Micellization Behavior of Morpholinium-Based Amide-Functionalized Ionic Liquids in Aqueous Media

Abstract

Morpholinium-based amide-functionalized ionic liquids (ILs) [C(n)AMorph][Br], where n = 8, 12, and 16, have been synthesized and characterized for their micellization behavior in aqueous medium using a variety of state of the art techniques. The adsorption and micellization behavior of [CnAMorph][Br] ILs at the air-solution interface and in the bulk, respectively, has been found to be much better compared to that observed for nonfunctionalized homologous ILs and conventional cationic surfactants, as shown by the comparatively higher adsorption efficiency, lower surface tension at the critical micelle concentraiton (γ(cmc)), and much lower critical micelle concentration (cmc) for [C(n)AMorph][Br] ILs. Conductivity measurements have been performed to obtain the cmc, degree of counterion binding (β), and standard free energy of micellization (ΔG(m)°). Isothermal titration calorimetry has provided information specifically about the thermodynamics of micellization, whereas steady-state fluorescence has been used to obtain the cmc, micropolarity of the cybotactic region, and aggregation number (N(agg)) of the micelles. Both dynamic light scattering and atomic force microscopy have provided insights into the size and shape of the micelles. 2D (1)H-(1)H nuclear Overhauser effect spectroscopy experiments have provided insights into the structure of the micelle, where [C16AMorph][Br] has shown distinct micellization behavior as compared to [C8AMorph][Br] and [C12AMorph][Br] in corroboration with observations made from other techniques.

Aggregation behavior of non-cytotoxic ester functionalized morpholinium based ionic liquids in aqueous media

“…The investigations on aggregation behavior of SAILs have gained momentum in the recent times. Numerous SAILs based on a variety of cationic head groups such as pyridinium [15], imidazolium [16], morpholinium [17], amino acids [18] and pyrrolidinium [19], have been synthesized, characterized and investigated for their aggregation behavior. These SAILs have been found to self-assemble where characteristic properties of aggregates depend on the nature of the solvent and nature of the constituent ions of SAILs.…”

“…Our own group has reported the aggregation behavior of a variety of SAILs including those based on amino acid based cations [15][16][17] where it has been established that the nature of ionic head group, cation and length of alkyl chain governs the aggregation behavior of SAILs. Further, a careful examination of literature regarding aggregation of SAILs reveals that the introduction of an amide [17], ether or hydroxyl [28], and ester group [29], in the molecular structure of SAILs led to marked changes in their surface as well as bulk behavior. In this regard, the hydrophobic alkyl chain of SAILs is a key moiety which can be functionalized with a variety of functional groups to achieve better aggregation behavior of SAILs.…”

“…In this regard, the hydrophobic alkyl chain of SAILs is a key moiety which can be functionalized with a variety of functional groups to achieve better aggregation behavior of SAILs. In this scenario, amide functionalized morpholinium based SAILs and ester functionalized imidazolium and pyridinium based SAILs possessing better surface active properties as compared to conventional ionic surfactants or non-functionalized SAILs have been reported [17,29]. The presence of easily cleavable functional group such as an ester group, if present in SAIL structure, has been found to increase the proclivity of SAILs towards biodegradation [30].…”

“…Therefore it is of interest from biological point of view to explore and access the bio-physicochemical properties of newly synthesized SAILs. Further, survey of the literature regarding synthesis and investigation on aggregation behavior of SAILs manifest that investigations on morpholinium based SAILs are much lacking [17,33].…”

Phase behavior of the surfactant ionic liquid trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate with water and dodecane

“…At the same time, it is often stated that ionic liquids can be designed to have a set of properties that are very interesting for industry: chemical and thermal stability, no vapor emissions, easily recovered, among others. More recently, there has been an interest in surfactant ionic liquids, that is, ionic liquids that also present surface active properties [4][5][6][7][8]. The key point is the introduction of the interesting properties from ionic liquids into a surface active component.…”