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5 Sep 2011

Volume 99, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 99, 103701 (2011); http://dx.doi.org/10.1063/1.3633066 (3 pages)

Yinan Zhang, David J. S. Birch, and Yu Chen
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Thermocapillary actuation of binary drops on solid surfaces

Yuejun Zhao, Fangjie Liu, and Chuan-Hua Chen

Appl. Phys. Lett. 99, 104101 (2011); http://dx.doi.org/10.1063/1.3632041 (3 pages) | Cited 1 time

Online Publication Date: 6 September 2011

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On hydrophobic solid surfaces, aqueous drops are typically not conducive to thermocapillary actuation. This letter reports thermal mobilization of water drops by encapsulating them with a long-chain alcohol. On a parylene-coated silicon substrate, a water-heptanol binary drop can assume a unique shape: the dome-shaped water drop is capped by a layer of heptanol, and the heptanol cap protrudes through a “foot” to a precursor film. For intermediate drop diameters, the speed of the binary drop is linearly proportional to its diameter and the imposed temperature gradient, with an offset accounting for the hysteresis force.
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47.55.dm Thermocapillary effects
68.03.-g Gas-liquid and vacuum-liquid interfaces
68.08.Bc Wetting

A self-sustaining micro thermomechanic-pyroelectric generator

S. K. T. Ravindran, T. Huesgen, M. Kroener, and P. Woias

Appl. Phys. Lett. 99, 104102 (2011); http://dx.doi.org/10.1063/1.3633350 (3 pages) | Cited 6 times

Online Publication Date: 7 September 2011

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Pyroelectric generators (PEGs) can be used for thermal energy harvesting and present a potential alternative to thermoelectric generators. However, in contrary to thermoelectric generators, the PEG principle requires thermal transients to stimulate the conversion process. Such suitable thermal transients are rare in nature, hindering the deployment. In this paper, we present a micro thermomechanic-pyroelectric energy generator (μTMPG) that converts a stationary spatial thermal gradient into the required transient temperature profile across the PEG. The measured power output of the μTMPG is 3 μW from a temperature difference of 79.5 K. However, with an optimized design, a power output of 39.4 mW is estimated for the same temperature difference.
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84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Flow-induced voltage generation in high-purity metallic and semiconducting carbon nanotubes

Seung Ho Lee, Duckjong Kim, Soohyun Kim, and Chang-Soo Han

Appl. Phys. Lett. 99, 104103 (2011); http://dx.doi.org/10.1063/1.3634209 (3 pages) | Cited 4 times

Online Publication Date: 8 September 2011

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We investigated the flow-induced voltage generation of single-walled carbon nanotubes (SWCNTs), comparing metallic and semiconducting types, flow velocity, and different ionic concentration solutions. The induced fluid-flow voltage was measured using a microfluidics chip that we fabricated with a SWCNT film embedded between its metal electrodes. We found that the voltage generated for semiconducting nanotubes was three times greater than that for metallic nanotubes and that both types of SWCNTs showed an unexpected reversal in signal sign, likely due to the switching of the major carrier between holes and electrons. These generated voltages increased proportionally for both types of SWCNTs as functions of flow velocity and ionic concentration.
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73.61.Cw Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.At Metal and metallic alloys

Effect of surface composition and roughness on the apparent surface free energy of silica aerogel materials

D. B. Mahadik, A. Venkateswara Rao, V. G. Parale, M. S. Kavale, P. B. Wagh, S. V. Ingale, and Satish C. Gupta

Appl. Phys. Lett. 99, 104104 (2011); http://dx.doi.org/10.1063/1.3635398 (3 pages)

Online Publication Date: 9 September 2011

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Surface chemical composition and morphology play an important role in determining the superhydrophobic behavior of solids. To provide insights on the influence of surface chemical composition and roughness on superhydrophobic behaviour of tetramethoxysilane based silica aerogel materials over a wide range, we have carried out a quantitative study of the effect of hydrophobic agent on contact angle and surface free energy of silica aerogels. The apparent surface free energy values were calculated using Zisman method and validated by Fowkes-Girifalco-Good theory.
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82.70.Gg Gels and sols
68.35.bt Other materials
68.03.Cd Surface tension and related phenomena
68.35.Md Surface thermodynamics, surface energies
68.35.Dv Composition, segregation; defects and impurities
65.40.gp Surface energy
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