Pressure-freezing of dodecane: exploring the crystal structures, formation kinetics and phase diagrams for colossal barocaloric effects in n -alkanes

• Published in: RSC advances 2023-11, Vol.13 (47), p.33305-33317
• Main Authors: Poręba, Tomasz, Kicior, Inga
• Format: Article
• Language: English
• Subjects: Alkanes; Alternative energy sources; Chemistry; Crystal growth; Crystal lattices; Crystal structure; Crystallization; Diamond anvil cells; Dodecane; Entropy; Freezing; Kinetics; Lattice energy; Phase diagrams; Pressure dependence; Raman spectroscopy; Refrigerants; Room temperature; Single crystals; Synchrotrons
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d3ra06957e

Barocaloric (BC) materials provide cheaper and more energy efficient alternatives to traditional refrigerants. Some liquid alkanes were recently shown to exhibit a colossal BC effect, matching the entropy changes in commercial vapour–liquid refrigerants. Dodecane was predicted to have the largest entropy change among the studied alkanes. Using synchrotron powder and single-crystal X-ray diffraction, Raman spectroscopy, and lattice energy calculations, we investigated the BC effects of n -dodecane at high pressures and room temperature. Remarkably, a colossal entropy change |Δ S | of 778 J kg −1 K −1 at 0.15(3) GPa and 295 K was observed. Spectroscopic studies revealed that this entropy change correlates closely with the conformational transition from mixed gauche to all- trans forms during pressure-induced crystallization. Additionally, the usage of a diamond anvil cell allowed the determination of the crystal structures of in situ crystallized n -un- and dodecane, as well as evaluation of the pressure-dependent crystal growth kinetics. Furthermore, our research suggests that the entropy change (per kilogram) upon compression should be similar for all n -alkanes within the range of 9–18 carbon atoms in the molecule, based on their lattice energies. Even-numbered alkanes are predicted to exhibit superior BC properties compared to their odd-numbered counterparts due to the more symmetric crystal structures and lower propensity to form plastic phases with lower transition entropy.