Knowing the thermodynamic stability of transition metal oxide nanoparticles is important for understanding and controlling their role in a variety of industrial and environmental systems. Using calorimetric data on surface energies for cobalt, iron, manganese, and nickel oxide systems, we show that surface energy strongly influences their redox equilibria and phase stability. Spinels (M(3)O(4)) commonly have lower surface energies than metals (M), rocksalt oxides (MO), and trivalent oxides (M(2)O(3)) of the same metal; thus, the contraction of the stability field of the divalent oxide and expansion of the spinel field appear to be general phenomena. Using tabulated thermodynamic data for bulk phases to calculate redox phase equilibria at the nanoscale can lead to errors of several orders of magnitude in oxygen fugacity and of 100 to 200 kelvin in temperature.
We investigate the effects of pH and temperature on the conformational changes of poly[2-(dimethylamino)ethyl methacrylate] (PDEM) chains at the air/water interface by using Langmuir balance and sum frequency generation vibrational spectroscopy. At pH 4, the tertiary amine groups are fully charged and the PDEM chains are so hydrophilic that they completely enter into the water phase and do not exhibit thermosensitivity. At pH 7, these groups are only partially charged, and the accompanying hydration/dehydration--followed by repartitioning into the water and air phases--gives rise to a marked thermosensitivty. Finally, at pH 10, the tertiary amine groups become uncharged and thus preferentially stay in the hydrophobic air phase, devoid of associated water molecules, which results in the surface-pressure change (DeltaPi) being nearly independent of the temperature. Our Langmuir-balance experiments, coupled with surface-sensitive spectroscopy, demonstrate that: 1) the thermosensitivity of the PDEM chains relates to the hydration/dehydration of the tertiary amine groups, 2) the phase transition of thermosensitive polymers is most likely initiated by the dehydration of the chains, and 3) the phase transition of thermosensitive polymers at the air/water interface is markedly different from that in aqueous solution because of the redistribution of the macromolecular segments induced by the asymmetric forces at the air/water interface.
A series of boranil complexes with aggregation-induced emission effects were facilely constructed, which can be utilized to image lipid droplets in living cells and yolk lipids in zebrafish.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.