22 research outputs found
Symmetrical Catalytically Active Colloids Collectively Induce Convective Flow
Although much attention has focused on self-motile asymmetrical catalytically active âJanusâ colloids as a route to enable new fluidic transport applications, the motion of symmetrical catalytically active colloids is less investigated. This is despite isotropically active colloids being more accessible and commonly used as supports for heterogeneous catalysis. Here, we addressed this by systematically investigating the motion of platinum-coated colloids capable of isotropically decomposing hydrogen peroxide. We observed the onset of collective convective flow as the colloidal volume fraction increased above a threshold. The ballistic velocities induced by the collective flow were quantified by particle tracking and were found to increase with the volume fraction. We also determined the associated increase in the PĂ©clet number as evidence of the potential to use convection as a simple method to enhance mass transport rates. By determining the persistence lengths, we were able to correlate the magnitude of convective flow with the overall catalytic activity per unit volume. This suggests that the mechanism for the collective flow is driven by chemical activity-induced local density differences. Finally, we discussed these results in the context of potential new fluidic applications and highlighted the role that activity-induced convection may play in experiments designed to investigate self-motile catalytic systems
pHâresponsive catalytic janus motors with autonomous navigation and cargoârelease functions
The fabrication of multifunctional polymeric Janus colloids that display catalytically driven propulsion, change their size in response to local variations in pH, and vary cargo release rate is demonstrated. Systematic investigation of the colloidal trajectories reveals that in acidic environments the propulsion velocity reduces dramatically due to colloid swelling. This leads to a chemotaxisâlike accumulation for ensembles of these responsive particles in lowâpH regions. In synergy with this chemically defined accumulation, the colloids also show an enhancement in the release rate of an encapsulated cargo molecule. Together, these effects result in a strategy to harness catalytic propulsion for combined autonomous transport and cargo release directed by a chemical stimulus, displaying a greater than 30 times local cargoâaccumulation enhancement. Lactic acid can be used as the stimulus for this behavior, an acid produced by some tumors, suggesting possible eventual utility as a drugâdelivery method. Applications for microfluidic transport are also discussed
Reactive inkjet printing and propulsion analysis of silk-based self-propelled micro-stirrers
In this study, a protocol for using reactive inkjet printing to fabricate enzymatically propelled silk swimmers with well-defined shapes is reported. The resulting devices are an example of self-propelled objects capable of generating motion without external actuation and have potential applications in medicine and environmental sciences for a variety of purposes ranging from micro-stirring, targeted therapeutic delivery, to water remediation (e.g., cleaning oil spills). This method employs reactive inkjet printing to generate well-defined small-scale solid silk structures by converting water soluble regenerated silk fibroin (silk I) to insoluble silk fibroin (silk II). These structures are also selectively doped in specific regions with the enzyme catalase in order to produce motion via bubble generation and detachment. The number of layers printed determines the three-dimensional (3D) structure of the device, and so here the effect of this parameter on the propulsive trajectories is reported. The results demonstrate the ability to tune the motion by varying the dimensions of the printed structures
Dynamics of a deformable self-propelled particle under external forcing
We investigate dynamics of a self-propelled deformable particle under
external field in two dimensions based on the model equations for the center of
mass and a tensor variable characterizing deformations. We consider two kinds
of external force. One is a gravitational-like force which enters additively in
the time-evolution equation for the center of mass. The other is an
electric-like force supposing that a dipole moment is induced in the particle.
This force is added to the equation for the deformation tensor. It is shown
that a rich variety of dynamics appears by changing the strength of the forces
and the migration velocity of self-propelled particle
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte