Anti-corrosive and oil sensitive coatings based on epoxy/polyaniline/magnetite-clay composites through diazonium interfacial chemistry

1 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 www.na u e.com/scien i ic epo s An i-co osi e and oil sensi i e coa ings based on epoxy/ polyaniline/magne i e-clay composi es h ough diazonium in e acial chemis y Khouloud Jlassi1, A. Bahga Radwan1, Kisho Kuma Sadasi uni1, Mi osla M lik2, Aboubak M. Abdullah 1, Mohamed M. Chehimi3 & Igo K upa1,4 Epoxy polyme nanocomposi es illed wi h magne i e (Fe3O4) clay (B), named (B-DPA-PANI@Fe3O4) ha e been p epa ed a di e en ille loading (0.1, 0.5, 1, 3, 5 w . %). The su ace modi ica ion o clay by polyaniline (PANI) is achie ed in he p esence o 4-diphenylamine diazonium sal (DPA). The e ec s o he nano ille loading on Tensile, mechanical and dielec ic p ope ies we e sys ema ically s udied. Imp o ed p ope ies was highligh ed o all ein o ced samples. The addi ion o only 3 w . % o he ille enhanced he ensile s eng h o he composi es by 256%, and he glass ansi ion empe a u e Tg by 37%. The dielec ic spec a o e a b oad equency showed a obus in e ace be ween he hyb id (B-DPA-PANI@Fe3O4) ille s and epoxy ma ix. The esul s showed mos signi ican imp o emen in co osion inhibi ion using elec ochemical impedance spec oscopy (EIS) in 3.5 w % NaCl, as well as a signi ican esponse in oil sensing es . High cha ge ans e esis ance o 110 × 106 Ω.cm2 using 3-w % o ille was no ed compa ed o 0.35 × 106 Ω.cm2 o he pu e epoxy. The esul s ob ained he ein will open new ou es o he p epa a ion o e icien an ico osion senso coa ings. Nowadays, In ensi e esea ch was de o ed o design a sma and in elligen mul i unc ional hyb id poly- me nanocomposi e ma e ials o eme ging applica ions1,2. Pa icula ly, hyb id bio-based ma e ials, in con- as o ossil esou ces ha e ecei ed much a en ion3,4. hey can be p oduced om many enewable sou ces. Mul i- unc ionali y may be added o hose ma e ials collec ed om enewable sou ces by combining hem wi h many di e en ma e ials o achie e he desi ed unc ionali y5,6. such mul i unc ional bio-based nanocomposi e ab ica ion may in ol e he inco po a ion o ino ganic componen and can p oduce a p oduc wi h use ul elec i- cal, mechanical, magne ic, and a wide ange o applica ions7,8. Clay, pa icula ly ben oni e, is a na u ally abundan esou ce and en i onmen ally iendly due o i s biode- g adable and enewable ea u es9. Mo eo e , clay is well known o add in e es ing p ope ies o a polyme ma ix, such as lame e a dancy10, and high s o age modulus11,12. Ben oni e is a swellable clay; i is composed o hin aluminosilica e laye s13, is hyd ophobic in na u e. Su ace p e-modi ica ion is a main key o designing new ma e- ials om ben oni e. The e a e a ious p ocesses o modi ica ions; Using silane-coupling agen s14, media ing he hyd oxyl g oups o ben oni e loca ed on he shee , he ca ion exchange me hod15, o , mo e ecen ly, he co alen modi ica ion using diazonium sal s16, which p oduces new in e aces be ween clay ille and di e en polyme s like poly(me hac yla es)17 and conduc i e polyme s18. Among hose polyme s, polyaniline is well known as one o he bes conduc ing polyme s due o i s easy p epa a ion, impo an elec ical and sensing p ope ies19,20. Polyaniline has been used o di e en senso applica ions such as gas, ola ile o ganic compound, p essu e and s ain15,21. Howe e , he weak mechanical p ope ies and poo solubili y o PANI limi ed i s comme cial uses 1Cen e o Ad anced Ma e ials, Qa a Uni e si y, P. O. Box 2713, Doha, Qa a . 2Cen e o Polyme Sys ems, Uni e si y Ins i u e, Tomas Ba a Uni e si y in Zlin, T ida T. Ba i 5678, 760 01, Zlin, Czech Republic. 3Uni e si y Pa is Es , CNRS, UMR7182, ICMPE, UPEC, F-94320, Thais, F ance. 4QAPCO Polyme Chai , Cen e o Ad anced Ma e ials, Qa a Uni e si y, P.O. Box 2713, Doha, Qa a . Co espondence and eques s o ma e ials should be add essed o K.J. (email: [email p o ec ed]) o I.K. (email: igo [email p o ec ed]) Recei ed: 22 Ma ch 2018 Accep ed: 10 Augus 2018 Published: xx xx xxxx OPEN www.na u e.com/scien i ic epo s/ 2 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 and expe imen al s udies. Thus, a en ion has been gi en o he immobiliza ion o PANI on a a ie y o ma e ials namely Clays ma e ials, in o de o enhance i s applicabili y20,22. The alliance o modi ied clays wi h polyaniline23, imp o e mechanical24, dielec ic25, magne ic p ope ies26, and may o e some added alue and applica ions o he inal clay-PANI composi es, especially in an i-co osi e coa ings27–30, and oil sensing applica ions31,32. On he one hand, me al co osion is one o he mos se e e p oblems in indus ies30,33. Ba ie p o ec i e coa - ings34–36 (e.g. pain s) p o ide an in e es ing app oach o p o ec agains co osion by using clay-PANI modi ied wi h me al oxides37,38, as unc ional addi i es in which hey ac as a ba ie o mois u e o oxygen anspo a ion pa hways. Clay-PANI composi es ha e al eady p o ed o be an i-co osi e and ha e become na u al candida es o u he esea ch39. Mo eo e , he edox beha io o PANI p o ided sel -healing p ope ies o he in en ionally sc a ched coa ings40. Fu he mo e, syn hesis o epoxy-doped Clay-PANI nanocomposi es wi h di e en me al oxide nanopa icles such as ZnO41,42, TiO243, SiO244, Fe2O345,46, Z O247 and Al2O348 was ound o imp o e he co - osion p o ec ion o ca bon s eel ia he adjus men o he in e ac ion be ween he clay-PANI nanocomposi es and he added me al oxide Nano-species49–51. The mos discussed mechanism o PANI based nanocomposi es in he li e a u e is he called “ennobling mechanism”52. I is ocused on he assump ion ha he conduc i e polyme ac s as an oxidan and main ains he me al in he passi i y domain. This mechanism could induce he oxida ion o he ee me al su ace a small de ec s in he passi e laye 53. On he o he hand, oil is conside ed as main easons o wa e con amina ion, pa icula ly in ma ine en i on- men 54. Oil spills could be caused by he elease o c ude oil om o sho e pla o ms55, by de i a e p oduc s used by huge ships56. Se e al se up con olling oil pollu ion a e a ailable, and hey mos ly measu e speci ic p ope ies such as ligh sca e ing, luo escence, and so on. These exis ing de ices a e usually huge (e.g. equi e wa e o be pumped in), expensi e and consume signi ican amoun s o ene gy57. The e o e, signi ican esea ch wo k has been dedica ed o designing new, low-cos , sma senso s2 ha can be di ec ly used, in o de o p o ide quick and quan i a i e e idence abou o ganic con aminan s in biosphe e. Indeed new hyb id ma e ials based on conduc i e polyme s, namely PANI ha e been de eloped58,59. The con- duc i e polyme s p o ide an app op ia e le el o elec ical conduc i i y o he ma e ial a low concen a ion. The ope a ion o his senso is based on he elec ical esis ance changes o he hyb id composi es when exposed o oil. In his way, we sough o design new hyb id and unc ional ma e ial ( ele an o co osion p o ec ion and oil sensing) by u ilizing a na u ally abundan ma e ial (ben oni e) as ac i e diazonium modi ied pla o m o he immobiliza ion o he p epa ed DPA-PANI@Fe3O4 magne i e hyb id ille . DGEBA epoxy esins a e selec ed as a ma ix o blending he p epa ed hyb id ille , as i is he mos widely used he mose ing esin. I is e y well documen ed ha he addi ion o well-dispe sed ille s in o DGEBA epoxy esin can signi ican ly inc ease he mechanical60, he mal61, an ico osion62, and o he impo an p ope ies63. The su ace modi ica ion o he clay wi h polyaniline (PANI) was achie ed using an in-si u su ace-ini ia ed polyme iza ion me hod in he p esence o g a ed diazonium sal s o he ben oni e su ace o p o ide well-dispe sed epoxy nanocomposi es. The loading e ec s o he p epa ed ille we e s udied. The he mal s abili y o he illed epoxy was s udied by he mog a ime - ic analysis (TGA) in addi ion o mechanical p ope ies such as dynamic mechanical (DMA) and ensile analysis. In e ace s udies be ween he p epa ed ille and he epoxy ma ix we e in es iga ed using he dielec ic p op- e ies. The ac u e su ace o he cu ed and illed epoxy was obse ed by scanning elec on mic oscope (SEM). Finally he DGEBA ma ix illed B-DPA-PANI@Fe3O4, was es ed simul aneously as oil senso and an i-co osion coa ing in 3.5 w % NaCl media. To he bes o ou knowledge, such an in es iga ion using B-DPA-PANI@Fe3O4 nanohyb ids, designed by he eac ion o ben oni e h ough he in si u polyme iza ion o aniline in he p esence o 4-diphenylamine diazonium sal , o sma an ico osion senso s, has no been p e iously epo ed. Tha was he mo i a ion o his p ojec . Expe imen al The DGEBA (Bisphenol A diglycidyl e he ), he 4,4′-diaminodiphenylsul one (DDS) we e pu chased om Sigma-Ald ich. Ben oni e was pu i ied acco ding o a s anda d p ocedu e64 esul ing in ∼80-μm-sized ben oni e (B). The ca ionic exchange capaci y (CEC) was equal o 101.9 meq/(100 g o clay). Fe3O4 nanopowde (Sigma Ald ich, 97% pu i y, 50–100 nm), N-phenyl-p-phenylenediamine (Ac os, 98% pu i y), isopen yl ni i e (Al a Aesa , pu i y 97%), ammonium pe sul a e (APS, Ac os, 98% pu i y), and ni ic acid (Ca lo E ba, 60% pu i y). Aniline (Ald ich, 99.5% pu e) was pu i ied and s o ed a low empe a u e be o e usage. Dis illa ed wa e o cleaning and dilu ions was used h oughou . Syn hesis o he Hyb id Fille B-DPA-PANI@Fe3O4 The B-DPA-PANI nanocomposi es clay/polyaniline we e p epa ed as unc ion o he ca ion exchange capaci y (CEC)18 by polyme iza ion o aniline on he 4-diphenylamino diazonium-exchanged clay as ac i e pla o m. The B-DPA-PANI@Fe3O4 hyb id magne i e ille we e p epa ed wi h e e ence o mechanochemical syn hesis p ocess65. B-DPA-PANI we e used as s a ing ma e iel and Fe3O4 nanopa icles (Sigma Ald ich) as magne i e subs a e. Samples we e mixed a a (in a 1:1 weigh pe cen a io) using a Re sch PM400 plane a y ball mill, wi h he milling speed o 450 pm in o de o ge a homogeneous pa icle dis ibu ion o 2 h and in he wo-s ep mill- ing ope a ion65. P epa a ion o he Composi es P epa a ion o B-DPA-PANI@Fe3O4/DGEBA Resin Suspensions. DGEBA esin suspensions con- aining (0.1, 0.5, 1, 3, 5 w . %) o he as-p epa ed hyb id ille we e p epa ed. Fille s in di e en a ios we e mixed wi h he DGEBA epoxy esin and sonica ed (p obe sonica o ) o 10 min be o e being mechanically s i ed o one hou . www.na u e.com/scien i ic epo s/ 3 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 Cu ing o he B-DPA-PANI@Fe3O4/DGEBA Resin. The DDS ha dene was added in o he B-DPA-PANI@ Fe3O4 (0.1, 0.5,1, 3, 5 w . %)/DGEBA esin suspensions a 180 °C wi h igo ous s i ing; i was hen pou ed in o a me allic mold (12 cm × 15 cm × 3 mm hick), cu ed o 4 h a 180 °C, pos cu ed a 200 °C o 1 h and cooled na u- ally o oom empe a u e. P epa a ion o coa ings o co osion, dielec ic and oil sensing s udy s udy. B-DPA-PANI@ Fe3O4/DGEBA esin coa ings we e p epa ed using p obe sonica o (UP 400 S ul asonic p ocesso ) by dispe sing (1, 3, 5 w . %) o B-DPA-PANI@Fe3O4 ille s in DGEBA epoxy esins. The DDS cu ing agen was hen added o he mix u e. The applica ion o coa ing was accomplished by using a doc o blade (500 mm). Cha ac e iza ion. TGA measu emen s we e accomplished unde ni ogen using a TGA 4000 (Pe kin Elme , USA) om 30 °C o 700 °C (hea ing a e o 10 °C/min). The X- ay di ac ion (XRD) measu emen s we e pe o med using PANaly ical ins umen (modelX’Pe PRO) wi h Co Kα (1.789 A°) adia ion. Tensile p ope ies we e es ed by using a LIoyd LR50K-Plus uni e sal es ing machine (UTM), equipped wi h a 10 kN load cell a a displacemen a e o 5 mm/min a oom empe a u e as pe ASTMD 638. Flexu al p ope ies we e de e mined using ec angula ba s ha ing dimensions o 127 mm × 12.5 mm × 4 mm on he same machine, a a speed o 10 mm/min as pe ASTM D 790. The ac u e su aces o he samples we e s udied using a No a Nano SEM 450 Scanning Elec on Mic oscope. Dynamic mechanical analyses we e conduc ed using a RSA-G2 (TA Ins umen s, USA) in 3-poin bending mode in he linea iscoelas ic egion (LVR). Rec angula samples (40 mm × 8 mm × 1.2 mm) we e p epa ed and in es- iga ed om 30–250 °C (3 °C/min hea ing a e), wi h a s ain de o ma ion o 0.007% and a equency o 1 Hz. The he mal s abili y o he samples was analyzed using a TGA Py is 4000 om 30–800 °C (hea ing a e o 10 °C/min). Dielec ic measu emen s we e pe o med using a No ocon ol GmbH Concep 40 b oadband dielec ic spec- ome e (Mon abau , Ge many), and da a we e collec ed a oom empe a u e o e he equency ange o 0.01 Hz–2 MHz. Sample discs (2 cm diame e ) we e sandwiched be ween wo gold-coa ed coppe elec odes (2 cm diame e ) and ans e ed o he ins umen o da a collec ion. Expe imen al da a we e desc ibed using Ha iliak-Negami model equa ion15, εω ε ε ω =′ + Δ′ +⋅ ∞ ⁎ i () (1 ()) (1) HN el ab whe e Δε′ = ε′s − ε′∞ is he dielec ic elaxa ion s eng h; ε′s and ε′∞ a e ela i e pe mi i i ies a ze o and in ini e equencies, , espec i ely; ω, is angula equency (=2 π ); el is he elaxa ion ime; and a and b a e shape pa ame e s desc ibing he asymme y o he dielec ic unc ion. Elec ochemical impedance spec oscopy (EIS) measu emen s we e pe o med in a NaCl solu ion (3.5 w . %) in a equency ange o 0.01 Hz o 100 kHz wi h a wa e ampli ude o 5 mV a 25 °C. EIS da a analysis was pe o med using Gam y Echem analys so wa e. Be o e conduc ing he EIS expe imen s, samples we e imme sed in he 3.5 w . % NaCl elec oly e o 30 min. The wa e con ac angles (WCA) o he ab ica ed coa ings we e measu ed using Da aphysics (OCA 35, Ge many) wi h 5 μL dis illed wa e . The oil sensing expe imen s we e conduc ed by measu ing he elec ical conduc i i y o sample using a No ocon ol GmbH Concep 40 b oadband dielec ic spec ome e (Mon abau , Ge many). The elec odes we e coa ed by using sil e pas e on he su ace o he sample and main aining a p esc ibed dis ance (1 mm). The oil d op was applied o he o he side o he elec ode o a oid oil and elec ode in e ac ions. Resul s and Discussion E ec o Diazonium Ca ion and Fe3O4 In e cala ion on clay/Polyaniline P ope ies. The B-DPA- PANI conduc i e hyb id ille s we e ini ially p epa ed by he co alen bonding o he diazonium ca ion o ben- oni e su ace, ollowed by he oxida i e polyme iza ion o he aniline monome as o me ly epo ed24. Then he B-DPA-PANI@Fe3O4 hyb id magne i e ille we e p epa ed wi h e e ence o mechanochemical syn hesis p ocess65 in o de o ge a homogeneous pa icle dis ibu ion inside clay galle ies. Figu e1 displays he in e ace chemis y o he as p epa ed magne i e hyb id nano ille wi h he DGEBA epoxy esin and he DDS ha dene . The as p epa ed hyb id magne i e ille has highly dispe sed and s able Fe3O4 nanopa icles, NH g oups om bo h DPA and PANI, which could eac wi h epoxy g oups ia ing opening, esul ing in co alen bonding o he esin o he clay shee s ( ia PANI and DPA). Mo eo e , The DDS ha dene has wo amino g oups, which may eac wi h epoxy by he same mechanism. Table1 summa ize he mos impo an p ope ies o he p epa ed hyb id ma e ials. The in oduc ion o he diazonium sal and Fe3O4 a e impo an o p epa e a new conduc i e and ex olia ed hyb id ille . He ea e , we will epo he impac hese new ille s had on In e acial, mo phology, mechanical, ensile, and die- lec ic p ope ies o DGEBA epoxy esins as well as i s po en ial applica ion in co osion p o ec ion and oil sensing. IR and XRD o he p epa ed nano ille s. The XRD pa e ns o he pu i ied ben oni e B, p epa ed B-DPA-PANI, and B-DPA-PANI@Fe3O4 nanocomposi es a e shown in Fig.2. Ben oni e is cha ac e ized by a di ac ion peak a 2 ϴ = 6.67 which co esponds o an in e laye dis ance equal o 1.37 nm; his di ac ion peak disappea ed o he B-DPA-PANI and DPA-PANI@Fe3O4 nanocomposi es and con i ms he ex olia ion o he ben oni e a e he polyme iza ion o aniline in he p esence o he diazonium (DPA) coupling agen . Mo eo e , he b oad peaks a 19–20° and 25–26° con i med he g a ing o PANI chains o he ben oni e shee s, co espond- ing o he (020) and (200) e lec ions o he eme aldine PANI sal 66. Fo he B-DPA-PANI@Fe3O4, di ac ion peaks appea ed a ∼30°, 35°, 43°, 53°, 57° and 62°, which may be assigned o (220), (311), (400), (422), (511) and (440), espec i ely— he in e se spinel phase o Fe3O4 (JCPDS 01-1111). www.na u e.com/scien i ic epo s/ 4 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 Mic os uc u e o ac u ed su ace o he nano ille illed epoxy. To con i m he p esence o he p epa ed ille in he epoxy composi es, SEM images in he mapping mode we e ob ained (Fig.SI2). The ed colo ed indi idual pa icles con ain he i on s uc u e; clea ly showing ha he pa icles a e homogenously dis- pe sed wi hin he cu ed DGEBA and can imp o e he physical cha ac e is ics o he p epa ed composi es. Figu e 1. Molecula iew o he DGEBA- B-DPA-PANI@Fe3O4 in e ace. B-/PANI18 B-DPA/PANI@Fe3O4 Su ace modi ie 4-diphenylamine diazonium sal (DPA) +Fe3O4 Expe imen al de ails Oxida i e polyme iza ion o aniline in p esence o pu i ied clay Pu i ied ben oni e (B) i s co alen ly bonded o he DPA, ollowed by he oxida i e polyme iza ion o aniline S uc u e and c ys allini y same basal dis ance as in pu i ied clay(1.38 nm) -ex olia ed ben oni e s uc u e -c ys alline s uc u e o Pani -c ys alline s uc u e o Fe3O4 Conduc i i y S·cm−1σ = 2.1 × 10−8σ = 3.4 × 10−2 Table 1. Summa y o P epa a ion Me hods as well as Elec ical and Mo phological Fea u es o Clay/PANI Nanocomposi es. Figu e 2. XRD pa e ns o B, B-DPA-PANI and B-DPA-PANI@Fe3O4. www.na u e.com/scien i ic epo s/ 5 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 Figu e3 displays ac u e su aces o un ea ed and DGEBA wi h di e en weigh loadings o B-DPA/ PANI-Fe3O4. Figu e3a shows a smoo h ac u e su ace oge he wi h he i e -like s uc u e67. Howe e , adical change was obse ed in he mo phology o he blended DGEBA. Figu e3(b–e) e eal he o ma ion o a s ong ne wo k mic os uc u e wi hin he DGEBA esin. This unusual mo phology is mos likely induced by a e y s ong ille −ma ix (hyb id magne i e ille -DGEBA) adhesion. Howe e , o he 5% added nano ille , he e is showed in Fig.3( ) some clea age in he ib il ne wo k s uc u e o a small b oken segmen s was obse ed. This could be asc ibed o he high numbe o c osslinks p esen in he cu ed DGEBA. Indeed, PANI can ac also as a (seconda y) c oss linke in addi ion o he DDS (p incipal ha dene ). This la e is mos likely he cause o he agglome a ion o he used ille , hence he agili y and b eaking o he ib il mic os uc u e. Mechanical P ope ies. The mechanical beha io o he composi es in he ensile mode was in es iga ed. The ensile s eng h o epoxy con aining a ious B-DPA/PANI ille loadings is shown in Fig.4. Addi ion o low nano ille loadings (0.1. 0.5, 1 and 3% w .) showed signi ican enhancemen s in he ensile s eng h o he epoxy nanocomposi es (~23%, 143%, 206% and ~256%, espec i ely). This inding could be due o e icien dispe sion o he nano ille as well as obus ille -ma ix physico-chemical in e aces achie ed be ween he pa - icles and he epoxy ma ix24, which no only inc eases he epoxy monome dispe sion o e as e in alamella eac ion bu also eac s wi h epoxy chains. This ein o cing mechanism will lead o an inc ease in he s eng hs o he epoxy nanocomposi es68. This can be likely due o he e y well dispe sion o nano ille (0.1–3 w %) loading, esul ing in he s ong in e ace be ween he hyb id magne i e ille and he DGEBA esin. Ne e heless, he obse ed lowe ensile wi h 5w % o nano ille , can be caused by he magne i e ille agglome a ion as desc ibed p e iously om SEM mic o-s uc u e. Viscoelas ic P ope ies o Filled Epoxy by DMA. Dynamic mechanical analyses p o ide e idence on he inco po a ion o he hyb id ille in he epoxy ma ix as well as o i s ex olia ion ia a mechanical pe o mance in es iga ion. In Fig.5, he glass ansi ion empe a u e (Tg) o he nea ma ix is close o ha obse ed o he 0.1 w . % composi e hyb id ille . Mo eo e , he Tg inc eased as he amoun o hyb id ille inc eased in he epoxy ma ix and shi ed om 150 °C o 205 °C; his shi ep esen s a signi ican enhancemen . In gene al, ex olia ion o he hyb id ille in he ma ix inc eases wi h homogenous ille dispe sion and is con i med by XRD and SEM mapping. The sys em inc eased he Tg due o he polyme chain mobili y es ic ions and su icien ly aised oughness as e idenced by DMA in es iga ion. Howe e , o 5w % composi e hyb id ille , he e is a adically dec ease o he (Tg), mos likely due o he agglome a ion o he magne i e hyb id ille in he DGEBA esin. This migh be a ibu ed o he high densi y o c osslinks p esen in he blended DGEBA: Resul ing in he agglom- e a ion o he ille , hus he dec ease o mechanical p ope ies, con i med in he p e ious sec ion by he SEM mic os uc u e and ensile s eng h p ope ies. Dielec ic P ope ies o Composi es. To in es iga e he in e acial p ocesses in he epoxy-based com- posi es, he oom empe a u e dielec ic spec a o e a b oad equency ange we e e alua ed. The expe - imen al da a we e hen i wi h Ha iliak-Negami model, and pa ame e iden i ica ion p o ided us wi h in o ma ion on how he hyb id ille in luenced he epoxy composi es. Gene ally, in he composi e sys ems, he Figu e 3. SEM images o he ac u e su aces aken om ensile specimens o cu ed pu e DGEBA, 0.1, 0.5, 1, 3 and 5-w % B-DPA/PANI-Fe3O4 illed DGEBA. www.na u e.com/scien i ic epo s/ 6 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 Wagne -Maxwell-Silla s (MWS) elaxa ion occu s a low equencies. The in e acial p ocesses a e in ensi ied because o he hyb id ille addi ion. As seen in Fig.6, he peak maxima inc ease as he amoun o ille inc eases up o 3 w %. In addi ion, he elaxa ion ime (Table2) as a measu e o he p ocess ac i i y dec eases, indica ing a s ong in e ac ion be ween he hyb id ille and ma ix. F om Table2, i can also be seen ha ela i e pe mi i i y ex apola ed o ze o equency inc eases as he ille con en inc eases, which con i ms he enhanced dielec ic p ope ies. These esul s p o ide clea e idence o imp o ed p ope ies due o he enhanced ille -ma ix in e ac- ion up o 3 w % and is in good ag eemen wi h he esul s ob ained om DMA, ensile s eng h and mic os uc- u e in es iga ions. TGA o he nano ille illed epoxy. The TGA spec a showed inSI1 ha he addi ion o he hyb id ille does no a ec he p ope ies o he composi es and is mos likely due o he low ille loading. E en i he he mal p ope ies we e no signi ican ly enhanced, he imp o emen impa ed in mechanical and dielec ic p ope ies is app eciable. An ico osion pe o mance. Elec ochemical impedance spec oscopy (EIS) expe imen s a e conduc ed o explo e how he magne i e polyme in he epoxy coa ings in luences hei co osion p o ec ion e iciency. Figu es7 and 8 show he Nyquis and he Bode plo s o he nanocomposi es in 3.5 w . % NaCl, espec i ely. The measu ed EIS da a a e p esen ed by he sca e ed symbols, and hei i ed lines a e he solid ones. Fi ing is done using he equi alen ci cui (Fig.9).Th ee measu emen s we e conduc ed ou o all o he as-p epa ed coa ings. The ep oducibili y o he esul s was good. The EIS pa ame e s, de i ed om i ing he EIS da a using he equi alen ci cui shown in Fig.9, a e lis ed in Table3. Figu e 4. Tensile load−displacemen cu es o he cu ed epoxy and epoxy nanocomposi es illed wi h di e en nano ille loadings (0.1, 0.5, 1, 3 and 5.w %). Figu e 5. Tempe a u e dependence o s o age ( igh ) and loss (le ) moduli o he cu ed pu e epoxy and illed epoxies wi h 0.1, 0.5, 1, 3 and 5 w . % B-DPA/PANI-Fe3O4 loadings. www.na u e.com/scien i ic epo s/ 7 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 Rs, Rpo and Rc a e he solu ion, po e and cha ge ans e esis ances, espec i ely. In addi ion, CPE and W a e he cons an phase elemen and Wa bu g impedance, espec i ely. The impedance o he CPE is calcula ed using he o mula 1/ZCPE = Qo (jw)α, whe e Q° (s. Ω−1) equals he admi ance (1/|Z|) a ω = 1 ad/s, ω is he angula e- quency o he AC signal (1/ ad) and α is he CPE exponen 69–76. As α app oaches 1, he CPE beha io app oaches ideal capaci o beha io . I is wo h men ioning ha bo h o CPE1 and CPE2 we e used ins ead o a egula capac- i o elemen , o es ima e he alue o he coa ing capaci ance (Cc) and he double laye capaci ance (Cdl); using he ollowing o mula77,78. =α− Cdl Q R(1) x n whe e, Q is CPE cons an , α is CPE exponen , espec i ely. Rx ep esen he po e esis ance (Rpo), o he cha ge ans e esis ance (Rc ). Good i ings we e ob ained wi h Chi-squa e (Χ2) using he equi alen ci cui in Fig.9, see Table3. The mag- ni ude o impedance modulus a low equency (|Z|0.01 Hz), is an sui able elemen o calcula ing he o e all co osion p o ec ion e iciency o he as-p epa ed coa ings, while he cha ge ans e esis ance (Rc ) e lec s he esis ance o elec on ans e ac oss he me al solu ion in e ace unde nea h he coa ing which is in e sely p o- po ional o he unde coa ing co osion a e. The high impedance alues ~106 Ω cm2 a he low equency egion in he EIS measu emen s con i ms he good co osion p o ec ion e iciency o he nanocomposi e coa ing. As he w . % o he magne i e polyme inc eases, he Rc and Rpo inc ease om 0.35 × 106 Ω cm2 and 0.2 × 106 Ω cm2 o pu e epoxy o 110 × 106 and 53 × 106 Ω cm2 espec i ely, a e he addi ion o 3 w . % o he ille . Howe e , a a highe con en o he ille (5 w . %), he Rc and Rpo dec ease signi ican ly o 0.6 × 106 and 0.5 × 106 Ω cm2, espec i ely. In addi ion, he double laye capaci ance a he coa ing/me al in e ace dis inc ly dec eased om 35 µF o he pu e epoxy o 0.4 µF o he 3 w . % composi e o he magne i e polyme , and he Wa bu g coe icien consequen ly dec eased om 89 × 10−6 o he pu e epoxy o 0.03 × 10−6 Ω cm2 s−1/2 o he 3 w .% nanocomposi e. Many epo s ha e sugges ed di e en mechanisms o he co osion p o ec ion o he doped PANI wi h an epoxy coa ing especially when a low con en o PANI is used. Ramezanzadeh e al.79 ound ha he addi ion o g aphene oxide/polyani- line (GO-PANI) o a zinc- ich epoxy inc eases he p o ec ion e iciency o he ca bon s eel because he depos- i ed PANI exis ed in he eme aldine sal (PANI-ES) o m, which was con e ed o eme aldine base (PANI-EB) by cap u ing he eleased zinc pa icles om he co osion p ocess. Howe e , in he p esence o Cl− ions, he PANI-EB was econ e ed o PANI-ES and comple ed he au oca aly ic cycle, which s abilized he Fe in he pas- si e egion and Zn in i s ac i e o m. Kinlen e al.80 used he scanning e e ence elec ode echnique (SRET) o Figu e 6. Dielec ic spec a in he b oad equency ange o he cu ed pu e epoxy and illed epoxy wi h 0.1, 0.5, 3 and 5-w % B-DPA/PANI-Fe3O4 loadings. Nea Epoxy 0.1% 0.5% 3% 5% ε″∞2.09 2.26 2.02 2.71 3.16 Δε′ 4.96 3.77 7.09 6.69 6.12 el [s] 2.31 0.72 0.41 0.07 0.25 a0.89 0.93 0.87 0.79 1 0.98 0.37 1.15 0.68 1.53 0.68 ε′s6.05 7.03 9.11 9.4 9.28 Table 2. Pa ame e s o he modi ied Ha iliak-Negami model (eq.1) o he a ious epoxy composi es. www.na u e.com/scien i ic epo s/ 8 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 p o e ha polyaniline (PANI) passi a es pinhole de ec s ha exis in he coa ing ma ix on ca bon s eel. On he o he hand, Hosseini e al.81 a ibu ed he co osion p o ec ion o hei nanocomposi e coa ing (EP/DBSA doped PANI-TiO2) o he i ania nanopa icles as an ine ma e ial in addi ion o he p oduced Fe2O3 a he coa ing/ me al in e ace ha ills he po es o he coa ing ma ix which hinde ed he a ack o he co osi e ions. In addi- ion o he a o emen ioned easons o he co osion esis ance o PANI, i is obse ed ha he ille used in his s udy dec eases he hyd ophilici y o he as-p epa ed coa ings up o a maximum amoun o ille , a e which he hyd ophilici y inc eases again which lowe s he co osion esis ance. The co osion p o ec ion o he magne i e polyme can be a ibu ed o ha ille which dec eases he po osi y o he nanocomposi e coa ing and he e o e dec eases he di usion o he chlo ide ions inside along wi h he co - osion p oduc s ou o he coa ing82. Howe e , a u he inc ease in he concen a ion o he magne i e nanopa - icles (>3 w .%), leads o a no iceable dec ease in he co osion p o ec ion o C-s eel, which could be a ibu ed o he agglome a ion o he magne i e nanopa icles pa icles83, ha lea es de ec s (such as pinholes o po es) in he coa ing ma ix and inc eases he di usion o he agg essi e ions h ough he coa ing81. The agglome a ion is p oduced by bo h an de Waals o ces and elec os a ic a ac ion o he cha ges ha exis on he magne i e nanopa icles su ace84. On he o he hand, inc easing he con en o he hyd ophobic PANI in he epoxy coa - ing dec eased he hyd ophilici y o he nanocomposi es and consequen ly inc eased he WCA om 50° ± 4 o 85° ± 2 o he 3 w .% o BP-DPA-PANI-Fe3O4 (Fig.10), which esul ed in a dec ease in he di usion o he ions h ough he coa ing. Howe e , u he addi ion o he ille (5 w . %) dec eased he WCA o 75° ± 3 and esul ed in a signi ican dec ease in he co osion esis ance. The dec ease in he hyd ophilici y a e he addi ion o he ille could be a ibu ed o he inc ease o he su ace oughness as shown inSI3. Ne e heless, a 5 w .% he su ace oughness p ominen ly dec eased o 10 nm due o agglome a ion and non-homogeneous dis ibu ion o he nanopa icles. Figu e 7. Nyquis (a–d) plo s o epoxy coa ings wi h 0 (a), 1 (b), 3 (c) and 5 (d) w . % BP-DPA-PANI@Fe3O4 polyme . www.na u e.com/scien i ic epo s/ 9 SCien i iC REpOR S | (2018) 8:13369 | DOI:10.1038/s41598-018-31508-0 Oil sensing applica ion. I has been desc ibed ha conduc ing polyme s composi es such as PANI and polypy ole a e being used as sensi i e ma e ials o oil sensing applica ions due o hei inexpensi e and acile oom empe a u e p epa a ion85. In his wo k, he sensi i i y o he composi es’ sensing p ope y was measu ed by connec ing bo h he ends o he ilms ip and dipping i in oil. One eme ging applica ion o hese composi e ilms is as an oil senso o de ec oil on he su ace o ma ine ehicles. I is also popula ly u ilized as an an ico - osi e coa ing. All sensing expe imen s undamen ally ely on he measu emen o elec ical conduc i i y o he de eloped samples. In he p e ious epo s, as well as in ou s udy, i ac s as elemen a y p inciple behind all sensing86,87. The chemical na u e o he ma ix is by a he mos i al pa ame e o sensing and in luences he elec ical p ope ies aside om o he a iables, such as he na u e o he polyme ma ix, ille concen a ion and esis ance88. As seen in Fig.11, measu emen s o conduc i i y we e pe o med in an oil media a 25 °C o all samples. The conduc i i y measu emen s ollowed a dec easing end o he samples, which is a a e and unlikely change. The highes conduc i i y change in he oil occu ed wi h epoxy illed wi h 3 w . % o B-DPA-PANI@ Fe3O4 ille s, a 5 w % he conduc i i y s a o dec ease due magne i e hyb id ille agglome a ion as desc ibed Figu e 8. Bode (e–h) plo s o epoxy coa ings wi h 0 (e), 1 ( ), 3 (g) and 5 (h) w . % BP-DPA-PANI@Fe3O4 polyme . Figu e 9. Equi alen elec ical ci cui used o i he EIS spec a o he di e en nanocomposi e coa ings in seawa e . The w . % o he ille Rc Ω.cm2Rpo Ω.cm2CPE1 μF cm−2 sα−1n1 Ccoa μF cm−2CPE2 μF cm−2 sα−1n2Cdl, μFW, Ω.cm2 s−1/2 Goodness o i 0 0.35 × 1060.2 × 10613 0.876 14 23 0.828 35 89 × 10−61 × 10−4 1 9.8 × 1067 × 1060.7 0.813 1 2 0.798 4 0.62 × 10−62.2 × 10−4 3 110 × 10653 × 1060.06 0.782 0.08 0.1 0.773 0.4 0.03 × 10−63.2 × 10−4 5 0.6 × 1060.5 × 1065 0.811 6 8 0.769 12 31 × 10−62.4 × 10−6 Table 3. Co osion pa ame e s ob ained om he EIS da a o he co osion o pu e epoxy con aining di e en concen a ions o BP-DPA-PANI-Fe3O4.