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oatioutinoerthlmofmust be met. In this respect, the present investigation proposes the design of self-s and the manufacturing of the corresponding thick coatings (approximately

ave achdesignical stac side)

Surface & Coatings Technology 236 (2013) 212223

Contents lists available at ScienceDirect

Surface & Coatin

l seprotection and/or functionalization by a tailor-made coating materialare pursued [3]. In addition, the potential of these coatings is greatlyemphasized because they offer good adhesion to various substrates [3].Furthermore, some of these coatings can dry/cure at relativelymoderatetemperature (i.e., ~70250 C [4]), making them suitable as topcoats fora large share of substrates, including some thermolable substrates. Nev-ertheless, organicinorganic hybrid coatings are often very brittle [57]and they can collapse if applied as thick lm on rigid substrates due toshrinkage during the drying/curing process [8,9]. Malzbender and deWith observed that the shrinkage phenomenon related to the drying/

organicinorganic hybrid coatings synthesized via the solgel route isof utmost interest as it would greatly extend applications of this classof materials. In this respect, many efforts have been made by scientistsand practitioners to widen the range of coatings that could be designedand manufactured via the solgel route. However, the proposedsolutions converged toward the implementation of very thin coatings(i.e., typically a few microns) to reduce the onset of the detrimentalstress eld bymaterial shrinking and toward the adhesion beingmainlyimproved through the combination of two or more organicinorganicmolecules, some with only mere grafting functionality. Such thin coat-curing process of organicinorganic hybrid colarge residual stress eld inside the coating man early failure of the coating if applied with

Corresponding author. Tel.: +39 0672597195; fax: +E-mail address: barletta@ing.uniroma2.it (M. Barletta)

0257-8972/$ see front matter 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.surfcoat.2013.09.049with the toughness andorganic side) [1,2]. Theseomains where substrate

can bulge or even delaminate from the substrate evenwithout the appli-cation of an external load.

Thus, preventing the bulging and delamination phenomena of

ductility typical of organic materials (i.e., thecoatings could be protably used in several d1. Introduction

Organicinorganic hybrid coatings henvironments because they can becombine the high hardness and chemor ceramic materials (i.e., the inorganiperformance of the coatings was tested using progressive- and constant-mode scratch tests, and the wearresistance was examined using dry sliding linear reciprocating tribological tests. The experimental ndingsdemonstrate how the role of the interface is crucial and howmicro-corrugation is extremely benecial in increas-ing the threshold of the maximum thickness beyond that at which coating bulging and delamination occur.

2013 Elsevier B.V. All rights reserved.

ieved success in scienticed via solgel route tobility typical of glass-like

critical values [9]. In particular, when the organicinorganic hybrid coat-ings are deposited on non-compliant substrates such as glass substrates,themismatch at the interface between the shrunk coatings and underly-ing substrates is strongly emphasized and this mismatch can increasethe possibility of a spontaneous collapse of the coating system, whichDamage mechanismsSiliconeepoxy ~120 mthick) on as-received andmicro-corrugated glass using an automatic drawdown applicator. The scratchScratch resistance mance and wear endurancedrying siliconeepoxy resinApplication and drying at ambient temperorganicinorganic hybrid coatings on glass

M. Barletta a,, M. Puopolo b, A. Gisario b, S. Vesco a

a Dipartimento di Ingegneria dell'Impresa, Universit degli Studi di Roma Tor Vergata, Via deb Dipartimento di Ingegneria Meccanica ed Aerospaziale, Sapienza Universit degli Studi di R

a b s t r a c ta r t i c l e i n f o

Article history:Received 3 August 2013Accepted in revised form 23 September 2013Available online 2 October 2013

Keywords:Adhesion

Organicinorganic hybrid cdesigned using the solgel rceramic materials (i.e., the(i.e., the organic side). Nevcollapse if applied as thick However, the manufacturing

j ourna l homepage: www.eatings can often induce aaterial, which can lead toa thickness over intrinsic

39 062021351..

ghts reserved.ure of thick

litecnico, 1-00133 Roma, Italy, Via Eudossiana, 18-00184 Roma, Italy

ngs have achieved success in scientic environments because they can bee to combine the high hardness and chemical stability typical of glass-like orrganic side) with the toughness and ductility typical of organic materialseless, organicinorganic hybrid coatings are often very brittle, and they canon rigid substrates because of the shrinkage during the drying/curing process.a thick coating is compulsory, when stringent requirements for scratch perfor-

gs Technology

v ie r .com/ locate /sur fcoatings have been used in industrial applications such as for optical, decora-tive or architectural materials. For example, the large-scale dip coatingprocess to prepare reective and antireective layers based on Pdcontaining TiO2 or SiO2/TiO2 systems has become a well-establishedtechnology (Irox, Amiran, Calorex, Schott Co.) [10]. Similarly, anti-reective coatings suitable as cover sheets for photovoltaic (PV) cellsand collectors have been commercially available from nearly a decade,although their preparation involves a relatively high temperature

(600 C) ring process [11,12]. Coatings for decorative and architecturalpurposes were industrialized by including pigments in the solgeldesign with a range of different features [13,14]. In contrast, themanufacturing of a thin coating excludes any possibility of developingsurface overlying materials that could meet the industrial standardfor anti-scratch or wear resistant barriers. This fact was conrmed byseveral experimental results reported in the literature [15]. Han et al.attempted to verify the scratch performance of a solgel deposited organ-icinorganic hybrid coating material based on TEOS, 3-(trimethoxysilyl)propylmethacrylate and urethane acrylate deposited on a oat glass byow coating with a thickness of approximately 3.5 m. The ultimatecritical load was nearly 2 N beyond which the coatings were found todelaminate [15].

Despite the signicant efforts made to produce versatile and indus-trially sustainable organicinorganic hybrid coating materials, thereare only a handful of practical applications in which these materialsare effectively in service. Thus, the present investigation proposes an

preserve the initial efciency of the underlying glass substrate over along period.

2. Experimental

2.1. Materials

Flat substrates, 3.8 mm thick, 25 100 mm2 wide and cut from a2 m2 tempered glass sheet, were coated with a high-solid two-packsiliconeepoxy resin (SILIKOPON EF, Evonik, Essen, Germany) dilutable(1:1) by esters, ketones and glycol ethers and cross-linked with bis(trimethoxysilylpropyl) amine (amine H-equivalent, 335 g/mol)supplied by Evonik (Ameo, Essen, Germany). Thickeners (TegoViscoplus 3030, Evonik, Essen, Germany) and ow promoters (TegoFlow 370, Evonik, Essen, Germany) were added to the formulation toobtain a homogenous coating thickness through strict control of themixture rheology.

213M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223alternative approach to controlling the shrinkage during post-dryingat ambient temperature of thick organicinorganic hybrid coatingson already in service glass. This approach would be extremely bene-cial as it would increase the threshold of the maximum thicknessbeyond which coating bulging and delamination would occur, thusexpanding the applicability of organicinorganic hybrid coatings inindustrial domains in which their combined high micro-mechanicalperformance and wear endurance cannot be ignored. The alternativeapproach consists of the development of a highly transparent organ-icinorganic hybrid material, whose structure is designed on a siliconeskeleton with lateral chains consisting of epoxy groups that are cross-linkable with amine-based organofunctional silane hardeners. Aftercross-linking, the hardener confers both high mechanical and tribolog-ical resistance to the coating material. Proper formulations of siliconeepoxy resins were designed and applied with a high thickness(approximately 120 m) using an automatic drawdown applicator onas-received and sandblasted glass substrates. The process was follow-ed by spontaneous drying to ensure the consolidation of the coatings.Sandblasting was thought to generate a high specic contact area atthe coatingsubstrate interface through the onset of widespreadmicro-asperities on the glass surface. Such micro-asperities werebelieved to act as obstacles to the stress eld generated by the strongshrinkage phenomenon during the drying/cross-linking of the thickoverlaying layer of the siliconeepoxy resin, thus avoiding or delayingthe coating failure by bulging or delamination. Characterization of themorphology, visual appearance, micro-mechanical and tribologicalperformance of the coatings was thus performed. The experimentalndings revealed that the siliconeepoxy coatings deposited on thesandblasted glass substrate were extremely suitable for protectingthe overlying layer from early failure due to scratches or wearphenomena. Accordingly, the coating demonstrated high potential toFig. 1. 3D maps of the as-received and coated glasses: (a) as-received glass, (b) san2.2. Manufacturing process

As received glass substrates were degreased by sonication in 95%EtOH for 30 min. Half of the specimens were sandblasted (6 bar, neglass beads, sandblasting equipment, 0580, Fervi Srl, Modena, Italy) tocoarsen the startingmorphology and favor coating adhesion. To removeall glass residuals from the previous process, the substrates were rinsedthoroughly by sonication in demineralized water. The siliconeepoxyformulation was then deposited after dilution (1:1) in acetone on boththe as-received and sandblasted glass substrates using an automaticdrawdown bar applicator (Automatic Film Applicator L, BYK-Gardner,Geretsried, Germany) equipped with a doctor blade. The resultingcoatings were left to cure at ambient temperature for 24 h. After curing,the coating thicknesses were measured using a digital Palmer caliber(293-816, Mitutoyo, Kawasaki, Japan) with a resolution of 0.001 m.All coatings with thicknesses falling outside the prescribed range of120 20 mwere discarded.

2.3. Characterization of the coatings

Themorphology of the coatingswas recorded using a contact induc-tive gauge of a CLI proler (TalySurf CLI 2000, Taylor Hobson, Leicester,UK). An area of 4 4 mm2was analyzed, and 2000 proles were storedwith a resolution of 1 m. The data were elaborated using TalyMap 3.1software (Taylor Hobson, Leicester, UK) to extrapolate the roughnessparameters and corresponding 3D maps. The scratch resistance of thehybrid coating was evaluated by constant-load scratch tests (Micro-Combi, CSM Instruments, Peseaux, Switzerland) using two differentRounded Conical Rockwell C diamond indenters with tip radii of 800and 200 m and an applied load of 20 N along the 2 mm scratchdblasted glass, (c) as-received coated glass, and (d) sandblasted coated glass.

pattern. The sliding speed of the scratch indenter was varied from 0.2 to100 mm/min.

Progressive load scratch tests were performed with the sameindenters (200 and 800 m tip radii). The applied load, along the3 mm pattern, was progressively increased from 0 to 30 N for the in-denters with the 800 and 200 m tip radii. The sliding speed was keptconstant at 1 mm/min.

The scratch equipment enabled themeasurement of the normal andtangential forces and of the penetration and residual depths, that is, thepenetration of the indenter tip inside the coating material during theapplication of the load and after the load release and recovery in theelastic eld of the indented material. For this purpose, the initial proleon which the scratch test was to be performed was measured by prob-ing it at a constant applied load of 0.03 N during the pre-scan and, then,subtracting the indenter position during the application of the load(scan), thus determining the penetration depths. The residual depthswere measured during the post-scan by applying the minimal load of0.03 N and probing the scratched surface again after the recovery ofthe material in the elastic eld. The analysis of the scratch patternafter the load release was also performed using a eld emission gun-scanning electron microscopy (FEG-SEM Leo, Supra35, Carl Zeiss SMT,Inc. Thornwood, NY, USA) and stereomicroscopy (SMZ 745T, Nikon,Japan).

The wear resistance of the siliconeepoxy coatings was investigatedby performing dry sliding linear reciprocating tribological tests(Tribometer, C.S.M. Instruments, Peseaux, Switzerland), using a spheri-cal antagonist (6 mm in diameter, 100Cr6 bearing steel). Incrementalsliding distances of up to 500 m were considered. The load during thetribological tests was set at 1 N, the sliding frequency was set at 3 Hz

214 M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223and the sliding distance for each strokewas set at 6 mm. The equipmentpermitted the measurement of the friction during the test. In addition,after the load release and recovery of the material in the elastic eld,the wear pattern was monitored by contact gauge prolometry, SEMand stereomicroscopy. The prolometry allowed for the 3D rebuildingof the wear pattern (resolution of 2 m) and thus the estimation ofthe amount of abraded material during the tribological tests.

Fig. 2. Siliconeepoxy coatings after the drying/cross-linking process: (a) spontaneousdelamination on the as-received glass substrate due to the shrinkage phenomenon; and

(b) good adherence of the coatingsubstrate on the sandblasted substrate.3. Results and discussion

3.1. Coating build-up and analysis of the morphological features

The deposition of thick siliconeepoxy coatings on a at glass sur-face at ambient temperature should necessarily involve the micro-roughening of the surface to ensure the establishment of a solid bondbetween the resin and substrate by gluing [16], whereas the establish-ment of satisfactory chemical bonds is prevented by the lack of a propercuring process at higher temperature [4,8]. In fact, the siliconeepoxyresin can ll the gaps among the asperities of the micro-roughenedsurface and adhere strongly via simple mechanical interlocking afterspontaneous drying [17].

Fig. 1a and b show the difference in the surfacemorphology of an as-received and sand-blasted substrate. The as-received glasses are verysmooth with an average roughness Ra and ISO 10-point height Rz of~0.2 and ~3.0 m, respectively. After sandblasting with very ne glassbeads, the resulting morphology of the glass substrates is micro-coarsened. The established morphology is the result of superimposedpeaks and valleys, which are generated from each individual impact ofthe glass beads on the relatively brittle glass surface. Thus, the nalmor-phology is spiky but displays a uniform distribution of the asperities,with the average roughness Ra and ISO 10-point height Rz increasingto ~3.0 m and ~17.9 m, respectively.

Fig. 1c and d show the morphology of the glass substrates after thedeposition of the siliconeepoxy resin. The resin deposits on the as-received glass, thus copying the initial morphology of the glass itself.However, the intrinsic self-leveling ability of the resin formulationcauses a further improvement in the smoothness of the substrate,with the average roughness Ra and ISO 10-point height Rz of the coatedsurface decreasing to 0.06 m and 0.8 m, respectively. In contrast,when the resin is deposited on the sandblasted glasses, it signicantlymodies their morphology. The resin inltrates the surface irregu-larities, lling the gaps among them. Thus, the morphology of thesandblasted glass is smoother after coating with the siliconeepoxyresin. The deposition process is benecial to both the visual appearanceof the substrate, which becomes fairly smooth again and the coating ad-hesion, which can be favored by themechanical anchoring between theresin layers and underlyingmicro-corrugated glass asmentioned earlier[18,19]. However, the micro-corrugation of the sandblasted glass doesnot allow the resin to elicit its maximum intrinsic self-leveling capabil-ity. The wetting of the sandblasted glass surface differs from that of theas-received glass. The micro-asperities on the sandblasted glass tend toretain the resin from owing on the surface and limit its self-levelingproperty. Thus, an orange-peelmorphology is established on the coat-ing surface. This morphology is essentially composed of the superimpo-sition of soft hills and valleys, which are uniformly sparse on the coatingsurface. Accordingly, the siliconeepoxy coating deposited on thesandblasted glass is characterized by an average roughness Ra and anISO 10-point height Rz of 0.3 and 2.9 m, respectively. These roughnessparameters conrm the smoothing of the sandblasted substrates afterthe deposition of the resin. However, these values differ considerablyfrom those achievable by depositing the siliconeepoxy resin on theas-received glass substrate and, overall, the coatings deposited on thesandblasted substrates maintain a signicant residual coarseness,which could certainly affect the interaction with the liquid-driven soils.

3.2. Scratch response

The hardness and scratch response of the coatings are ascribable toboth the intrinsic properties of the materials selected and the overallcoating system, particularly the latter. Thus, the hardness and scratchresponse may be related to the substrate features, coating thicknessesand nature of the bonding at the interface between coatings and sub-strates. For in-service glass substrates, the routes to increasing hardness

and scratch performance should adhere to the following steps: (i) the

215M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223selection of a coating material with extreme performance, as the classof the siliconeepoxy resin cross-linked with amine-based organo-functional silane ensures; (ii) the application of coatings that are suf-ciently thick to ensure a high micro-mechanical response but withoutbeing overly brittle or stressed because of the shrinkage phenomenonof the resin during the drying and cross-linking process; and (iii) pre-treatments of the glass substrates to increase the potential contactsurface at the interface.

For the rst step, thematerial formulation investigated here is basedon a siliconeepoxy resin with a substantially inert silicone skeleton onwhich lateral chains consisting of reactive epoxy groups lay. The epoxygroups can react in the presence of amine-based organofunctional

Fig. 3. SEM images of to the residual scratch pattern after constantmode scratch tests. ThemeasuThe test was performed on the as-received substrates (ae) and sandblasted substrates (fl). The sand (e, l) 100 mm/min.silane hardeners. Cross-linking generates complex networks that areextremely hard and scratch resistant. High hardness can be achievedafter hardening of siliconeepoxy resin with the amine-based hard-eners and spontaneous drying. A pencil hardness of 67H is measuredwhen depositing the resulting coating system on already in-serviceglass. Higher hardness could potentially be achieved by controlling thereaction of the siliconeepoxy resin with amine-based hardeners.Nevertheless, drying should be performed at a moderate temperatureof 6070 C. The temperature would increase the motility of eachindividual molecule, thus increasing the degree of curing and delayinggelation. Higher drying temperatures (N6070 C) are counterproduc-tive as they would favor the evaporation of the hardeners, thus

rement conditionswere: an indenterwith an 800 mtip radius and a normal load of 20 N.liding speeds were: (a, f) 0.2 mm/min, (b, g) 1 mm/min (c, h) 5 mm/min, (d, i) 25 mm/min,

216 M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223signicantly decreasing the reaction grade. However, thermal cross-linking is impractical when it should be performed on in-service glasspanels. At ambient temperature, although the reagents (i.e., the epoxygroups on the silicone skeleton and the amine groups on the hardeners)have considerable time to combine, their motility is limited by theintrinsic viscosity of the formulation. The viscosity can be regulated bythe solvent concentration. However, the viscosity of the mixture in-creases rapidly once cross-linking begins. The corresponding motilityof the molecule inside the mixture is largely reduced and gelationcan occur rather quickly, thus limiting the maximum degree of cross-linking and the maximum coating hardness achievable.

In the present investigation, the coating thickness was alwaysmaintained at ~120 m,which is at least one order ofmagnitude greaterthan the thickness selected for the application of common coatings onglass manufactured via the solgel route [4,20,21]. The deposition ofsuch a thick coating on an already in-service stiff glass substrate at ambi-ent temperature is troublesome. In fact, it involves a massive shrinkageof the resin during the simultaneous drying/cross-linking process witha non-compliant substrate. Thus, shrinkage is one source for the onset

Fig. 4. Trends in the friction force during constant-mode scratch testing. The test wasperformed using an indenter with an 800 m tip radius at an applied load of 20 N.of a major stress eld that is retained inside the coating. The stress istensile, acting parallel to the coatingsubstrate interface, andmay be suf-ciently high to lead to spontaneous breakage and delamination at theinterface of the coating from the underlying substrate as shown inFig. 2a and reported in the literature [8,9]. Such a stress eld cannot berelieved when the coating is deposited on a non-compliant substratesuch as stiff glass. However, a proper design of the coatingsubstrateinterface can oppose the action of the stresseld. In particular, this oppo-sition can be performed by increasing the interfacial contact surfacebetween the coating and substrate by corrugation. Corrugation createsinterruptions on the very smooth glass surface in the form of micro-asperities. The widespread presence of micro-asperities that are welldistributed on the coating surface acts as an obstacle against the actionof the stress eld generated by the shrinkage phenomenon of the resinon the stiff glass during the drying/cross-linking process. Thus, suchmicro-asperities mechanically oppose the spread of the stress eld,potentially preventing early failure of the coating (Fig. 2b).

The implementation of the latter step includes the selectionbetween two methods of increasing the interfacial adhesion on inservice glass: (i) chemical etching of the glass substrate with aggres-sive (acidic) solutions to promote micro-coarsening of the surface;and (ii) sandblasting of the glass surface with ne glass-beads toachieve micro-coarsening due to the impingements of the beads onthe brittle substrate. The former route is substantially impracticalbecause it is characterized by a massive environmental impact relatedto the usage of powerful reactants and the need to remove of them.The latter route is simpler because it involves only inert materialsthat can also be left in the environment after use and can adherentlydeposit coating formulation on a micro-roughened surface, as statedin Section 3.1.

Fig. 3 presents the residual scratch pattern of the siliconeepoxycoatings deposited on both the as-received (panels on the left side)and sandblasted (panels on the right side) glass after a constant-modescratch test at a 20 N load with a sliding speed of 0.2100 mm/min,against an indenter with a tip radius of 800 m. The superior scratchresponse of the coating on the sandblasted substrate is neat because itdoes not exhibit any damage or signicant residual deformation. Thecoating deposited on the as-received glass does not exhibit any signi-cant residual deformation either. However, there is signicant damageon the coating surface in the formof large transversal and approximate-ly C-shaped fractures, which fall well within the expected scratch pat-tern, that is, the area of real contact between the sliding indenter andcoating surface. These fractures are compatible with those presentedby Bull et al. for the fragile tensile crack mechanism [22,23]. This frac-ture mechanism is typical of brittle or partially brittle materials, and itis characterized by cracks whose shape is neat; visible pile up or otherplastic deformations could not be detected. The failure mechanism bytensile cracking is ascribable to the compressive stresses accumulatedwithin the coatingmaterialwhen it comes in contactwith the sliding in-denter and is thus submitted to the corresponding tangential force.When a compressive stress eld is generated ahead of the advancing in-denter tip, a tensile stress eld is generated at its back.When the tensilestress exceeds the critical load of the indented material, failure occurswith the concurrent onset of fractures, which are usually C-shapedand occur behind the last contact position between the indenter tipand coating material. Otherwise, the fractures can occur even earlier,that is, under the application of softer loading conditions, when thestress eld inside the coating material is sufciently high to overcomethe adhesive toughness at the interface between the coating and glasssubstrate. In the present investigation, fractures only occur on the coat-ings deposited on the as-received glass, whereas coatings deposited onthe sandblasted glasses do not fail. Thus, sandblasting of the glasssubstrate is particularly useful for improving the interfacial adhesion,by generating the mechanical interlocking of the coating material andunderlying glass substrates [18]. The increase in the local specic con-tact area between the coating and substrate, as well as the inltrationof the resin into the irregularities of the substrate surface, also playsan important role in improving the scratch performance of the investi-gated systems, which is consistent with the ndings observed by[24,25]. The increase in the contact surface between the coating andsandblasted glass together with the presence of a peak to valley mor-phology at the interface should create a discontinuity in the tensilestress eld generated at the back of the advancing indenter. This phe-nomenon is believed to delay the onset of fractures inside the coatingmaterial because it signicantly increases the adhesive toughnessof the coating to the underlying substrate, as stated in the literatureon different coatingsubstrate systems [18,19]. Another interestinghypothesis regarding the difference in the onset of fractures in the coat-ings deposited on the as-received and sandblasted glasses can arise byexamining the trends of the tangential forces (Fig. 4) during constant-mode scratch tests at a load of 20 N with the speeds of 0.2 and100 mm/min and using an indenter with the tip radius of 800 m. Theexperimentallymeasured tangential forces applied by the advancing in-denter on the coating materials depend on the intrinsic features of thecoatings. The coatings on the sandblasted glasses are stressed with alow tangential force, which could experimentally lead to the conclusionthat the lack of fractures on the coatings deposited on the sandblastedsubstrates could also be related to the lower tangential forces actingon them. The reason why the tangential forces should be lower on the

coatings deposited on the sandblasted substrates is difcult to explain.

217M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223However, the tangential forces enables the indenter tip to move alongthe scratch pattern with the nal purpose of maintaining the normalapplied load at the set value of 20 N. Thus, the coatingmaterial opposesresistance to the advancing indenter. The resistance that the indenter isable to oppose depends largely on the intrinsic features of the materialand the mechanism by which the material deforms during the applica-tion of the scratch load. As stated above, the indenter presses thematerial ahead of its advancing tip, generating a compressive stresseld inside the coating and its local plastic deformation. This phenome-non leads to the accumulation of some coatingmaterial in the form of aplastic pile-up in front of the advancing indenter. It could be speculatedthat the micro-roughened interface is better able to withstand the

Fig. 5.Penetration and residual depths of: (a, c) as-received substrates, (b, d) sandblasted substrat an applied load of 20 N.

Fig. 6. SEM images of the residual scratch patterns after progressive-mode scratch test. The meaload of 030 N and a sliding speed of 1 mm/min. The test was performed on the (a) as-receivegeneration of the compressive stress eld inside the coating material.Accordingly, the plastic deformation of the coating and its accumulationin front of the advancing indenter tip would be limited. Thus, less resis-tancewould be offered to the advancing indenter by the deformed coat-ing material and lower tangential forces would be necessary for theindenter to move along the scratch pattern. This process would explainthe lower tangential forcesmeasured during the constant-mode scratchtests. Similarly, this process would support the lack of any fracture phe-nomenon on the coatings deposited on the sandblasted glasses, as theyare submitted to less severe loading conditions.

However, the scratch performance, failure route and critical loadwere often found strictly correlated to the physical afnity between

ates. The testwas a constant-mode scratch test using an indenterwith an 800 mtip radius

surement conditions were: an indenter with an 800 m tip radius, an incremental normald substrate and (b) sandblasted substrate.

the coating and substrate [15], with the substrate corrugation oftenplaying a fundamental role for different systems (for instance, epoxyon sandblasted carbon laminates [26]).

The SEM images in Fig. 3 also reveal that both the number and size ofthe transversal cracks are recorded when varying the sliding speed. Inparticular, at the higher sliding speeds of 25 and 100 mm/min, no signif-icant crack damage is visible either on the deposited coatings or as-received glass. The sensitivity of the coating material to the slidingspeed is likely ascribed to the organic moieties of the resin. The organicmaterials are extremely sensitive to the speed atwhich a load is applied,that is, to the load rate [27]. Polymeric materials can exhibit a stifferresponse as the load rate is increased [28]. The stiffer deformationresponse is typically ascribed to the time-dependent response of themacromolecules, which have an intrinsic time to respond to an externalload and deform accordingly [29]. When the loading rate is excessive,the macromolecules that the organic material is composed of have avery short time to comply with the load and behave stify. In contrast,when the loading rate is low, the macromolecules have more time tocomply with the load, thus deforming signicantly and behaving withmore compliance. In this case, the contribution of the organic moietiesof the resin cannot be neglected. Thus, when the coating material issubjected to an increasing load rate, the organic moieties of the resinbehaves stify because of their intrinsic visco-elasticity and the coating

218 M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223system is better able to withstand the action of the sliding indenter,with no visible cracks appearing along the scratch pattern, regardlessof the geometrical features of the interface between the coating andsubstrate surface.

Fig. 5 presents the trend of the penetration and residual depthmeasured on the siliconeepoxy coatings deposited on both the as-received (panel 2ac) and sandblasted glass (panel 2bd) afterconstant-mode scratch tests at a load of 20 N and variable slidingspeed (0.2100 mm/min) against an indenter with a tip radius of800 m. The extent of deformation under the application of the load issimilar for all coatings regardless of whether they were deposited onas-received or sandblasted glasses, with an average penetration depthof ~30 m. In addition, the aforementioned sensitivity of the coatingmaterial to the imposed sliding speed is conrmed, as the penetrationdepth increases by severalmicronswhen the sliding speed is decreased.Because the residual depth is nearly negligible for all investigated sce-narios (always less than 3.5 m), the deformation response of the coat-ing can be considered visco-elastic. The coatings are considered viscousbecause they are sensitive to the imposed sliding speed during the

Fig. 7. Penetration and residual depth in progressive-mode scratch tests performed at anincremental load of 030 N with a sliding speed of 1 mm/min against an indenter with

an 800 m tip radius.constant-mode scratch test, with the extent of deformation under theload increasing when a lower sliding speed is imposed. The coatingsare considered elastic because they recover almost all of the deforma-tion imposed during the application of the scratch load after its release.The residual depth trends in panels 5c and 5d also enable the detectionof the failure of the coating material after the constant-mode scratchtest and recovery in the elastic eld. In fact, the trend of the residualdepth measured on the coating deposited on the as-received glass is ir-regular, as expected for the coating surface after failure (Fig. 3a, forexample) [26,30]. In contrast, the trend of the residual depth measuredon the coating deposited on the as-received glass is smooth, as the coat-ing surface is not affected by the scratch indentation in this case (Fig. 3f,for example) [26,30]. Although the role of the interface is crucial indetermining the scratch resistance of the coatings, the interface onlyplays a minor role in determining the extent of deformation under theapplication of the load. In terms of the deformation response, a certainrole can be ascribed to the different interface only when the residualdepths are examined. However, the difference largely resides in thefracture events that characterize the coatings deposited on the as-received glass and therefore in the corresponding trends of the residualdepth. Thus, the siliconeepoxy coatings on the as-received glass underthe indenter with a tip radius of 800 m belong to the class of visco-elastic brittle materials. Under such loading conditions, the siliconeepoxy coatings on the sandblasted glass only reveal their intrinsicvisco-elastic nature.

Progressive-load scratch tests performed with an incremental loadof 030 N at sliding speed of 1 mm/min and using the indenter with atip radius of 800 m yield similar ndings as the SEM images in Fig. 6and the penetration and residual depth trends in Fig. 7. The coating de-posited on the sandblasted glass does not display any damage. The cor-responding trends for penetration and residual depth are increasing andfairly smooth. The penetration depth follows a power-law trend, with amaximum penetration depth of ~40 m under 30 N load. The residualdepth increases nearly linearly, whereas it decreases at high load. How-ever, the maximum residual depths are ~22.5 m (~5% of the maxi-mum penetration depth) and can thus be neglected. In fact, it isdifcult to discern any residual deformation on the SEM images inFig. 6. However, these depth trends are fairly common [31]. In particu-lar, the small decreasing branch at the end of the residual depth trendis attributed to the material accumulated by plastic deformation infront of the advancing indenter and, in particular, around the last con-tact position between the indenter tip and coating material. As shownbefore, the coating deposited on the as-received glass reveals certainC-shaped fracture events after constant-mode scratch tests. In thiscase, the route to failure is similar to that observed after the constant-mode scratch tests. Therefore, the involvedmechanisms should be iden-tical. The trend of residual depth for the coating deposited on the as-received glass is characterized by a fairly uneven trend at high loads(N2324 N). Such irregularities in the residual depth trends are attrib-uted to the onset of fractures in the coating, as they were for theconstant-mode scratch tests on similar coating systems.

Increasing the nominal contact pressure during constant- andprogressive-mode scratch tests allows the difference in the scratch per-formance of the coatings deposited on the as-received and sandblastedglasses to be emphasized. In particular, the loading conditions of theconstant-mode scratch testswere exacerbated by applying sharper con-tacts using an indenter with a tip radius of 200 m, setting the load to20 N and varying the sliding speed from 0.2 to 100 mm/min. The SEMimages in Fig. 8 reveal that the coatings deposited on the as-receivedsubstrate collapse under the scratch indenter. The coatings arecompletely detached from the underlying substrates and the rupturespreads far away from the actual contact between the indenter tip andcoating surface. This result implies that the coating material delami-nates on an area that is considerably larger than the actual contactarea with the indenter during the scratch indentation. In addition,

delamination begins at a moderate scratch distance, that is, at the

219M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223beginning of the scratch pattern, within the rst 0.5 mm. This result isdemonstrated by the sudden jump of the penetration and residualdepths to values near the average coating thickness (Fig. 9a and c).The observed failuremechanism can fall within themechanismof buck-ling and brittle spallation, which is consistentwith [22]. As stated previ-ously, the coating material is subjected to a load that is greater than itscritical load or, otherwise, greater than its adhesive strength to theunderlying substrate. Thus, a brittle fracture is generated at the interfacebetween the coating and substrate. The fracture propagates rapidly andcauses the delamination of the coating on a very large area. The SEMimages in Fig. 8ae only allow the delamination of the material to bediscerned. No differences were observed with varying sliding speeds;furthermore, the fastest load rate causes the complete failure of the

Fig. 8. SEM images of the residual scratch patterns after constant-mode scratch tests. ThemeasuThe testwas performed on as-received substrates (ae) and sandblasted substrates (fl). The sli(e, l) 100 mm/min.coating. The stereoscope failure image (sliding speed of 1 mm/min,Fig. 10a) also enables the massive bulging phenomenon of the coatingat the beginning of the scratch pattern to be emphasized. The coatingis already completely delaminated during the rst moment of thescratch test and it bulges over the substrate, thus involving a verylarge zone. The surrounding coating keeps the bulged zone weaklybonded to the substrate, although there is no adherence at the interface.Delamination is associated with the complete detachment of the coat-ing from the underlying substrate along the scratch pattern and at ahigher scratchdistance (Fig. 10a). The complete detachment of the coat-ing from the substrate is ascribable to the instability generated by the tipof the advancing indenter on the bulged material, which is consistentwith [32]. The bulged material is overstressed by the pushing indenter

rement conditions were: an indenter with a 200 m tip radius and a normal load of 17 N.ding speeds were: (a, f) 0.2 mm/min, (b, g) 1 mm/min (c, h) 5 mm/min, (d, i) 25 mm/min

220 M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223and is completely torn off from the underlying substrate, thus generat-ing an extended delamination zone, that is smaller than the bulgedzone. The coatings deposited on the sandblasted substrates exhibiteda clearly improved scratch response. Although several and repeatedcracks can be observed on the coating surface in Fig. 8fl, there is nodelamination and the coating damage is connedwell within the actualcontact area between the scratch indenter and surface. In Fig. 10b (slid-ing speed of 1 mm/min), the coating is not characterized by any bulgingphenomenon and remains rmly adhered to the underlying substratedespite the onset of fairly severe cracks. The failure mechanisms of thecoatings deposited on the sandblasted substrates are signicantlyaffected by the sliding speed (Fig. 8fl). The damage on the coating

Fig. 9. Penetration and residual depth: (ac) as-received substrates, and (bd) sandblasted subsand an applied load of 20 N.

Fig. 10.Optical microscope images of the residual scratch pattern after constant mode scratch teof 20 N and a sliding speed of 1 mm/min. Samples: (a) coating on an as-received substrate ansurface is larger at the lowest sliding speed (0.2 and 1 mm/min). Thedamage consists of the superimposition of two failure mechanisms:(i) the aforementioned C-shaped cracks, which imply the presence ofthe brittle tensile cracking mechanism; and (ii) linear cracks (i.e., layerbreak [20]) that develop along the axis of the scratch pattern relatedto a presumable cutting of the coating material by the sharp indentertip. The lattermechanism is compatiblewith the nature of the glass sub-strate, which is extremely rigid and not compliant when submitted toan external load. In the present case, as the overlying siliconeepoxycoatings lay on the undeformable glass substrate, they can also be cutoff along the sliding direction of the indenter when indented with asharp tip, beyond being fractured according to the tensile cracking

trates. The testwas performed in constantmode using an indenterwith a 200 mtip radius

st. Themeasurement conditionswere: an indenterwith a 200 m tip radius, a normal loadd (b) coating on a sandblasted substrate.

erfoan

221M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223mechanism. The second mechanism disappears at a sliding speed ofover 1 mm/min, and only the C-shaped cracks remain visible on theresidual scratch pattern. In addition, the frequency of the C-shapedcracks along the scratch pattern diminishes when the sliding speed isincreased, thus conrming the visco-elastic response of the coatingmaterial. The visco-elasticity of the coating material is conrmed byexamining the trends of the penetration and residual depths inFigs. 9b and 9d, despite the presence of a certain plastic contribution.In fact, the average penetration depths were observed to increase withdecreasing sliding speed, thus conrming that the coating behavedstify when higher load rates were applied. The residual depths are nolonger negligible (maximum values of ~10 m at a sliding speed of0.2 mm/min) and clearly decreases with an increasing load rate.Thus, an overall visco-elastic and partially visco-plastic but still brittle(i.e., the fractures spread over the scratch pattern) behavior can be re-ported for the coatings deposited on the sandblasted glass subjectedto the sharper indenter with a tip radius of 200 m. The trends for thepenetration and, in particular, residual depths also transform fromirregular (i.e., higher number of fracture events) at a lower load rate(0.2 and 1 mm/min) to smoother (i.e., lower number of fracture events)at a higher load rate (N1 mm/min), thus demonstrating the dissimilar-ity in terms of the scratch resistance of the coatings subjected to the dif-ferent sliding speeds. This result agreeswith the SEM images in Fig. 8fl,where the disappearance of the second damage mechanisms and thereductions in the frequency of the C-shaped fracture are observed forsliding speeds greater than 1 mm/min.

The indenter with a tip radius of 200 mwas also used to test thecoatings using progressive-load scratch tests at a sliding speed of1 mm/min and an incremental load of 030 N. The coating depositedon the as-received glass substrate exhibited a massive failure with asignicant delamination, whose area extended beyond the expectedscratch pattern (Fig. 11a). In contrast, the coating deposited on the

Fig. 11. SEM images of the residual scratch pattern after progressive-mode scratch test pconditions were: an indenter with a 200 m tip radius, an incremental load from 0 to 30 Nsandblasted glass substrate exhibited a better overall scratch response(Fig. 11b). At low and moderate loads, only damage in the form of C-shaped cracks attributable to the tensile cracking mechanisms couldbe detected. At higher loads, this mechanism was displaced by theonset of linear cracks (i.e., layer breakage and adhesive failure [20])

Table 1Denition of the critical loads of the siliconeepoxy coatings on the as-received andsandblasted glass substrates after scratch tests using an indenterwith a 200 m tip radius.

Critical loads/progressive, 200 m Coatings on thesandblasted glass

Coatings on theas-received glass

Onset of scratch visibility Not applicable Not applicableOnset of C-shaped cracks ~2 N ~7 NOnset of layer break ~13 N ~21 NOnset of adhesive failure Not applicable ~24 NOnset of buckling/spallation ~16 N ~26 Nin the direction of the advancing indenter. The latter mechanism hada more severe effect on the coating, which exhibited partial delamina-tion from the underlying substrate (i.e., by buckling and/or brittlespallation) at the highest load. However, the delamination is connedaround the expected scratch pattern and further conrms the superiorscratch resistance of the coatings deposited on the micro-roughnessglass compared to the as-received glass substrate.

The experimental results allowed ve different critical loads to bedened for the siliconeepoxy coatings deposited on both the as-received and sandblasted glass substrates after progressive-modescratch tests using the indenter with a 200 m tip radius (Table 1).Sandblasting enables the increase of the scratch resistance of the sili-coneepoxy coatings. The superior scratch performance of the coatingson the sandblasted glasses was ascribed to the good mechanicalinterlocking at the interface promoted by the micro-corrugation. Inaddition, the micro-roughened morphology may also be able to opposeresistance to the stresses generated inside the coatings because of theshrinkage phenomenon during the resin drying after its application onthe substrate surface. As mentioned previously, the differential shrink-age between the resin and stiff glass generates high residual stressesinside the resin itself. Such stresses are manifested through the onsetof forces acting parallel to the interface between the coating and sub-strate. The presence of asperities on themicro-corrugated substrate cre-ates a discontinuity at the interface, opposing the action of the stresseld. Accordingly, the coatings become better able to withstand exter-nal loading conditions because the presence of internal stresses ismitigated by the corrugated morphological features of the substratesurface itself. This result is crucial because it enables the deposition ofa thick lm despite the potential onset of high internal residual stressesdue to the resin shrinkage during the drying/cross-linking process. Thisresult is translated into a large increase in critical loads if the thick coat-ings investigated here are compared with thinner coatings of similar

rmed on a) an as-received substrate and b) a sandblasted substrate. The measurementd a sliding speed of 1 mm/min.composition reported in the literature [15,20,21,33]. In particular, theonset of coating failure by buckling and/or brittle spallation is increasedbymore than one order of magnitudewhen the contact pressure is heldconstant [15,20,21,33].

Fig. 12.Wear volumes vs. sliding distance.

3.3. Wear endurance

The wear resistance of organic or hybrid organicinorganic coatingsis minimally affected by the substrate interface. This behavior is con-rmed by the coatings deposited on the as-received and sandblastedglass substrates, with awear volume that increases similar to the slidingdistance regardless of the intrinsic features of the interface (Fig. 12).

breaking of adhesive bonds occasionally formed between the coatingsand counterpart. The interaction in this step can also be attributed toploughing, that is, to the resistance originating from the elastic and po-tentially plastic deformation generated by the action of the counterpartwhen it slides on the surface of coatings supported by a stiffer substrate(i.e., the presumably softer thick siliconeepoxy coatings on the stifferglass substrates). Indeed, the coating is subject to signicant deforma-tion, at least, in the elastic eld even when submitted to moderate con-tact pressure (as is the case in the initial step of the progressive-modescratch tests). Accordingly, ploughing can be assumed to be the mainfriction mechanism. The mechanisms should be the same during thelatter step, which involves material loss, with both adhesion andploughing being potentially able to generate the formation of coatingdebris along the sliding contact (see the details of the debris inFig. 13). In particular, the removal of material from the coating can beattributed to both adhesion + fracture and abrasion + fracture inagreement with what is reported in [34]. In fact, the action of the slidingcounterpart can generate an adhesive lifting or, otherwise, a signicantdeformation in the elastic and/or plastic eld in the coating fromwhichshear stresses much higher than the intrinsic strength of the coatingmaterial itself can originate and thus cause the formation of surfacecracks and the concurrent onset of debris.

The experimental analysis of the fractures on the coating surfacesupports the aforementioned hypothesis and elicits ploughing and, ac-cordingly, abrasion + fracture as the main mechanism responsible for

Fig. 13. Details of debris generated during the tribological tests.

222 M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223Observing the trends in the wear volume, a distance of at least 100 mis necessary to activate signicant mass loss under the prescribedtesting conditions. However, the process accelerates rapidly and themeasured wear volume increases once signicant wear is measured.After a sliding distance of 500 m, the coatings deposited on both theas-received and sandblasted glass substrates are still anchored on theunderlying substrate, although much of the initial material has beentorn off.

The trends of material loss during the tribological tests suggest thepresence of two interaction mechanisms between the coatings investi-gated and the counterpart: (i) a rst step during which no materialremoval is observed and interaction is essentially ruled by friction;and (ii) a second step involving material removal and thus the forma-tion of some debris along the contact zone. During the former step,the interaction by friction can be ascribed to adhesion, that is, to theFig. 14. SEM images of the wear pattern of: (a) the as-received substrate after a sliding distancsubstrate after a sliding distance of 200 m, and (d) the sandblasted substrate after a sliding disthe removal of material from the coating surface during the tribologicaltests (Fig. 14). In fact, despite the wear pattern being achieved by a drysliding reciprocating motion of the counterpart, which should hinderthe nature of the damage, the material is primarily removed by theformation of fractures by brittle tensile cracking regardless of whetherthe coatings are deposited on as-received or sandblasted glasses(Fig. 14). Fractures originate in the form of C-shaped cracks, whichalways is directed toward the advancing direction of the counterpart(i.e., themotion of the counterpart is reciprocating and thus it is possibleto discern the presence of both left- and right-trending C-shaped cracks,as shown in Fig. 14). In addition, no signicant residual deformation isvisible on the wear pattern. The presence of C-shaped cracks and thelack of signicant residual deformation on the coating surface underlinethe elastic brittle response of the coatingmaterial during the tribologicaltests. Accordingly, most of the material loss can be attributed to the

e of 5 m, (b) the sandblasted substrate after a sliding distance of 5 m, (c) the as-received

tance of 200 m.

mechanism of ploughing in the elastic eld, that is, by the abrasion +fracture wearmechanism, with the friction by adhesion and the corre-sponding wear mechanism by adhesion + fracture playing a minorrole, if any, in agreement with [34].

4. Conclusions

This study investigated the application of thick organicinorganichybrid materials on non-compliant substrates. Alternative solutionswere proposed using a class of epoxysilicone to overcome the commondrawback of the shrinkagewhich generates large stresses inside the resinsynthesized by the solgel route when deposited on a stiff substrate andleft to dry/cross-link at ambient temperature. Micro-corrugation of theglass was observed to be the key factor in ensuring good interfacialadhesion and preventing early delamination of the overlaying coatings.The micro-asperities act as discontinuities that oppose the forces that,primarily, take action parallel to the interface and signicantly increasethe micro-mechanical performance of the coating system.

In addition, the following conclusions can be drawn:

sandblasting of the glass substrate improves the interfacial adhesionbetween the coating and substrate by promoting their reciprocalmechanical interlocking;

References

[1] S. Amberg-Schwab, E. Arpac, W. Glaubitt, K. Rose, G. Schottner, U. Schubert, in: P.Vincencini (Ed.), Materials Science Monographs-High Performance Ceramic Filmsand Coatings, Elsevier, Amsterdam, 1991, pp. 203210.

[2] K.H. Haas, H. Wolter, Properties of polymerinorganic composites, Encyclopedia ofMaterials: Science and Technology, Second ed., 2001. 75847594.

[3] G. Schottner, Chem. Mater. 13 (2001) 34223435.[4] D.R. Uhlmann, T. Suratwala, K. Davidson, J.M. Boulton, G. Teowee, J. Non-Cryst.

Solids 218 (1997) 113122.[5] K.T. Chou, B.I. Lee, Ceram. Int. 19 (1993) 315325.[6] P. Innocenzi, M.O. Abdirashid, M. Guglielmi, J. Sol-Gel Sci. Technol. 3 (1994) 4755.[7] F. Mammeri, E. Le Bourhis, L. Rozes, C. Sanchez, J. Mater. Chem. 15 (2005)

37873797.[8] H. Schmidt, J. Sol-Gel Sci. Technol. 1 (1994) 217231.[9] J. Malzbender, G. de With, J. Non-Cryst. Solids 265 (2000) 5160.

[10] H. Dislich, J. Non-Cryst. Solids 57 (1983) 371388.[11] W. Glaubitt, D. Sporn, E. Hussmann, A. Gombert, V. Wittwer, Glas. Sci. Technol. 73

(2000) 193.[12] M. Kursawe, T.A. Hofmann, in: H.A. Meinema, C.I.M.A. Spee, M.A. Aegerter (Eds.),

Proceedings of the 3rd International Conference on Coated Glass (3rd-ICCG), 681,Universal Press, Veenendaal, The Netherlands, 2000.

[13] A. Shirakura, Development of Easy-to-Recycle Coloured Glass Bottles, Product Infor-mation, Kirin Brewery Co. Ltd., Yokohama, Japan, 2000.

[14] Y. Akamatsu, K. Makita, H. Inaba, H. Nakazumi, T. Minami, J. Sol-Gel Sci. Technol. 19(2000) 387391.

[15] Y.-H. Han, A. Taylor, K.M. Knowles, Surf. Coat. Technol. 203 (2009) 28712877.[16] S. Ebnesajjad, Chapter 8: Characteristics of adhesive materials, Handbook of Adhe-

sives and Surface Preparation, 2011. 137183.[17] W.C. Wake, Polymer 19 (1978) 291308.[18] A.J. Kinloch, J. Mater. Sci. 15 (1980) 21412166.

223M. Barletta et al. / Surface & Coatings Technology 236 (2013) 212223detection of the critical loads; the onset of the critical loads during progressive mode scratch tests ofthe thick siliconeepoxy coatings is at least one order of magnitudehigher than that of the critical loads observed in comparative coatingsystems reported in the literature;

abrasion + fracture were observed as the main mechanism of mate-rial loss during the tribological tests; however, the wear endurancewas not found to be related to the interface features.

Lastly, the experimental ndings demonstrate that the siliconeepoxy coatings deposited on sandblasted glass substrates are extremelysuitable for protecting overlying layers from early failure due toscratches or wear phenomena. Accordingly, the coating demonstratedhigh potential to preserve the initial efciency of the underlying glasssubstrate over long periods.[19] V. Bellido-Gonzalez, N. Stefanopoulos, F. Deguilhen, Surf. Coat. Technol. 7475(1995) 884889.

[20] Y. Bautista, M.P. Gomez, C. Ribes, V. Sanz, Prog. Org. Coat. 70 (2011) 358364.[21] J. Malzbender, G. de With, Thin Solid Films 386 (2001) 6878.[22] S.J. Bull, Surf. Coat. Technol. 50 (1991) 2532.[23] V. Jardret, P. Morel, Prog. Org. Coat. 48 (2003) 322331.[24] F. Awaja, M. Gilbert, G. Kelly, B. Fox, P.J. Pigram, Prog. Polym. Sci. 34 (2009)

948968.[25] M. Barletta, D. Bellisario, Prog. Org. Coat. 70 (2011) 259272.[26] M. Barletta, D. Bellisario, G. Rubino, N. Ucciardello, Prog. Org. Coat. 68 (2010)

100110.[27] N. Aleksy, G. Kermouche, A. Vautrin, J.M. Bergheau, Int. J. Mech. Sci. 52 (2010)

455463.[28] C. Gauthier, R. Schirrer, J. Mater. Sci. 35 (2000) 21212130.[29] S.G. Bardenhagen, M.G. Stout, G.T. Gray, Mech. Mater. 25 (1997) 235253.[30] A. Krupicka, M. Johansson, A. Hult, Prog. Org. Coat. 46 (2003) 3248.[31] V. Jardret, H. Zahouani, J.L. Loubet, T.G. Mathia, Wear 218 (1998) 814.[32] S.J. Bull, E.G. Berasetegui, Tribol. Int. 39 (2006) 99114.[33] X. Chen, S. Zhou, B. You, L. Wu, Prog. Org. Coat. 74 (2012) 540548.[34] K. Holmberg, H. Ronkainen, A. Laukkanen, K. Wallin, Surf. Coat. Technol. 202 (2007)

10341049. scratch adhesion of the epoxysilicone coatings deposited on thesandblasted glasses is improved considerably, as conrmed by the

Application and drying at ambient temperature of thick organicinorganic hybrid coatings on glass1. Introduction2. Experimental2.1. Materials2.2. Manufacturing process2.3. Characterization of the coatings

3. Results and discussion3.1. Coating build-up and analysis of the morphological features3.2. Scratch response3.3. Wear endurance

4. ConclusionsReferences