INFLUENCE OF EVAPORATION ON CONTACT ANGLES ON HYDROLYZED PET FOILS

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1 Mrtin NAGY,. Jiří ŠKVARLA INFLUENCE OF EVAPORATION ON CONTACT ANGLES ON HYDROLYZED PET FOILS ABSTRACT: Tis ontriution presents results from mesuring ontt ngles on moertely yrolyze PET foils immerse in soium yroxie solutions of onentrtion % (istille wter), %, % n 6% t tempertures C n C. Contt ngles n geometri prmeters on tese sustrtes were monitore s funtion of evportion time. After te evportion ourse, four elementry stges ve een evlute, tt llow etermining vning n reeing ontt ngles n wetting evior of tese sustrtes. KEYWORDS: ontt ngle, ontt ngle ysteresis, rop imension, evportion, wetting INTRODUCTION Moifition of soli surfes is very tive fiel of reser. By nging te surfe omposition we otin mteril wit new surfe properties [Seml et l., 999]. One of te si experiments for gtering informtion out surfe properties of PET is te mesurement of ontt ngles of wter rops on it. Te ontt ngles llow simple n yet effetive evlution of te yropoiity of low-energy surfe su s polymers n re n importnt prmeter in wet proessing of soli sustrtes [Cu et l., 9; Extrn n Kumgi, 997]. Terefore te evlution of ontt ngles of wter on soli surfes plys n importnt role in surfe rteriztion [Snn n Bourgés, 99]. In priniple, given pure liqui on n iel (flt, omogenous, isotropi, smoot n rigi) soli in te presene of given environment soul give unique vlue of equilirium ontt ngle e s etermine y Young s eqution (Eq.): γ SV = γ SL + γ LV os e (), were γ represents te interfil (or surfe) tension n te suffixes efine te interfe. However in prtie, it is rre for su unique vlue of e to e oserve [Snn n Bourgés, 99]. A surfe wi meets ll te requirements of te Young s eqution is referre to s n iel surfe. However, most prtil surfes re non-iel n te mesurle ontt ngle vlues on su surfes re referre to s te pprent ontt ngle p. As onsequene tis vlue is not unique ut flls into more or less wie intervl etween te vning n te reeing r ontt ngle. Te ifferene etween tem is lle ontt ngle ysteresis (CAH) (Eq.) [Cu et l., 9]. Δ = r () Hysteresis of ontt ngle is ue to evitions of surfe from iel onitions [Eril et l., 999]. Interest in CAH is stipulte y te ft tt CAH governs te wetting properties of te soli surfe to lrge extent [Bormsenko et l., 8]. Inee, severl soures of wetting ysteresis re reognize, of wi te mjor ones re onsiere to e eiter emil (emil ttk, inomogeneity of emil ompositions of te soli surfe, swelling, issolution, et.) or pysil (surfe rougness, lol sorption, moleulr orienttion, soli strin ner te triple line, et.) Anlogous effets my lso e oserve wen tere is mss trnsfer ue to evportion of te liqui. A ontt ngle initilly impose in te vning moe will iminis n ten towrs reeing vlue wen te liqui forming te menisus strts to evporte. Unless te tmospere in te immeite viinity of te rop is sturte in te vpor of te liqui, tis trnsfer is inevitle n experiments onute in non-equilirium onitions my give erroneous vlues for. Altoug tis omplition is firly ovious tis omplition in ontt ngle mesurement, it seems to ve een lrgely neglete [Snn n Bourgés, 99; Monnier n Snn, 995]. It is terefore importnt to evlute reltionsip etween ontt ngles (vning n reeing) n its vritions uring evportion. Wole evportion 7

2 simultes te onitions of vning ontt ngle formtion in initil pse n tn slowly les to formtion of te reeing ontt ngle wen ontt line is rupture. Te purpose of tis ontriution is terefore to exmine evior of sessile rop of wter on yrolyze PET foils in milest onition uring te evportion. It involves oservtion vlues of te ontt ngle n relte nges of rop imensions: ontt imeter n rop eigt s funtion of time t. Wter rops were ple on ifferent pretrete PET foils tt simulte in tis se surfe rougness. Te morpology n surfe rougness of tese foils were evlute y tomi fore mirosopy (AFM n SEM). Susequently reltionsip etween surfe wettility (ontt ngles) n relte nges of surfe tension were evlute. Results of surfe rougness, wettility n nges in surfe tension of tese pretrete surfes re presente elsewere [Škvrl et l., ]. EXPERIMENTAL Smples pretretment. Smples of PET foils ut from post-onsumer plsti ottles were use. Te foil smples wit te size of. 5 5 mm n witout ny preliminry lening proeure were immerse in series of queous soium yroxie solutions wit onentrtion of,, n 6 wt% NOH t tempertures n C n stirre ontinuously for te perio of minutes. Te NOH-trete smples were tken out of te t, rinse wit lrge mount of istille wter to remove te remining NOH n ir rie t 5 C. Te PET smples will e in te next text referre to s for exmple PET/ or PET/, mening te PET surfe pre-trete in % NOH t C or in % NOH t C, respetively. Contt ngle goniometry. A sessile rop tenique ws use to mesure te stti ontt ngles of smll wter rops on te pretrete PET foil smples in ir t mient temperture. All of te mesurements were rrie out y te Krüss EsyDrop Contt Angle Mesuring System, llowing te etermintion of spe n size of mesure rops from teir imges. Te evlution of igitize vieo imges n te lultion of ontt ngles were me wit te Drop Spe Anlysis (DSA) softwre. Te resulting ontt ngle vlues were otine s verges of ot left n rigt sie ontt ngle of liqui rop every seon s well s rop imensions. Evporting time vrying (from s to 9 s) epening on volume of wter rops (from ~ μl to ~ μl) n PET smple pretretment. Drops were eposite on te sustrte using mirosyringe. During te experiment nges of sizes of ontt ngles n rop imensions were monitore: ontt imeter n rop eigt s funtion of time t. RESULTS AND DISCUSSION Typilly, te evolution of sessile rop eposite on polymer surfe emonstrte four istint stges. In stge I, ontt imeter remine lmost 8 onstnt in Fig., n, n ontt imeter iminise n vrile more rpily t iger gre pretretment (Fig., n, ). Drop eigt iminise sligtly n ontt ngle iminise quite mrkely t ll pretretments. Initil ontt ngle erese simultneously wit pretretment (from ~ 8 to ~ 5 ) t C n (from ~ 8 to ~ 5 ) t C. In stge II ontt imeter, rop eigt n ontt ngle erese more rpily tn in stge I. In stge III ws oserve tt ot rop eigt n ontt imeter iminise rougly in proportion, so tt te ontt ngle stye pproximtely onstnt (smll plteu in Fig.,,, n ). It is of interest to note tt stge III ws foun to e totlly sent t iger pretretment t C (Fig.,, ). Vlues of ontt ngle t forementione smll plteus in Fig.,,, n my e tken effetively s reeing ontt ngle r. Stge IV orrespons to te finl ispperne of te sessile rop. It ws foun to e exeeingly iffiult to follow tis stge, ot te tul size of te sessile rops n te vlues of its ontt ngles eing very smll. Towrs te en, tens to zero n, s onsequene its vlue is well elow tt orresponing to lssi reeing ontt ngle r. Stge IV is poorly unerstoo n is proly influene y noring effet of te triple line on surfe eterogeneities. Differenes of rop imensions n ontt ngles on ll of te exmine smples in stge IV re use y surfe rougness inue y NOH pretretment, imiitions of wter into te pores n revies of te surfe or intertions etween wter n polr moleules. For etter visuliztion Fig. sow epenenes of te normlize ontt ngle * on te normlize time groupe togeter for triplets of wter roplets evporting on te PET surfe pretrete in istille wter (), % (), % () 6 % NOH () t temperture of C. Anlogous epenenes for PET surfes pretrete t C re presente in Fig.. We n see immeitely tt te rter of ot epenenes is nging wen te polrity or yropiliity of te surfes renere y te yrolysis inrese (in te orer to ), irrespetive of te size of rops. Normlize vlues of ontt ngles n time were lulte oring to reltionsips (Eq.): * t * t =, t = () i t f Te normlize ontt ngle is efine s te rtio etween te ontt ngle t time t t n te ontt ngle t initil time i. Te normlize time is efine y te rtio etween te time of e mesurement t n te finl time, wen te rop s ompletely isppere t f [Cioultjin et l., ]. Anlogous epenenes of rops volume V on time t uring evportion on te PET surfe pretrete in istille wter, %, % n 6 % NOH t C () n t C () re presente in Fig.5, irrespetive of te size of rops. Volumes of rops were lulte from Eq.:

3 ( R ) πr os + os π V = + sin () 6 were R is ontt rius, is ontt ngle n is eigt of rop., [mm], [mm], [mm], [mm] Figure. Contt ngle (), ontt imeter () n rop eigt () s funtion of time (t) t C. Smple pretretment: PET/ (), PET/ (), PET/ () n PET6/ () , [mm], [mm], [ ], [mm] Figure. Contt ngle (), ontt imeter () n rop eigt () s funtion of time (t) t C. Smple pretretment: PET/ (), PET/ (), PET/ () n PET6/ ()

4 * * * *,,9,8,7,6,5,,,, rop rop rop,,,,,,,5,6,7,8,9,,,9,8,7,6,5,,,, rop rop rop,,,,,,,5,6,7,8,9,,,9,8,7,6,5,,,, rop rop rop,,,,,,,5,6,7,8,9,,,9,8,7,6,5,,,, rop rop rop,,,,,,,5,6,7,8,9, Figure. Depenene of te normlize ontt ngle on te normlize time of wter roplets evporting on te PET surfe pretrete in istille wter (), n % (), % () n 6 % () NOH solutions t C. * * * *,,9,8,7,6,5,,,, rop rop rop,,,,,,,5,6,7,8,9,,,9,8,7,6,5,,,, rop rop rop,,,,,,,5,6,7,8,9,,,9,8,7,6,5,,,,,,,,,,,5,6,7,8,9,,,9,8,7,6,5,,,, rop rop rop rop rop rop,,,,,,,5,6,7,8,9, Figure. Depenene of te normlize ontt ngle on te normlize time of wter roplets evporting on te PET surfe pretrete in istille wter (), n % (), % () n 6 % () NOH solutions t C.

5 V [μl] V [μl] PET - DW PET - % NOH PET - % NOH PET - 6% NOH PET - DW PET - % NOH PET - % NOH PET - 6% NOH Figure 5. Depenene of te volume of wter roplets on te PET surfe pretrete in istille wter, % NOH, % NOH n 6% NOH solutions t C () n t C (). CONCLUSION Sessile rops of wter eposite on soli surfe of PET foils present n vning ontt ngle only for sort perio in ir t mient temperture. Initil ontt ngles erese proportionlly wit pretretment of PET smples s well s in ourse of evportion wen liqui evportes from rop menisus. During evportion four si stges were oserve. Initilly, rop eigt n ontt ngle erese wile ontt imeter remins lmost onstnt. Moest isrepnies of ontt imeter we n see t iger gre of pretretment (PET/, PET6/ n PET/, PET 6/). Vlues of ontt ngles re etween te initil vning vlues n reeing ontt ngle; lower tn te lssi reeing ngle mesure on eqully pretrete PET foils (result not sown ere) otine y menil retrtion of triple line. Te resons for tese lower vlues of reeing ontt ngle re not solutely ler, ut it my e relte to te ft tt evportion lone reues te ontt ngle. In stge III ws oserve tt ot rop eigt n ontt imeter iminise rougly in proportion, so tt te ontt ngle stye pproximtely onstnt n proue smll plteu (initil vlues of reeing ontt ngles). Stge III is solutely sent t iger pretrete PET smples. Finlly, te rop isppers n rop imensions n ontt ngles tening to zero. Tis stge is very iffiult lrify experimentlly euse it is proly use y surfe rougness of PET surfe erivle from NOH pretretment (inipient lkline yrolysis) n oter retions tking ple t PET surfe (swelling, issolution et.). REFERENCES [.] Bormsenko, E., Bormsenko, Y., Wymn, G., Pogre, R., Musin, A., Jger, R., Brky, Z.: Contt ngle ysteresis on polymer sustrtes estlise wit vrious experimentl teniques, its interprettion, n quntittive rteriztion, Lngmuir vol. (), No. 8, p. 5, 8. [.] Cu, T. T., Brukr, W. J., Ko, P. T. L., Nguyen, A. V.: A review of ftors tt ffet ontt ngle n implitions for flottion prtie, Avnes in Colloi n Interfe Siene vol. (5), No., p. 6 5, 9. [.] Cioultjin, S.: Experimentl investigtion of wter rop evportion uner moist ir or sturte vpour onitions, Interntionl Journl of Terml Sienes vol. (9), No. 6, p ,. [.] Eril, Y. H., MHle, G., Rown, M. S., Newton, I. M.: Determintion of te reeing ontt ngle of sessile rops on polymer surfes y evportion, Lngmuir vol. (5), No., p , 999. [5.] Extrn, W. C., Kumgi, Y.: An experimentl stuy of ontt ngle ysteresis, Journl of Colloi n Interfe Siene vol. (9), No., p. 78 8, 997. [6.] Monnier, B. C., Snn, R. E. M.: Influene of evportion on ontt ngle, Lngmuir vol. (), No. 7, p. 8 89, 995. [7.] Seml, S., Blke, D. T., Geskin, V., e Ruijter, J. M., Cstelein, G., De Conink, J.: Influene of surfe rougness on wetting ynmis, Lngmuir vol. (5), No. 5, p , 999. [8.] Snn, R. E. M., Bourgès, C.: Effet of evportion on ontt ngles on polymer surfes, Interntionl Journl of Aesion n Aesives vol. (), No., p. 5, 99. [9.] Škvrl, J., Luxer, T., Ngy, M., Sisol, M.: Reltionsip of surfe yropiliity, rge n rougness of PET foils stimulte y inipient lkline yrolysis, ACS Applie Mterils n Interfes vol. (), No. 7, p. 6 7,. AUTHORS & AFFILIATION Mrtin NAGY,. Jiří ŠKVARLA - INSTITUTE OF MONTANEOUS SCIENCES AND ENVIRONMENTAL PROTECTION, CENTER OF PRIMARY AND SECONDARY RAW MATERIALS PROCESSING, TECHNICAL UNIVERSITY OF KOŠICE, PARK KOMENSKÉHO 9, 8 KOŠICE, SLOVAKIA