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      Thermal conductance of hydrophilic and hydrophobic interfaces.

      Physical review letters

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          Abstract

          Using time-domain thermoreflectance, we have measured the transport of thermally excited vibrational energy across planar interfaces between water and solids that have been chemically functionalized with a self-assembled monolayer (SAM). The Kapitza length--i.e., the thermal conductivity of water divided by the thermal conductance per unit area of the interface--is analogous to the "slip length" for water flowing tangentially past a solid surface. We find that the Kapitza length at hydrophobic interfaces (10-12 nm) is a factor of 2-3 larger than the Kapitza length at hydrophilic interfaces (3-6 nm). If a vapor layer is present at the hydrophobic interface, and this vapor layer has a thermal conductivity that is comparable to bulk water vapor, then our experimental results constrain the thickness of the vapor layer to be less than 0.25 nm.

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          Nanoshell-mediated near-infrared thermal therapy of tumors under magnetic resonance guidance.

          Metal nanoshells are a class of nanoparticles with tunable optical resonances. In this article, an application of this technology to thermal ablative therapy for cancer is described. By tuning the nanoshells to strongly absorb light in the near infrared, where optical transmission through tissue is optimal, a distribution of nanoshells at depth in tissue can be used to deliver a therapeutic dose of heat by using moderately low exposures of extracorporeally applied near-infrared (NIR) light. Human breast carcinoma cells incubated with nanoshells in vitro were found to have undergone photothermally induced morbidity on exposure to NIR light (820 nm, 35 W/cm2), as determined by using a fluorescent viability stain. Cells without nanoshells displayed no loss in viability after the same periods and conditions of NIR illumination. Likewise, in vivo studies under magnetic resonance guidance revealed that exposure to low doses of NIR light (820 nm, 4 W/cm2) in solid tumors treated with metal nanoshells reached average maximum temperatures capable of inducing irreversible tissue damage (DeltaT = 37.4 +/- 6.6 degrees C) within 4-6 min. Controls treated without nanoshells demonstrated significantly lower average temperatures on exposure to NIR light (DeltaT < 10 degrees C). These findings demonstrated good correlation with histological findings. Tissues heated above the thermal damage threshold displayed coagulation, cell shrinkage, and loss of nuclear staining, which are indicators of irreversible thermal damage. Control tissues appeared undamaged.
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            Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto gold

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              Role of hydration and water structure in biological and colloidal interactions.

              The conventional explanation of why hydrophilic surfaces and macromolecules remain well separated in water is that they experience a monotonically repulsive hydration force owing to structuring of water molecules at the surfaces. A consideration of recent experimental and theoretical results suggests an alternative interpretation in which hydration forces are either attractive or oscillatory, and where repulsions have a totally different origin. Further experiments are needed to distinguish between these possibilities.
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                Author and article information

                Journal
                16712374
                10.1103/PhysRevLett.96.186101

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