Direct experimental observation of mesoscopic fluorous domains in fluorinated room temperature ionic liquids

Abstract

Fluorinated room temperature ionic liquids (FRTILs) represent a class of solvent media that are attracting great attention due to their IL-specific properties as well as features stemming from their fluorous nature. Medium-to-long fluorous tails constitute a well-defined apolar moiety in the otherwise polar environment. Similarly to the case of alkyl tails, such chains are expected to result in the formation of self-assembled fluorous domains. So far, however, no direct experimental observation has been made of the existence of such structural heterogeneities on the nm scale. We report here the first experimental evidence of the existence of mesoscopic spatial segregation of fluorinated domains, on the basis of highly complementary X-ray and neutron scattering data sets (highlighting the importance of the latter probe) and NMR spectroscopy. Data are interpreted using atomistic molecular dynamics simulations, emphasizing the existence of a self-assembly mechanism that delivers segregated fluorous domains, where preferential solubilisation of fluorinated compounds can occur, thus paving the way for several smart applications.

Structural features of selected protic ionic liquids based on a super-strong base

“…Although the presently considered anion is different from [TFSI] that was studied in reference 56 , we can determine that the occurrence of this HB interaction is quite rare with the present choice of cation and anion: the integrated number of neighbour anion nitrogen around the reference cation hydrogen is <0.1 for r<3 Å (corresponding to Recently, we undertook a series of investigations on a variety of AILs containing fluorous chains in their anions. 36,48,55,[57][58][59][60] Therein, we observed that, in agreement with other experimental 61 Figure 2), that typically would fingerprint the existence of segregated domains with mesoscopic spatial extent. 36,48,55,[57][58][59][60] Recently, we showed in a number of examples that while neutrons can successfully appreciate such a feature, due to contrast reasons, X-ray may fail to detect it.…”

“…36,48,55,[57][58][59][60] Therein, we observed that, in agreement with other experimental 61 Figure 2), that typically would fingerprint the existence of segregated domains with mesoscopic spatial extent. 36,48,55,[57][58][59][60] Recently, we showed in a number of examples that while neutrons can successfully appreciate such a feature, due to contrast reasons, X-ray may fail to detect it. 36,55,[57][58][59][60]66 Neutron diffraction measurements therefore might indicate the presence of a further low Q peak centred at ca.…”

“…36,48,55,[57][58][59][60] Recently, we showed in a number of examples that while neutrons can successfully appreciate such a feature, due to contrast reasons, X-ray may fail to detect it. 36,55,[57][58][59][60]66 Neutron diffraction measurements therefore might indicate the presence of a further low Q peak centred at ca. 0.4 Å -1 , fingerprinting the existence of fluorous domains.…”

Mesoscopic structural organization in fluorinated pyrrolidinium-based room temperature ionic liquids

“…Results from ab initio calculations, carried out on other pyrrolidinium-based ILs, are in agreement with the heteronuclear NOE measurements, which show anion interactions with the cation ring [14]. The spatial segregation of fluorinated chains, in asymmetric bis(perfluoroalkylsulfonyl)imide anions, into nm-sized heterogeneities was also evidenced by Lo Celso et al [15,16] through small angle X-ray and neutron scattering. Before that, experimental X-ray scattering experiments [17] and Molecular Dynamics simulations [18] in protic ILs with fluorinated chains showed related observations, although influenced by the strong hydrogen bonding interactions between opposite ions.…”

From Solvent-Free to Dilute Electrolytes: Essential Components for a Continuum Theory

“…Besides the multiple applications, IL either with or without dilution also pose several physicochemical properties that extend the phenomenology of concentrated electrolytes: (i ) multiple timescales, 17,32 (ii ) self-assembly, [33][34][35] and (iii ) non-monotonic variation (exhibiting qualitatively three distinct regions) of EDL with concentration, 15,36 a.k.a., the phenomenon of under-screening. These phenomenologies emphasize that besides the vast progress in concentrated electrolytes, a unified framework that combines altogether the above mentioned phenomena is still missing.…”