Solvent selective gelation of cetyltrimethylammonium bromide: structure, phase evolution and thermal characteristics

We report herein the gelation behaviour of cetyltrimethylammonium bromide (CTAB), a cationic surfactant, in a variety of solvent compositions. A turbid gel of CTAB in a binary solvent mixture at a critical composition was observed to be 1 : 3 v/v toluene : water. The molecular structure of the as-formed gel was investigated by X-ray diffraction and microscopic techniques, namely, optical and polarizing microscopy, scanning electron microscopy and small-angle X-ray scattering (SAXS). The phase evolution has been studied using UV-visible transmittance measurements and the thermal characteristics of the gel by differential scanning calorimetry measurements. SAXS studies, in conjunction with molecular modelling, revealed the gel to assemble as lamellae with high interdigitation of bilayer assembly of CTAB molecules with predominant non-covalent interactions, where the gel lamellae were inferred from the interplanar spacings. Rheological studies revealed the viscoelastic nature of the CTAB gels. The ability to form a gel has been evaluated in several polar solvents, such as methanol and chloroform, and non-polar solvents, such as toluene and carbon tetrachloride.

Oil-Dispersible Green-Emitting Carbon Dots: New Insights on a Facile and Efficient Synthesis

Carbon dots (CDs) have been progressively attracting interest as novel environmentally friendly and cost-effective luminescent nanoparticles, for implementation in light-emitting devices, solar cells, photocatalytic devices and biosensors. Here, starting from a cost-effective bottom-up synthetic approach, based on a suitable amphiphilic molecule as carbon precursor, namely cetylpyridinium chloride (CPC), green-emitting CDs have been prepared at room temperature, upon treatment of CPC with concentrated NaOH solutions. The investigated method allows the obtaining, in one-pot, of both water-dispersible (W-CDs) and oil-dispersible green-emitting CDs (O-CDs). The study provides original insights into the chemical reactions involved in the process of the carbonization of CPC, proposing a reliable mechanism for the formation of the O-CDs in an aqueous system. The ability to discriminate the contribution of different species, including molecular fluorophores, allows one to properly single out the O-CDs emission. In addition, a mild heating of the reaction mixture, at 70 °C, has demonstrated the ability to dramatically decrease the very long reaction time (i.e. from tens of hours to days) at room temperature, allowing us to synthesize O-CDs in a few tens of minutes while preserving their morphological and optical properties.

Hexadecyl-Containing Organic Salts as Novel Organogelators for Ionic, Eutectic, and Molecular Liquids

The incorporation of a hexadecyl group on imidazolium, pyridinium, and pyrrolidinium scaffolds produces low-molecular-weight ionic organogelators that can gel several types of ionic liquids, deep eutectic solvents (DESs), and several molecular organic solvents. Minimum gelator concentrations fall in the 0.9-15.0% (w/v) range, with the lower end of the gelator concentrations observed in the gelation of DESs. On the basis of polarized optical microscopy, differential scanning calorimetry, and X-ray data, crystallization of these salts appear to produce high-surface-area crystals, which generate sufficiently stable three-dimensional networks that are capable of trapping the solvent molecules. Importantly, the nature of the fluid component of the gel appears to have a profound effect on the morphology of the crystallized organogelators. On the other hand, the organogelators appeared to modulate phase transitions of the liquids.