Influence of Small Quantities of Water on the Physical Properties of Alkylammonium Nitrate Ionic Liquids

In e na ional Jou nal o Molecula Sciences A icle In luence o Small Quan i ies o Wa e on he Physical P ope ies o Alkylammonium Ni a e Ionic Liquids Da id Ausín1, Juan J. Pa ajó2,3 , JoséL. T enzado 4, Luis M. Va ela 2, Osca Cabeza 1and Luisa Segade 1,*   Ci a ion: Ausín, D.; Pa ajó, J.J.; T enzado, J.L.; Va ela, L.M.; Cabeza, O.; Segade, L. In luence o Small Quan i ies o Wa e on he Physical P ope ies o Alkylammonium Ni a e Ionic Liquids. In . J. Mol. Sci. 2021,22, 7334. h ps://doi.o g/ 10.3390/ijms22147334 Academic Edi o s: JoséS. U ie a and Ana M. Maina Recei ed: 8 June 2021 Accep ed: 2 July 2021 Published: 8 July 2021 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 : © 2021 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/). 1Depa amen o de Física, Facul ade de Ciencias, Campus da Zapa ei a, Uni e sidade da Co uña, 15071 A Co uña, Spain; [email p o ec ed] (D.A.); osca [email p o ec ed] (O.C.) 2 G upo de Nanoma e iais, Fo ónica e Ma e ia B anda, Depa amen o de Física de Pa ículas y Depa amen o de Física Aplicada, Uni e sidade de San iago de Compos ela, Campus Vida s/n, 15782 San iago de Compos ela, Spain; [email p o ec ed] (J.J.P.); [email p o ec ed] (L.M.V.) 3Depa amen o de Química e Bioquímica, CIQUP-Cen o de In es igaçao em Química da Uni e sidade do Po o, Uni e sidade do Po o, P-4169-007 Po o, Po ugal 4 Depa amen o de Física, Uni e sidad de Las Palmas de G an Cana ia, 35017 Las Palmas G an Cana ia, Spain; [email p o ec ed] *Co espondence: [email p o ec ed]; Tel.: +34-981167000 Abs ac : This pape p esen s a comp ehensi e s udy o wo alkylammonium ni a e ionic liquids. As pa o his amily o ma e ials, mainly e hylammonium ni a e (EAN) and also p opylammo- nium ni a e (PAN) ha e a ac ed a g ea deal o a en ion du ing he las decades due o hei po en ial applica ions in many ields. Al hough he e ha e been nume ous publica ions ocused on he measu emen o hei physical p ope ies, a g ea dispe sion can be obse ed in he esul s ob ained o he same magni ude. One o he c i ical poin s o be aken in o accoun in hei physical cha ac e iza ion is hei wa e con en . Thus, he main objec i e o his wo k was o de e mine he deg ee o in luence o he p esence o small quan i ies o wa e in EAN and PAN on he measu emen o densi y, iscosi y, elec ical conduc i i y, e ac i e index and su ace ension. Fo his pu pose, he i s h ee p ope ies we e de e mined in samples o EAN and PAN wi h wa e con en s below 30,000 ppm in a wide ange o empe a u es, be ween 5 and 95 ◦ C, while he las wo we e ob ained a 25 ◦ C. As a esul o his s udy, i has been concluded ha he p esence o wa e is c i ical in hose physical p ope ies ha in ol e mass o cha ge anspo p ocesses, esul ing in he inding ha he absolu e alue o he a e age pe cen age change in bo h iscosi y and elec ical conduc i i y is abo e 40%. Meanwhile, e ac i e index ( ≤ 0.3%), densi y ( ≤ 0.5%) and su ace ension ( ≤ 2%) p esen much less signi ican changes. Keywo ds: ionic liquid; e hylammonium ni a e; p opylammonium ni a e; wa e - ee; densi y; iscosi y; elec ical conduc i i y; e ac i e index; su ace ension 1. In oduc ion Du ing he las decades, he s udy o ionic liquids (ILs) has a oused eno mous in- e es in he scien i ic communi y because o hei ex ao dina y physical p ope ies and e sa ili y, which ha e made hem wo hy o becoming a ue ield o esea ch [ 1 ]. The main ea u e ha made hem a ac i e is ha hey can be ailo -made by combining he ca ions and anions o which hey can be composed, ob aining a g ea a ie y o ILs wi h e y di e en p ope ies and applica ions. A e a couple o decades o ex ensi e de elopmen in he s udy o he po en ial uses o ILs, hei applica ions a e now a eali y in many b anches o science and indus y. Thus, hei uses ha e been demons a ed in a wide ange o a eas o analy ical chemis y [ 2 ], o ganic chemis y [ 3 , 4 ], elec ochemical con e sion and ene gy s o age [ 5 ], biosensing echnology [ 6 ], pha maceu ical and biomedical indus y [ 7 , 8 ] o eco e y o indus ial sol en s [ 9 , 10 ], o name bu a ew. In his con ex , he cha ac e iza ion o hese ma e i- In . J. Mol. Sci. 2021,22, 7334. h ps://doi.o g/10.3390/ijms22147334 h ps://www.mdpi.com/jou nal/ijms In . J. Mol. Sci. 2021,22, 7334 2 o 15 als h ough expe imen al, heo e ical o compu a ional me hods plays a decisi e ole o p omo e hei indus ial applica ions [11]. In his wo k, we con inue wi h he expe imen al s udy o ILs o which ou g oups ha e been de o ed in he pas yea s [12–14], and speci ically, we ocus on one o ou lines o wo k dedica ed o p o ic ionic liquids (PILs) [ 15 , 16 ], he use ulness o which has been widely es ed. Wi hin his class o ma e ials, wo ep esen a i es o he amily o alkylam- monium ni a es, e hylammonium ni a e (EAN) and p opylammonium ni a e (PAN), ha e a ac ed g ea a en ion as a esul o hei mul iple applica ions. Many examples o hem can be ound in ields as di e se as elec odeposi ion, elec ochemical ex olia ion, liquid–liquid ex ac ion, o ganic o ino ganic syn hesis, bioca alysis, lub ica ion o biologi- cal medium sol en s, among o he s [ 17 , 18 ]. Mo e ecen wo ks ha e al eady explo ed hei u ili y as componen s o sma ma e ials [ 19 ], in hyd ogen so p ion p ocesses [ 20 ], in he - moelec ic gene a o de ices [ 21 ] o in s udies on he s uc u al s abili y and agg ega ion s a e o p o eins [ 22 ]. In gene al, EAN and PAN ha e been he subjec o many s udies, epo ed in mo e han 700 bibliog aphic e e ences (SciFinde n da abase), as can be seen in Figu e 1. A la ge pa o hese e e ences has been de o ed o explo ing he uses o hese compounds, while app oxima ely hal o hem ha e ocused on he de e mina ion o hei physicochemical p ope ies. In . J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 2 o 15 h ough expe imen al, heo e ical o compu a ional me hods plays a decisi e ole o p o- mo e hei indus ial applica ions [11]. In his wo k, we con inue wi h he expe imen al s udy o ILs o which ou g oups ha e been de o ed in he pas yea s [12–14], and speci ically, we ocus on one o ou lines o wo k dedica ed o p o ic ionic liquids (PILs) [15,16], he use ulness o which has been widely es ed. Wi hin his class o ma e ials, wo ep esen a i es o he amily o al- kylammonium ni a es, e hylammonium ni a e (EAN) and p opylammonium ni a e (PAN), ha e a ac ed g ea a en ion as a esul o hei mul iple applica ions. Many ex- amples o hem can be ound in ields as di e se as elec odeposi ion, elec ochemical ex- olia ion, liquid–liquid ex ac ion, o ganic o ino ganic syn hesis, bioca alysis, lub ica ion o biological medium sol en s, among o he s [17,18]. Mo e ecen wo ks ha e al eady ex- plo ed hei u ili y as componen s o sma ma e ials [19], in hyd ogen so p ion p ocesses [20], in he moelec ic gene a o de ices [21] o in s udies on he s uc u al s abili y and agg ega ion s a e o p o eins [22]. In gene al, EAN and PAN ha e been he subjec o many s udies, epo ed in mo e han 700 bibliog aphic e e ences (SciFinde n da abase), as can be seen in Figu e 1. A la ge pa o hese e e ences has been de o ed o explo ing he uses o hese compounds, while app oxima ely hal o hem ha e ocused on he de e mina ion o hei physicochemical p ope ies. Figu e 1. Inc ease in he numbe o bibliog aphic e e ences ela ed o EAN and PAN om hei disco e y o nowadays (SciFinde n da abase). Conside ing ha a ho ough and accu a e cha ac e iza ion o hese ma e ials has a di ec impac on he knowledge o hei s uc u e and in he design o hei po en ial ap- plica ions, we ha e pe o med an exhaus i e compila ion o some o he mos ele an physical p ope ies. Thus, we ha e e iewed he s a e o he a o densi y, iscosi y, elec- ical conduc i i y, e ac i e index and su ace ension o EAN and PAN a di e en empe a u es [23–89]. These p ope ies enable us o an icipa e he sui abili y o an IL in some applica ions. Fo ins ance, densi y and e ac i e index a e wo ema kably in e es ing pa ame e s be- cause, besides being use ul o iden i y a subs ance, hey allow ob aining o he in o ma ion such as ionic conduc i i ies o elec onic pola izabili ies, espec i ely. Viscosi y could be ela ed o ex ac ion p ocesses, ei he acili a ing dispe sion (low iscosi y) o by a oiding losses (high iscosi y) [2]. In he case o ba e ies o elec ochemical sensing sys ems, i is essen ial in o ma ion o know he mal s abili y, elec ochemical s abili y, elec ical con- duc i i y and iscosi y [5]. O he s udies ha ha e analyzed he abili y o ce ain ILs o ac as su ac an s ha e made use o he in o ma ion p o ided by su ace ension da a, wi h he aim o de eloping d ug deli e y sys ems [8]. In all cases, i mus be aken in o accoun ha he p ope ies end o depend on empe a u e, especially hose ela ed o mass o 0 10 20 30 40 50 60 1914 1946 1950 1953 1969 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 NUMBER OF REFERENCES YEAR EAN PAN Figu e 1. Inc ease in he numbe o bibliog aphic e e ences ela ed o EAN and PAN om hei disco e y o nowadays (SciFinde nda abase). Conside ing ha a ho ough and accu a e cha ac e iza ion o hese ma e ials has a di ec impac on he knowledge o hei s uc u e and in he design o hei po en ial applica ions, we ha e pe o med an exhaus i e compila ion o some o he mos ele an physical p ope ies. Thus, we ha e e iewed he s a e o he a o densi y, iscosi y, elec ical conduc i i y, e ac i e index and su ace ension o EAN and PAN a di e en empe a u es [23–89]. These p ope ies enable us o an icipa e he sui abili y o an IL in some applica ions. Fo ins ance, densi y and e ac i e index a e wo ema kably in e es ing pa ame e s be- cause, besides being use ul o iden i y a subs ance, hey allow ob aining o he in o ma ion such as ionic conduc i i ies o elec onic pola izabili ies, espec i ely. Viscosi y could be ela ed o ex ac ion p ocesses, ei he acili a ing dispe sion (low iscosi y) o by a oiding losses (high iscosi y) [ 2 ]. In he case o ba e ies o elec ochemical sensing sys ems, i is essen ial in o ma ion o know he mal s abili y, elec ochemical s abili y, elec ical conduc i i y and iscosi y [ 5 ]. O he s udies ha ha e analyzed he abili y o ce ain ILs o ac as su ac an s ha e made use o he in o ma ion p o ided by su ace ension da a, wi h he aim o de eloping d ug deli e y sys ems [ 8 ]. In all cases, i mus be aken in o accoun ha he p ope ies end o depend on empe a u e, especially hose ela ed o mass o cha ge anspo , which could limi hei applica ions, i being necessa y o ha e s udies ha es ablish his dependence. In . J. Mol. Sci. 2021,22, 7334 3 o 15 The a o emen ioned highligh s he ac ha , in o de o p ope ly design a p ocess, he sys ema ic and p ecise measu emen o physicochemical p ope ies is o he u mos impo ance. Despi e his, we ha e ound ha he published esul s o a gi en p ope y a he same empe a u e a y e y signi ican ly. Acco ding o all he da a ga he ed in he li e a u e, i could be assumed ha wa e abso p ion om he a mosphe e is one o he main easons o he dispe sion obse ed o a gi en p ope y and empe a u e, since he wo ILs s udied he e a e hyg oscopic subs ances, as a e many ILs [ 90 ]. As a ep esen a i e case, p e iously published densi ies ( ρ ) o EAN measu ed a 25 ◦ C a e p esen ed in Figu e 2 , along wi h he expe imen al densi ies s udied he e. In his igu e, he p ope y as a unc ion o he wa e con en (w) accu a ely epo ed in he pape s is ep esen ed using solid symbols, and wi h open ones i i was no . In . J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 3 o 15 cha ge anspo , which could limi hei applica ions, i being necessa y o ha e s udies ha es ablish his dependence. The a o emen ioned highligh s he ac ha , in o de o p ope ly design a p ocess, he sys ema ic and p ecise measu emen o physicochemical p ope ies is o he u mos impo ance. Despi e his, we ha e ound ha he published esul s o a gi en p ope y a he same empe a u e a y e y signi ican ly. Acco ding o all he da a ga he ed in he li e a u e, i could be assumed ha wa e abso p ion om he a mosphe e is one o he main easons o he dispe sion obse ed o a gi en p ope y and empe a u e, since he wo ILs s udied he e a e hyg oscopic subs ances, as a e many ILs [90]. As a ep esen a i e case, p e iously published densi ies (ρ) o EAN measu ed a 25 °C a e p esen ed in Figu e 2, along wi h he expe imen al densi ies s udied he e. In his igu e, he p ope y as a unc ion o he wa e con en (w) accu a ely epo ed in he pape s is ep esen ed using solid symbols, and wi h open ones i i was no . Figu e 2. Expe imen al and published densi ies, ρ, o EAN as a unc ion o he wa e con en , w, a 25 °C. Symbols: p esen wo k (black solid iangles) and a compila ion o hose published da a wi h an accu a e measu e o wa e con en (solid) o no (open): [15] ( ed squa es), [23] (g een do s), [24] (yellow do s), [27] (o ange do s), [28] (cyan do s), [29] ( ed do s), [32] (pink do s), [36] (g ey do s), [41] (da k g een do s), [46] (b own do s), [48] (blue do s), [52] (da k ed do s), [58] (pu ple do s), [60] (g een squa es), [65] (yellow squa es), [67] (o ange squa es), [70] (cyan squa es), [71] (pink squa es), [75] (g ey squa es), [76] (da k g een squa es), [77] (b own squa es), [81] (blue squa es), [82] (da k ed squa es), [85] (pu ple squa es), [86] (g een hombs), [87] (cyan hombs) and [89] (o ange hombs). In iew o he esul s, i seems c i ical o con ol and de e mine he wa e con en i an accu a e cha ac e iza ion is o be made. Fo his eason, in his wo k we ha e p oposed as an objec i e o s udy sys ema ically he in luence o he con en o small quan i ies o wa e ( om abou 300 o 30,000 ppm) in EAN and PAN on he measu emen o densi y, Figu e 2. Expe imen al and published densi ies, ρ , o EAN as a unc ion o he wa e con en , w, a 25 ◦ C. Symbols: p esen wo k (black solid iangles) and a compila ion o hose published da a wi h an accu a e measu e o wa e con en (solid) o no (open): [ 15 ] ( ed squa es), [ 23 ] (g een do s), [ 24 ] (yellow do s), [ 27 ] (o ange do s), [ 28 ] (cyan do s), [ 29 ] ( ed do s), [ 32 ] (pink do s), [ 36 ] (g ey do s), [ 41 ] (da k g een do s), [ 46 ] (b own do s), [ 48 ] (blue do s), [ 52 ] (da k ed do s), [ 58 ] (pu ple do s), [ 60 ] (g een squa es), [ 65 ] (yellow squa es), [ 67 ] (o ange squa es), [ 70 ] (cyan squa es), [ 71 ] (pink squa es), [ 75 ] (g ey squa es), [ 76 ] (da k g een squa es), [ 77 ] (b own squa es), [ 81 ] (blue squa es), [ 82 ] (da k ed squa es), [85] (pu ple squa es), [86] (g een hombs), [87] (cyan hombs) and [89] (o ange hombs). In iew o he esul s, i seems c i ical o con ol and de e mine he wa e con en i an accu a e cha ac e iza ion is o be made. Fo his eason, in his wo k we ha e p oposed as an objec i e o s udy sys ema ically he in luence o he con en o small quan i ies o wa e ( om abou 300 o 30,000 ppm) in EAN and PAN on he measu emen o densi y, iscosi y and elec ical conduc i i y om 5 o 95 ◦ C, and he e ac i e index and su ace ension a 25 ◦ C. To ou knowledge, his comp ehensi e s udy o EAN and PAN has no been ca ied ou o e such a wide empe a u e ange wi h a s ic con ol o wa e con en . In . J. Mol. Sci. 2021,22, 7334 4 o 15 2. Resul s The cha ac e iza ion o EAN and PAN in ol es he measu emen o physical p ope - ies co e ing a wide ange o empe a u es, be ween 5 and 95 ◦ C, when possible. This was he case o densi y, iscosi y and elec ical conduc i i y, which we e measu ed e e y 5 ◦ C o he i s wo and 10 ◦ C o he la e . Thus, Figu e 3a,b shows he esul s ob ained o he densi y o EAN and PAN as a unc ion o he wa e con en , espec i ely. In he same way, Figu e 4a,b and Figu e 5a,b display he expe imen al esul s o iscosi y (on a semi loga i hmic scale) and elec ical conduc i i y. Finally, he e ac i e index and su ace en- sion a 25 ◦ C o bo h LIs a e plo ed in Figu e 6. As can be seen, all he physical p ope ies s udied depend linea ly on he composi ion in he concen a ion ange s udied, wi h he excep ion o he e ac i e index o EAN and he iscosi y o PAN, whose ela ionship is be e i ed h ough a polynomial o deg ee 2. All he expe imen al esul s ob ained a e shown in Tables S1–S5 in he Suppo ing Ma e ials sec ion. In all cases, he da a we e i ed o an equa ion o he ype: Q=QIL + N ∑ i=1 Aiwi, (1) whe e Q is he p ope y s udied ( ρ , η , κ , n D o σ ) o he IL a a gi en empe a u e and con en in wa e (w), Q IL is he co esponding p ope y o he IL wi hou any wa e con en ( ρIL , ηIL , κIL , n D,IL o σIL ) and Q IL and A i a e i ing pa ame e s. All he bes alues o he i ing pa ame e s, Q IL and A i , oge he wi h he coe icien o de e mina ions, a e shown in Tables 1–4. In . J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 4 o 15 iscosi y and elec ical conduc i i y om 5 o 95 °C, and he e ac i e index and su ace ension a 25 °C. To ou knowledge, his comp ehensi e s udy o EAN and PAN has no been ca ied ou o e such a wide empe a u e ange wi h a s ic con ol o wa e con en . 2. Resul s The cha ac e iza ion o EAN and PAN in ol es he measu emen o physical p op- e ies co e ing a wide ange o empe a u es, be ween 5 and 95 °C, when possible. This was he case o densi y, iscosi y and elec ical conduc i i y, which we e measu ed e e y 5 °C o he i s wo and 10 °C o he la e . Thus, Figu e 3a,b shows he esul s ob ained o he densi y o EAN and PAN as a unc ion o he wa e con en , espec i ely. In he same way, Figu es 4a,b and 5a,b display he expe imen al esul s o iscosi y (on a semi loga i hmic scale) and elec ical conduc i i y. Finally, he e ac i e index and su ace en- sion a 25 °C o bo h LIs a e plo ed in Figu e 6. As can be seen, all he physical p ope ies s udied depend linea ly on he composi ion in he concen a ion ange s udied, wi h he excep ion o he e ac i e index o EAN and he iscosi y o PAN, whose ela ionship is be e i ed h ough a polynomial o deg ee 2. (a) (b) Figu e 3. Densi ies, ρ, o EAN (a) and PAN (b) as a unc ion o he wa e con en , w, o he empe a u es s udied: 5 (g een do s), 10 (g een squa es), 15 (da k g een do s), 20 (da k g een squa es), 25 (black do s), 30 (cyan squa es), 35 (cyan do s), 40 (blue squa es), 45 (blue do s), 50 (g ey squa es), 55 (g ey do s), 60 (o ange squa es), 65 (o ange do s), 70 ( ed squa es), 75 ( ed do s), 80 (pink squa es), 85 (pink do s), 90 (pu ple squa es) and 95 °C (pu ple do s). Solid lines we e ob ained om Equa ion (1). Figu e 3. Densi ies, ρ , o EAN ( a ) and PAN ( b ) as a unc ion o he wa e con en , w, o he empe a u es s udied: 5 (g een do s), 10 (g een squa es), 15 (da k g een do s), 20 (da k g een squa es), 25 (black do s), 30 (cyan squa es), 35 (cyan do s), 40 (blue squa es), 45 (blue do s), 50 (g ey squa es), 55 (g ey do s), 60 (o ange squa es), 65 (o ange do s), 70 ( ed squa es), 75 ( ed do s), 80 (pink squa es), 85 (pink do s), 90 (pu ple squa es) and 95 ◦ C (pu ple do s). Solid lines we e ob ained om Equa ion (1). In . J. Mol. Sci. 2021,22, 7334 5 o 15 In . J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 5 o 15 (a) (b) Figu e 4. Viscosi ies, η, o EAN (a) and PAN (b) as a unc ion o he wa e con en , w, on a semi loga i hmic scale o he empe a u es s udied: 5 (g een do s), 10 (g een squa es), 15 (da k g een do s), 20 (da k g een squa es), 25 (black do s), 30 (cyan squa es), 35 (cyan do s), 40 (blue squa es), 45 (blue do s), 50 (g ey squa es), 55 (g ey do s), 60 (o ange squa es), 65 (o ange do s), 70 ( ed squa es), 75 ( ed do s), 80 (pink squa es), 85 (pink do s), 90 (pu ple squa es) and 95 °C (pu ple do s). Solid lines we e ob ained om Equa ion (1). (a) (b) Figu e 5. Elec ical conduc i i ies, κ, o EAN (a) and PAN (b) as a unc ion o he wa e con en , w, o he empe a u es s udied: 5 (g een do s), 15 (da k g een do s), 25 (black do s), 35 (cyan do s), 45 (blue do s), 55 (g ey do s), 65 (o ange do s), 75 ( ed do s), 85 (pink do s) and 95 °C (pu ple do s). Solid lines we e ob ained om Equa ion (1). Figu e 4. Viscosi ies, η , o EAN ( a ) and PAN ( b ) as a unc ion o he wa e con en , w, on a semi loga i hmic scale o he empe a u es s udied: 5 (g een do s), 10 (g een squa es), 15 (da k g een do s), 20 (da k g een squa es), 25 (black do s), 30 (cyan squa es), 35 (cyan do s), 40 (blue squa es), 45 (blue do s), 50 (g ey squa es), 55 (g ey do s), 60 (o ange squa es), 65 (o ange do s), 70 ( ed squa es), 75 ( ed do s), 80 (pink squa es), 85 (pink do s), 90 (pu ple squa es) and 95 ◦ C (pu ple do s). Solid lines we e ob ained om Equa ion (1). In . J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 5 o 15 (a) (b) Figu e 4. Viscosi ies, η, o EAN (a) and PAN (b) as a unc ion o he wa e con en , w, on a semi loga i hmic scale o he empe a u es s udied: 5 (g een do s), 10 (g een squa es), 15 (da k g een do s), 20 (da k g een squa es), 25 (black do s), 30 (cyan squa es), 35 (cyan do s), 40 (blue squa es), 45 (blue do s), 50 (g ey squa es), 55 (g ey do s), 60 (o ange squa es), 65 (o ange do s), 70 ( ed squa es), 75 ( ed do s), 80 (pink squa es), 85 (pink do s), 90 (pu ple squa es) and 95 °C (pu ple do s). Solid lines we e ob ained om Equa ion (1). (a) (b) Figu e 5. Elec ical conduc i i ies, κ, o EAN (a) and PAN (b) as a unc ion o he wa e con en , w, o he empe a u es s udied: 5 (g een do s), 15 (da k g een do s), 25 (black do s), 35 (cyan do s), 45 (blue do s), 55 (g ey do s), 65 (o ange do s), 75 ( ed do s), 85 (pink do s) and 95 °C (pu ple do s). Solid lines we e ob ained om Equa ion (1). Figu e 5. Elec ical conduc i i ies, κ , o EAN ( a ) and PAN ( b ) as a unc ion o he wa e con en , w, o he empe a u es s udied: 5 (g een do s), 15 (da k g een do s), 25 (black do s), 35 (cyan do s), 45 (blue do s), 55 (g ey do s), 65 (o ange do s), 75 ( ed do s), 85 (pink do s) and 95 ◦C (pu ple do s). Solid lines we e ob ained om Equa ion (1). In . J. Mol. Sci. 2021,22, 7334 6 o 15 In . J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 6 o 15 Figu e 6. Re ac i e index, n D (do s), and su ace ension, σ (squa es), o EAN (solid symbols) and PAN (open symbols) as a unc ion o he wa e con en , w, a 25 °C. Solid lines we e ob ained om Equa ion (1). All he expe imen al esul s ob ained a e shown in Tables S1–S5 in he Suppo ing Ma e ials sec ion. In all cases, he da a we e i ed o an equa ion o he ype: Q=Q+∑Aw   , (1) whe e Q is he p ope y s udied (ρ, η, κ, n D o σ) o he IL a a gi en empe a u e and con en in wa e (w), Q IL is he co esponding p ope y o he IL wi hou any wa e con en (ρ IL , η IL , κ IL , n D,IL o σ IL ) and Q IL and A i a e i ing pa ame e s. All he bes alues o he i ing pa ame e s, Q IL and A i , oge he wi h he coe icien o de e mina ions, a e shown in Tables 1–4. Table 1. Fi ing Equa ion (1) o densi y da a (g·cm −3 ) o EAN and PAN as a unc ion o wa e con en (ppm): pa ame e s and coe icien o de e mina ion R 2 . EAN PAN T (°C) ρ IL A 1 (10 7 ) R 2 ρ IL A 1 (10 7 ) R 2 5 1.2234 −1.4448 0.9963 1.1639 −0.66515 0.9941 10 1.2202 −1.4610 0.9971 1.1608 −0.67382 0.9941 15 1.2171 −1.4745 0.9988 1.1577 −0.70588 0.9958 20 1.2140 −1.5136 0.9939 1.1546 −0.73063 0.9913 25 1.2108 −1.5354 0.9989 1.1516 −0.76511 0.9945 30 1.2077 −1.5516 0.9978 1.1485 −0.79664 0.9938 35 1.2046 −1.5800 0.9934 1.1456 −0.83059 0.9926 40 1.2016 −1.6151 0.9988 1.1425 −0.83760 0.9920 45 1.1986 −1.6151 0.9988 1.1396 −0.89210 0.9908 50 1.1956 −1.6805 0.9977 1.1366 −0.90778 0.9920 55 1.1927 −1.6700 0.9944 1.1337 −0.96657 0.9944 60 1.1898 −1.6959 0.9969 1.1309 −1.0122 0.9956 65 1.1869 −1.7551 0.9947 1.1279 −1.0033 0.9986 70 1.1840 −1.7654 0.9913 1.1250 −1.0411 0.9980 75 1.1812 −1.8331 0.9907 1.1222 −1.0732 0.9995 80 1.1783 −1.8467 0.9922 1.1193 −1.0732 0.9995 Figu e 6. Re ac i e index, n D (do s), and su ace ension, σ (squa es), o EAN (solid symbols) and PAN (open symbols) as a unc ion o he wa e con en , w, a 25 ◦ C. Solid lines we e ob ained om Equa ion (1). Table 1. Fi ing Equa ion (1) o densi y da a (g · cm −3 ) o EAN and PAN as a unc ion o wa e con en (ppm): pa ame e s and coe icien o de e mina ion R2. EAN PAN T (◦C) ρIL A1(107) R2ρIL A1(107) R2 5 1.2234 −1.4448 0.9963 1.1639 −0.66515 0.9941 10 1.2202 −1.4610 0.9971 1.1608 −0.67382 0.9941 15 1.2171 −1.4745 0.9988 1.1577 −0.70588 0.9958 20 1.2140 −1.5136 0.9939 1.1546 −0.73063 0.9913 25 1.2108 −1.5354 0.9989 1.1516 −0.76511 0.9945 30 1.2077 −1.5516 0.9978 1.1485 −0.79664 0.9938 35 1.2046 −1.5800 0.9934 1.1456 −0.83059 0.9926 40 1.2016 −1.6151 0.9988 1.1425 −0.83760 0.9920 45 1.1986 −1.6151 0.9988 1.1396 −0.89210 0.9908 50 1.1956 −1.6805 0.9977 1.1366 −0.90778 0.9920 55 1.1927 −1.6700 0.9944 1.1337 −0.96657 0.9944 60 1.1898 −1.6959 0.9969 1.1309 −1.0122 0.9956 65 1.1869 −1.7551 0.9947 1.1279 −1.0033 0.9986 70 1.1840 −1.7654 0.9913 1.1250 −1.0411 0.9980 75 1.1812 −1.8331 0.9907 1.1222 −1.0732 0.9995 80 1.1783 −1.8467 0.9922 1.1193 −1.0732 0.9995 85 1.1755 −1.8688 0.9945 1.1164 −1.1194 0.9981 90 1.1727 −1.9341 0.9969 1.1136 −1.1428 0.9953 95 1.1699 −1.9799 0.9954 1.1106 −1.1107 0.9927 In . J. Mol. Sci. 2021,22, 7334 7 o 15 Table 2. Fi ing Equa ion (1) o iscosi y da a (mPa · s) o EAN and PAN as a unc ion o wa e con en (ppm): pa ame e s o Equa ion (1) and coe icien o de e mina ion R2. EAN PAN T (◦C) ηIL A1(104) R2ηIL A1(104) A2(109) R2 5 86.5 −15.60 0.9981 201.6 −57.29 70.74 0.9990 10 69.3 −12.10 0.9983 153.7 −41.82 50.26 0.9990 15 56.3 −9.517 0.9983 119.7 −31.40 37.31 0.9989 20 46.3 −7.504 0.9984 94.8 −23.98 28.02 0.9989 25 38.7 −6.084 0.9982 76.3 −18.51 21.00 0.9988 30 32.7 −4.960 0.9989 62.3 −14.56 16.29 0.9988 35 27.9 −4.125 0.9985 51.6 −11.64 12.83 0.9987 40 24.05 −3.439 0.9987 43.2 −9.434 10.30 0.9984 45 20.92 −2.901 0.9987 36.5 −7.642 8.041 0.9987 50 18.33 −2.468 0.9987 31.2 −6.293 6.465 0.9986 55 16.19 −2.120 0.9989 26.9 −5.220 5.206 0.9983 60 14.40 −1.832 0.9989 23.39 −4.362 4.224 0.9982 65 12.88 −1.600 0.9989 20.56 −3.748 3.623 0.9989 70 11.59 −1.405 0.9990 18.15 −3.191 2.991 0.9991 75 10.48 −1.239 0.9988 16.11 −2.722 2.455 0.9993 80 9.53 −1.094 0.9987 14.40 −2.340 2.026 0.9995 85 8.69 −0.9741 0.9987 12.93 −2.021 1.673 0.9996 90 7.97 −0.8775 0.9989 11.68 −1.764 1.419 0.9998 95 7.34 −0.7932 0.9989 10.59 −1.534 1.157 0.9999 Table 3. Fi ing Equa ion (1) o elec ical conduc i i y da a (mS · cm −1 ) o EAN and PAN as a unc ion o wa e con en (ppm): pa ame e s and coe icien o de e mina ion R2. EAN PAN T (◦C) κIL A1(104) R2κIL A1(104) R2 5 10.55 1.989 0.9991 3.50 1.053 0.9982 15 15.10 2.566 0.9990 5.52 1.451 0.9987 25 20.4 3.436 0.9978 8.12 1.891 0.9986 35 27.1 3.849 0.9982 11.34 2.364 0.9984 45 33.9 4.469 0.9980 15.11 2.831 0.9990 55 41.1 5.141 0.9968 19.37 3.450 0.9954 65 48.7 5.780 0.9911 24.4 3.875 0.9927 75 56.3 6.504 0.9951 29.9 4.185 0.9984 85 64.7 6.795 0.9936 35.5 4.361 0.9981 95 73.2 7.087 0.9942 41.6 4.548 0.9974 Table 4. Fi ing Equa ion (1) o e ac i e index and su ace ension (mN · m −1 ) da a a 25 ◦ C o EAN and PAN as a unc ion o wa e con en (ppm): pa ame e s and coe icien o de e mina ion R2. EAN PAN P ope y QIL A1A2R2QIL A1R2 nD1.45395 −5.14135 ×10−8−3.00678 ×10−12 0.9979 1.45536 −1.08059 ×10−70.9980 σ(mN·m−1)47.75 2.008 ×10−50.9932 38.72 2.201 ×10−50.9929 3. Discussion 3.1. Expe imen al Measu emen s as a Func ion o Wa e Con en Analyzing he esul s ob ained om he pe spec i e o he in luence o a low wa e con en on he physical cha ac e iza ion o EAN and PAN, i can be clea ly obse ed ha no all p ope ies a e equally a ec ed. Thus, he quan i ies mos signi ican ly modi ied by he p esence o wa e a e hose o anspo . The pe cen age change in iscosi y a e aged In . J. Mol. Sci. 2021,22, 7334 8 o 15 o e all empe a u es be ween wa e - ee con en ( ηIL ) and 30,000 ppm eaches − 39% and − 42% o EAN and PAN, espec i ely. Meanwhile, in he case o elec ical conduc i i y, he co esponding pe cen age change is e en g ea e , ep esen ing 43 and 56%, espec i ely. A he o he ex eme, we ind e ac i e index ( − 0.11% and − 0.22%, espec i ely), densi y (−0.42% and −0.22%) and su ace ension (1.3% and 1.7%). As can be deduced om he da a ob ained, he p esence o small quan i ies o wa e gene a es a conside able inc ease in bo h he luidi y o he liquid and he mobili y o he cha ge. Al hough om a olume ic and su ace poin o iew he liquids do no unde go such a ma ked change, i can be su icien ly signi ican when a cha ac e iza ion o he liquid s uc u e is pu sued. 3.2. Expe imen al Measu emen s as a Func ion o Tempe a u e F om he i ing pa ame e Q IL o each p ope y a each empe a u e, which co e- sponds o he alues o he p ope ies a wa e con en w = 0, in Figu es 7and 8we ha e plo ed he densi ies, iscosi ies and elec ical conduc i i ies o EAN and PAN as a unc ion o empe a u e. In . J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 8 o 15 3. Discussion 3.1. Expe imen al Measu emen s as a Func ion o Wa e Con en Analyzing he esul s ob ained om he pe spec i e o he in luence o a low wa e con en on he physical cha ac e iza ion o EAN and PAN, i can be clea ly obse ed ha no all p ope ies a e equally a ec ed. Thus, he quan i ies mos signi ican ly modi ied by he p esence o wa e a e hose o anspo . The pe cen age change in iscosi y a e aged o e all empe a u es be ween wa e - ee con en (ηIL) and 30,000 ppm eaches −39 and −42% o EAN and PAN, espec i ely. Meanwhile, in he case o elec ical conduc i i y, he co esponding pe cen age change is e en g ea e , ep esen ing 43 and 56%, espec- i ely. A he o he ex eme, we ind e ac i e index (−0.11 and −0.22%, espec i ely), densi y (−0.42 and −0.22%) and su ace ension (1.3 and 1.7%). As can be deduced om he da a ob ained, he p esence o small quan i ies o wa e gene a es a conside able inc ease in bo h he luidi y o he liquid and he mobili y o he cha ge. Al hough om a olume ic and su ace poin o iew he liquids do no unde go such a ma ked change, i can be su icien ly signi ican when a cha ac e iza ion o he liquid s uc u e is pu sued. 3.2. Expe imen al Measu emen s as a Func ion o Tempe a u e F om he i ing pa ame e QIL o each p ope y a each empe a u e, which co e- sponds o he alues o he p ope ies a wa e con en w = 0, in Figu es 7 and 8 we ha e plo ed he densi ies, iscosi ies and elec ical conduc i i ies o EAN and PAN as a unc- ion o empe a u e. Figu e 7. Calcula ed densi ies, ρIL, o wa e - ee EAN (solid do s) and PAN (open do s) as a unc ion o he empe a u e, ob ained om Equa ion (1). Solid line ob ained om he bes s aigh line. The densi y da a ollow a linea end wi h empe a u e as ollows: ρ=A,+A,T, (2) whe e ρIL is he densi y o wa e - ee IL, T is he empe a u e in °C and Aρ,0 and Aρ,1 a e he i ing pa ame e s p esen ed in Table 5. These densi ies o bo h wa e - ee ILs p esen a e y simila slope, di e ing by 1.3%. In he case o iscosi y and elec ical conduc i i y, hey can be co ela ed by he Vo- gel–Tammann–Fulche (VTF) equa ion, as is usual o liquids o his na u e [91]. This equa ion can be gene ally w i en as: Q=Qe/(,), (3) 1.10 1.12 1.14 1.16 1.18 1.20 1.22 1.24 0 20406080100 ρIL (g·cm−3) T (°C) Figu e 7. Calcula ed densi ies, ρIL , o wa e - ee EAN (solid do s) and PAN (open do s) as a unc ion o he empe a u e, ob ained om Equa ion (1). Solid line ob ained om he bes s aigh line. The densi y da a ollow a linea end wi h empe a u e as ollows: ρIL =Aρ,0 +Aρ,1T, (2) whe e ρIL is he densi y o wa e - ee IL, T is he empe a u e in ◦ C and A ρ,0 and A ρ,1 a e he i ing pa ame e s p esen ed in Table 5. These densi ies o bo h wa e - ee ILs p esen a e y simila slope, di e ing by 1.3%. In he case o iscosi y and elec ical conduc i i y, hey can be co ela ed by he Vogel– Tammann–Fulche (VTF) equa ion, as is usual o liquids o his na u e [ 91 ]. This equa ion can be gene ally w i en as: QIL =Q∞eB/(T+273,15−T0), (3) whe e Q IL desc ibes ηIL o κIL , Q∞ is he limi o iscosi y o elec ical conduc i i y a in ini e empe a u e, B is ela ed o he ac i a ion ene gy o ions o low o o he ac i a ion ene gy o he ion hopping and, inally, T 0 is ela ed wi h he glass ansi ion empe a u e in K [ 12 , 92 – 94 ] and T is he empe a u e exp essed in ◦ C. The i ing pa ame e s Q∞ , B In . J. Mol. Sci. 2021,22, 7334 9 o 15 and T 0 a e gi en in Table 5, as well as he co esponding pe cen ual de ia ion, which is de ined as: s=100 u u ∑N i=1QIL, i−QVTF,i QIL, i 2 N−1, (4) whe e Q VTF is he alue o he calcula ed quan i y ob ained om he bes i o he VTF equa ion. The esul ing cu es a e shown in Figu e 8, showing a e y good ag eemen wi h QIL da a. In . J. Mol. Sci. 2021, 22, x FOR PEER REVIEW 9 o 15 whe e QIL desc ibes ηIL o κIL, Qis he limi o iscosi y o elec ical conduc i i y a in ini e empe a u e, B is ela ed o he ac i a ion ene gy o ions o low o o he ac i a ion ene gy o he ion hopping and, inally, T0 is ela ed wi h he glass ansi ion empe a u e in K [12,92–94] and T is he empe a u e exp essed in °C. The i ing pa ame e s Q, B and T0 a e gi en in Table 5, as well as he co esponding pe cen ual de ia ion, which is de ined as: s=100 ∑,, ,     , (4) whe e QVTF is he alue o he calcula ed quan i y ob ained om he bes i o he VTF equa ion. The esul ing cu es a e shown in Figu e 8, showing a e y good ag eemen wi h QIL da a. Figu e 8. Calcula ed iscosi ies, ηIL, and calcula ed elec ical conduc i i ies, κIL, o wa e - ee EAN (solid symbols) and PAN (open symbols) as a unc ion o he empe a u e, ob ained om Equa ion (1). Do s co espond o he le axis ( iscosi y) and squa es o he igh axis (elec ical conduc i i y). Solid line ob ained om VTF Equa ion (3). Table 5. Fi ing o densi y (g·cm−3), iscosi y (mPa·s) and elec ical conduc i i y (mS·cm−1) da a o wa e - ee EAN and PAN as unc ion o empe a u e: pa ame e s o Equa ions (2) and (3), coe icien o de e mina ion R2 and pe cen ual de i- a ion (s). IL Aρ,0 A ρ,1 (104) R2ρ 𝐐,ƞ Bƞ T0,ƞ sƞ 𝐐,𝛋 Bκ T0,κ sκ EAN 1.2257 −5.9379 0.9996 0.2111 778.8 148.7 0.06 666.2 −424.9 175.8 0.7 PAN 1.1664 −5.8998 0.9998 0.1823 869.5 154.1 0.10 904.1 −620.8 166.4 0.3 3.3. Expe imen al Measu emen s as a Func ion o Wa e Con en and Tempe a u e The wo p ope ies mos a ec ed by he p esence o wa e impu i ies can be ex- p essed as a unc ion o wa e con en and empe a u e by means o a single equa ion. Thus, he i ing equa ion o he iscosi y and elec ical conduc i i y o he IL a a gi en wa e con en and empe a u e is: Q(w,T)=Q(T)+∑A,(T) w   , (5) whe e Q(w,T) is η(w,T) o κ(w,T), QIL(T) is he calcula ed wa e - ee iscosi y o elec i- cal conduc i i y o he IL gi en by Equa ion (3) and he co esponding i ing pa ame e s can be de ined as: Aƞ, (T)=(−1)e∑   , (6) 0 20 40 60 80 0 20406080100 0 30 60 90 120 150 180 210 κIL (mS·cm−1) T (°C) ƞIL (mPa·s) Figu e 8. Calcula ed iscosi ies, ηIL , and calcula ed elec ical conduc i i ies, κIL , o wa e - ee EAN (solid symbols) and PAN (open symbols) as a unc ion o he empe a u e, ob ained om Equa ion (1). Do s co espond o he le axis ( iscosi y) and squa es o he igh axis (elec ical conduc i i y). Solid line ob ained om VTF Equa ion (3). Table 5. Fi ing o densi y (g · cm −3 ), iscosi y (mPa · s) and elec ical conduc i i y (mS · cm −1 ) da a o wa e - ee EAN and PAN as unc ion o empe a u e: pa ame e s o Equa ions (2) and (3), coe icien o de e mina ion R 2 and pe cen ual de ia ion (s). IL Aρ,0 Aρ,1 (104) R2ρQ∞,ηBηT0,ηsηQ∞,κBκT0,κsκ EAN 1.2257 −5.9379 0.9996 0.2111 778.8 148.7 0.06 666.2 −424.9 175.8 0.7 PAN 1.1664 −5.8998 0.9998 0.1823 869.5 154.1 0.10 904.1 −620.8 166.4 0.3 3.3. Expe imen al Measu emen s as a Func ion o Wa e Con en and Tempe a u e The wo p ope ies mos a ec ed by he p esence o wa e impu i ies can be exp essed as a unc ion o wa e con en and empe a u e by means o a single equa ion. Thus, he i ing equa ion o he iscosi y and elec ical conduc i i y o he IL a a gi en wa e con en and empe a u e is: Q(w, T)=QIL(T)+ N ∑ i=1 AQ,i(T)wi, (5) whe e Q(w,T) is η(w, T) o κ(w, T) , Q IL (T) is he calcula ed wa e - ee iscosi y o elec ical conduc i i y o he IL gi en by Equa ion (3) and he co esponding i ing pa ame e s can be de ined as: Aη, i (T)=(−1)ie M ∑ j=0 CjTj , (6) Aκ,i(T)= M ∑ j=0 CjTj, (7)