Speaker
Description
The development of sustainable solvent systems is a central objective in green chemistry, with aqueous mixtures playing a key role due to their environmental compatibility and tunable properties. In this context, water-diol mixtures have attracted increasing attention, as diols combine hydrophilic and hydrophobic characteristics and can modulate the physicochemical behavior of water. Liquid water exhibits complex and anomalous physicochemical properties, which become even more intricate in multicomponent systems, like water-diol mixtures, and under confinement. In such environments, competing hydrogen-bonding and hydrophobic interactions govern the phase behavior, which remains difficult to predict when molecular structure, composition and confinement effects are combined.
To address this, phase transitions in water-diol mixtures are systematically compared between bulk systems and confined spaces, while differences between individual diols are used to gain insight into underlying interactions.
The phase behavior of water-diol mixtures is investigated in both bulk and confined spaces. A homologous series of diols with varying OH-group separation including 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol and 1,5-pentanediol, is considered in order to assess the role of molecular structure. Measurements are carried out over a wide temperature range (30 °C to 160 °C) using differential scanning calorimetry (DSC), with particular focus on melting, crystallization, and glass transition phenomena. In addition to bulk systems, confinement effects are examined using mesoporous SBA-15 with a characteristic pore size of 7 nm, representing model systems for porous materials relevant to sustainable technologies.
In the bulk, a systematic depression of the melting temperature is observed with increasing diol concentration, eventually leading to mixtures in which crystallization is fully suppressed. In contrast, the glass transition temperature remains largely constant across compositions. Pronounced differences between individual diols are identified, reflecting the influence of chain length and odd-even effects, and providing insight into the underlying diol-water interactions.
Under confinement, an additional melting point depression is observed, which appears to be largely independent of composition. Furthermore, significant modifications of the phase behavior occur, including changes in crystallization tendencies and glass transition characteristics. Systematic differences between diols indicate that molecular structure influences how confinement affects phase transitions. These findings highlight the impact of spatial confinement and surface interactions on thermodynamic and kinetic properties.
Overall, these results contribute to a deeper understanding of aqueous diol systems in confined spaces and support the development of predictive models for complex fluids in nanoporous materials, relevant for the design of sustainable solvents.
| Country | Germany |
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