Dr. Christopher Wirth
Dr. Christopher Wirth
Assistant Professor
Department of Chemical Engineering
Case Western Reserve University, USA
Influence of Nanoparticles on the Dynamics and Clustering of Active Colloids Proximate to a Boundary
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Active colloidal particles regularly interact with surfaces in applications ranging from microfluidics to sensing. Herein, experiments and simulations were conducted to illustrate the impact of nanoparticles on the propulsion dynamics and clustering behavior of micrometer scale catalytic active Janus colloids near a boundary. The addition of either negatively charged 20 nm polystyrene particles or polyethylene glycol (PEG) of molecular weight 6K and 600K decreased the apparent propulsion of a Janus colloid at infinite dilution to near zero. These experiments were extended to more concentrated systems in which the same active Janus colloids, in the absence of added nanoparticles, formed clusters. The extent of clustering tended to increase with fuel concentration. Similar to the case of Janus colloids at infinite dilution, the addition of polymers had a dramatic impact on clustering behavior. Following the addition of either 6K or 600K PEG, clustering was significantly mitigated, with the higher molecular weight polymer having a more dramatic effect. Complementary agent-based simulations considering the impact of hydrodynamics for active Janus colloids were conducted in the range of separation distances inferred from experiment. These simulations showed that propulsion speed decreased monotonically with decreasing average separation distance and also that clustering was reduced with decreasing propulsion speed. Taken together, these experiments and simulations demonstrate the impact of depletion and conductivity arising from the addition of nanoparticles on the dynamics and clustering of active colloids proximate to a boundary.
Dr. Laura Bradley
Dr. Laura Bradley
Assistant Professor
Department of Polymer Science and Engineering
University of Massachusetts Amherst, USA
Opportunities Beneath the Janus Surface
Colloids with anisotropic chemical or physical properties give rise to oriented interactions in bulk solutions and at interfaces. Advances in synthetic methods enable auxiliary properties such as cargo-carrying capacity, catalytic activity, or stimuli-responsive shape-change to amplify colloid utility for a wide range of applications spanning environmental remediation to drug delivery. Tuning colloid surface properties, which dictate colloid behaviors in bulk solutions or at fluid interfaces, separate from auxiliary functions is essential to designing smart colloids that can navigate their environment independent of advanced functions. Decoupling colloid surface properties and the auxiliary functions requires a detailed understanding of the colloid interior morphology. Heterogeneous polymerization offers scalable and highly tunable methods to produce colloids with controlled morphologies. This talk will describe the internal structures of anisotropic composite colloids produced by heterogeneous polymerization and outline opportunities for decoupling the functions of the surface and interior.
Dr. Xin Yong
Dr. Xin Yong
Assistant Professor
Department of Mechanical Engineering
Binghamton University, State University of New York, USA
Computational and Theoretical Modeling of Janus Particles at Interfaces and Surfaces
Janus particles and assembly provide new opportunities to tune properties of interfaces and surfaces and impart functionality, which enable broad applications in composite materials, coating, drug delivery, sensing, etc. This talk will describe our recent efforts in understanding the behavior of Janus particles at polymer interfaces and coating surfaces. The first part of the presentation will discuss bicomponent hydrogel formation with Janus particle surfactants using coarse-grained simulations and machine learning. A counterintuitive spontaneous mixing was observed in immiscible polymer mixtures with high water content when amphiphilic Janus particles were introduced. The analysis reveals that the mixing is driven by a significant entropic gain of small Janus particles being well dispersed in aqueous solvent of high-volume fraction. With the help of supervised machine learning, a full phase diagram was constructed for nanocomposite bicomponent hydrogels. Second, we demonstrate theoretical modeling of amphiphilic Janus particle stratification when mixed with hydrophilic homogeneous binder particles in drying coating films. Contrasting with homogeneous particle mixtures where stratification is driven passively by evaporation, Janus particles vigorously accumulate at the air–water interface in fast kinetics, with their hydrophobic sides orienting towards air. The results suggest that the stratification is partially due to the strong adsorption of Janus particles at the water–air interface, although the detailed mechanisms require more thorough investigation.
Dr. Yan Yu
Dr. Yan Yu
Associate Professor
Department of Chemistry
Indiana University, USA
Interrogating Immune Functions with Janus Particles
Understanding and controlling the response of immune cells holds great promise for the development of precision medicine, particularly for cancer immunotherapy. Functions of immune cells are known to depend on the intricately organized chemical reactions and physical forces. Examples range from the engulfment of invading bacteria that relies on a fine balance of competing mechanical forces, to the activation of T-lymphocytes that requires collective interactions between thousands of receptors at the junction between cells. Owing to the complexity of these processes, understanding immune functions using traditional biological tools is highly challenging. In this talk, I will present my group’s research progress towards designing unique biointerfaces to enable the quantitative understanding and manipulation of immune functions. Our research so far has capitalized on Janus particles, which, like the two-faced Roman god Janus, are made chemically, biologically, optically or magnetically asymmetric. We developed Janus particle-based toolsets for measuring cell dynamics in multi-dimensions beyond translational motion and for spatiotemporally controlling cell functions. Using these methods, we uncovered new mechanisms in immune regulation and achieve spatiotemporal control of immune processes, from phagocytosis to intracellular trafficking, which would otherwise be difficult to access with traditional means.
Dr. Sepideh Razavi
Dr. Sepideh Razavi
Assistant Professor
School of Chemical, Biological and Materials Engineering
University of Oklahoma, USA
Harnessing the Janus Character at Fluid Interfaces
The amphiphilic character of Janus particles combined with their colloidal nature has opened up a path to engineering interfacial systems with superior properties and tunable functions. An underlying motivation driving the use of Janus particles is their enhanced binding energies to fluid interfaces. For this assumption to be realized, a fundamental understanding on the role of Janus particle surface properties in the resulting interfacial behavior is essential. In this talk, we will focus on the following two factors linked to the Janus character: the Janus balance (the difference in the wettability of polar and apolar regions) and the nature of Janus character (chemical vs. physical modification of the particle surface). We will review the surface activity of these particles at the air/water interface. We will also discuss the impact of particle amphiphilicity on the flow behavior of the colloidal monolayers, important for applications in which the interface undergoes large deformations producing compression and shear stresses at the interface. Our findings illustrate the influence of particle surface properties on the stability and rheology of interfaces decorated with Janus particles, key components towards harnessing the full promise of Janus particles at fluid interfaces.
Dr. José Rafael Bordin
Dr. José Rafael Bordin
Adjunct Professor
Department of Physics
Federal University of Pelotas, Brazil
Janus Dumbbells with Extra Competition
The two-faces characteristic of Janus nanoparticles lead to unique properties for materials made by their self-assembly. Dumbbells shaped nanoparticles with hydrophobic/hydrophilic faces are particularly interesting since they can mimic the behavior of other amphiphilic chemical building blocks, as surfactants and lipids, but with the advantage that we can tune and control the assembled structures morphology tuning and controlling the nanoparticle property. In this talk I will show the myriad of morphology that we can obtain when extra competitions are added in the system – from competitive interactions in one of the Janus dumbbell monomer to confinement in distinct geometries.
Dr. Ubaldo Córdova-Figueroa
Dr. Ubaldo Córdova-Figueroa
Professor
Department of Chemical Engineering
University of Puerto Rico, Puerto Rico
Rich Self-Assembly Behavior of Magnetic Colloids with Radially Shifted Dipoles
Anisotropic potentials in Janus particles provide additional freedom to control particle aggregation into clusters with different sizes and morphologies. In order to study the process of aggregation on magnetic Janus colloids dynamically –nucleation and growth–Brownian dynamic simulations of a dilute suspension of magnetic spherical Janus colloids with their magnetic dipole moments shifted radially towards the surface of the particle were performed. Different aggregation modes were found depending on the dipolar shift(s)—the ratio between the displacement of the dipole and the particle radius—and the dipolar coupling constant (λ) —the ratio between the magnetic dipole-dipole and Brownian forces, were the λ regimens is a strong factor in the stability of the cluster. Each structure phase of the colloids was depended on the combination of s and λ, which was used to build a "phase" diagram showing unique behavior for each region on the dynamical process of aggregation. In low λ regime, the particles aggregate and disaggregate resulting in short-live clusters at small s, while at high s the particles aggregate in permanent triplets. On the other hand, in high λ regime, building blocks–triplets and quadruplets with unique orientational ordering depended of s– were formed during the nucleation process. The different building blocks form larger structures, such as single-chain, ring-like, island-like, worm-like, and double-chain aggregates.
Dr. Giovanni Volpe
Dr. Giovanni Volpe
Professor
Department of Physics
University of Gothenburg, Sweden
Light-controlled Assembly of Active Colloidal Molecules
Activity and life have emerged from a primordial broth of simple building blocks when the presence of energy flows made these blocks come together and interact in non-trivial ways. Here, we use experiments and simulations demonstrating that active molecules can be created and controlled by light. Shining light on a primordial broth containing passive particles of two different species, we create active colloidal molecules of increasing complexity, which behave as migrators, spinners and rotators. This demonstrates a powerful new route for nonequilibrium self-assembly, which may help explaining the emergence of complex systems in living matter and may also proof useful as a design principle for the construction of flexible micromotors and cargo transport in health care applications.
Dr. Sujin Babu
Dr. Sujin Babu
Assistant Professor
Department of Physics
Indian Institute of Technology Delhi, India
A Simple 2-Patch Model for Mimicking Protein Aggregation
Patchy particles are considered to be a good model for protein aggregation. We propose a novel method to generate different structures of glucose isomerase protein such as chains, crystals and bundles by utilizing aggregation of two-patch colloidal particles in presence of competing isotropic and anisotropic potential. Irreversible aggregation leads to bundle formation and at a much latter time a percolated cluster of bundle is formed. When we make the system reversible we observe coexistence of different phases like disordered clusters, chains, crystals and bundles depending on the relative strength of isotropic and anisotropic potential. The network of bundles is metastable against the formation of thermodynamically favored finite sized bundles along with thermodynamically stable crystals. These bundles appear to be helical in structure similar to that observed in sickle cell hemoglobin. The results show that the modal can qualitatively mimic the phase behavior of glucose isomerase protein, which provides a novel tool to unveil self-assembly mechanism of protein under different conditions.
Dr. Mykola Tasinkevych
Dr. Mykola Tasinkevych
Senior Research Scientist
Department of Physics
University of Lisbon, Portugal
Designing Chemically Active "Microswimmers"
Autonomous microscopic agents moving through confined, liquid-filled spaces are envisioned as a key component of future lab-on-a-chip and drug delivery systems. Chemically active Janus particles offer a realization of such agents. Depending on the system, various self-propulsion mechanisms emerge, such as bubble propulsion, self-electrophoresis or self-diffusiophoresis. Here, we discuss the self-propulsion of a Janus spheroidal particle driven by self-diffusiophoresis. First, we describe how the swimming velocity depends on the particle's aspect ratio and on the catalyst coverage. Next we analise how such active particles can be used as carriers of micro-cargo, and show that the velocity of the carrier-cargo composite strongly depends on the relative orientation of the link between the active and passive particles. Near a hard wall, a Janus active particle reveals a very interesting behavior, including novel sliding and hovering steady states. The sliding steady state provides a starting point to engineer a stable and predictable motion of microswimmers. For example, at topographically patterned walls, novel states of guided motion along the edges of the geometrical patterns can emerge. We also predict that the trajectories of chemical microswimmers can be efficiently controlled by using chemically patterned walls. The induced chemi-osmotic flows at the wall can cause particles to either “dock” at the chemical step or to robustly follow a thin chemical stripe. Finally, we demonstrate that platinum microparticles move spontaneously in solutions of hydrogen peroxide and that their motions can be rationally designed by controlling particle shape. The observed relationships between particle shape and motion provide evidence for a self-electrophoretic propulsion mechanism, whereby anodic oxidation and cathodic reduction occur at different rates at different locations on the particle surface.
Dr. Miguel Angel Fernandez-Rodriguez
Dr. Miguel Angel Fernandez-Rodriguez
Juan de la Cierva PostDoc Researcher
Department of Applied Physics
University of Granada, Spain
Active Janus Particles with Feedback-Controlled Space-Dependent Rotational Dynamics
Active Brownian Particles (ABPs) can harvest energy from a uniform source and convert it into propulsion thanks to an asymmetry in their shape or composition. Janus particles with two hemispheres or dumbbells with two lobes of different composition fulfill this requirement and self-propel under spatially uniform AC fields at 1 kHz [1,2]. Self-propulsion is due to unbalanced electrohydrodynamic flows, and the the persistence length of the active trajectories is constrained by the rotational diffusion, usually tied to the thermal bad. Here, we decouple rotational diffusion from thermal fluctuations by using Janus particles with a magnetic halve driven by external magnetic fields, tuning the rotational diffusivity above and below its thermal value at will. Moreover, we implement discrete-time feedback loops, also present in biological microswimmers, with a delay between sensing and adapting to their surroundings. With these ingredients we find a rich range of phenomena including anomalous diffusion, directed transport, and localization. These findings add a new degree of freedom to the control of active matter, and to the understanding of microswimmers with sensorial delays.
Dr. Javier Diaz Brañas
Dr. Javier Diaz Brañas
Scientist
CECAM Centre Européen de Calcul Atomique et Moléculaire
École Polytechnique Fédérale de Lausanne, Switzerland
Mesoscopic Simulations of Janus Nanoparticles in Block Copolymer Systems
Janus Nanoparticles (JNPs) have been shown to anchor at the interface of binary mixtures, while block copolymers (BCP) can be used to template the position of colloids. The orientational degrees of freedom of JNPs offer new co-assembly possibilities within BCP melts. The ordering of Janus colloids in BCP melts is studied using mesoscopic simulations, as well the effect of colloids on the BCP matrix. The role of chemical inhomogeneity in the NP assembly is systematically studied, finding JNPs to be strongly trapped at BCP interfaces while preserving the BCP periodic structure, as opposed to homogeneous neutral counterparts. JNPs are found to form ordered structures within BCP lamellar domains at high concentrations due to the chemical affinity towards each block in the BCP chain. Simple rules lead to a precise control of the orientational and translational colloidal order. A side-by-side, lamellar-like ordering of BCP/JNPs systems is compared to similarly ordered BCP/nanorod mixtures in experiments and simulations. A simplified model of active self-propelled colloids is used to study the co-assembly of active Brownian particles in BCP melts establishing different regimes due to competing effects due to the activity and to the coupling interactions with the BCP.
Dr. Amir Masoud Pourrahimi
Dr. Amir Masoud Pourrahimi
Postdoctoral Fellow
Department of Chemistry and Chemical Engineering
Chalmers University of Tehcnology, Sweden
Catalytic and Light‐Driven ZnO/Pt Janus Nano/Micromotors: Switching of Motion Mechanism via Size, Interface Roughness and Defect Tailoring
Recent progress in autonomous self-propelled multifunctional Janus nano/micromotors based on ZnO, which can convert chemical or light energy into mechanical motion, is presented. This technology of moving micro- and nanodevices is at the forefront of materials research and is a promising and growing technology with the possibility of using these motors in both biomedical and environmental applications. The development of novel multifunctional ZnO Janus motors together with their motion mechanisms is discussed. The effects of the size, interfacial structures, and porosity on the directional motion and the speed of Janus micromotors are elaborated. For light-derived Janus micromotors, charge transfer at the interfaces, which was less highlighted in micromotor communities, is found the dominant phenomenon that controls electrophoresis motion. This study aims to encourage further research in the field of micromotors using new and facile methodologies for obtaining novel Janus motors with enhanced motion and activity.
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