Periodic Reporting for period 1 - PhotoActive (Macroscopic active particles driven by light)
Periodo di rendicontazione: 2023-04-01 al 2025-03-31
In the last years, there has been an outstanding growing interest in active matter. In these complex systems, a number of interacting
agents consume and convert energy into mechanical motion, representing nice examples of out-of-equilibrium behavior. Such
systems are important because they can be found in nature ranging from the microscopic to the macroscopic scale, e.g. molecular
motors, cells, bird flocks, or human crowds. Interestingly, and despite the obvious differences among the agents that compose these
systems, common behavioral patterns have been identified such as collective motion, anomalous diffusion, segregation, or clogging
in the flow through constrictions. Aiming for a better understanding of these complex active systems a reductionist strategy is
necessary, and this is why the study of active granular matter (very simple self-propelled agents that interact uniquely by contacts) is
widely acknowledged.
Within active grains, we can distinguish between internally excited ones (such as Hexbugs) or externally forced ones. Certainly, the
former have the advantage to closely resemble real active matter but, to date, also have the drawback of not allowing testing their
response to external stimulus. My proposal, PhotoActive, aims to fill this gap by designing novel macroscopic self-propelled agents
that are internally excited but can be driven by an external stimulus as it occurs with all natural systems. The idea is to develop and
implement Hexbug-like particles whose source of energy comes from a photovoltaic cell. The great advantage of these novel agents
concerns the versatility that provides using a fully controllable illumination panel with which we can impose spatial intensity
gradients or temporally evolving patterns. In this way, and applying an interdisciplinary approach involving experiments, numerical
modeling, and simulations, we ambition boosting the existing understanding of active matter systems.
agents consume and convert energy into mechanical motion, representing nice examples of out-of-equilibrium behavior. Such
systems are important because they can be found in nature ranging from the microscopic to the macroscopic scale, e.g. molecular
motors, cells, bird flocks, or human crowds. Interestingly, and despite the obvious differences among the agents that compose these
systems, common behavioral patterns have been identified such as collective motion, anomalous diffusion, segregation, or clogging
in the flow through constrictions. Aiming for a better understanding of these complex active systems a reductionist strategy is
necessary, and this is why the study of active granular matter (very simple self-propelled agents that interact uniquely by contacts) is
widely acknowledged.
Within active grains, we can distinguish between internally excited ones (such as Hexbugs) or externally forced ones. Certainly, the
former have the advantage to closely resemble real active matter but, to date, also have the drawback of not allowing testing their
response to external stimulus. My proposal, PhotoActive, aims to fill this gap by designing novel macroscopic self-propelled agents
that are internally excited but can be driven by an external stimulus as it occurs with all natural systems. The idea is to develop and
implement Hexbug-like particles whose source of energy comes from a photovoltaic cell. The great advantage of these novel agents
concerns the versatility that provides using a fully controllable illumination panel with which we can impose spatial intensity
gradients or temporally evolving patterns. In this way, and applying an interdisciplinary approach involving experiments, numerical
modeling, and simulations, we ambition boosting the existing understanding of active matter systems.
The overall goal of PhotoActive is to design and optimize internally excited, self-propelled, photosensitive, macroscopic particles, which allows the study of the diffusion, mixing, and clustering of macroscopic agents for the first time by externally imposing spatial gradients of activity.
An initial major step is the development of particles and the optimization of the light source. The goal is to have a high degree of control over the distinct variables by controlling the driving force and apply intrinsically active particles instead of externally excited ones. This is summarized in the first objective: Design and optimization of particles that self-propel under proper illumination (O1), related to WP1.
In the following, to pursue the second and third objectives, experimental, numerical, and theoretical work will be done in parallel, complementing each other. First, spatially homogeneous illumination will be applied in the system to pursue the second objective: Characterise and understand the macroscopic collective motion under spatially homogeneous illumination (O2), related to WP2, WP3, and WP4.
The third objective is: Explore the response of the system to temporally and spatially varying intensity illuminations (O3). To pursue this goal, on the one hand, gradient light fields will be applied to the system (WP2 and WP4). On the other hand, a fully controllable, intelligent light panel will be designed, which will allow us to study the behavior of agents when the driving force is changed locally, depending on the density of particles (WP3 and WP4).
An initial major step is the development of particles and the optimization of the light source. The goal is to have a high degree of control over the distinct variables by controlling the driving force and apply intrinsically active particles instead of externally excited ones. This is summarized in the first objective: Design and optimization of particles that self-propel under proper illumination (O1), related to WP1.
In the following, to pursue the second and third objectives, experimental, numerical, and theoretical work will be done in parallel, complementing each other. First, spatially homogeneous illumination will be applied in the system to pursue the second objective: Characterise and understand the macroscopic collective motion under spatially homogeneous illumination (O2), related to WP2, WP3, and WP4.
The third objective is: Explore the response of the system to temporally and spatially varying intensity illuminations (O3). To pursue this goal, on the one hand, gradient light fields will be applied to the system (WP2 and WP4). On the other hand, a fully controllable, intelligent light panel will be designed, which will allow us to study the behavior of agents when the driving force is changed locally, depending on the density of particles (WP3 and WP4).
Despite the interest aroused by granular active matter, an obvious drawback markedly limits the range of
experimental scenarios that can be implemented; and therefore the sort of analogies that can be attempted with
microscopic active matter. The fact is that for internally excited particles, it is experimentally difficult to impose
spatial gradients of activity, a strategy that has been proven to be useful to investigate several physical processes
such as diffusion, mixing, or clustering. With this project, my intention is to overcome this problem by
designing and optimizing a novel version of internally excited agents. The idea is to attach a photovoltaic cell
on the top of Hexbug® particles, and use this source of energy instead of the battery that the original ones have. In
this way, a lighting panel with an intensity gradient, for instance, should be enough to induce density gradients in
the concentration of particles, which will accumulate in the regions of lower intensities. Then, a diffusion process
could be triggered by simply inverting the gradient. More ambitiously, the versatility of the system will also allow
the design of a fully controllable illumination panel that is able to locally change the illumination intensity
depending on the density of particles in each position. In this way, we hypothesize that the formation of clusters
could be prevented or even split up by locally increasing the light intensity.
experimental scenarios that can be implemented; and therefore the sort of analogies that can be attempted with
microscopic active matter. The fact is that for internally excited particles, it is experimentally difficult to impose
spatial gradients of activity, a strategy that has been proven to be useful to investigate several physical processes
such as diffusion, mixing, or clustering. With this project, my intention is to overcome this problem by
designing and optimizing a novel version of internally excited agents. The idea is to attach a photovoltaic cell
on the top of Hexbug® particles, and use this source of energy instead of the battery that the original ones have. In
this way, a lighting panel with an intensity gradient, for instance, should be enough to induce density gradients in
the concentration of particles, which will accumulate in the regions of lower intensities. Then, a diffusion process
could be triggered by simply inverting the gradient. More ambitiously, the versatility of the system will also allow
the design of a fully controllable illumination panel that is able to locally change the illumination intensity
depending on the density of particles in each position. In this way, we hypothesize that the formation of clusters
could be prevented or even split up by locally increasing the light intensity.