Author: Falko Schmidt

Light-driven Assembly and Optical Manipulation of Active Colloidal Molecules

Falko Schmidt, Benno Liebchen, Hartmut Loewen & Giovanni Volpe
OSA Biophotonics Congress, Tucson (AZ), USA
16 April 2019

Active matter, consisting of self-propelled units locally injecting energy into the system, opens new horizons for the creation of functional soft materials with designable properties. Experiencing a constant energy input, allows active matter to self-assemble into phases with a complex architecture and functionality such as living clusters which dynamically form, reshape and break-up but would be forbidden in equilibrium material by the entropy maximization (or free energy minimization) principle. The challenge to control this active self-assembly has evoked widespread efforts typically hinging on an engineering of the properties of individual motile constituents. Here, we provide a different route, where activity occurs as an emergent phenomenon only when individual building blocks bind together, in a way which we control by laser light. Using experiments and simulations of two species of immotile microspheres, we exemplify this route by creating active molecules featuring a complex array of behaviors, becoming migrators, spinners and rotators. The possibility to control the dynamics of active self-assembly via light-controllable nonreciprocal interactions will inspire new approaches to understand living matter and to design active materials.

Session: Nanothermodynamics
8:00 AM–10:00 AM, Tuesday, April 16, 2019
Chair: Agnese Callegari; Bilkent University, Turkey

Light-driven Assembly of Motile Colloidal Clusters from Immotile Building Blocks
Falko Schmidt, Benno Liebchen, Hartmut Löwen & Giovanni Volpe
APS March Meeting 2019, Boston, USA
6 March 2019 at 8:36-8:48 a.m., Room 258B

Active matter, consisting of self-propelled units locally injecting energy into the system, opens new horizons for the creation of functional soft materials with designable properties. Experiencing a constant energy input, allows active matter to self-assemble into phases with a complex architecture and functionality such as living clusters which dynamically form, reshape and break-up but would be forbidden in equilibrium material by the entropy maximization (or free energy minimization) principle. The challenge to control this active self-assembly has evoked widespread efforts typically hinging on an engineering of the properties of individual motile constituents. Here, we provide a different route, where activity occurs as an emergent phenomenon only when individual building blocks bind together, in a way which we control by laser light. Using experiments and simulations of two species of immotile microspheres, we exemplify this route by creating active molecules featuring a complex array of behaviors, becoming migrators, spinners and rotators. The possibility to control the dynamics of active self-assembly via light-controllable nonreciprocal interactions will inspire new approaches to understand living matter and to design active materials.

Reference: Schmidt et al. Light-controlled Assembly of Active Colloidal Molecules arXiv:1801.06868 (2018)

Light-controlled Assembly of Active Colloidal Molecules
Falko Schmidt, Benno Liebchen, Hartmut Löwen & Giovanni Volpe
IONS Scandinavia 2018, Copenhagen, Denmark
5-9 June 2018

We experimentally demonstrate the light-controlled assembly of active colloidal molecules from a suspension of two species of passive microspheres. When light is shone on the sample, the ac- tive molecules form and acquire motility through non-reciprocal interactions between their passive components. As their size grows, they feature a complex array of behaviors, becoming propellers, spinners and rotators. Their shape and functionality can be tuned by applying periodic illumination. We also provide a theoretical model allowing to predict the complete table of emerging active molecules and their properties in quantitative agreement with the experiments.

Reference: Schmidt et al. Light-controlled Assembly of Active Colloidal Molecules arXiv:1801.06868 (2018)

Microscopic Engine Powered by Critical Demixing
Falko Schmidt, Alessandro Magazzu, Agnese Callegari, Luca Biancofiore, Frank Cichos & Giovanni Volpe
APS March Meeting 2018, Los Angeles (CA), USA
5-9 March 2018

During the last few decades much effort has gone into the miniaturization of machines down to the microscopic scale with robotic solutions indispensable in modern industrial processes and play a central role in many biological systems. There has been a quest in understanding the mechanism behind molecular motors and several approaches have been proposed to realize artificial engines capable of converting energy into mechanical work. These current micronsized engines depend on the transfer of angular momentum of light, are driven by external magnetic fields, due to chemical reactions or by the energy flow between two thermal reservoirs [1-5]. Here we propose a new type of engine that is powered by the local, reversible demixing of a critical binary liquid. In particular, we show that an absorbing, optically trapped particle performs revolutions around the optical beam because of the emergence of diffusiophoresis and thereby produces work. This engines is adjustable by the optical power supplied, the temperature of the environment and the criticality of the system.

References:
1. P.A. Quinto-Su, Nat. Comm. 5 (2014).
2. V. Blickle et al., Nat. Phys. 8 (2012).
3. I.A. Martinez et al., Nat. Phys. 12 (2016).
4. S.L. Neale et al., Nat. Mater. 4 (2005).
5. A. Argun et al., arXiv preprint (2017)

Session R57: Active Matter I
8:00 AM–11:00 AM, Thursday, March 8, 2018
LACC Room: 518
Sponsoring Units: GSOFT DBIO GSNP
Chair: Paulo Arratia, Univ of Pennsylvania