P

Ewfi

A

DS

RA

h2l

erspectives in Science (2016) 8, 472—474

Available online at www.sciencedirect.com

ScienceDirect

j our na l homepage: www.elsev ier .com/pisc

ffect of coating current density on theettability of electrodeposited copper thinlm on aluminum substrate�

run Augustin ∗, K. Rajendra Udupa, K. Udaya Bhat

epartment of Metallurgical and Materials Engineering, National Institute of Technology Karnataka,urathkal, Mangalore, Karnataka 575025, India

eceived 20 February 2016; accepted 5 June 2016vailable online 30 June 2016

KEYWORDSCopper thin film;SEM, TEM;Contact angle

Summary Copper is the only one solid metal registered by the US Environmental ProtectionAgency as an antimicrobial touch surface. In touch surface applications, wettability of the sur-face has high significance. The killing rate of the harmful microbes depends on the wetting ofpathogenic solution. Compared to the bulk copper, coated one on aluminum has the advan-tage of economic competitiveness and the possibility of manufacturing complex shapes. In thepresent work, the copper coating on the aluminum surface has successfully carried out by elec-trodeposition using non cyanide alkaline bath. To ensure good adhesion strength, the substratehas been pre-zincated prior to copper deposition. The coating current density is one of theimportant parameters which determine the nucleation density of the copper on the substrate.To understand the effect of current density on wettability, the coating has done at differentcurrent densities in the range of 3 A dm−2 to 9 A dm−2 for fixed time interval. The grain sizehas been measured from TEM micrographs and showed that as current density increases, grainsize reduces from 62 nm to 35 nm. Since the grain size reduces, grain boundary volume hasincreases. As a result the value of strain energy (calculated by Williamson—Hall method) hasincreased. The density of nodular morphology observed in SEM analysis has been increased withcoating current density. Further, wettability studies with respect to double distilled water onthe electrodeposited copper coatings which are coated at different current densities are car-

ried out. At higher current density the coating is more wettable by water because at theseconditions grain size of the coating decreases and morphology of grain changes to a favorabledense nodularity.© 2016 Published by Elsevier Gm(http://creativecommons.org/l

� This article belongs to the special issue on Engineering and Material

∗ Corresponding author. Tel.: +91 9740641930.E-mail address: arunmalabar@yahoo.com (A. Augustin).

ttp://dx.doi.org/10.1016/j.pisc.2016.06.003213-0209/© 2016 Published by Elsevier GmbH. This is an open access articenses/by-nc-nd/4.0/).

bH. This is an open access article under the CC BY-NC-ND licenseicenses/by-nc-nd/4.0/).

Sciences.

icle under the CC BY-NC-ND license (http://creativecommons.org/

ro(a2bXtm

R

M

Fidtdmhcprg

Effect of coating current density on wettability

Introduction

Copper is the most proved antimicrobial metal which can beused in hospital as antimicrobial touch surfaces. More overUS Environmental Protection Agency (EPA) has declared thatcopper is the only solid metal which can be used as antimi-crobial touch surfaces. 99.99% pure copper thin film withnano crystalline size can be easily deposited on aluminumtouch surface by electrodeposition method (Lu et al., 2009).The surface energy of the coating is one of the key fac-tors, which determine the rapidity of antimicrobial actionbecause as surface energy increases, pathogenic solutionspreads faster on the copper coating. The increased wett-ability makes the maximum surface contact between copperand pathogens, as a result antimicrobial action will be faster(Nie et al., 2010). The crystalline size has a direct impreca-tion on the surface energy of the coating. Along with surfaceenergy, surface morphology also play significant role in thewettability of surfaces. As current density (j) of electrode-position changes, the coating morphology and crystallitesize varies (Augustin et al., 2015). In the present study,the microstructural changes of the coating and changes inspreading rate of the distilled water with variation in currentdensity of coating has been analyzed.

Experimental details

The copper thin film has been electrodeposited using DCpower source on aluminum substrate at the current density

tta9

Figure 1 SEM micrograph of copper coating at deposition curren9 A dm−2 respectively.

Figure 2 Bright field TEM micrograph of copper coating done at cu

473

ange of 3—9 A dm−2 for the duration of 10 min. The morphol-gy has been studied using Scanning Electron MicroscopeSEM, JSM-6380, JEOL). The crystallite structure has beennalyzed using Transmission Electron Microscope (TEM, JEM-100, JEOL). The strain energy density of the film haseen calculated from X-ray diffraction profile obtained from-Ray Difractometer (XRD, JDX-8P, JEOL). The dynamic con-act angle of distilled water on the coated sample waseasured for the duration of 300 s using FTA 200 equipment.

esults and discussion

icrostructural analysis of the coating

ig. 1 shows the SEM images (topography) of copper coat-ng done at different coating current densities. As currentensities of coating increases from 3 A dm−2 to 9 A dm−2,he continuity and roughness of coating changes. This isue to the increased nucleation of copper ions on alu-inum surface. The increased supply of copper ions at

igher current density facilitates the increased growth ofopper nodules. As a result uneven copper nodules growerpendicular to the surface as shown in Fig. 1(d). So theoughness of the coating is observed to be more. TEM micro-raph of the copper coating is shown in Fig. 2 reveals

hat each nodule is formed by number of nanosized crys-allites. The average crystallite size of the coating donet 3 A dm−2 was found to be 62.7 nm, where as that of

A dm−2 was 35.4 nm. The improved nucleation of copper

t densities of (a) 3 A dm−2, (b) 5 A dm−2, (c) 7 A dm−2 and (d)

rrent density of (a) 3 A dm−2 and (b) 9 A dm−2 respectively.

474

Fo

arHrarteTwtfe

C

Fdctwmftmcoi(cAcr

aWatorsi2

C

Mdpifctsfp

A

ArlitI

R

A

B

D

L

igure 3 Contact angle of distilled water on copper coatingf different current densities (j).

t higher current density can be assigned to the increasedate of copper ion movement toward cathode in the bath.ence electron microscopic studies revealed that as cur-ent density of the deposition increases, faster nucleationnd improved growth of nodules occurred. As crystallite sizeeduces, crystallite boundary volume increases. This leadso the increase in strain energy density, which has beenstimated by Williamson—Hall method (Biju et al., 2008).he values were increased from 158.4 kJ m−3 to 288.6 kJ m−3

ith the increase of coating current density from 3 A dm−2

o 9 A dm−2. Along with crystallite size boundaries, twinsormed in the copper thin film also contributes to the strainnergy density.

ontact angle analysis

ig. 3 shows the dynamic contact angle measurement ofistilled water on copper thin film deposited at differenturrent densities. Except j = 3 A dm−2, all coating has an ini-ial contact angle <90◦ (hydrophilic nature). The maximumetting was observed for the sample j = 9 A dm−2. This can beainly attributed to the increased surface energy and sur-

ace roughness of the coating. As crystallite size reduced,he strain energy density (calculated from Williamson—Hallethod) has increased. Hence the surface energy of the

oating is expected to be increased. The spreading ratebtained from the slope of the graph (shown in Fig. 3) alsoncreased slightly for the coating of small crystallite sizej = 9 A dm−2). The topography and surface roughness of the

oating also affects the contact angle (Drelich et al., 2011).t higher current density of coating, the unevenly grownopper nodule (shown in Fig. 1(d)) increases the coatingoughness. The effect of surface roughness on the contact

N

A. Augustin et al.

ngle is given by the relation; cos �′ = rcos � (Wenzal model).here, r is the roughness factor defined by the ratio of

ctual surface area to geometrical surface area, � is the con-act angle on the corresponding smooth surface and �′ is thatf rough surface. Because of r > 1 contact angle is reduced inough surfaces. As coating is meant for antimicrobial touchurfaces applications, the super hydrophilic nature of coat-ng enhances biocidal activity of copper coatings (Nie et al.,010).

onclusions

orphology of the coating is changed with different currentensities of coating because nucleation is driven by cop-er ion transferring rate. As current density of the coatingncreases from 3 A dm−2 to 9 A dm−2, crystallite size reducedrom 62.7 nm to 35.4 nm. The contact angle has reduced withurrent density of the coating due to the reduction in crys-allite size and increase in surface roughness. As crystalliteize reduces, the strain energy density has increased. There-ore coating done at higher current density is expected toerform better biocidal activity.

cknowledgements

uthors would like to thank Dr. Narayana Prabhu and hisesearch student Ms. Mrunali Sona, Department of Metal-urgical and Materials Engineering, NITK, India, for helpingn contact angle measurements. Arun Augustin would like tohank the National Institute of Technology Karnataka (NITK),ndia, for the research fellowship.

eferences

ugustin, A., Bhat, K.U., Udupa, K.R., Hegde, A.C.,2015. Electronmicroscopic study of nodules formed during electrodeposition ofcopper on aluminium. In: Materials Science Forum. Trans TechPubl, pp. 371—374.

iju, V., Sugathan, N., Vrinda, V., Salini, S.L., 2008. Estima-tion of lattice strain in nanocrystalline silver from X-raydiffraction line broadening. J. Mater. Sci. 43, 1175—1179,http://dx.doi.org/10.1007/s10853-007-2300-8.

relich, J., Chibowski, E., Meng, D.D., Terpilowski, K., 2011.Hydrophilic and superhydrophilic surfaces and materials. SoftMatter 7, 9804—9828, http://dx.doi.org/10.1039/C1SM05849E.

u, L., Chen, X., Huang, X., Lu, K., Lu, L., Chen, X., Huang, X.,Lu, K., 2009. Revealing the maximum strength in nanotwinnedcopper. Science 323, 607—610, http://dx.doi.org/10.1126/science.1167641.

ie, Y., Kalapos, C., Nie, X., Murphy, M., Hussein, R., Zhang, J.,2010. Superhydrophilicity and antibacterial property of a Cu-dotted oxide coating surface. Ann. Clin. Microbiol. Antimicrob.9, 1—10, http://dx.doi.org/10.1186/1476-0711-9-25.