1,721,180 research outputs found
Toward Design Rules of Directional Janus Colloidal Assembly
No full textBurgeoning interest in supracolloidal assembly has reached the point at which the field can seek so-called intelligent design rather than solely rely on evolution. Emphasizing Janus and triblock particles, this review presents a progress report on formulating design rules for the assembly of interesting structures. We discuss how to design building blocks, bearing in mind that patchy particles embody not just geometric shape but also chemical shape, that chemical shape determines particle-particle interactions, and that the assembly process can be designed to proceed in hierarchical stages. Remarks are included about the potential of kinetic and nonequilibrium control, as well as the potential for the augmented use of soft building blocks. Whereas the reverse design problem, in which arbitrarily selected structures can be designed from the bottom up, still stands as a grand challenge, the field has reached the point of understanding necessary, although not always sufficient, conditions
Copyright (c) 2015 by Annual Reviews.646
Comment on "Following Molecular Mobility during Chemical Reactions: No Evidence for Active Propulsion" and "Molecular Diffusivity of Click Reaction Components: The Diffusion Enhancement Question"
No full textWe provide arguments why we consider as inaccurate two recent JACS Articles which disagree with our laboratory's report of boosted diffusion during the copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reaction. In the first paper (DOI: 10.1021/jacs.1c09455), Fillbrook et al. claim that their diffusion NMR experiments offer no evidence for boosted diffusion, but we argue that their use of Gd3+-chelates to speed up NMR relaxations times is flawed conceptually, the authors interpreting Gd3+-chelates as inert. Actually, the same features that make gadolinium ions useful as contrast agents in magnetic resonance imaging render them unsuitable for diffusion NMR. Nonetheless, by correctly adjusting technical aspects of the measurements, we confirm boosted diffusion even in the presence of this MRI contrast agent. The second paper of which we are skeptical, by Rezaei-Ghaleh et al. (DOI: 10.1021/jacs.1c11754), makes comparisons to a reference state that is not physically meaningful.11Nsciescopu
Ionic Janus Liquid Droplets Assembled and Propelled by Electric Field
No full textTraditional Janus particle approaches to produce active motion are based on using solid particles, but it is interesting to consider liquid droplets instead, because for solid particles, the self-assembly of synthetic active matter requires moving objects to sit in a near-planar 2D geometry. Emulsions, cross-linked polymers, and porous materials have been proposed for 3D self-assembly but with limitations to propel them. It is now demonstrated that Janus liquid droplets can be used as building block in an active propulsion system. Using an ionic liquid motif, the droplet system can be tuned from core-shell to Janus and multipatches, using facile surfactant-based methods. The approach was stimulated by the success of electro-hydrodynamic flow produced by an alternating electric field to produce motion of colloidal particles; its usefulness to also propel ionic liquids is demonstrated
Active phase separation by turning towards regions of higher density
No full text© 2021, The Author(s), under exclusive licence to Springer Nature Limited.Studies of active matter, from molecular assemblies to animal groups, have revealed two broad classes of behaviour: a tendency to align yields orientational order and collective motion, whereas particle repulsion leads to self-trapping and motility-induced phase separation. Here we report a third class of behaviour: orientational interactions that produce active phase separation. Combining theory and experiments on self-propelled Janus colloids, we show that stronger repulsion on the rear than on the front of these particles produces non-reciprocal torques that reorient particle motion towards high-density regions. Particles thus self-propel towards crowded areas, which leads to phase separation. Clusters remain fluid and exhibit fast particle turnover, in contrast to the jammed clusters that typically arise from self-trapping, and interfaces are sufficiently wide that they span entire clusters. Overall, our work identifies a torque-based mechanism for phase separation in active fluids, and our theory predicts that these orientational interactions yield coexisting phases that lack internal orientational order.11Nsciescopu
Machine learning assembly landscapes from particle tracking data
No full textBottom-up self-assembly offers a powerful route for the fabrication of novel structural and functional materials. Rational engineering of self-assembling systems requires understanding of the accessible aggregation states and the structural assembly pathways. In this work, we apply nonlinear machine learning to experimental particle tracking data to infer low-dimensional assembly landscapes mapping the morphology, stability, and assembly pathways of accessible aggregates as a function of experimental conditions. To the best of our knowledge, this represents the first time that collective order parameters and assembly landscapes have been inferred directly from experimental data. We apply this technique to the nonequilibrium self-assembly of metallodielectric Janus colloids in an oscillating electric field, and quantify the impact of field strength, oscillation frequency, and salt concentration on the dominant assembly pathways and terminal aggregates. This combined computational and experimental framework furnishes new understanding of self-assembling systems, and quantitatively informs rational engineering of experimental conditions to drive assembly along desired aggregation pathways.
© The Royal Society of Chemistry 2015161
Real-Space, in Situ Maps of Hydrogel Pores
No full textWe characterize the porosity of hydrogels by imaging the displacement trajectories of embedded tracer particles. This offers the possibility of characterizing the size and projected shape of individual pores as well as direct, real space maps of heterogeneous porosity and its distribution. The scheme shows that when fluorescent spherical particles treated to avoid specific adsorption are loaded into the gel, their displacement trajectories from Brownian motion report on the size and projected shape in which the pore resides, convoluted by the particle size. Of special interest is how pores and their distribution respond to stimuli. These ideas are validated in agarose gels loaded with latex particles stabilized by adsorbed bovine serum albumin. Gels heated from room temperature produced an increasingly more monodisperse pore size distribution because increasing temperature preferentially enlarges smaller pores, but this was irreversible upon cooling, and shearing agarose gels beyond the yield point destroyed larger pores preferably. The method is considered to be generalizable beyond the agarose system presented here as proof of concept.clos
Natural selection in the colloid world: active chiral spirals
No full textWe present a model system in which to study natural selection in the colloid world. In the assembly of active Janus particles into rotating pinwheels when mixed with trace amounts of homogeneous colloids in the presence of an AC electric field, broken symmetry in the rotation direction produces spiral, chiral shapes. Locked into a central rotation point by the centre particle, the spiral arms are found to trail rotation of the overall cluster. To achieve a steady state, the spiral arms undergo an evolutionary process to coordinate their motion. Because all the particles as segments of the pinwheel arms are self-propelled, asymmetric arm lengths are tolerated. Reconfiguration of these structures can happen in various ways and various mechanisms of this directed structural change are analyzed in detail. We introduce the concept of VIP (very important particles) to express that sustainability of active structures is most sensitive to only a few particles at strategic locations in the moving self-assembled structures.clos
Reincarnations of the phase separation problem
Full text linkPhase separation is familiar and useful, yet opportunities to manipulate it are
surprisingly subtle and complex.11Nsciescopu
Effective temperature concept evaluated in an active colloid mixture
Full text linkThermal energy agitates all matter, and its competition with ordering tendencies is a fundamental organizing principle in the physical world; this observation suggests that an effective temperature might emerge when external energy input enhances agitation. However, despite the repeated proposal of this concept based on kinetics for various nonequilibrium systems, the value of an effective temperature as a thermodynamic control parameter has been unclear. Here, we introduce a two-component system of driven Janus colloids, such that collisions induced by external energy sources agitate the system, and we demonstrate quantitative agreement with hallmarks of statistical thermodynamics for binary phase behavior: the archetypal phase diagram with equilibrium critical exponents, Gaussian displacement distributions, and even capillarity. The significance is to demonstrate a class of dynamical conditions under which thermodynamic analysis extends quantitatively to systems that are decidedly nonequilibrium except that the effective temperature differs from the physical temperature
Single-crosslink microscopy in a biopolymer network dissects local elasticity from molecular fluctuations
Full text linkPolymer networks are fundamental from cellular biology to plastics technology but their intrinsic inhomogeneity is masked by the usual ensemble-averaged measurements. Here, we construct direct maps of crosslinks-symbolic depiction of spatially-distributed elements highlighting their physical features and the relationships between them-in an actin network. We selectively label crosslinks with fluorescent markers, track their thermal fluctuations, and characterize the local elasticity and cross-correlations between crosslinks. Such maps display massive heterogeneity, reveal abundant anticorrelations, and may contribute to address how local responses scale up to produce macroscopic elasticity. Single-crosslink microscopy offers a general, microscopic framework to better understand crosslinked molecular networks in undeformed or strained states
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