During the past decade, increasing attention has been paid to photoluminescent nanocarbon materials, namely, carbon quantum dots (CQDs). It is gradually accepted that surface engineering plays a key role in regulating the properties and hence the applications of the CQDs. In this paper, we prepared highly charged CQDs through a one-pot pyrolysis with citric acid as carbon source and a room-temperature imidazolium-based ionic liquid as capping agent. The as-prepared CQDs exhibit high quantum yields up to 25.1% and are stable under various environments. In addition, the amphiphilicity of the CQDs can be facilely tuned by anion exchange, which leads to a spontaneous phase transfer between water and oil phase. The promising applications of the CQDs as ion sensors and fluorescent inks have been demonstrated. In both cases, these ionic-liquid-modified CQDs were found to possess novel characteristics and/or superior functions compared to existing ones.
Mixtures of cationic and anionic (catanionic) single-chain surfactants can readily form bilayers in aqueous solutions, [1] in which uni-and multilamellar onion phases (the so-called vesicle phase) are often observed to be in equilibrium. [2] Since vesicles represent simple model systems for biological membranes and have practical applications (for example, for controlled drug or DNA release), [3] investigations of vesicle phases are of considerable interest in different areas, including surfactants, materials, and life sciences. Recently, two new self-assembled structures of controlled size (nanodisks and regular hollow icosahedra) were observed in dilute catanionic surfactants with H + and OH À counterions by Zemb and coworkers. [4][5][6] Such so-called "true" catanionic systems, with a nonswelling but finite uptake of water, and with a spacing of the same order as described in the current study were studied and documented by Jokela et al. [7] It was also later established by Rand, Parsegian, and Leiken [8] that the lamellar phase at maximum swelling of salt-free catanionic systems with a zero osmotic pressure, that is, the repulsive hydration interaction is compensated by van der Waals force at that point. The molar ratio r of the anionic to cationic components controls the structural surface charge and, hence, controls the long-range repulsive interaction independently of the weight volume fraction (f), which in turn controls the average colloidcolloid distance. The salt-free catanionic systems can be represented in a ternary phase diagram whose two independent variables are f and r.[6]Herein we report, for the first time to our knowledge, the discovery of a "true", salt-free concentrated catanionic uniand multilamellar onion phase that differs from the catanionic surfactant systems with excess salt that are formed by the combination of the counterions, as evident from our freezefracture transmission electron microscopy (FF-TEM) observations and small-angle X-ray scattering (SAXS) measurements. This molecular catanionic couple comprises the longest hydrocarbon chains described to date, so it was essential to determine if the carbon chains were in a frozen (gel) or liquid state. The size of the unilamellar vesicles ranges from about 20 to 700 nm and that of the large onions are several micrometers. The interlamellar spacing between the bilayers of onions is about 35 nm, thus suggesting rather compact packing of the bilayers. The high osmotic pressure sustains the highly stable colloidal suspension of the catanionic onion phase. The observations of the onion phase may prove valuable and stimulating to fellow specialists, not least as "true" catanionic surfactant systems do not seem to be exhaustively investigated yet.The "true" salt-free catanionic vesicle phase was obtained by mixing aqueous solutions of trimethyltetradecylammonium hydroxide (TTAOH) and oleic acid (OA; see Figure 3). The stock solution of TTAOH (pH 12-13) was prepared from the commercial bromide form (TTABr) by anion exchange with a strong b...
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