Nanocage formation and structural anomalies in imidazolium ionic liquid glasses governed by alkyl chains of cations

Abstract

Intriguing nanostructuring anomalies have been recently observed in imidazolium ionic liquids (ILs) near their glass transition points, where local density around a nanocaged solute progressively grows up with temperature. Herewith,...

Inherent heterogeneities and nanostructural anomalies in organic glasses revealed by EPR

“…As was demonstrated in our previous work, 30,32,33 the data from CW and pulse EPR fruitfully complement each other and help to reveal the structural dynamics of glassy ILs and their structural anomalies. CW EPR allows disentangling the observed signal vs. temperature into two fractions of mobile (denoted M(T)) and immobile (1 À M) probes.…”

“…51 However, nanoscale structural anomalies in glassy phthalates have not been known till our recent study providing the rst example with DBP. 30 In this work we for the rst time demonstrate the broad scope and ubiquity of nanostructural anomalies in organic glasses. Below we systematically investigate the inuence of phthalate's alkyl chain length on the anomaly and detail this phenomenon for other common glass-forming solvents containing alkyl moiety, thus shaping the general trends of this new set of phenomena.…”

“…Methodology, glasses and probes Scheme 1 shows chemical structures of studied phthalates and other glass-formers with variable length of alkyl chain, as well as ILs [C n mim]BF 4 , whose data were obtained previously 30 and are used here for comparison.…”

“…1 mM. [30][31][32][33]53 Pulse EPR measurements were performed using a commercial Bruker Elexsys E580 spectrometer at X-band (9 GHz). CW EPR spectra were obtained at X-band Bruker EMX spectrometer.…”

“…21,22 Recently, we have discovered unprecedented suppression of molecular mobility with temperature in a series of ionic liquids (ILs) in a glassy state near T g , which was assigned to unusual structural rearrangements on the nanometer scale. [30][31][32][33] In particular, the coexistence of two types of IL environments was observed, one of which progressively suppresses the molecular mobility upon temperature increase between ($T g -60 K) and T g . This is a highly uncommon behavior, since most known substances, including the same ILs, become less dense in the bulk upon temperature increase; therefore it was termed a "structural anomaly".…”