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Melting is one of the most studied phase transitions important for atomic, molecular, colloidal, and protein systems. However, there is currently no microscopic experimentally accessible criteria that can be used to reliably track a system evolution across the transition, while providing insights into melting nucleation and melting front evolution. To address this, we developed a theoretical mean-field framework with the normalised mean-square displacement between particles in neighbouring Voronoi cells serving as the local order parameter, measurable experimentally. We tested the framework in a number of colloidal and in silico particle-resolved experiments against systems with significantly different (Brownian and Newtonian) dynamic regimes and found that it provides excellent description of system evolution across melting point. This new approach suggests a broad scope for application in diverse areas of science from materials through to biology and beyond. Consequently, the results of this work provide a new guidance for nucleation theory of melting and are of broad interest in condensed matter, chemical physics, physical chemistry, materials science, and soft matter. [ABSTRACT FROM AUTHOR]

Using a combination of experimental Raman, FTIR, UV–VIS absorption and emission data, together with the corresponding DFT calculations we propose the mechanism of modification of the folic acid specifically under the hydrothermal treatment at 200 °C. We established that folic acid breaks down into fragments while the pteridine moiety remains intact likely evolving into 6-formylpterin with the latter responsible for the increase in fluorescence emission at 450 nm. The results suggest that hydrothermal approach can be used for production of other purpose-engineered fluorophores. [ABSTRACT FROM AUTHOR]

We investigated light emission of hydrothermally treated citric acid and ethylenediamine (EDA) with various precursor ratios using gel-electrophoresis. We show that this relatively simple approach can deliver significant insights into the origins of photoluminescence. We found that products of the synthesis consist of both positively and negatively charged species and exhibit large dispersion in electrophoretic mobility (i.e. charge-to-size ratio). We observed that despite the large dispersion of the reaction products the blue light emission is confined to discrete bands clearly identifiable in the gel. We demonstrate clear evidence that this emission originates from the negatively charged light molecular fraction with the highest mobility which shows no excitation-dependent light emission. This molecular fluorophore exhibits spectral characteristics similar to previously reported 1,2,3,5-tetrahydro-5-oxo-imidazo[1,2-a]pyridine-7-carboxylic acid (IPCA). Secondary gel electrophoresis run performed on the bands extracted from the first run indicates that no further separation takes place. On the basis of our experimental results, we conclude that relatively stable binding exists between IPCA and EDA-derived product. Thus, the products of the reaction contain IPCA both in molecular form and in complexes with EDA-derived products. We conclude that excitation-dependent emission is related to the fluorophore binding to the positively charged EDA-derived products with a positive charge. [ABSTRACT FROM AUTHOR]

Synthesis of hydrophobic luminescent carbon nanostructures in non-aqueous solution has been performed. The system consisted of hexane as nonpolar “oil” phase, nonionic polyoxyethylene (4) lauryl ether (Brij L4) as a surfactant, and either water or dextran sulfate aqueous solution as a polar phase. Carbon nanodots (CND) with a particle size of 5.0 ± 0.7 nm were formed by solvothermal treatment at 180 °C of two- (hexane-Brij L4) and three-component (hexane-Brij L4-aqua solutions) systems. It was found that CND with blue-green-yellow photoluminescence (PL) with linear dependence of emission peak position on excitation wavelength and stability of PL over at least 3 weeks were formed from Brij L4. We found that using small volume of water as the third component helps to reorganize Brij L4 molecules which results in CND PL intensity increase by a factor of 1.5 and quantum yield increase from 2.0 to 2.6% compared to CND from the two-component micellar system. Replacing water with dextran sulfate solution resulted in a lower quantum yield to 2.2%. Thus, addition of small amount of water clearly shows an effect of molecular level organization on properties of CND and results in enhanced quantum yield.ᅟ [ABSTRACT FROM AUTHOR]