PC and

able 1haracteristic ATR-FTIR bands for PC and PEN [8].

Substrate Wavelength (cm–1) Bond vibration

PC 2960, 2980 Symmetric and asymmetric stretching CH3

PC 1774 C O stretching from carbonate esterPC 1509 Aromatic C C in phenyl ring structurePC 1165, 1194,1228 C O stretchPEN 2930, 2865 Symmetric and asymmetric stretching CH2

PEN 1710 C O stretching from carbonate esterPEN 1250,1175,1095,1090 C O stretchingPEN 755 CH2 rocking in C (CH2)2 C

ated PC (a) and PEN (b) as a function of treatment time and �Plasma treated PC (c)

PEN. Comparing the ATR-FTIR spectra of the �Plasma treated PCwith the untreated PC, the overall intensity of the characteris-tic bands has decreased. A new broad absorption band appearsbetween 3600 and 3000 cm–1. This band can be attributed to

OH stretching vibrations, indicating the appearance of hydroxylgroups on the PC surface. In addition, another band appears at1675 cm–1. This band can be assigned to a C O stretch vibration. For�Plasma treated PEN a similar effect can be seen in the ATR-FTIRspectra with the appearance of the same broad absorption bandat 3600–3000 cm–1, also indicating the appearance of hydroxylgroups on the surface. Similar results were obtained with UV-ozonetreatment.

For further comprehension of the modification caused by theUV-ozone and �Plasma treatment, spectral subtraction was per-formed for a series of experiments with different treatment times.The results are presented in Fig. 5. The subtracted spectra are shownfor wavenumbers between 4000 and 2000 cm–1 as most interestingregion. For all subtracted spectra, a baseline correction is performedand they are vertically shifted with increasing intensity of treat-ment for clarity. For both treatment methods and both polymers,an increase in the absorption band between 3600 and 3000 cm–1 isvisible with increasing intensity of the treatments. As mentionedabove, this absorption band shows the existence of hydroxyl groupson the surface of the substrate. As no hydroxyl groups previouslyexisted before treatment, these groups have to be formed due to theUV-ozone and �Plasma treatment. The �Plasma treatments alsoseem to form more hydroxyl groups on the substrate compared toUV-ozone, as the intensity of the hydroxyl-band shows a strongerresponse with increasing number of treatments. This indicates amore specific chemical modification on the surface for the �Plasma

treatment compared to the UV-ozone treatment. This is interesting,as a single �Plasma treatment on a single spot last approx. 17 ms.With 500 treatments, this equals to roughly 9 s of treatment timecompared to the 60 min for UV-ozone.

R.O.F. Verkuijlen et al. / Applied Surface Science 290 (2014) 381– 387 385

F PEN (

4

abisssToA

Pmc2gop

Ft

ig. 4. ATR-FTIR spectra as measured for untreated and �Plasma treated PC (a) and

.3. XPS analysis

To complement the surface energy and ATR-FTIR analysis, XPS-nalysis was performed on the treated PC and PEN substrates. Foroth substrates and treatment methods, three different treatment

ntensities were measured. First, an untreated substrate was mea-ured as a reference. Second, a treated substrate, just saturated inurface energy was measured to determine the chemical compo-ition of the samples used for the surface energy measurements.hird, substrates with intensive treatment, i.e. 30 min UV-ozoner 500 �Plasma treatments, were analysed to compare with theTR-FTIR results.

Fig. 6 shows the high resolution carbon 1s XPS spectra for bothC and PEN, and both UV-ozone and �Plasma treatment. For bothethods and both polymers an increase in effect of the treatment

an be seen in the XPS spectra. Untreated PC displays a peak at

85.0 eV for C C aromatic and C C aliphatic, 286.3 eV for C Oroups and 290.6 eV for O (C O) C groups [27,29]. After UV-zone treatment a peak appears at 289.3 eV for C O groups and theeak at 286.3 (C O groups) becomes more distinct. Also, a strong

ig. 5. Subtracted ATR-FTIR spectra of UV-ozone treated PC (a) and PEN (b) and �plasmareatment increases in vertical direction. For (a) and (b) the intensity is shown in minutes

b). The structural formulas of PC and PEN are included for illustrative purposes.

decrease of the peak at 285.0 eV is visible, indicating a decreasein aromatic C C bonds. For the �Plasma treatment a decrease inaromatic C C bonds at 285.0 eV is also visible, but the decreaseis less strong. Also a peak at 298.3 eV appears for C O groups.The carbon 1s XPS spectrum for untreated PEN shows three peaksat the binding energies of 285.0, 286.5 and 289.8 eV, correspond-ing to C C aromatic, C O C and O C O groups, respectively. Adecrease in the C C aromatic peak can be seen in both the spectrafor UV-ozone and �Plasma treatment, although the decrease forthe �Plasma treatment is much less. For the UV-ozone treatment aslight increase at 289.8 eV (O C O groups) is also visible. Table 2shows the XPS O/C ratio for PC and PEN before and after treat-ment with UV-ozone and �Plasma. An increase in O/C ratio is seenfor both methods with prolonged exposure, as expected from theother measurements. Less oxygen is incorporated in the substratefor the �Plasma treatment. These results support the findings from

the surface energy and ATR-FTIR measurements above, in which anincrease in the polar part of the surface energy was found as wellas an increase of oxygen containing groups. It also shows that UV-ozone treatment does more damage to the substrate by degrading

treated PC (c) and PEN (d). The spectra are shifted for clarity, the intensity of the of UV-ozone treatment, for (c) and (d) in number of �Plasma treatments.

386 R.O.F. Verkuijlen et al. / Applied Surface Science 290 (2014) 381– 387

Fig. 6. Carbon 1s high resolution XPS spectra for UV-ozone treated

Table 2XPS O/C ratio of PC and PEN for untreated, surface energy saturated (i.e.10 min and5 min UV-ozone treatment for PC and PEN respectively, or 5 �Plasma treatmentsfor both PC and PEN) and intensive treatment (i.e. 30 min UV-ozone or 500 �Plasmatreatments).

O/C ratio (%) PC PEN

UV-ozone �Plasma UV-ozone �Plasma

Untreated 17 19 27 29

tg

5

�pttattccTaamaaua

SE saturation 49 32 51 45Intensive treatment 60 39 69 51

he C C aromatic bonds, replacing these for oxygen containingroups.

. Discussion and conclusions

In this study, we investigated the effects of UV-ozone andPlasma treatments on the surface modification of PC and PEN. Inarticular we focused on the change in wettability due to thesereatments and its relationship to the chemical modification ofhe substrate surface. Both UV-ozone and �Plasma printing aren effective way to modify the wettability, increasing the wet-ing envelope of both polymer substrates substantially after a shortreatment period. The increase in wetting envelope is primarilyaused by the increase of the polar part of the surface energy indi-ating the formation of polar groups on the surface of the substrate.his was confirmed by the ATR-FTIR and XPS-analysis which shown increase in oxygen containing groups and degradation of the C Cromatic bonds on the surface of the polymer films. For both poly-ers, the formation of CO, C O C and O C O groups was detected

s a result of the UV-ozone and �Plasma treatment. The ATR-FTIRnd XPS-analysis also show that this chemical modification contin-es with on-going treatment even as the wetting envelope reaches

maximum and no further improvement in wetting was seen.

PC (a) and PEN (b) and �Plasma treated PC (c) and PEN (d).

Comparing the UV-ozone treatment with the �Plasma treatment, adifference in intensity was seen. The wettability of both polymerscan be more easily controlled using UV-ozone treatment as aftertwo �Plasma treatments the maximum wetting envelope is alreadyreached whilst for the UV-ozone treatment this occurs more gradu-ally. The chemical modification of the substrate surface also showsdifferences for both treatment methods. For the samples with satu-rated surface energy and intensively treated samples, the increasein O/C ratio after UV-ozone treatment is larger than after �Plasmatreatment. This was visible in the larger decrease in C C aromaticbonds for the UV-ozone treatment. Also, a difference in the formedoxygen containing groups was found. Whereas, the formation ofC O, C O C and O C O groups is seen for both treatment meth-ods, the formation of those groups is more present after UV-ozonetreatment, while hydroxyl groups are more present after �Plasmaprinting. This indicates that UV-ozone does more damage to thesubstrate surface compared to �Plasma printing. This is probablydue to the differences in the chemistry and reactivity of the plasma-generated species and UV-ozone-generated species. Overall, it canbe concluded that �Plasma printing results in a more chemicallyselective modification as compared to UV-ozone. In the case thatchemical selectivity and treatment duration time are consideredimportant, �Plasma printing is favourable over UV-ozone.

Acknowledgements

Wouter Brok, Ed Bos and Peter Verhoeven from InnoPhysicsB.V. are thanked for their cooperation and technical support onthe �Plasma print system. Roel Aben, Tom Verstraaten, Antje vanden Berg and Frans Caris are thanked for their support on the ATR-

FTIR measurements and Tatiana Fernández Landaluce from theEindhoven University of Technology is thanked for the XPS mea-surements and analysis. This work is financially supported by theFoundation Innovation Alliance (SIA - Stichting Innovatie Alliantie).

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R.O.F. Verkuijlen et al. / Applied

eferences

[1] M. Berggren, D. Nilsson, N.D. Robinson, Organic materials for printed electron-ics, Nat. Mater. 6 (2007) 3–5.

[2] B.J. de Gans, P.C. Duineveld, U.S. Schubert, Inkjet printing of poly-mers: state of the art and future developments, Adv. Mater. 16 (2004)203–213.

[3] T.W. Kelley, P.F. Baude, C. Gerlach, D.E. Ender, D. Muyres, M.A. Haase, D.E.Vogel, S.D. Theiss, Recent progress in organic electronics: materials, devices,and processes, Chem. Mater. 16 (2004) 4413–4422.

[4] M. Geoghegan, G. Krausch, Wetting at polymer surfaces and interfaces, Prog.Polym. Sci. 28 (2003) 261–302.

[5] S. Merilampi, T. Laine-Ma, P. Ruuskanen, The characterization of electricallyconductive silver ink patterns on flexible substrates, Microelectron. Reliab. 49(2009) 782–790.

[6] B.J. Kang, Y.S. Kim, Y.W. Cho, J.H. Oh, Effects of plasma surface treatments oninkjet-printed feature sizes and surface characteristics, Microelectron. Eng. 88(2011) 2355–2358.

[7] U. Kogelschatz, Fundamentals and applications of dielectric-barrier discharges,in: HAKONE VII Int. Symp. On High Pressure Low Temperature Plasma Chem-istry, Greifswald, 2000.

[8] M. Lehocky, H. Drnovska, B. Lapcı′ková, A. Barros-Timmons, T. Trindade, M.Zembala, L. Lapcı′k, Plasma surface modification of polyethylene, Colloids Surf.,A 222 (2003) 125–131.

[9] C.M. Chan, T.M. Ko, H. Hiraoka, Polymer surface modification by plasmas andphotons, Surf. Sci. Rep. 24 (1996) 1–54.

10] A. Holländer, R. Wilken, J. Behnisch, Subsurface chemistry in the plasma treat-ment of polymers, Surf. Coat. Tech. 116 (1999) 788–791.

11] R. Rochotzki, M. Nitschke, M. Arzt, J. Meichsner, Plasma modification of polymerfilms studied by ellipsometry and infrarot spectroscopy, Phys. Status Solidi A145 (1994) 289–297.

12] J.R. Vig, UV/ozone cleaning of surfaces, J. Vac. Sci. Technol. A 3 (1985)1027–1034.

13] A. Oláh, H. Hillborg, G.J. Vancso, Hydrophobic recovery of UV/ozone treated poly(dimethylsiloxane): adhesion studies by contact mechanics and mechanism ofsurface modification, Appl. Surf. Sci. 239 (2005) 410–423.

14] M. Strobel, M.J. Walzak, J.M. Hill, A. Lin, E. Karbashewski, C.S. Lyons, A compari-son of gas-phase methods of modifying polymer surfaces, J. Adhes. Sci. Technol.9 (1995) 365–383.

15] J.M. Grace, L.J. Gerenser, Plasma treatment of polymers, J. Disper. Sci. Technol.24 (2003) 305–341.

[

e Science 290 (2014) 381– 387 387

16] G. Borcia, C. Anderson, N. Brown, The surface oxidation of selected polymersusing an atmospheric pressure air dielectric barrier discharge. Part II, Appl. Surf.Sci. 225 (2004) 186–197.

17] G. Borcia, C. Anderson, N. Brown, The surface oxidation of selected polymersusing an atmospheric pressure air dielectric barrier discharge. Part I, Appl. Surf.Sci. 221 (2004) 203–214.

18] A. Petryakov, Y.S. Akishev, A. Balakirev, M. Grushin, M. Trushkin, On the inducedageing of hydrophilic and hydrophobic properties of polymer films treated bynon-thermal plasma, in: Modification of Materials with Particle Beams andPlasma Flows, Russian Academy of Sciences, Tomsk, Russia, 2010, pp. 368–371.

19] W. Brok, A. Stevens, E. Bos, T.N. Huiskamp, v.H. Hijningen, d. Haan, The potentialof plasma printing, Mikroniek (2011) 32–39.

20] T. Huiskamp, W. Brok, A. Stevens, E. van Heesch, A. Pemen, Maskless patterningby pulsed-power plasma printing, IEEE Trans. Plasma Sci. 40 (2012) 1913–1925.

21] M.H.A. van Dongen, E.J. Nieuwenhuis, L. Verbraeken, R.O.F. Verkuijlen, J.P.C.Bernards, Plasma printing of hydrophobic and hydrophilic patterns to improvewetting behaviour for printed electronics, in: Proceedings LOPE-C, 2012.

22] M.H.A. van Dongen, E.J. Nieuwenhuis, L. Verbraeken, R.O.F. Verkuijlen, P.H.J.M.Ketelaars, J.P.C. Bernards, Digital printing of (plasmas to selectively improvewetting behavior of functional inks for printed electronics, in: Proceedings NIP28 and Digital Fabrication 2012, 2012, pp. 436–439.

23] M.H.A. van Dongen, R.O.F. Verkuijlen, J.P.C. Bernards, Inkjet printing of func-tional materials on selectively plasma treated surfaces, in: Proceedings LOPE-C2011, 2011, pp. 181–185.

24] D.K. Owens, R. Wendt, Estimation of the surface free energy of polymers, J. Appl.Polym. Sci. 13 (1969) 1741–1747.

25] G. Ström, M. Fredriksson, P. Stenius, Contact angles, work of adhesion, andinterfacial tensions at a dissolving hydrocarbon surface, J. Colloid Interf. Sci.119 (1987) 352–361.

26] R. Morent, N. De Geyter, C. Leys, L. Gengembre, E. Payen, Comparison betweenXPS and FTIR analysis of plasma treated polypropylene film surfaces, Surf.Interface Anal. 40 (2008) 597–600.

27] J.F. Moulder, J. Chastain, R.C. King, Handbook of X-ray photoelectron spec-troscopy: a reference book of standard spectra for identification andinterpretation of XPS data, Physical Electronics, Eden Prairie, MN, 1995.

28] N. De Geyter, R. Morent, C. Leys, L. Gengembre, E. Payen, Treatment of polymer

films with a dielectric barrier discharge in air, helium and argon at mediumpressure, Surf. Coat. Technol. 201 (2007) 7066–7075.

29] K. Fricke, H. Tresp, R. Bussiahn, K. Schröder, K. Weltmann, T. von Woedtke,Modification of the physicochemical surface properties of polymers during theplasma-based decontamination.