Hybrid nanofillers creating the stable PVDF nanocomposite films and their effect on the friction and mechanical properties

Ci a ion: ˇ Cech Ba abaszo á, K.; Holešo á, S.; Plesník, L.; Kolská, Z.; Joszko, K.; Gzik-Z oska, B. Hyb id Nano ille s C ea ing he S able PVDF Nanocomposi e Films and Thei E ec on he F ic ion and Mechanical P ope ies. Polyme s 2022,14, 3831. h ps://doi.o g/10.3390/ polym14183831 Academic Edi o : Ki ill Che ednichenko Recei ed: 22 Augus 2022 Accep ed: 8 Sep embe 2022 Published: 14 Sep embe 2022 Publishe ’s No e: MDPI s ays neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional a il- ia ions. Copy igh : © 2022 by he au ho s. Licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). polyme s A icle Hyb id Nano ille s C ea ing he S able PVDF Nanocomposi e Films and Thei E ec on he F ic ion and Mechanical P ope ies Ka la ˇ Cech Ba abaszo á1,* , Syl a Holešo á1, Lukáš Plesník1, Zdeˇnka Kolská2, Kamil Joszko 3 and Bo˙ zena Gzik-Z oska 4 1Nano echnology Cen e, CEET, VŠB-Technical Uni e si y o Os a a, 17. Lis opadu 15/2172, 708 00 Os a a-Po uba, Czech Republic 2CENAB, Facul y o Science, J. E. Pu kynˇe Uni e si y, Pas eu o a 15, 400 96 Ús ínad Labem, Czech Republic 3Depa men o Biomecha onics, Silesian Uni e si y o Technology, Roose el a 40, 41-800 Zab ze, Poland 4Depa men o Bioma e ials and Medical De ice Enginee ing, Facul y o Biomedical Enginee ing, Silesian Uni e si y o Technology, 41-800 Zab ze, Poland *Co espondence: [email p o ec ed] Abs ac : The sol en cas ing me hod was used o i e ypes o poly inylidene di luo ide (PVDF) nanocomposi e ilm p epa a ion. The e ec o nano ille s in PVDF nanocomposi e ilms on he s uc u al, phase, and ic ion and mechanical p ope ies was examined and compa ed wi h ha o he na u al PVDF ilm. The su ace opog aphy o PVDF nanocomposi e ilms was in es iga ed using a scanning elec on mic oscope (SEM) and co ela i e imaging (CPEM, combina e AFM and SEM). A selec ion o 2D CPEM images was used o a de ailed s udy o he sphe uli ic mo phologies (g ains size a ound 6–10 µ m) and su ace oughness ( alue o 50–68 nm). The chemical in e ac ions we e e alua ed by Fou ie ans o m in a ed spec oscopy (FTIR). Dominan pola γ -phase in he o iginal PVDF, PVDF_ZnO and PVDF_ZnO/V, he mos s able non-pola α -phase in he PVDF_V_CH nanocomposi e ilm and mix u e o γ and α phases in he PVDF_V and PVDF_ZnO/V_CH nanocom- posi e ilms we e con i med. Mode a ely hyd ophilic PVDF nanocomposi e ilms wi h wa e con ac angle alues (WCA) in he ange o 58 ◦ –69 ◦ showed su ace s abili y wi h espec o he Ze a po en ial alues. The e ec o posi i e o nega i e Ze a-po en ial alues o nano ille s ( ζn ) on he esul ing nega i e Ze a-po en ial alues ( ζ ) o PVDF nanocomposi e ilms was demons a ed. In e ac ion o PVDF chains wi h hyd oxy g oups o e miculi e and amino and imino g oups o CH caused ans o ma ion o γ -phase o α . The ic ion p ope ies we e e alua ed based on he wea es ing and mechanical p ope ies we e e alua ed om he ensile es s based on Young’s modulus (E) and ensile s eng h (Rm) alues. Used nano ille s caused dec easing o ic ion and mechanical p ope ies o PVDF nanocomposi e ma e ial ilms. Keywo ds: PVDF nanocomposi e ilms; zinc oxide; e miculi e; chlo hexidine; nano ille s; co ela i e imaging; su ace oundness; Ze a-po en ial alues; ic ion and mechanical p ope ies 1. In oduc ion Poly inylidene di luo ide (PVDF) belongs o equen ly used ma e ials in a ious applica ion a eas, including semiconduc o equipmen componen s, cons uc ions, luid sys ems (oil-and-gas) and ood indus ies. PVDF is mainly used whe e a en ion is paid o an excellen chemical esis ance, a high deg ee o pu i y, excellen mechanical p ope ies and ab asion esis ance. The new unc ional nanoma e ials a e PVDF composi es (nanocomposi es), which ha e been b oadly applied in he ields o memb anes and biomedicine indus y. Due o hei ligh weigh , hinness, and good compa ibili y, hei good s eng h is equi ed in p ac ical applica ions [ 1 ]. Su ace and mo phological [ 2 ] ypes o phase ans o ma ions [ 3 ], mechanical [ 4 ] and also ic ion p ope ies a e he impo an conside a ions ha decide he a eas o applica ion and he quali y o he PVDF inal p oduc s [5]. Polyme s 2022,14, 3831. h ps://doi.o g/10.3390/polym14183831 h ps://www.mdpi.com/jou nal/polyme s Polyme s 2022,14, 3831 2 o 15 PVDF is a semic ys alline he moplas ic polyme wi h pola ype oids [ 6 ]. PVDF p ope ies a e dependen on i s c ys alline s uc u e, which has i e common c ys alline phases/polymo phs: α , β , γ , δ and ε . The mos equen ly occu ing phases a e non- pola α -phase, pola β -phase, and pola γ -phase, which a e di e en in mac omolecula chain con o ma ions [ 2 ]. The α -phase domina es among PVDF nanocomposi e ma e ials, and i is easily ob ained because o i s he modynamic s abili y; he β and he γ phases canno be shaped na u ally. The c ys alline phases can be ans o med using se e al p epa a ion me hods and mainly by hei p epa a ion condi ions [ 7 ], bu also nano ille addi ions [ 8 ]. Adding nano ille s such as ca bon nano ubes [ 4 ], i anium oxide [ 9 , 10 ], o silica nanopa icles [ 11 ] o p omo e he pola phases o he PVDF nanocomposi e ma e ials has ecen ly been epo ed. The ype o nano ille , especially i s mo phology, su ace p ope ies, and agglome a- ion abili y, a ec no only he c ys alline phase bu also he mo phology, oughness, su ace and mechanical s abili y o he PVDF nanocomposi e ma e ials. The mechanical p ope ies o polyme ma e ials a e s ongly co ela ed wi h he unde lying mic os uc u e o PVDF nanoma e ials. On he con a y, ille s based on clay mine als such as mon mo illoni e [ 12 ], cloisi e [ 13 ] and nanoclay [ 14 ] also imp o e he mechanical and ibological p ope ies o PVDF because he clay a he low con en may ac as he ein o cing elemen o bo e load and hus dec ease he plas ic de o ma ion. Non-negligible changes in he PVDF ma e ial can be expec ed om a nano ille based on e miculi e, which due o su ace g oups and in e laye ed spacing can in luence he hyd ophilic o hyd ophobic p ope ies and s uc u al s abili y o he polyme [ 15 ]. I can be assumed ha hyb id nano ille s in polyme ma ices will show syne gis ic e ec s o he o ganic phase and he ino ganic componen , especially wi h ad an ages including he expec ed excellen mechanical p ope ies, chemical and s uc u al s abili ies. This wo k deals wi h he s uc u al, ic ion and mechanical p ope ies o PVDF nanocomposi e ilms p epa ed by he sol en cas ing me hod wi h he use o i e nano ille pa icle ypes. In he wo k, a sys ema ic in es iga ion was unde aken on he in luence o he o ganic (chlo hexidine) and ino ganic (zinc oxide nanopa icles) componen s o e mi- culi e based nano ille s on he c ys al phase changes in PVDF nanocomposi e ilms. Thei in luence on su ace changes wi h espec o changes in he oughness and hyd ophilic cha - ac e o he PVDF ma e ials was obse ed. The esul ing changes we e always compa ed wi h he o iginal PVDF p ope ies. A g ea con ibu ion o he wo k is he disco e y ha an impo an pa ame e o hese changes is also knowledge o he Ze a-po en ial o indi idual nano ille s, which ells us abou he s abili y o he inal PVDF nanocomposi e ilms. 2. Ma e ials and Me hods 2.1. Nano ille Pa icles and PVDF Nanocomposi e Films P epa a ion The i e nano ille pa icle ypes we e used o PVDF nanocomposi e ilms p epa a ion: (1) he na u al Mg- e miculi e pa icles (V, G ena Co., Veselínad Lužnicí, Czech Republic) wi h a s uc u al o mula (Si 6.32 Al 1.58 Ti 0.1 ) (Mg 4.75 Ca 0.34 Fe 0.91 ) O 20 (OH) 4 (Ca 0.04 K 0.38 ); (2) zinc oxide nanopa icles p epa ed by he sonochemical p ocess (ZnO) and nanocom- posi e pa icle samples p epa ed by he sonochemical p ocess; (3) zinc oxide/ e miculi e (ZnO/V); (4) e miculi e_chlo hexidine (V_CH); and (5) zinc oxide/ e miculi e_chlo hexidine (ZnO/V_CH). De ailed p ocedu es and condi ions o he sonochemical p ocess o he p epa a ion o nanocomposi e pa icles we e used based on he me hod p oposed in ou p e ious wo k [ 16 , 17 ]. Table 1summa izes pa icles cha ac e is ics as a pa icle size (e alu- a ed based on mode d m diame e s alues), speci ic su ace a ea (SSA) and ZnO c ys alli e size (Lc). A sol en cas ing me hod, wi h dichlo ome hane (DCM, Sigma Ald ich, Czech Re- public) as sol en , was used o he p epa a ion o PVDF ilms. The mix u e o he 1 g o PVDF pelle s (Sigma Ald ich, Czech Republic), 10 mL o N,N-dime hyl o mamide (Sigma Ald ich, Czech Republic, M w = 73.095 g/mol) and 7 mL o ace one (Sigma Ald ich, Czech Republic, M w = 58.081 g/mol) was s i ed a 80 ◦ C o 30 min in an ul asonic ba h un il Polyme s 2022,14, 3831 3 o 15 he PVDF pelle s we e comple ely dissol ed. Then he solu ion was pou ed in o a Pe i dish wi h a diame e o 11 cm and d ied in an o en wi h con inuous suc ion a 160 ◦ C o 24 h. The na u e poly( inylidene luo ide) ilm was deno ed as PVDF. Table 1. The nano ille pa icles cha ac e is ics: mode pa icle size (d m ), speci ic su ace a ea (SSA) and ZnO c ys alli e size (Lc). Nano ille Samples dm (µm) SSA (m2·g−1) Lc (nm) V 12.4 90.6 - ZnO 0.15 2.98 52.7 16.0 ZnO/V 0.17 10.10 23.6 12.36 V_CH 0.29 11.5 32.0 - ZnO/V_CH 0.23 11.6 24.3 7.05 The PVDF nanocomposi e ilms we e p epa ed unde he same condi ions as he o igi- nal PVDF ilm, bu o he PVDF solu ion he 3 w % o nano ille pa icles we e addi ionally added and he solu ion was in ensi ely mixed ( o be e dispe sion o nano ille s in poly- me ic solu ion) in ul asound ba h o 20 min. The nanocomposi e ilms we e deno ed as PVDF_V, PVDF_ZnO. PVDF_ZnO/V, PVDF_V_CH and PVDF_ZnO/V_CH. 2.2. Cha ac e iza ion Me hods The su ace opog aphy o he o iginal PVDF and PVDF nanocomposi e ilms and a angemen s o he nano ille s in he PVDF ma ix we e in es iga ed using a scanning ansmission elec on mic oscope (STEM, JEOL JSM-7610F Plus, Tokyo, Japan). The samples we e no spu e ed, and he SEM images we e ob ained in a low acuum using a seconda y elec on de ec o (SE, LEI). The co ela i e imaging (CPEM) combina e co ela i e p obe (AFM, Li eScope ™ , NenoVision, B no, Czech Republic) and elec on mic oscopy (STEM, JEOL JSM-7610F Plus, Tokyo, Japan) we e used o he de ail cha ac e isa ion o he su ace opog aphy and oughness o he PVDF samples. The “in si u” measu emen was ca ied ou in non-con ac mode wi h an 8 µ m z-linea ized d y scanne . The 2D and 3D images and oughness da a we e e alua ed using he Gwyddion 2.55 so wa e. The wa e con ac angle (WCA) o PVDF and PVDF nanocomposi e ilms was mea- su ed using a h ee-poin echnique a 22.5 ◦ C, 995 mba and ela i e humidi y 65%. An amoun o 0.1 mL o dis illed wa e was deposi ed on o he su ace o he PVDF nanocom- posi e ilms using a mic opipe e; each d op (0.1 mL) was eco ded using a Mi u oyo ideocame a (Tokyo, Japan) and i s images we e e alua ed using Pixel Fox p og am (Ge - many). The examined WCA a e he esul s o 4 epea ed measu emen s. Elec okine icanalysis(de e mina iono Ze a-po en ial, ζ )o hePVDFandPVDFnanocom- posi e ilms was accomplished on Su PASS Ins umen (An on Paa , Aus ia). Samples we e s udied inside he adjus able gap cell in con ac wi h he elec oly e ( 0.001 mol dm3KCl ) a oom empe a u e. Fo each measu emen a pai o polyme ilms wi h he same op laye was ixed on wo sample holde s (wi h a c oss sec ion o 20 × 10 mm 2 and gap be ween 100 µ m). All samples we e measu ed 6 imes a cons an pH (pH = 6.6) wi h a ela i e e - o o 5%. Fo de e mina ion o he ζ he s eaming cu en me hod was used and he Helmhol ze–Smoluchowski equa ion was applied o calcula e ζ alues. The Ze a-po en ial o he PVDF nanocomposi e ilms ( ζ ) was compa ed wi h he Ze a-po en ial o he nano ille pa icles ( ζ n), which was measu ed by a nanopa icle analyse (HORIBA Nanopa ica SZ-100, Kyo o, Japan) equipped wi h a mic op ocesso Polyme s 2022,14, 3831 4 o 15 uni o di ec ly calcula e he ζn alues. A quan i y o 0.1 g o each nano ille sample was mechanically mixed wi h 25 mL o dis illed wa e , and 0.1 mL o he suspension was in oduced in o he disposable Ze a po en ial cell. Each da a poin is an a e age o 4 measu emen s ealised a 22.5 ◦C. The FTIR spec a o he o iginal PVDF and PVDF nanocomposi e ilms we e measu ed by he ATR (a enua ed o al e lec ance, USA) echnique. The samples we e laid and p essed wi h a p essu e de ice on a single- e lec ion diamond ATR c ys al. The FTIR spec a we e collec ed using an FT-IR spec ome e , Nicole iS50 (The moScien i ic, Wal ham, MA, USA), wi h a DTGS de ec o on a Sma O bi ATR accesso y. The measu emen pa ame e s we e as ollows: spec al egion, 4000–400 cm −1 ; spec al esolu ion, 4 cm −1 ; 64 scans; and Happ-Genzel apodiza ion. The ic ion and wea es ing o he o iginal PVDF and PVDF nanocomposi e ilms we e accomplished using he mechanical es e UMT T ibolab (B uke Co po a ion, Bille ica, MA, USA) and op ical p o ilome e Con ou GTX (B uke Co po a ion, USA) by he ball- on- la me hod. The s eel balls wi h a diame e o 10 mm and mic oha dness o 60 HRC we e used. The s oke leng h o he ecip oca ing mo emen was se as 10 mm. The es was ca ied ou wi h a 2 N loading o ce and equency o 5 Hz o 5 min, which mean 1000 passes o e he sample su ace. The wea ack dep h ( he geome y o he wea ) was e alua ed using a 5 × objec i e in VSI mode. Til ing o he measu emen da a was pe o med by plane i ing, and he measu ed poin s we e e alua ed using he Legacy me hod. The analysis o he mechanical p ope ies o he PVDF nanocomposi e ilms was ca ied ou using he MTS C i e ion Model 43 s a ic es ing machine. The ensile es was ca ied ou in acco dance wi h he ecommenda ions o he PN-EN ISO 527 s anda d. The samples we e subjec ed o a s a ic ensile es a a speed o 50 mm/min. The esul s o o ce measu emen s we e collec ed wi h an accu acy o 1N. The measu emen o each sample was epea ed 4 imes. 3. Resul s and Discussion 3.1. PVDF Nanocomposi e Ma e ials Cha ac e iza ion The PVDF and PVDF nanocomposi e ilms p epa ed by he ul asonica ion assis ed sol- en cas ing me hod wi h di e en nano ille pa icles we e in es iga ed using a scanning elec on mic oscope (SEM) and a e show in Figu e 1. Su ace mo phology and oughness o he PVDF ilm samples was obse ed om he op su ace o he ilm samples, i.e., opposi e o he su ace in con ac wi h he glass subs a e (bo om su ace). Polyme s 2022, 13, x FOR PEER REVIEW 5 o 16 Figu e 1. SEM images o he PVDF and PVDF nanocomposi e ilms and hei op ical images o he wa e d ops. The iangle on he le side o he images ep esen s he AFM ip. The o iginal PVDF ilm was o med by egula ly epea ing hexagonal and cubic g ains wi h an a e age size (wid h and leng h) o 36.8 μm. Whi e pa icles we e isible on he su ace o he sphe uli ic g ains due o he p esence o su ace impu i ies (all ilms we e cha ac e ized wi hou su ace ea men ) and po es wi h an a e age size o 2.8 μm. PVDF_V nanocomposi e ilm was o med by sphe uli ic g ains o i egula shapes and sizes in he ange o 5.1–10.8 μm. Ca i ies whose diame e did no exceed 4 μm oc- cu ed spo adically be ween hese g ains. The e miculi e pa icles (as a e e ence ille ) we e ound bo h in he olume o he PVDF ma ix and on he su ace o he sphe uli ic g ains and did no exceed an a e age size o 3.8 μm. Compac sphe uli ic g ains o wo sizes, 11.5 μm wi h a p edominan i egula hexagonal shape and 7.5 μm o i egula i- angula and hexagonal shape, w cha ac e ized in PVDF_ZnO nanocomposi e ilms. The sphe uli ic g ains we e close oge he connec ed by he edges. The e we e ca i ies o non- uni o m size in he place o he g ain ops. On he su ace o PVDF_ZnO nanocomposi e ilms whi e impu i ies and sc a ches caused by handling he polyme ilm we e p esen . The PVDF_ZnO/V and PVDF_V_CH nanocomposi e ilms consis ed o sphe uli ic g ains o wo sizes, 13.4 μm and 6.4 μm in he case o PVDF_ZnO/V, and 14.0 μm and 6.9 μm in he case o PVDF_V_CH. The e we e ca i ies o di e en sizes and shapes be ween he indi idual g ains. The ZnO/V and V_CH nanopa icles we e inco po a ed in he olume o he polyme ma ix. The comple ely compac (non-po ous) PVDF_ZnO/V_CH ilm was o med by la ge sphe uli ic g ains wi h sizes in he ange o 18–22.4 μm, a he bounda ies o which he e we e pa icles o ZnO/V_CH nano ille s wi h a size o 0.7–1.14 μm. These nanopa icles we e p edominan ly o ien ed as pe pendicula o a an angle o 45° in he polyme ma ix. The opog aphy o PVDF and PVDF nanocomposi e ilms was cha ac e ized in de ail using co ela i e imaging (CPEM), combined co ela i e p obe (AFM) and scanning elec- on mic oscopy (SEM). In he le pa o Figu e 1 is he isible loca ion o he AFM ip. To cha ac e ize he opog aphy and oughness o he indi idual sphe uli ic g ains, a eas wi h a low occu ence o oids we e selec ed. Indi idual 2-dimensional (2D) scans and 3- dimensional (3D) p o iles a e shown in Figu e 2. Figu e 1. SEM images o he PVDF and PVDF nanocomposi e ilms and hei op ical images o he wa e d ops. The iangle on he le side o he images ep esen s he AFM ip. Polyme s 2022,14, 3831 5 o 15 The o iginal PVDF ilm was o med by egula ly epea ing hexagonal and cubic g ains wi h an a e age size (wid h and leng h) o 36.8 µ m. Whi e pa icles we e isible on he su ace o he sphe uli ic g ains due o he p esence o su ace impu i ies (all ilms we e cha ac e ized wi hou su ace ea men ) and po es wi h an a e age size o 2.8 µm. PVDF_V nanocomposi e ilm was o med by sphe uli ic g ains o i egula shapes and sizes in he ange o 5.1–10.8 µ m. Ca i ies whose diame e did no exceed 4 µ m occu ed spo adically be ween hese g ains. The e miculi e pa icles (as a e e ence ille ) we e ound bo h in he olume o he PVDF ma ix and on he su ace o he sphe uli ic g ains and did no exceed an a e age size o 3.8 µ m. Compac sphe uli ic g ains o wo sizes, 11.5 µ m wi h a p edominan i egula hexagonal shape and 7.5 µ m o i egula iangula and hexagonal shape, w cha ac e ized in PVDF_ZnO nanocomposi e ilms. The sphe uli ic g ains we e close oge he connec ed by he edges. The e we e ca i ies o non-uni o m size in he place o he g ain ops. On he su ace o PVDF_ZnO nanocomposi e ilms whi e impu i ies and sc a ches caused by handling he polyme ilm we e p esen . The PVDF_ZnO/V and PVDF_V_CH nanocomposi e ilms consis ed o sphe uli ic g ains o wo sizes, 13.4 µ m and 6.4 µ m in he case o PVDF_ZnO/V, and 14.0 µ m and 6.9 µ m in he case o PVDF_V_CH. The e we e ca i ies o di e en sizes and shapes be ween he indi idual g ains. The ZnO/V and V_CH nanopa icles we e inco po a ed in he olume o he polyme ma ix. The comple ely compac (non-po ous) PVDF_ZnO/V_CH ilm was o med by la ge sphe uli ic g ains wi h sizes in he ange o 18–22.4 µ m, a he bounda ies o which he e we e pa icles o ZnO/V_CH nano ille s wi h a size o 0.7–1.14 µ m. These nanopa icles we e p edominan ly o ien ed as pe pendicula o a an angle o 45 ◦ in he polyme ma ix. The opog aphy o PVDF and PVDF nanocomposi e ilms was cha ac e ized in de ail using co ela i e imaging (CPEM), combined co ela i e p obe (AFM) and scanning elec- on mic oscopy (SEM). In he le pa o Figu e 1is he isible loca ion o he AFM ip. To cha ac e ize he opog aphy and oughness o he indi idual sphe uli ic g ains, a eas wi h a low occu ence o oids we e selec ed. Indi idual 2-dimensional (2D) scans and 3-dimensional (3D) p o iles a e shown in Figu e 2. F om 2D CPEM images i is e iden ha he sphe uli ic mo phologies o he PVDF g ains a e signi ican ly in luenced by he addi ion o speci ic nano ille s in o he polyme ma ix. The la ges sphe uli ic g ains occu ed in he PVDF sample wi h maximum heigh s a a ound 8.2 µ m, ollowed by he PVDF_ZnO/V_CH nanocomposi e ilm wi h heigh s o 3.9 µ m and PVDF_V_CH wi h heigh s o 3.7 µ m. The highes heigh di e ences co espond wi h he ypical lamellae shee s o he PVDF sphe uli ic g ains ha p oduce ou wa ds om hei nuclea ion cen es, whe e mo phology is cha ac e ized by jammed ci cula pla ele s (diame e < 1 µm) and make up he en i e olume o PVDF g ains. I should be men ioned ha he o iginal PVDF ilm was o med by wo ypes o sphe uli ic g ains. The i s g ains ( ep esen ing a mino pa ) we e o med by egula ly b anching lamellae shee s, be ween which lamellae o he dend i ic ype also appea ed in he amo phous egion. The second ype o g ain ha p edomina ed in he bulk o he PVDF ilm we e plana sphe uli e mo phologies. Thanks o he p esence o hese mo phologically di e en g ains i was possible o e alua e he di e ences in he a e age alue o hei oughness. While lamellae g ains eached a oughness o 52.9 nm (Ra), g ains o plana mo phology possessed only 27.0 nm (Ra). In he o e all con ex , he oughness o PVDF hen eached 31.9 nm (Ra), Table 2. The sphe uli ic g ains o he PVDF_ZnO/V_CH nanocomposi e ilm we e o med by lamellae mo phology wi h a dend i ic c ys al on he cen e. As can be seen om he image, nume ous pa icles wi h a size o a ound 200 nm we e andomly dis ibu ed on he edges o he sphe uli ic g ains. These pa icles we e he ZnO/V_CH nano ille s on he su ace o he PVDF ma ix and ep esen ed a mino size ac ion o hese nano ille . Polyme s 2022,14, 3831 6 o 15 Polyme s 2022, 13, x FOR PEER REVIEW 6 o 16 Figu e 2. 2D and 3D CPEM images o he PVDF and PVDF nanocomposi e su aces. Scanning a ea: 40 m × 40 m. F om 2D CPEM images i is e iden ha he sphe uli ic mo phologies o he PVDF g ains a e signi ican ly in luenced by he addi ion o speci ic nano ille s in o he polyme ma ix. The la ges sphe uli ic g ains occu ed in he PVDF sample wi h maximum heigh s a a ound 8.2 µm, ollowed by he PVDF_ZnO/V_CH nanocomposi e ilm wi h heigh s o 3.9 µm and PVDF_V_CH wi h heigh s o 3.7 µm. The highes heigh di e ences co e- spond wi h he ypical lamellae shee s o he PVDF sphe uli ic g ains ha p oduce ou - wa ds om hei nuclea ion cen es, whe e mo phology is cha ac e ized by jammed ci - cula pla ele s (diame e < 1 μm) and make up he en i e olume o PVDF g ains. I should be men ioned ha he o iginal PVDF ilm was o med by wo ypes o sphe uli ic g ains. The i s g ains ( ep esen ing a mino pa ) we e o med by egula ly b anching lamellae shee s, be ween which lamellae o he dend i ic ype also appea ed in he amo phous egion. The second ype o g ain ha p edomina ed in he bulk o he PVDF ilm we e plana sphe uli e mo phologies. Thanks o he p esence o hese mo pho- logically di e en g ains i was possible o e alua e he di e ences in he a e age alue o hei oughness. While lamellae g ains eached a oughness o 52.9 nm (Ra), g ains o plana mo phology possessed only 27.0 nm (Ra). In he o e all con ex , he oughness o PVDF hen eached 31.9 nm (Ra), Table 2. Figu e 2. 2D and 3D CPEM images o he PVDF and PVDF nanocomposi e su aces. Scanning a ea: 40 µm×40 µm. Table 2. The a e age alues o he su ace oughness (Ra, RMS) e alua ed om he AFM measu e- men s o he PVDF su aces. Wa e con ac angles alues (WCA). S anda d de ia ions a e p o ided in pa en heses. PVDF Nanocomposi e Films Ra (nm) RMS (nm) WCA (◦) PVDF 31.9 ±11.9 43.2 ±15.3 43 ±0.2 PVDF_V 53.9 ±17.1 68.0 ±22.0 64 ±4.2 PVDF_ZnO 44.4 ±15.4 59.0 ±19.6 69 ±4.4 PVDF_ZnO/V 38.1 ±9.8 50.2 ±14.7 64 ±3.9 PVDF_V_CH 45.0 ±9.2 59.5 ±14.3 67 ±3.0 PVDF_ZnO/V_CH 37.2 ±7.0 52.4 ±13.3 58 ±5.2 In con as o he SEM images, based on he 2D (o 3D) CPEM scan o he PVDF_V_CH nanocomposi e ilm i was ound ha on he su ace o he sphe uli ic g ains he e we e po es occu ed in he polyme ma ix wi h an a e age size o 6 µ m and a dep h abou 1 µ m. These po es eme ging i egula ly on he su ace o he en i e PVDF_V_CH sample c ea ed he so-called hallo e ec in he cen e o which he e we e e y ine pa icles. This s uc u al a e ac has no been showed in any o he o he polyme ilms. Polyme s 2022,14, 3831 7 o 15 The smoo hes su aces o sphe uli e g ains we e cha ac e ized on he su ace o he PVDF_V, PVDF_ZnO and PVDF_ZnO/V nanocomposi e ilms. The g ains we e hexagonal o sphe ical in shape, made up o o de ed lamellae which a e connec ed by an amo phous egion, wi hou oids, c acks and o he de o ma ions. Only spo adically, dus pa icles did occu a he g ain bounda ies. Su ace oughness alues we e also cha ac e ized using he CPEM scan, which co e- la e wi h su ace mo phology o he PVDF ilms. These alues a e signi ican ly a ec ed by many sphe uli ic g ain peaks and oids ha appea ed in he PCEM images. Fo his eason, he oughness o he PVDF ilms was e alua ed ia he a e age oughness (Ra, measu ed by p o ile/linea analysis) and oo mean squa e oughness (RMS) alues ( Table 2 ). All we e ob ained om he en measu emen s a di e en loca ions o he each PVDF ilms. The oughness wi h he lowes alues o 31.9 nm (Ra) and 43.2 nm (RMS) was measu ed and e alua ed o he na u al PVDF ilm. Nano ille s in he PVDF ma ix caused an inc ease in he oughness alues in he ange o Ra alue om 37.2 nm ( o PVDF_ZnO/V_CH sample) o 53.9 nm ( o PVDF_V sample). The oo means squa e oughness (RMS) eached highe alues han he a e age oughness alues (Ra), while he dec easing cha ac e was main ained. The lowes oughness was measu ed o PVDF ilm (RMS = 43.2 nm), and he highes alues we e e alua ed o PVDF_V (RMS = 68.0 nm) and PVDF_V_CH ( RMS = 59.5 nm ) nanocomposi e ilms. Wi h ega d o oughness alues, he ascending cha ac e o hese alues was eco ded in he ollowing o de o nanocomposi e ilms: PVDF_ZnO/V < PVDF_ZnO/V_CH < PVDF_ZnO < PVDF_V_CH < PVDF_V. I was ound ha he change in oughness alues does no co ela e wi h lamella o plana su ace o- pog aphy o he PVDF nanocomposi e ma e ials bu wi h he size o he speci ic su ace a ea o he indi idual nano ille s. I can be s a ed ha he oughness o polyme nanocomposi e ilms dec eases wi h he dec easing alue o he speci ic su ace a ea o nano ille s. The su ace we abili y o he PVDF samples was e alua ed om he wa e con ac angles (Table 2). The WCA alues con i med he we able (hyd ophilic) su ace o all PVDF samples when he lowes WCA alue measu ed o he o iginal PVDF ilm was 43 ◦ . The nano ille s in he PVDF ma ix p ese ed he hyd ophilic na u e o he nanocomposi e ilms bu caused an inc ease in WCA alues in he ange o 58 ◦ –69 ◦ . The WCA alues a e in good ag eemen wi h no only he su ace oughness bu also su ace mo phology and opog a- phy. The ac ha a mino pa o he nano ille s in he PVDF_ZnO/V_CH, PVDF_ZnO/V and PVDF_V nanocomposi e ilms was loca ed on he su ace o he sphe uli ic g ains had a non-negligible e ec on he lowe WCA alues. I is known ha e miculi e pa i- cles (V) as pa o nano ille s a e cha ac e ized by a high adso p ion capaci y and a la ge su ace a ea (see Table 1) [ 18 ], and he e o e i can be assumed ha hey adso bed wa e molecules in o hei in e laye space du ing he measu emen . The lowe hyd ophilici y o PVDF nanocomposi e ma e ials also con ibu es o he nume ous p esences o oids loca ed be ween indi idual PVDF sphe uli ic g ains. O e all, PVDF nanocomposi e ilms a e mode a ely hyd ophilic. Table 3p esen s Ze a-po en ial alues o indi idual samples. The le column p esen s alues o nano ille pa icles ( ζn ) and he igh column alues o PVDF nanocomposi e ilms wi h hese nano ille s. The Ze a-po en ials o nanopa icles ζn a y signi ican ly, especially when nanopa icles a e co e ed wi h chlo ohexidine (CH). I changes o he posi i e alues due o a p esence o amino and imino g oups in chlo ohexidine molecules which causes he posi i e su ace cha ge [ 19 ]. The alues o PVDF nanocomposi e ilms show he simila end. The o iginal PVDF ilm is nega i ely cha ged due o p esence o luo ine in i s s uc u e. Ze a-po en ial o PVDF nanocomposi e ilms wi h indi idual nanopa icles changes acco ding o he Ze a-po en ial o used nano ille s. When nano ille s a e co e ed wi h chlo ohexidine, Ze a-po en ial o PVDF changed signi ican ly o he lowe nega i e alue (in compa ison wi h o iginal PVDF) due o he p esence o amino and imino g oups. This change is mo e signi ican o ZnO/V_CH in compa ison wi h only V_CH he same as he ZnO/V_CH pa icles ha e much posi i e Ze a-po en ial. Due o less nega i e ( o ZnO and ZnO/V) o e en posi i e ( o V_CH and ZnO/V_CH) su ace cha ge o Polyme s 2022,14, 3831 8 o 15 used nanopa icles i is expec ed o c ea e s ong elec os a ic in e ac ions be ween used nanopa icles and PVDF wi h a s ongly nega i e su ace cha ge. Due o his i is expec ed o p epa a ion o s able PVDF nanocomposi e ilms. I is con i med by e y small s anda d de ia ion o Ze a-po en ial du ing measu emen o indi idual samples (samples a e we ed by elec oly e unde p essu e). Table 3. Ze a-po en ial ( ζn ) o he nano ille s PVDF and Ze a-po en ial ( ζ ) o he PVDF nanocomposi e ilms wi h s anda d de ia ions (S.D.) a pH = 6.6. Nano ille s ζn (mV) PVDF and PVDF Nanocomposi e Films ζ (mV) - - PVDF −63.5 ±1.4 V−60.0 ±3.5 PVDF_V −60.1 ±1.5 ZnO −39.8 ±1.1 PVDF_ZnO −58.8 ±0.6 ZnO/V −20.6 ±0.8 PVDF_ZnO/V −53.7 ±0.0 V_CH +19.8 ±1.6 PVDF_V_CH −36.1 ±0.2 ZnO/V_CH +36.7 ±2.2 PVDF_ZnO/V_CH −16.6 ±0.3 3.2. Fou ie T ans o m In a ed Spec oscopy The FTIR echnique is a e y use ul ool p o iding us wi h in o ma ion abou he s uc u e o semi-c ys alline polyme PVDF which exis s in h ee basic dis inc polymo phs and allows us o dis inguish be ween hem [ 20 , 21 ]. The FTIR spec um o he o iginal PVDF ilm (Figu es 3and 4) shows ypical bands o γ -phase a 1429, 1231 and 835 and 510 cm −1 a ibu ed o CH 2 bending, C-F ou -o -plane de o ma ion and CH 2 ocking ib a ions, espec i ely [ 21 ]. In he case o spec a o PVDF_ZnO and PVDF_ZnO/V nanocomposi e ilm (Figu e 4) we can obse e almos he same ib a ions as o o iginal PVDF ilm which indica es ha bo h nano ille s did no change PVDF polymo ph ype. Polyme s 2022, 13, x FOR PEER REVIEW 9 o 16 Figu e 3. FTIR spec a o PVDF, PVDF_V and PVDF_V_CH nanocomposi e ilms. Figu e 4. FTIR spec a o PVDF, PVDF_ZnO, PVDF_ZnO/V and PVDF_ZnO/V_CH nanocomposi e ilms. A di e en si ua ion occu s in he case o FTIR spec um o PVDF_V nanocomposi e ilm (Figu e 3). Excep p edominan γ-phase in his sample he addi ion o V nano ille led Figu e 3. FTIR spec a o PVDF, PVDF_V and PVDF_V_CH nanocomposi e ilms. Polyme s 2022,14, 3831 9 o 15 Polyme s 2022, 13, x FOR PEER REVIEW 9 o 16 Figu e 3. FTIR spec a o PVDF, PVDF_V and PVDF_V_CH nanocomposi e ilms. Figu e 4. FTIR spec a o PVDF, PVDF_ZnO, PVDF_ZnO/V and PVDF_ZnO/V_CH nanocomposi e ilms. A di e en si ua ion occu s in he case o FTIR spec um o PVDF_V nanocomposi e ilm (Figu e 3). Excep p edominan γ-phase in his sample he addi ion o V nano ille led Figu e 4. FTIR spec a o PVDF, PVDF_ZnO, PVDF_ZnO/V and PVDF_ZnO/V_CH nanocomposi e ilms. A di e en si ua ion occu s in he case o FTIR spec um o PVDF_V nanocomposi e ilm (Figu e 3). Excep p edominan γ -phase in his sample he addi ion o V nano ille led o he o ma ion o small amoun o α -phase o which ollowing ib a ions a e ypical: 1211, 976, 797, 763, 614 and 531 cm −1 which belong o CH 2 bending, C-H ou -o -plane de o ma ion, CH2 ocking, CF2bending and scele al bending, espec i ely [21]. The p esence o o ganic componen chlo hexidine CH in nano ille s caused o ma ion o α -phase, when FTIR spec um o PVDF_V_CH (Figu e 3) con i med c ea ion solely o his polymo ph, on he o he hand on combina ion wi h ZnO in sample PVDF_ZnO/V_CH FTIR spec um (Figu e 4) showed a mix u e o αand γphases. I can be assumed ha hyd oxy g oups o e miculi e, as well as amino and imino g oups o chlo hexidine h ough nega i ely cha ged PVDF due o he p esence o luo ine, cause ans o ma ion o PVDF phases om pola γ o non-pola α , bu on he con a y, he p esence o ZnO inhibi s his p ocess. These indings ag ee wi h alues o Ze a-po en ials ζn o abo e men ioned nano ille s (Table 3). 3.3. F ic ion and Mechanical P ope ies o he PVDF Nanocomposi e Films The ic ion/ ibological p ope ies o he PVDF samples we e e alua ed by s a ic wea es s pe o med agains s eel balls by he ball-on- la me hod. The es ing condi ions (1N o 5 min.) we e chosen wi h ega d o he simula ion o no mal in ensi ely loading and wea o he polyme ilm. Table 4summa izes he ic ion coe icien s (COF, a e age alues measu ed du ing he es based on ou epe i ions o each es , wi h he minimum s anda d de ia ions ± 0.05) and ab asion dep hs (AD, s anda d de ia ions ± 0.3 µ m). The ep esen a i e ic ion/ ibological plo s a e shown in Figu e 5and p o ilome y images a e shown in Figu e 6o PVDF and PVDF nanocomposi e ilms.