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In the context of green chemistry, the ongoing search for alternative green solvents remains a key area of research. Given that aqueous solutions in nature typically occur in confined spaces, such as in stone or clay, the study of aqueous solutions in small confinement is particularly intriguing. Additionally, the concept of binary water-hydrotrope solutions is of particular interest. Hydrotropes are amphiphilic organic molecules that significantly enhance the solubility of non-polar compounds in water. While they serve a similar phase-modulating role as surfactants, hydrotropes are generally much shorter in chain length and do not form micelles.[1] Alkanediamines, with ethylenediamine (EDA) being the most commonly studied representative, well-known for its CO2 capture capabilities and use as ligand in coordination chemistry. Numerous studies have been conducted on the behaviour of confined water[2] [3] [4] and its binary solutions with other compounds, such as salts or alcohols.[5] [6] [7] In contrast, the aqueous solutions of alkanediamines have yet to be extensively studied.
To investigate the bulk phase behaviour of aqueous alkanediamine solutions, we performed differential scanning calorimetry (DSC) measurements on the bulk solutions. While our DSC measurements of the bulk systems yielded consistent and clear results, the complex phase behaviour of binary diamine-water solutions remained ambiguous. Recent wide-angle X-ray scattering (WAXS) measurements have suggested the presence of multiple coexisting phases, which appear to be dependent on both temperature and system composition. Furthermore, spectroscopic approaches agree with these findings. Of particular interest is the interplay between different types of phenomena, such as thermal and structural transformations, as well as thermodynamic effects. These include glass transitions, the depression of a substance’s melting point when another is introduced, and observable phase separations during cooling. Based on the bulk phase behaviour of the solutions, even more intriguing phase behaviour is anticipated for aqueous alkanediamine solutions in confinement, ranging from melting point depression to suppressed phase separation and crystallization. This aspect is primarily studied using DSC, with a variety of mesoporous host materials, such as SBA-15 and MCM-41silica as well as periodic mesoporous organosilicas (PMOs). This methodological approach allows for the investigation of how pore size and surface chemistry influence phase behaviour in confinement.
| References | [1] T. K. Hodgdon, E. W. Kaler, COCIS 2007, 12, 121. [2] S. Cerveny, J. Swenson, J. Chem. Phys.2019, 150, 234904. [3] S. Jähnert, F. Vaca Chávez, G. E. Schaumann, A. Schreiber, M. Schönhoff, G. H. Findenegg, PCCP 2008, 10, 6039. [4] B. Malfait, A. Jani, J. B. Mietner, R. Lefort, P. Huber, M. Fröba, D. Morineau, J. Phys. Chem. C 2021, 125, 16864. [5] E. Jantsch, C. Weinberger, M. Tiemann, T. Koop, J. Phys. Chem. C 2019, 123, 24566. [6] B. Kumari, M. Brodrecht, H. Breitzke, M. Werner, B. Grünberg, H.-H. Limbach, S. Forg, E. P. Sanjon, B. Drossel, T. Gutmann et al., J. Phys. Chem. C 2018, 122, 19540. [7] B. Malfait, A. Pouessel, A. Jani, D. Morineau, J. Phys. Chem. Lett. 2020, 11, 5763. |
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| Country | Germany |
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