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Boundary Guidance in Self-propelled Colloidal Motors
Başlık:
Boundary Guidance in Self-propelled Colloidal Motors
Yazar:
Mozaffari, Ali, author.
ISBN:
9780438002593
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (160 pages)
Genel Not:
Source: Dissertation Abstracts International, Volume: 79-10(E), Section: B.
Advisors: Charles Maldarelli; Joel Koplik Committee members: Kyle Bishop; Joel Koplik; Charles Maldarelli; Jeffrey Morris; David Rumschitzki.
Özet:
Microbots are ultra-miniaturized, colloid-sized engines (100 nm - 10 mu in size). As locomotors, they are engineered to be autonomous, reacting with solute fuel in a solution in which they are immersed, and converting the chemical energy into mechanical propulsion without moving parts. Designed to transverse liquids along small scale pathways, these microbots are at the center of highly imaginative applications on the technological horizon including rovers for sensing molecular species or binding targets, or transporters for taxing cargo. Navigation of microbots is essential to their applications. While steering can be achieved by external direction, here we present theoretical results on how the chemo-mechanical interaction of a locomotor with boundaries can reflect the engine from the boundary, or guide or even statically position the microbot along the boundary. As a model system we choose an engine design in which a Janus colloid coated with a symmetrical catalyst cap converts fuel into a product solute on one side of the colloid. The solute is repelled from the colloid through a short range repulsive interaction in a thin layer around the particle which creates a slip velocity that propels the swimmer in the direction opposite to the cap (self-diffusiophoresis).
Solutions for the motion of the Janus locomotor are obtained by solving the product mass conservation and Stokes hydrodynamic equations in the vicinity of the wall in bispherical coordinates. Our results indicate that, from a few particle radii away, the microbot moves towards the planar boundary when its catalyst cap faces obliquely away from the wall. We show that as the locomotor approaches the wall in this orientation, it begins to rotate. For small cap sizes (less than approximately sixty percent of the colloid area), the colloid rotates rapidly until its active area faces the wall, and the locomotor moves away from the boundary. However, for larger active areas, the colloid rotates more slowly bringing the locomotor closer to the wall, and the orientation becomes locked due to a balance of torques driven by the hydrodynamic wall interaction and the diffusiophoretic slip motion. In this orientation, the locomotor skims along the surface at a fixed distance. For cap sizes larger than approximately eighty percent of the total area, the particle rotates slowly in an opposite direction until its active area faces directly away from the wall. Rotation ceases due to symmetry, as does translation, as diffusiophoretic propulsion becomes zero due to a accumulation of product near the wall, and the particle becomes stationary. We further study the effect of thermal noise on these skimming and stationary regimes through Brownian dynamic simulations to identify the microbot size for which deterministic motion is realized, and below which less predictable behavior is found.
Moreover, we demonstrate more advanced and intricate examples of boundary guidance: We examine the motion of a spherical Janus locomotor in a two dimensional channel, and the trajectory of spheroidal locomotors around a spherical obstacle. Locomotors with small catalyst areas in a channel repeatedly reflect off of the channel wall until they become rotated to a symmetrical cap orientation which focuses them to move at the channel centerline. For larger coverages, the swimmers approach one wall of the channel and skim directly without reflection. For ellipsoidal and spherical locomotors approaching a spherical obstacle, locomotors becomes locked in an orbit around the obstacle for large obstacles, but, for smaller obstacles, only partly navigate around the obstacle before leaving the orbit and moving away from the obstacle.
Notlar:
School code: 1606
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
---|---|---|---|
XX(677946.1) | 677946-1001 | Proquest E-Tez Koleksiyonu | Arıyor... |
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