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Platinum-coated Janus colloids exhibit self-propelled motion in aqueous solution via the catalytic decomposition of hydrogen peroxide. Here, we report their motion in a uniformly aligned nematic phase of lyotropic chromonic liquid crystal, disodium cromoglycate (DSCG). When active Janus colloids are placed in DSCG, we find that the anisotropy of the liquid crystal imposes a strong sense of direction to their motion; the Janus colloids tend to move parallel to the nematic director. Motion analysis over a range of timescales reveals a crossover from ballistic to anomalous diffusive behavior on timescales below the relaxation time for liquid crystal elastic distortions. Surprisingly we observe that smaller particles roll during ballistic motion, whereas larger particles do not. This result highlights the complexity of phoretically-driven particle motion, especially in an anisotropic fluid environment.
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Patchy Bubble‐Propelled Colloids at Interfaces
Abstract Liquid–liquid or liquid–air interfaces provide interesting environments to study colloids and are ubiquitous in nature and industry, as well as relevant in applications involving emulsions and foams. They present a particularly intriguing environment for studying active particles that exhibit a host of phenomena not seen in passive systems. Active particles can also provide on‐demand controllability that greatly expands their use in future applications. However, research on active particles at interfaces is relatively rare compared to those at solid surfaces or in the bulk. It is studied magnetically steerable active colloids at a liquid–air interface that self‐propel by bubble production via the catalytic decomposition of chemical fuel in the liquid medium. It is investigated the bubble formation and dynamics of “patchy” colloids with a patch of catalytic coating on their surface and compare to more traditional Janus colloids with a hemispherical coating. It is found that the patchy colloids have a tendency to produce smaller bubbles and undergo smoother motion which makes them beneficial for applications such as precise micro‐manipulation. this it is demonstrated by using them to manipulate and assemble patterns of passive spheres on a substrate as well as at an air–liquid interface. It is also characterized the propulsion and bubble formation of both the Janus and patchy colloids and find that previously proposed theories are insufficient to fully describe their motion and bubble bursting mechanism. Additionally, it is observed that the colloids, which reside at the air–liquid interface, demonstrate novel interfacial positive gravitaxis toward the droplet edges, which it is attributed to a torque resulting from opposing downward and buoyant forces on the colloids.
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- Award ID(s):
- 2218980
- PAR ID:
- 10451462
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Understanding the interactive behavior of Janus particles (JPs) is a growing field of research. The enhancement in binding energy, in comparison to homogenous particles, and the dual characteristic of JPs open up new possibilities for novel applications. In many such applications, interfacial materials become subjected to flows that produce dilational and shear stresses. Therefore, it is important to understand the impact that the Janus character brings to interfaces. In this work, we study the microstructure of two-dimensional (2D) JP monolayers formed at the air–water interface and examine the shear viscoelasticity with an interface rheometer that was adapted for in situ surface pressure control via a Langmuir trough. We extend concepts from bulk rheology to data obtained from interfacial rheology as a tool to understand and predict the monolayer’s viscoelastic behavior. Finally, by calculating the time relaxation spectrum from the measured 2D dynamic moduli, we conclude that a phenomenon similar to glass transition is taking place by analogy.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/admi.202300226
