title: The quest for extreme water repellency: Superhydrophobicity made easy

authors: Saunders, Graham C.

subjects: chemistry

abstract: In his seminal work On Floating Bodies I Archimedes of Syracuse provided an explanation of the action of solid bodies on water. Although his thesis immediately benefitted King Heiro II² and has continued to serve mankind well, it ignores the effect of the interfacial interactions between the solid, water and air (surface tension). These interactions are negligible, or at least are considered negligible, compared to forces arising from the effect of gravity on large bodies. However, as the mass of the body decreases, the surface interactions become increasingly important leading to some unusual and potentially useful phenomena. The understanding and application of these effects is currently driving much fundamental research by physicists, chemical engineers, material scientists, and chemists into surfaces that display extreme properties, in particular extreme water repellency, or superhydrophobicitv. It is only comparatively recently that detailed mathematical expressions for the interaction between a liquid, solid and gas at these extremes have been developed, making progress that parallels that for the fabrication of these surfaces.

text: The quest for extreme water repellency: Superhydrophobicity made easy In his seminal work On Floating Bodies I Archimedes of Syracuse provided an explanation of the action of solid bodies on water. Although his thesis immediately benefitted King Heiro II² and has continued to serve mankind well, it ignores the effect of the interfacial interactions between the solid, water and air (surface tension). These interactions are negligible, or at least are considered negligible, compared to forces arising from the effect of gravity on large bodies. However, as the mass of the body decreases, the surface interactions become increasingly important leading to some unusual and potentially useful phenomena. The understanding and application of these effects is currently driving much fundamental research by physicists, chemical engineers, material scientists, and chemists into surfaces that display extreme properties, in particular extreme water repellency, or superhydrophobicitv. It is only comparatively recently that detailed mathematical expressions for the interaction between a liquid, solid and gas at these extremes have been developed, making progress that parallels that for the fabrication of these surfaces.

year: 2009-07

title: Theoretical study of the structures of 4-(2,3,5,6-tetrafluoropyridyl)diphenylphosphine oxide and tris(pentafluorophenyl)phosphine oxide: Why does the crystal structure of (tetrafluoropyridyl)diphenylphosphine oxide have two different P=O bond lengths?

authors: Lane, Joseph R.

subjects: Science & Technology

abstract: The crystal structure of 4-(2,3,5,6-tetrafluoropyridyl)diphenylphosphine oxide (1) contains two independent molecules in the asymmetric unit. Although the molecules are virtually identical in all other aspects, the P=O bond distances differ by ca. 0.02 Å. In contrast, although tris(pentafluorophenyl)phosphine oxide (2) has a similar crystal structure, the P=O bond distances of the two independent molecules are identical. To investigate the reason for the difference, a density functional theory study was undertaken. Both structures comprise chains of molecules. The attraction between molecules of 1, which comprises lone pair–π, weak hydrogen bonding and C–H···arene interactions, has energies of 70 and 71 kJ mol⁻¹. The attraction between molecules of 2 comprises two lone pair–π interactions, and has energies of 99 and 100 kJ mol−1. There is weak hydrogen bonding between molecules of adjacent chains involving the oxygen atom of 1. For one molecule, this interaction is with a symmetry independent molecule, whereas for the other, it also occurs with a symmetry related molecule. This provides a reason for the difference in P=O distance. This interaction is not possible for 2, and so there is no difference between the P=O distances of 2.

text: Theoretical study of the structures of 4-(2,3,5,6-tetrafluoropyridyl)diphenylphosphine oxide and tris(pentafluorophenyl)phosphine oxide: Why does the crystal structure of (tetrafluoropyridyl)diphenylphosphine oxide have two different P=O bond lengths? The crystal structure of 4-(2,3,5,6-tetrafluoropyridyl)diphenylphosphine oxide (1) contains two independent molecules in the asymmetric unit. Although the molecules are virtually identical in all other aspects, the P=O bond distances differ by ca. 0.02 Å. In contrast, although tris(pentafluorophenyl)phosphine oxide (2) has a similar crystal structure, the P=O bond distances of the two independent molecules are identical. To investigate the reason for the difference, a density functional theory study was undertaken. Both structures comprise chains of molecules. The attraction between molecules of 1, which comprises lone pair–π, weak hydrogen bonding and C–H···arene interactions, has energies of 70 and 71 kJ mol⁻¹. The attraction between molecules of 2 comprises two lone pair–π interactions, and has energies of 99 and 100 kJ mol−1. There is weak hydrogen bonding between molecules of adjacent chains involving the oxygen atom of 1. For one molecule, this interaction is with a symmetry independent molecule, whereas for the other, it also occurs with a symmetry related molecule. This provides a reason for the difference in P=O distance. This interaction is not possible for 2, and so there is no difference between the P=O distances of 2.

year: 2020

title: Keepa Te Wharau: a Ngati Rahiri rangatira

authors: Hart, Philip

abstract: Keepa Te Wharau’s whakapapa linked him, unusually, to both Ngati Maru and Ngati Haua. Through these connections he was associated with the Te Aroha district from an early age, visiting it on several occasions and even cultivating there, briefly. When the block was before the land court he gave evidence – though his evidence in a later succession case was clearly wrong, deliberately so. Having interests in several blocks of land, he falsely claimed not to have received money for the Aroha Block, using the excuse of drunkenness, for which he was before the court on several occasions. He would sell land, as would his children, to meet living expenses. He invested in two goldfields, Thames and Te Aroha, very modestly. A leading rangatira, he was notable for his loyalty to the Crown.

text: Keepa Te Wharau: a Ngati Rahiri rangatira Keepa Te Wharau’s whakapapa linked him, unusually, to both Ngati Maru and Ngati Haua. Through these connections he was associated with the Te Aroha district from an early age, visiting it on several occasions and even cultivating there, briefly. When the block was before the land court he gave evidence – though his evidence in a later succession case was clearly wrong, deliberately so. Having interests in several blocks of land, he falsely claimed not to have received money for the Aroha Block, using the excuse of drunkenness, for which he was before the court on several occasions. He would sell land, as would his children, to meet living expenses. He invested in two goldfields, Thames and Te Aroha, very modestly. A leading rangatira, he was notable for his loyalty to the Crown.

year: 2016