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We describe reshaping of active textiles actuated by bending of Janus fibres comprising both active and passive components. A great variety of shapes, determined by minimising the overall energy of the fabric, can be produced by varying bending directions determined by the orientation of Janus fibres. Under certain conditions, alternative equilibrium states, one absolutely stable and the other metastable coexist, and their relative energy may flip its sign as system parameters, such as the extension upon actuation, change. A snap-through reshaping in a specially structured textile reproduces the Venus flytrap effect.
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We investigate actuation of woven fabrics including active Janus fibres with an imposed twist, which bend in variable directions upon phase transition between isotropic and nematic state. The essential feature of textiles incorporating a pair of Janus fibres with a mismatched pitch or handedness of coiling is the existence of multiple stable shapes with different energies within a certain range of the extension coefficient. If the active fibres are closed into a ring, torsion develops to accommodate adjustment of the direction of bending. The structure is generally stabilised by adding more passive filaments, and multistability is observed also in this case.
In this article, we study the phenomenology of a two dimensional dilute suspension of active amphiphilic Janus particles. We analyze how the morphology of the aggregates emerging from their self-assembly depends on the strength and the direction of the active forces. We systematically explore and contrast the phenomenologies resulting from particles with a range of attractive patch coverages. Finally, we illustrate how the geometry of the colloids and the directionality of their interactions can be used to control the physical properties of the assembled active aggregates and suggest possible strategies to exploit self-propulsion as a tunable driving force for self-assembly.
Crystals melt when thermal excitations or the concentration of defects in the lattice is sufficiently high. Upon melting, the crystalline long-range order vanishes, turning the solid to a fluid. In contrast to this classical scenario of solid melting, here we demonstrate a counter-intuitive behavior of the occurrence of crystalline long-range order in an initially disordered matrix. This unusual solidification is demonstrated in a system of passive colloidal particles accommodating chemically active defects -- photocatalytic Janus particles. The observed crystallization occurs when the amount of active-defect-induced fluctuations (which is the measure of the effective temperature) reaches critical value. The driving mechanism behind this unusual behavior is purely internal and resembles a blast-induced solidification. Here the role of internal micro-blasts is played by the photochemical activity of defects residing in the colloidal matrix. The defect-induced solidification occurs under non-equilibrium conditions: the resulting solid exists as long as a constant supply of energy in the form of ion flow is provided by the catalytic photochemical reaction at the surface of active Janus particle defects. Our findings could be useful for understanding of the phase transitions of matter under extreme conditions far from thermodynamic equilibrium.
We analyze the various morphing structures obtained by actuating Janus filaments comprising driven and passive sectors and textiles incorporating driven and passive filaments. Transitions between alternative shapes and coexistence of absolutely stable and metastable states within a certain range of relative extension upon actuation are detected both in Janus rings and textiles. Both single filaments and textiles can be reverse designed to bend into desired shapes by controlling both the size and orientation of driven sectors.
Surface bound catalytic chemical reactions self-propel chemically active Janus particles. In the vicinity of boundaries, these particles exhibit rich behavior, such as the occurrence of wall-bound steady states of sliding. Most active particles tend to sediment as they are density mismatched with the solution. Moreover Janus spheres, which consist of an inert core material decorated with a cap-like, thin layer of a catalyst, are gyrotactic (bottom-heavy). Occurrence of sliding states near the horizontal walls depends on the interplay between the active motion and the gravity-driven sedimentation and alignment. It is thus important to understand and quantify the influence of these gravity-induced effects on the behavior of model chemically active particles moving near walls. For model gyrotactic, self-phoretic Janus particles, here we study theoretically the occurrence of sliding states at horizontal planar walls that are either below (floor) or above (ceiling) the particle. We construct state diagrams characterizing the occurrence of such states as a function of the sedimentation velocity and of the gyrotactic response of the particle, as well as of the phoretic mobility of the particle. We show that in certain cases sliding states may emerge simultaneously at both the ceiling and the floor, while the larger part of the experimentally relevant parameter space corresponds to particles that would exhibit sliding states only either at the floor or at the ceiling or there are no sliding states at all. These predictions are critically compared with the results of previous experimental studies and our experiments conducted on Pt-coated polystyrene and silica-core particles suspended in aqueous hydrogen peroxide solutions.
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