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The design of autonomous, dynamically selfassembled robots that perform collective motion at the microscale can help in advancing the fundamental principles of self-assembly and coordinated behavior of complex structures. Here, we discuss the dissipative collective dynamics of soft colloidal micro-rotators driven by magnetic rotating fields with different orientation. The micro-rotators were polydimethylsiloxane microbeads with internally aligned magnetic nanoparticle chains, which respond to the torque created by rotating magnetic fields. The dynamic assembly patterns and their collective motion when actuated by in-plane and by transversal rotating fields were characterized. In all cases, we observed a rich variety of new modes of collective dynamics of the micro-rotor ensembles. We categorized these dynamics into three different types including caterpillar motion and cartwheel motion in case of a transverse-plane rotating field and gear-like motion in case of an in-plane field. The influence of field parameters such as rotational speed was studied. These fascinating dynamic patterns and motility modes could find application in future microrobots operating in complex biological fluids. 

Colloidal particles with anisotropic geometries and interactions display rich phase behavior and hence have the potential to serve as the basis of functional materials, which can tunably and reversibly self-assemble into different configurations. External fields are one design parameter that can be used to manipulate how systems of colloidal particles assemble with one another. One challenge in designing new materials using anisotropic colloidal particles is understanding how an individual particle’s various anisotropic features, like geometry, affect their overall self-assembly. Here, we present the results of simulation studies that explore the self-assembly of 2D colloidal squares with offset magnetic dipoles in the presence of an external field. Annealing simulations are used to measure the equilibrium-phase behavior of systems of these particles in the ground state, when the magnetic interactions dominate over the thermal forces of the system. We find that the magnetic properties of these systems are strongly influenced by the relative number of squares with opposite “handedness”, or chirality, that are present within the system. Systems of squares that contain equal numbers of either chirality are extremely responsive to the external field; a relatively weak external field is required to magnetize them. In contrast, systems that contain only one chirality of squares are significantly less responsive to the external field; a significantly stronger external field is required to elicit the same magnetic response. Ultimately, the differing macroscopic magnetic properties of these systems are related to their microscopic self- assembly in an external field. Simulation snapshots and ground state phase diagrams illustrate how the absence of opposite chirality squares prevents systems of these particles from leaving an energetically favorable antiparallel configuration in the presence of an external field. When opposite chirality squares are present, these magnetic particles assemble into a head-to-tail configuration, therefore inducing a magnetic state 

Hypothesis: Symmetry breaking in an electric field-driven active particle system can be induced by applying a spatially uniform, but temporally non-uniform, alternating current (AC) signal. Regardless of the type of particles exposed to sawtooth AC signals, the unevenly induced polarization of the ionic charge layer leads to a major electrohydrodynamic effect of active propulsion, termed Asymmetric Field Electrophoresis (AFEP). Experiments: Suspensions containing latex microspheres of three sizes, as well as Janus and metal-coated particles were subjected to sawtooth AC signals of varying voltages, frequencies, and time asymmetries. Particle tracking via microscopy was used to analyze their motility as a function of the key parameters. Findings: The particles exhibit field-colinear active propulsion, and the temporal reversal of the AC signal results in a reversal of their direction of motion. The experimental velocity data as a function of field strength, frequency, and signal asymmetry are supported by models of asymmetric ionic concentration-polarization. The direction of particle migration exhibits a size-dependent crossover in the low frequency domain. This enables new approaches for simple and efficient on-chip sorting. Combining AFEP with other AC motility mechanisms, such as induced-charge electrophoresis, allows multiaxial control of particle motion and could enable development of novel AC field-driven active microsystems. 

Complex materials that change their optical properties in response to changes in environmental conditions can find applications in displays, smart windows, and optical sensors. Here a class of biphasic composites with stimuli-adaptive optical transmittance is introduced. The biphasic composites comprise aqueous droplets (a mixture of water, glycerol, and surfactant) embedded in an elastomeric matrix. The biphasic composites are tuned to be optically transparent through a careful match of the refractive indices between the aqueous droplets and the elastomeric matrix. We demonstrate that stimuli (e.g., salinity and temperature change) can trigger variations in the optical transmittance of the biphasic composite. The introduction of such transparency-changing soft matter with liquid inclusions offers a novel approach to designing advanced optical devices, optical sensors, and metamaterials. 

Abstract Direct disposal of used soft electronics into the environment can cause severe pollution to the ecosystem due to the inability of most inorganic materials and synthetic polymers to biodegrade. Additionally, the loss of the noble metals that are commonly used in soft electronics leads to a waste of scarce resources. Thus, there is an urgent need to develop “green” and sustainable soft electronics based on eco‐friendly manufacturing that may be recycled or biodegraded after the devices’ end of life. Here an approach to fabricating sustainable soft electronics is demonstrated where the expensive functional materials can be recycled and the soft substrate can be biodegradable. A stretchable agarose/glycerol gel film is used as the substrate, and silver nanowires (AgNWs) are printed on the film to fabricate the soft electronic circuits. The mechanical and chemical properties of the agarose/glycerol gel films are characterized, and the functionality of the printed AgNW electrodes for electrophysiological sensors is demonstrated. The demonstration of the biodegradability of the agarose/glycerol and the recyclability of AgNWs points toward ways to develop sustainable and eco‐friendly soft electronics. 

There are a set of primordial features and functions expected of any modern information system: a substrate stably carrying data; the ability to repeatedly write, read, erase, reload, and compute on specific data from that substrate; and the overall ability to execute such functions in a seamless and programmable manner. For nascent molecular information technologies, proof of principle realization of this set of primordial capabilities would advance the vision for their continued development. Here, we present a DNA-based store and compute engine that captures these primordial capabilities. This system comprises multiple image files encoded into DNA and adsorbed onto ~50 um diameter, highly porous, hierarchically branched, colloidal substrate particles comprised of naturally abundant cellulose acetate. Their surface areas are over 200 cm2/mg with binding capacities of over 1012 DNA oligos/mg, 10 terabytes/mg, or 104 terabytes/cm3. This “dendricolloid” stably holds DNA files better than bare DNA with an extrapolated ability to be repeatedly lyophilized and rehydrated over 170 times compared to 60 times, respectively. Accelerated aging studies project half-lives of ~6000 and 2 million years at 4 ˚C and -18 ˚C, respectively. The data can also be erased and replaced, and non-destructive file access is achieved through transcribing from distinct synthetic promoters. The resultant RNA molecules can be directly read via nanopore sequencing and can also be enzymatically computed to solve simplified 3x3 chess and sudoku problems. Our study establishes a feasible route for utilizing the high information density and parallel computational advantages of nucleic acids.