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Geometric tuning of self-propulsion for Janus catalytic particles

View Article: PubMed Central - PubMed

ABSTRACT

Catalytic swimmers have attracted much attention as alternatives to biological systems for examining collective microscopic dynamics and the response to physico-chemical signals. Yet, understanding and predicting even the most fundamental characteristics of their individual propulsion still raises important challenges. While chemical asymmetry is widely recognized as the cornerstone of catalytic propulsion, different experimental studies have reported that particles with identical chemical properties may propel in opposite directions. Here, we show that, beyond its chemical properties, the detailed shape of a catalytic swimmer plays an essential role in determining its direction of motion, demonstrating the compatibility of the classical theoretical framework with experimental observations.

No MeSH data available.


Related in: MedlinePlus

Swimming velocity of a non-axisymmetric spheroidal Janus particle.The right half of the particle is chemically-active, while the rest of the particle is passive. Top: Solute concentration on the surface of the particle and on the planes of symmetry for three representative geometries (A–C). Bottom: Dependance of the swimming velocity on the aspect ratio, ξ, for three different mobility distributions: uniform mobility (M1 = M2, dash-dotted line); a fully-inert left-hand hemisphere (M2 = 0, solid line); opposite mobilities on both sites (M1 = −M2, dashed line). The three geometries (A–C) from the top panels are indicated.
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f3: Swimming velocity of a non-axisymmetric spheroidal Janus particle.The right half of the particle is chemically-active, while the rest of the particle is passive. Top: Solute concentration on the surface of the particle and on the planes of symmetry for three representative geometries (A–C). Bottom: Dependance of the swimming velocity on the aspect ratio, ξ, for three different mobility distributions: uniform mobility (M1 = M2, dash-dotted line); a fully-inert left-hand hemisphere (M2 = 0, solid line); opposite mobilities on both sites (M1 = −M2, dashed line). The three geometries (A–C) from the top panels are indicated.

Mentions: This critical role of the geometry of a particle on the sign of the swimming velocity, demonstrated above for simple axisymmetric particles, is in fact a very general feature. In the case of more complex shapes and chemical patterns, geometry still controls, and possibly reverses, the swimming velocity. This is illustrated now by considering chemically-asymmetric spheroidal Janus particles. These have a spheroidal geometry and are divided into two distinct chemically-homogeneous portions with a dividing plane that includes (instead of being perpendicular to) their axis of geometric symmetry (Fig. 3, top). Here again, rods and disks propel in opposite directions. For rods, the maximum concentration is this time reached at the center of the active site (which lies in the geometric equatorial plane), while it is shifted toward the dividing plane between active and passive sites for flattened geometries (Fig. 3, bottom).


Geometric tuning of self-propulsion for Janus catalytic particles
Swimming velocity of a non-axisymmetric spheroidal Janus particle.The right half of the particle is chemically-active, while the rest of the particle is passive. Top: Solute concentration on the surface of the particle and on the planes of symmetry for three representative geometries (A–C). Bottom: Dependance of the swimming velocity on the aspect ratio, ξ, for three different mobility distributions: uniform mobility (M1 = M2, dash-dotted line); a fully-inert left-hand hemisphere (M2 = 0, solid line); opposite mobilities on both sites (M1 = −M2, dashed line). The three geometries (A–C) from the top panels are indicated.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5304220&req=5

f3: Swimming velocity of a non-axisymmetric spheroidal Janus particle.The right half of the particle is chemically-active, while the rest of the particle is passive. Top: Solute concentration on the surface of the particle and on the planes of symmetry for three representative geometries (A–C). Bottom: Dependance of the swimming velocity on the aspect ratio, ξ, for three different mobility distributions: uniform mobility (M1 = M2, dash-dotted line); a fully-inert left-hand hemisphere (M2 = 0, solid line); opposite mobilities on both sites (M1 = −M2, dashed line). The three geometries (A–C) from the top panels are indicated.
Mentions: This critical role of the geometry of a particle on the sign of the swimming velocity, demonstrated above for simple axisymmetric particles, is in fact a very general feature. In the case of more complex shapes and chemical patterns, geometry still controls, and possibly reverses, the swimming velocity. This is illustrated now by considering chemically-asymmetric spheroidal Janus particles. These have a spheroidal geometry and are divided into two distinct chemically-homogeneous portions with a dividing plane that includes (instead of being perpendicular to) their axis of geometric symmetry (Fig. 3, top). Here again, rods and disks propel in opposite directions. For rods, the maximum concentration is this time reached at the center of the active site (which lies in the geometric equatorial plane), while it is shifted toward the dividing plane between active and passive sites for flattened geometries (Fig. 3, bottom).

View Article: PubMed Central - PubMed

ABSTRACT

Catalytic swimmers have attracted much attention as alternatives to biological systems for examining collective microscopic dynamics and the response to physico-chemical signals. Yet, understanding and predicting even the most fundamental characteristics of their individual propulsion still raises important challenges. While chemical asymmetry is widely recognized as the cornerstone of catalytic propulsion, different experimental studies have reported that particles with identical chemical properties may propel in opposite directions. Here, we show that, beyond its chemical properties, the detailed shape of a catalytic swimmer plays an essential role in determining its direction of motion, demonstrating the compatibility of the classical theoretical framework with experimental observations.

No MeSH data available.


Related in: MedlinePlus