Thermodynamic studies of micellization of surface active ionic liquids

Čobanov Marinković, Isidora (author), Bešter Rogač, Marija (mentor), Vraneš, Milan (comentor)

In this work, 13 surface active ionic liquids, SAILs, were synthesized and their micellization properties were examined by isothermal titration calorimetry, ITC. An improved mass-action model, which describes micellization as the equilibrium between micelles and monomers with the constant aggregation number, was used for interpretation of the obtained data. Additionally, molecular dynamics, MD, simulations were performed for all the systems confirming the experimentally obtained results. Finally, the toxicity of studied systems towards wheat culture was tested in order to study the impact of the structural change of SAILs on the level of toxicity. From the thermodynamic study, it was found that the investigated systems behave mainly like common ionic surfactants and already investigated SAILs: the micellization process is entropically driven at low temperatures (due to the hydrophobic effect), while at high temperatures the enthalpy contribution becomes equally important (possibly due to counterion binding). Moreover, it was confirmed that the counterion isomerism influences the micellization process the most, followed by the prolongation of the shorter alkyl chain length on the imidazolium ring and isomerism of cation. MD simulations have revealed that, in addition to hydration and ion-ion interactions, steric hindrance plays a very important role in the process of self-aggregation. Additionally, toxicity tests with wheat culture showed that the prolongation of the shorter alkyl chain on cation, as well as the anion/cation isomerism, do not play an important role in increasing or decreasing the germination level. Therefore, the hydrophobicity of the compound is a key property dictating the degree of toxicity, so it can be concluded that the longest substituent on the cation has the biggest influence on the overall toxicity of SAILs.

• Language: English
• Keywords: thermodynamics, surface active ionic liquids, micellization
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2021
• PID: 20.500.12556/RUL-128498
• COBISS.SI-ID: 74772995
• Publication date in RUL: 15.07.2021

Secondary language

• Language: Slovenian
• Title: Termodinamske raziskave micelizacije površinsko aktivnih ionskih tekočin

Abstract

V tej disertaciji smo sintetizirali 13 površinsko aktivnih ionskih tekočin, surface active ionic liquids, SAILs, in njihove micelizacijske lastnosti preučevali z izotermično titracijsko kalorimetrijo, ITC. Eksperimentalne podatke smo analizirali s pomočjo modela, ki predpostavlja ravnotežje med monomeri in micelami s konstantnim agregacijskim številom. Za potrditev doblejnih rezultatov smo za vse sisteme izvedli simulacije molekularne dinamike, MD. Raziskave smo zaključili s testiranjem toksičnosti preučevanih sistemov na kulturo pšenice, da bi preučili vpliv strukturnih sprememb SAIL na stopnjo toksičnosti. Pridobljeni termodinamski parametri za micelizacijo kažejo, da se preiskovani sistemi obnašajo podobno kot večina običajnih ionskih površinsko aktivnih snovi in že preučevanih SAILs: pri nizkih temperaturah je micelizacija entropijsko voden proces (zaradi hidrofobnega efekta), medtem ko pri višjih temperaturah entalpijski prispevek postane enako pomemben (možno zaradi vezave protiionov). Ugotovili smo, da izomerija protiionov in najbolj vpliva na proces micelizacije, potem sledi podaljšanje dolžine krajše alkilne verige na imidazolijevom obroču, najmanjši efekt pa ima izomerija kationov. Simulacije MD so pokazale, da imajo sterična ovira poleg hidracije in ionsko-ionskih interakcij zelo pomembno vlogo v procesu samoagregacije. Dodatno smo s testi toksičnosti na pšenici pokazali, da podaljšanje krajše alkilne verige na kationu in izomerija aniona in/ali kationa nimata pomembne vloge pri povečanju ali zmanjšanju toksičnosti. Očitno je hidrofobni karakter spojine ključna lastnost, ki narekuje stopnjo toksičnosti, zato lahko sklepamo, da ima najdaljši substituent na kationu največji vpliv na celotno toksičnost SAILs.

• Keywords: termodinamika, površinsko aktivne ionske tekočine, micelizacija