Abstract
Bimetallic nanorods are propelled without chemical fuels in megahertz (MHz) acoustic fields, and exhibit similar behaviors to single-metal rods, including autonomous axial propulsion and organization into spinning chains. Shape asymmetry determines the direction of axial movement of bimetallic rods when there is a small difference in density between the two metals. Movement toward the concave end of these rods is inconsistent with a scattering mechanism that we proposed earlier for acoustic propulsion, but is consistent with an acoustic streaming model developed more recently by Nadal and Lauga (Phys. Fluids 2014, 26, 082001). Longer rods were slower at constant power, and their speed was proportional to the square of the power density, in agreement with the acoustic streaming model. The streaming model was further supported by a correlation between the disassembly of spinning chains of rods and a sharp decrease in the axial speed of autonomously moving motors within the levitation plane of the cylindrical acoustic cell. However, with bimetallic rods containing metals of different densities, a consistent polarity of motion was observed with the lighter metal end leading. Speed comparisons between single-metal rods of different densities showed that those of lower density are propelled faster. So far, these density effects are not explained in the streaming model. The directionality of bimetallic rods in acoustic fields is intriguing and offers some new possibilities for designing motors in which shape, material, and chemical asymmetry might be combined for enhanced functionality.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 4763-4769 |
| Number of pages | 7 |
| Journal | ACS nano |
| Volume | 10 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 26 2016 |
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All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Engineering(all)
- Physics and Astronomy(all)
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Density and Shape Effects in the Acoustic Propulsion of Bimetallic Nanorod Motors. / Ahmed, Suzanne; Wang, Wei; Bai, Lanjun; Gentekos, Dillon T.; Hoyos, Mauricio; Mallouk, Thomas E.
In: ACS nano, Vol. 10, No. 4, 26.04.2016, p. 4763-4769.Research output: Contribution to journal › Article
TY - JOUR
T1 - Density and Shape Effects in the Acoustic Propulsion of Bimetallic Nanorod Motors
AU - Ahmed, Suzanne
AU - Wang, Wei
AU - Bai, Lanjun
AU - Gentekos, Dillon T.
AU - Hoyos, Mauricio
AU - Mallouk, Thomas E.
PY - 2016/4/26
Y1 - 2016/4/26
N2 - Bimetallic nanorods are propelled without chemical fuels in megahertz (MHz) acoustic fields, and exhibit similar behaviors to single-metal rods, including autonomous axial propulsion and organization into spinning chains. Shape asymmetry determines the direction of axial movement of bimetallic rods when there is a small difference in density between the two metals. Movement toward the concave end of these rods is inconsistent with a scattering mechanism that we proposed earlier for acoustic propulsion, but is consistent with an acoustic streaming model developed more recently by Nadal and Lauga (Phys. Fluids 2014, 26, 082001). Longer rods were slower at constant power, and their speed was proportional to the square of the power density, in agreement with the acoustic streaming model. The streaming model was further supported by a correlation between the disassembly of spinning chains of rods and a sharp decrease in the axial speed of autonomously moving motors within the levitation plane of the cylindrical acoustic cell. However, with bimetallic rods containing metals of different densities, a consistent polarity of motion was observed with the lighter metal end leading. Speed comparisons between single-metal rods of different densities showed that those of lower density are propelled faster. So far, these density effects are not explained in the streaming model. The directionality of bimetallic rods in acoustic fields is intriguing and offers some new possibilities for designing motors in which shape, material, and chemical asymmetry might be combined for enhanced functionality.
AB - Bimetallic nanorods are propelled without chemical fuels in megahertz (MHz) acoustic fields, and exhibit similar behaviors to single-metal rods, including autonomous axial propulsion and organization into spinning chains. Shape asymmetry determines the direction of axial movement of bimetallic rods when there is a small difference in density between the two metals. Movement toward the concave end of these rods is inconsistent with a scattering mechanism that we proposed earlier for acoustic propulsion, but is consistent with an acoustic streaming model developed more recently by Nadal and Lauga (Phys. Fluids 2014, 26, 082001). Longer rods were slower at constant power, and their speed was proportional to the square of the power density, in agreement with the acoustic streaming model. The streaming model was further supported by a correlation between the disassembly of spinning chains of rods and a sharp decrease in the axial speed of autonomously moving motors within the levitation plane of the cylindrical acoustic cell. However, with bimetallic rods containing metals of different densities, a consistent polarity of motion was observed with the lighter metal end leading. Speed comparisons between single-metal rods of different densities showed that those of lower density are propelled faster. So far, these density effects are not explained in the streaming model. The directionality of bimetallic rods in acoustic fields is intriguing and offers some new possibilities for designing motors in which shape, material, and chemical asymmetry might be combined for enhanced functionality.
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U2 - 10.1021/acsnano.6b01344
DO - 10.1021/acsnano.6b01344
M3 - Article
AN - SCOPUS:84967223711
VL - 10
SP - 4763
EP - 4769
JO - ACS Nano
JF - ACS Nano
SN - 1936-0851
IS - 4
ER -