Browsing by Author "Ding, Xiaodan (TTU)"
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Item Colossal Anisotropic Thermal Expansion in a Diazo-Functionalized Compound with Switchable Solid-State Behavior(2023) Ding, Xiaodan (TTU); Unruh, Daniel K. (TTU); Ma, Liulei (TTU); van Aalst, Evan J. (TTU); Reinheimer, Eric W.; Wylie, Benjamin J. (TTU); Hutchins, Kristin M. (TTU)Achieving substantial anisotropic thermal expansion (TE) in solid-state materials is challenging as most materials undergo volumetric expansion upon heating. Here, we describe colossal, anisotropic TE in crystals of an organic compound functionalized with two azo groups. Interestingly, the material exhibits distinct and switchable TE behaviors within different temperature regions. At high temperature, two-dimensional, area zero TE and colossal, positive linear TE (α=211 MK−1) are attained due to dynamic motion, while at low temperature, moderate positive TE occurs in all directions. Investigation of the solid-state motion showed the change in enthalpy and entropy are quite different in the two temperature regions and solid-state NMR experiments support motion in the solid. Cycling experiments demonstrate that the solid-state motions and TE behaviors are completely reversible. These results reveal strategies for designing significant anisotropic and switchable behaviors in solid-state materials.Item Controlling thermal expansion within mixed cocrystals by tuning molecular motion capability(2020) Ding, Xiaodan (TTU); Unruh, Daniel K. (TTU); Groeneman, Ryan H.; Hutchins, Kristin M. (TTU)Controlling thermal expansion (TE) behaviors of organic materials is challenging because several mechanisms can govern TE, such as noncovalent interaction strength and structural motions. Here, we report the first demonstration of tuning TE within organic solids by using a mixed cocrystal approach. The mixed cocrystals contain three unique molecules, two of which are present in variable ratios. These two molecules either lack or exhibit the ability to undergo molecular motion in the solid state. Incorporation of higher ratios of motion-capable molecules results in larger, positive TE along the motion direction. Addition of a motion-incapable molecule affords solids that undergo less TE. Fine-tuned TE behavior was attained by systematically controlling the ratio of motion-capable and -incapable molecules in each solid.Item Controlling thermal expansion within mixed cocrystals by tuning molecular motion capability(2020) Ding, Xiaodan (TTU); Unruh, Daniel K. (TTU); Groeneman, Ryan H.; Hutchins, Kristin M. (TTU)Controlling thermal expansion (TE) behaviors of organic materials is challenging because several mechanisms can govern TE, such as noncovalent interaction strength and structural motions. Here, we report the first demonstration of tuning TE within organic solids by using a mixed cocrystal approach. The mixed cocrystals contain three unique molecules, two of which are present in variable ratios. These two molecules either lack or exhibit the ability to undergo molecular motion in the solid state. Incorporation of higher ratios of motion-capable molecules results in larger, positive TE along the motion direction. Addition of a motion-incapable molecule affords solids that undergo less TE. Fine-tuned TE behavior was attained by systematically controlling the ratio of motion-capable and-incapable molecules in each solid.Item Differences in thermal expansion and motion ability for herringbone and face-to-face π-stacked solids(2022) Ding, Xiaodan (TTU); Zahid, Ethan (TTU); Unruh, Daniel K. (TTU); Hutchins, Kristin M. (TTU)A series of aromatic organic molecules functionalized with different halogen atoms (I/ Br), motion-capable groups (olefin, azo or imine) and molecular length were designed and synthesized. The molecules self-assemble in the solid state through halogen bonding and exhibit molecular packing sustained by either herringbone or face-to-face π-stacking, two common motifs in organic semiconductor molecules. Interestingly, dynamic pedal motion is only achieved in solids with herringbone packing. On average, solids with herringbone packing exhibit larger thermal expansion within the halogen-bonded sheets due to motion occurrence and molecular twisting, whereas molecules with face-to-face π-stacking do not undergo motion or twisting. Thermal expansion along the π-stacked direction is surprisingly similar, but slightly larger for the face-to-face π-stacked solids due to larger changes in π-stacking distances with temperature changes. The results speak to the importance of crystal packing and intermolecular interaction strength when designing aromatic-based solids for organic electronics applications.