Article
Mechanics
John F. Brady
Summary: A new continuous perspective for phoretic motion applicable to particles of any shape in 'microstructured' fluids has been developed, explaining how the local osmotic pressure of solute adjacent to the phoretic particle generates a thrust force. The study covers passive Brownian bath particles in suspension and active particles with characteristic speed and run length variations, showing that phoretic motion arises from a gradient in swim pressure of active matter.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Lloyd Fung, Rachel N. Bearon, Yongyun Hwang
Summary: This study presents a new model for describing the non-trivial transport phenomena of dilute suspension of motile microorganisms subjected to a strong ambient flow. By transforming the Smoluchowski equation into a transport equation, the model allows for approximation of drifts and dispersions as a function of the local flow field. The model shows the contributions of biased motility and shear-induced migration, as well as other drifts and dispersions caused by interactions between orientational dynamics and passive advection-diffusion.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Physics, Multidisciplinary
Brato Chakrabarti, Michael J. Shelley, Sebastian Furthauer
Summary: This study discovers a distinct mechanism for the transition of active particles into a state of collective motion at high density, leading to the formation of stationary chimera patterns. In addition, it reveals the existence of oscillatory flows and robust unidirectional pumping states under confinement, which can be selectively controlled. These findings provide important insights for the design of new active materials.
PHYSICAL REVIEW LETTERS
(2023)
Article
Physics, Fluids & Plasmas
T. C. Rebocho, M. Tasinkevych, C. S. Dias
Summary: Active colloids are nonequilibrium systems where individual particles have self-propelled motion and exhibit surprising collective behavior. In this work, the structure and dynamics of aggregates of self-propelled particles near confining solid surfaces are studied. It is found that the particle aspect ratio has a nonmonotonic effect on the cluster structure and formation time, with ellipsoidal particles forming more stable clusters compared to rodlike particles.
Article
Mechanics
Emma Gonzalez, Christian Aponte-Rivera, Roseanna N. Zia
Summary: In this study, a computational investigation was conducted on the equilibrium dynamics of a polydisperse hard-sphere colloidal dispersion confined in a spherical cavity. The results showed that although polydispersity tends to homogenize structure in a suspension, strong correlations induced by the cavity resist this homogenization. The effects of polydispersity on particle dynamics were found to weaken lubrication effects near the cavity wall and drive diffusivity changes by affecting many-body hydrodynamic couplings.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Chemistry, Physical
Mohammed Elismaili, Lydiane Becu, Hong Xu, David Gonzalez-Rodriguez
Summary: This study experimentally and theoretically investigates the dynamics of two-dimensional clusters of paramagnetic colloids under a time-varying magnetic field, revealing collective viscoelastic properties and rapid cluster disassembly dynamics. A theoretical model is developed to explain these phenomena, capturing the observed dependence on particle, cluster, and field characteristics, and providing estimates of cluster viscoelasticity. The findings highlight physical mechanisms that may be relevant to biological aggregates with similar dynamic behaviors.
Article
Mechanics
Zhiwei Peng, Tingtao Zhou, John F. Brady
Summary: This study proposes an osmotic mechanism for the propulsion of a vesicle, which generates a seepage flow across a semipermeable membrane by maintaining a solute gradient inside the vesicle. It is found that any osmotic solute can propel the vesicle as long as there is a concentration gradient. Additionally, using active Brownian particles as the solute can maintain a symmetry-breaking concentration gradient and further enhance the vesicle's motion.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Multidisciplinary Sciences
Ondrej Kucera, Jeremie Gaillard, Christophe Guerin, Manuel Thery, Laurent Blanchoin
Summary: By combining microtubules and actin filaments and utilizing a feedback loop, we have created an artificial active cytoskeletal composite that exhibits both structural stability and plasticity. The system is sensitive to external stimuli and shows potential for self-regulation.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2022)
Article
Mechanics
Laurel Ohm, Michael J. Shelley
Summary: By analyzing the Saintillan-Shelley kinetic model, we have determined exactly how the isotropic suspension loses stability in different parameter settings. We have studied the various types of bifurcations admitted by the system, which helps in comparing this model with other physical systems and predicting the bifurcations in active suspensions that can be explored experimentally.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Lloyd Fung
Summary: In a dilute suspension, analytical solutions have been found for the steady distributions of sinking spheroids or motile gyrotactic micro-organisms under arbitrary continuous vertical shear flow. The nonlinear two-way coupling between their distribution and the vertical flow leads to a bifurcation of the uniform base state into a structure resembling streamers or plumes. This bifurcation depends on a single parameter proportional to the average number of particles on a horizontal cross-section. In a three-dimensional axisymmetric system, the plume structure undergoes a blow-up when the parameter exceeds a threshold. We discuss the analogy of this singularity to the chemotactic collapse of a Keller-Segel model and its significance.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Chemistry, Physical
Martin Wagner, Sergi Roca-Bonet, Marisol Ripoll
Summary: The study demonstrates that colloids driven by phoresis play a crucial role in the design of synthetic microswimmers, as their specific interactions significantly influence the dynamics of the swimmers. Simulations show that the phoretic character and relative size of beads strongly impact the resulting solvent velocity fields, leading to different behaviors of dimeric Janus active colloids. Additionally, hydrodynamic flows can transition from puller-type to pusher-type, creating unique phenomena in three-dimensional bulk conditions.
EUROPEAN PHYSICAL JOURNAL E
(2021)
Article
Multidisciplinary Sciences
Jaideep Katuri, Ruben Poehnl, Andrey Sokolov, William Uspal, Alexey Snezhko
Summary: This study reveals unconventional motion states in ensembles of active discoidal particles powered by induced-charge electrophoresis. Through experiments and computational modeling, researchers demonstrate that the shape asymmetry of the particles promotes the formation of active particles' bound states, ultimately leading to a spontaneous collective state with arrested motility.
Article
Physics, Multidisciplinary
Chun-Jen Chen, Clemens Bechinger
Summary: Many animal species organize in groups to achieve advantages, and this study demonstrates that robotic swarms can also escape from hazardous areas through cooperative group formation, even in the presence of incomplete individual information.
NEW JOURNAL OF PHYSICS
(2022)
Article
Chemistry, Physical
Rodrigo C. Coelho, Nuno A. M. Araujo, Margarida M. Telo da Gama
Summary: The dynamics of nutrient mixing in bacterial colonies and other active nematics are complex due to the coupling between nutrients concentration and velocity field. The dispersion of the conserved activity field is found to be subdiffusive, hindered by a barrier of negative defects at the active-passive interface.
Review
Chemistry, Physical
Jordi Ignes-Mullol, Francesc Sagues
Summary: In this review, recent experimental research on active colloidal particles in non-Newtonian fluids is focused. Different propulsion strategies, enabled or modified by the presence of a complex medium, are presented. This provides new insights into active transport in biofluids or other non-Newtonian fluids. The differentiation between disordered complex fluids and liquid crystals, considering their distinct colloidal driving and steering mechanisms, leads to the development of active quasi-particles.
CURRENT OPINION IN COLLOID & INTERFACE SCIENCE
(2022)
Article
Chemistry, Physical
Rohit Jain, Felix Ginot, Johannes Berner, Clemens Bechinger, Matthias Krueger
Summary: Micro-rheological experiments with a colloidal bead driven through a viscoelastic fluid reveal two distinct shear thinning regimes, with the second process exhibiting unique characteristics at small Weissenberg numbers. A simple model is able to capture the observed behavior and suggest the presence of two different length scales in the fluid. The analysis also indicates the existence of a mysterious length scale of a few micrometers.
JOURNAL OF CHEMICAL PHYSICS
(2021)
Article
Physics, Multidisciplinary
Chun-Jen Chen, Clemens Bechinger
Summary: Many animal species organize in groups to achieve advantages, and this study demonstrates that robotic swarms can also escape from hazardous areas through cooperative group formation, even in the presence of incomplete individual information.
NEW JOURNAL OF PHYSICS
(2022)
Article
Physics, Multidisciplinary
Felix Ginot, Juliana Caspers, Matthias Krueger, Clemens Bechinger
Summary: In this study, we investigated the hopping dynamics of a colloidal particle across a potential barrier within a viscoelastic bath. We observed two distinct timescales in the waiting time distributions, with the longer one depending exponentially on the barrier height and the shorter one similar to the relaxation time of the fluid. The short timescale indicates the storage and release of elastic energy in the bath, resulting in a significant increase in the hopping rate.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Multidisciplinary
Shuvojit Paul, Ashreya Jayaram, N. Narinder, Thomas Speck, Clemens Bechinger
Summary: In this study, we experimentally determined the force exerted by a bath of active particles onto a passive probe as a function of its distance to a wall and compared it to the measured averaged density distribution of active particles around the probe. We demonstrated that both quantities are directly related to each other, up to a factor, within the framework of an active stress. Our results were in excellent agreement with a minimal numerical model and confirmed a general and system-independent relationship between the microstructure of active particles and transmitted forces.
PHYSICAL REVIEW LETTERS
(2022)
Article
Physics, Multidisciplinary
Xin Cao, Andrea Silva, Emanuele Panizon, Andrea Vanossi, Nicola Manini, Erio Tosatti, Clemens Bechinger
Summary: Compared to translational friction, rotational friction has received less attention. In this study, we experimentally and theoretically investigate the rotational depinning and orientational dynamics of two-dimensional colloidal crystalline clusters on periodically corrugated surfaces under the influence of magnetically exerted torques. Our results show that the traversal of locally commensurate areas of the moiré pattern through the edges of clusters, hindered by potential barriers during cluster rotation, controls its rotational depinning. The experimentally measured depinning thresholds collapse onto a universal theoretical curve, suggesting the possibility of a superlow-statictorque state for large clusters. We also find a cluster-size-independent rotation-translation depinning transition when lattice-matched clusters are driven jointly by a torque and a force.
Article
Multidisciplinary Sciences
Li Tian, Clemens Bechinger
Summary: Despite the technological relevance of glasses, there is still a lack of complete microscopic understanding. This study experimentally investigates the surface of a two-dimensional glass and reveals the formation of a liquid film on the surface during the melting process. Additionally, a region with highly mobile particles is found underneath the liquid film. This surface glassy layer may provide insights into the properties of thin glassy films used in various technical applications.
NATURE COMMUNICATIONS
(2022)
Article
Chemistry, Physical
Juliana Caspers, Nikolas Ditz, Karthika Krishna Kumar, Felix Ginot, Clemens Bechinger, Matthias Fuchs, Matthias Krueger
Summary: The motion of a colloidal probe in a viscoelastic fluid is determined by friction or mobility. The Einstein relation, which applies to Newtonian solvents, and the concept of time-dependent memory kernels are generalized to viscoelastic fluids. By investigating two observables - recoil and equilibrium mean squared displacement (MSD) - we establish a relation between the two based on linear response theory. However, MSD and recoil show distinct behaviors with increasing concentration due to different behaviors of the two kernels. Theoretical models reveal a Volterra relation between the two kernels, explaining the varying timescales in friction and mobility kernels with changing concentration.
JOURNAL OF CHEMICAL PHYSICS
(2023)
Article
Chemistry, Multidisciplinary
Emanuele Panizon, Andrea Silva, Xin Cao, Jin Wang, Clemens Bechinger, Andrea Vanossi, Erio Tosatti, Nicola Manini
Summary: The understanding of nano-scale friction, governed by atomic arrangements, is incomplete. This study provides a unified understanding of friction by researching the potential energy of contacting surfaces and categorizing contacts into three types based on geometrical features. These types include structurally lubricated contacts, corrugated and interlocked contacts, and a newly discovered directionally structurally lubricated contact. The findings have implications for a wide range of materials in contact.
Article
Physics, Multidisciplinary
Felix Ginot, Juliana Caspers, Luis Frieder Reinalter, Karthika Krishna Kumar, Matthias Krueger, Clemens Bechinger
Summary: The research investigates the transient recoil dynamics of a colloidal probe particle in a viscoelastic fluid, displaying two distinct timescales that agree with a microscopic model. The model reveals two sets of eigenmodes which correspond to reciprocal and non-reciprocal force conditions, confirming in experiments. The findings are expected to be relevant in conditions where particles are exposed to non-steady shear forces.
NEW JOURNAL OF PHYSICS
(2022)
Article
Multidisciplinary Sciences
Hongri Gu, Marino Moeckli, Claas Ehmke, Minsoo Kim, Matthias Wieland, Simon Moser, Clemens Bechinger, Quentin Boehler, Bradley J. Nelson
Summary: Magnetic continuum soft robots can actively control their tip and navigate in complex in vivo environments. MaSoChains are a type of magnetic soft-robotic chains that can self-fold into large assemblies with stable configurations and programmable shapes and functions. They provide many desirable features and functions that are difficult to achieve with existing surgical tools.
NATURE COMMUNICATIONS
(2023)
Article
Chemistry, Physical
N. Narinder, M. F. Bos, C. Abaurrea-Velasco, J. de Graaf, C. Bechinger
Summary: In this study, enhanced rotational diffusion (ERD) of colloidal rods in complex fluids, known as active Brownian particles (APs), is experimentally observed and its microscopic origin is numerically corroborated. The findings have implications for the microrheological characterization of complex fluids and our understanding of the dynamics of microorganisms in such media.
Article
Physics, Fluids & Plasmas
N. Narinder, Shuvojit Paul, Clemens Bechinger
Summary: Investigated work fluctuations of active Brownian particles in viscoelastic medium, finding deviations from work fluctuation theorem due to increased rotational dynamics. By adjusting work distributions and considering effective temperature, alignment with WFT can be achieved. Validation of this approach through comparison of torque and angular velocity confirms its effectiveness.
Article
Chemistry, Physical
Laurent Helden, Timo Knippenberg, Li Tian, Aubin Archambault, Felix Ginot, Clemens Bechinger
Summary: The temperature-dependence of critical Casimir interactions in a nonionic surfactant solution and the pair interactions of colloidal particles were studied using total internal reflection microscopy. Good agreement was found between experimental results and theory, with deviations at surface-to-surface distances below 160 nm attributed to micelle adsorption to interacting surfaces.
Article
Physics, Fluids & Plasmas
Xin Cao, Emanuele Panizon, Andrea Vanossi, Nicola Manini, Erio Tosatti, Clemens Bechinger
Summary: Understanding the drift motion and dynamical locking of crystalline clusters on patterned substrates is crucial for the diffusion and manipulation of nano- and microscale objects. Locking features are shown to be correlated with Moire patterns of contacting surfaces, with complexities arising from different surface symmetries. A generalized formalism is provided to describe the relation between locking orientation and direction with arbitrary lattice symmetries.