Adelé Poynor - Academia.edu (original) (raw)
Papers by Adelé Poynor
Bulletin of the American Physical Society, Mar 5, 2007
APS March Meeting Abstracts, Mar 1, 2003
Much controversy has attended the theoretically-motivated proposition that water, in intimate con... more Much controversy has attended the theoretically-motivated proposition that water, in intimate contact with a hydrophobic surface, nucleates vapor-like films spontaneously. We have tested this idea using a phase-modulated ellipsometer of unusually-large sensitivity that allowed in situ measurements of hydrophobic surfaces immersed in water. Not only does the ellipticity indicate the presence of a nanometer-thick film of low refractive index, but (more surprisingly) this film exhibits giant fluctuations, even when averaged over the millimeter-sized area probed by this measurement. The power spectrum of these fluctuations was quantified in detail as a function of ionic strength, temperature, and content of gas dissolved in the water. Productive comparison was made to nonpolar fluids (especially tetradecane) also in contact with partially-wetting surfaces comprised of methyl-terminated self-assembled monolayers. A picture emerges in which the predicted thin vapor layer at such surfaces is attended by intriguing power-law fluctuations.
Hydrophobic surfaces are those that resist contact with water. When water and a hydrophobic surfa... more Hydrophobic surfaces are those that resist contact with water. When water and a hydrophobic surface are forced into contact with each other complicated interactions ensue. Previous research predicts a layer of low density water exists at the interface between the water and hydrophobic surface which is known as depletion layer. We investigated the interaction between bulk water and a hydrophobic
Previous x-ray reflectivity measurements of the interface between water and hydrophobic surfaces ... more Previous x-ray reflectivity measurements of the interface between water and hydrophobic surfaces with contact angle >100 indicate the existence of depletion layer. However, x-ray measurements provide little information of the fluctuation dynamics. In this presentation, surface plasmon resonance imaging technique with < 1ms temporal resolution and < 1mum lateral resolution has been built to investigate interface between water and methyl-terminated gold surface. This technique enables to examine the fluctuation dynamics of the depletion layer with temporal and spatial correlation analysis. The characteristic time and length scales of this fluctuation are explored.
Physical review letters, Jan 31, 2006
Synchrotron x-ray reflectivity measurements of the interface between water and methyl-terminated ... more Synchrotron x-ray reflectivity measurements of the interface between water and methyl-terminated octadecylsilane monolayers with stable contact angle >100 degrees conclusively show a depletion layer, whether or not the water is degassed. The thickness is of order one water molecule: 2-4 Angstrom with electron density <40% that of bulk water. Considerations of coherent and incoherent averaging of lateral inhomogeneities show that the data cannot be explained by "nanobubbles." When the contact angle is lower, unstable in time, or when monolayers fail to be sufficiently smooth over the footprint of the x-ray beam, there is no recognizable depletion.
Physical Review Letters, 2008
The author replies to comments on his original article. The abstract from the original item is in... more The author replies to comments on his original article. The abstract from the original item is included here. Synchrotron x-ray reflectivity measurements of the interface between water and methyl-terminated octadecylsilane monolayers with stable contact angle >100{sup o} conclusively show a depletion layer, whether or not the water is degassed. The thickness is of order one water molecule: 2-4 with electron
Physical Review Letters, 2008
The author replies to comments on his original article. The abstract from the original item is in... more The author replies to comments on his original article. The abstract from the original item is included here. Synchrotron x-ray reflectivity measurements of the interface between water and methyl-terminated octadecylsilane monolayers with stable contact angle >100{sup o} conclusively show a depletion layer, whether or not the water is degassed. The thickness is of order one water molecule: 2-4 with electron density <40% that of bulk water. Considerations of coherent and incoherent averaging of lateral inhomogeneities show that the data cannot be explained by 'nanobubbles'. When the contact angle is lower, unstable in time, or when monolayers fail to be sufficiently smooth over the footprint of the x-ray beam, there is no recognizable depletion.
Bulletin of the American Physical Society, Mar 5, 2007
APS March Meeting Abstracts, Mar 1, 2003
Much controversy has attended the theoretically-motivated proposition that water, in intimate con... more Much controversy has attended the theoretically-motivated proposition that water, in intimate contact with a hydrophobic surface, nucleates vapor-like films spontaneously. We have tested this idea using a phase-modulated ellipsometer of unusually-large sensitivity that allowed in situ measurements of hydrophobic surfaces immersed in water. Not only does the ellipticity indicate the presence of a nanometer-thick film of low refractive index, but (more surprisingly) this film exhibits giant fluctuations, even when averaged over the millimeter-sized area probed by this measurement. The power spectrum of these fluctuations was quantified in detail as a function of ionic strength, temperature, and content of gas dissolved in the water. Productive comparison was made to nonpolar fluids (especially tetradecane) also in contact with partially-wetting surfaces comprised of methyl-terminated self-assembled monolayers. A picture emerges in which the predicted thin vapor layer at such surfaces is attended by intriguing power-law fluctuations.
Hydrophobic surfaces are those that resist contact with water. When water and a hydrophobic surfa... more Hydrophobic surfaces are those that resist contact with water. When water and a hydrophobic surface are forced into contact with each other complicated interactions ensue. Previous research predicts a layer of low density water exists at the interface between the water and hydrophobic surface which is known as depletion layer. We investigated the interaction between bulk water and a hydrophobic
Previous x-ray reflectivity measurements of the interface between water and hydrophobic surfaces ... more Previous x-ray reflectivity measurements of the interface between water and hydrophobic surfaces with contact angle >100 indicate the existence of depletion layer. However, x-ray measurements provide little information of the fluctuation dynamics. In this presentation, surface plasmon resonance imaging technique with < 1ms temporal resolution and < 1mum lateral resolution has been built to investigate interface between water and methyl-terminated gold surface. This technique enables to examine the fluctuation dynamics of the depletion layer with temporal and spatial correlation analysis. The characteristic time and length scales of this fluctuation are explored.
Physical review letters, Jan 31, 2006
Synchrotron x-ray reflectivity measurements of the interface between water and methyl-terminated ... more Synchrotron x-ray reflectivity measurements of the interface between water and methyl-terminated octadecylsilane monolayers with stable contact angle >100 degrees conclusively show a depletion layer, whether or not the water is degassed. The thickness is of order one water molecule: 2-4 Angstrom with electron density <40% that of bulk water. Considerations of coherent and incoherent averaging of lateral inhomogeneities show that the data cannot be explained by "nanobubbles." When the contact angle is lower, unstable in time, or when monolayers fail to be sufficiently smooth over the footprint of the x-ray beam, there is no recognizable depletion.
Physical Review Letters, 2008
The author replies to comments on his original article. The abstract from the original item is in... more The author replies to comments on his original article. The abstract from the original item is included here. Synchrotron x-ray reflectivity measurements of the interface between water and methyl-terminated octadecylsilane monolayers with stable contact angle >100{sup o} conclusively show a depletion layer, whether or not the water is degassed. The thickness is of order one water molecule: 2-4 with electron
Physical Review Letters, 2008
The author replies to comments on his original article. The abstract from the original item is in... more The author replies to comments on his original article. The abstract from the original item is included here. Synchrotron x-ray reflectivity measurements of the interface between water and methyl-terminated octadecylsilane monolayers with stable contact angle >100{sup o} conclusively show a depletion layer, whether or not the water is degassed. The thickness is of order one water molecule: 2-4 with electron density <40% that of bulk water. Considerations of coherent and incoherent averaging of lateral inhomogeneities show that the data cannot be explained by 'nanobubbles'. When the contact angle is lower, unstable in time, or when monolayers fail to be sufficiently smooth over the footprint of the x-ray beam, there is no recognizable depletion.