A simple two-dimensional model system to study electrostatic-self-assembly

Cademartiri, Rebecca; Stan, Claudiu A.; Tran, Vivian M.; Wu, Eileen; Friar, Liam; Vulis, Daryl I.; Clark, Logan W.; Tricard, Simon; Whitesides, George M.

doi:10.1039/c2sm26192h

Cited by 47 publications

(60 citation statements)

References 60 publications

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“…The type of dish did not matter: beads of different materials charged similarly on an aluminum (conductor) dish, a grounded aluminum dish, and a poly-(methyl methacrylate) (insulator) dish. 25 This observation further indicates that the charges on the beads are not electrons; otherwise the electrons on the beads would have dissipated into ground in a grounded aluminum dish. Before the experiments, we rinsed the beads and dish with deionized water and ethanol, and dried them in a stream of nitrogen.…”

Section: Journal Of the American Chemical Societymentioning

confidence: 99%

Contact De-electrification of Electrostatically Charged Polymers

et al. 2012

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The contact electrification of insulating organic polymers is still incompletely understood, in part because multiple fundamental mechanisms may contribute to the movement of charge. This study describes a mechanism previously unreported in the context of contact electrification: that is, “contact de-electrification”, a process in which polymers charged to the same polarity discharge on contact. Both positively charged polymeric beads, e.g., polyamide 6/6 (Nylon) and polyoxymethylene (Delrin), and negatively charged polymeric beads, e.g., polytetrafluoroethylene (Teflon) and polyamide-imide (Torlon), discharge when the like-charged beads are brought into contact. The beads (both with charges of ∼±20 μC/m2, or ∼100 charges/μm2) discharge on contact regardless of whether they are made of the same material, or of different materials. Discharge is rapid: discharge of flat slabs of like-charged Nylon and Teflon pieces is completed on a single contact (∼3 s). The charge lost from the polymers during contact de-electrification transfers onto molecules of gas in the atmosphere. When like-charged polymers are brought into contact, the increase in electric field at the point of contact exceeds the dielectric breakdown strength of the atmosphere and ionizes molecules of the gas; this ionization thus leads to discharge of the polymers. The detection (using a Faraday cup) of charges transferred to the cup by the ionized gas is compatible with the mechanism. Contact de-electrification occurs for different polymers and in atmospheres with different values of dielectric breakdown strength (helium, argon, oxygen, carbon dioxide, nitrogen, and sulfur hexafluoride): the mechanism thus appears to be general.

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Section: Journal Of the American Chemical Societymentioning

confidence: 99%

Contact De-electrification of Electrostatically Charged Polymers

et al. 2012

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“…There are obvious limitations, for example, the metafluid cannot flow through a pipe; it cannot be compressed, nor is there an easy way to define pressure; and it is confined to two dimensions. However, we have already shown it to be useful in observing the atomistic dynamics of 2D polymer analogs (23), and we believe that it will prove elucidating in many open questions of the thermal world, such as self-assembly and 2D pattern formation (24)(25)(26). Perhaps, emergent metafluids such as ours exist throughout the macroscopic world, be they swarms, turbulent weather, financial markets, or any other system with intrinsic randomness.…”

Section: Significancementioning

confidence: 99%

Fluids by design using chaotic surface waves to create a metafluid that is Newtonian, thermal, and entirely tunable

Welch

Liebman‐Pelaez

Corwin

2016

Proc. Natl. Acad. Sci. U.S.A.

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In conventional fluids, viscosity depends on temperature according to a strict relationship. To change this relationship, one must change the molecular nature of the fluid. Here, we create a metafluid whose properties are derived not from the properties of molecules but rather from chaotic waves excited on the surface of vertically agitated water. By making direct rheological measurements of the flow properties of our metafluid, we show that it has independently tunable viscosity and temperature, a quality that no conventional fluid possesses. We go on to show that the metafluid obeys the Einstein relation, which relates many-body response (viscosity) to single-particle dynamics (diffusion) and is a fundamental result in equilibrium thermal systems. Thus, our metafluid is wholly consistent with equilibrium thermal physics, despite being markedly nonequilibrium. Taken together, our results demonstrate a type of material that retains equilibrium physics while simultaneously allowing for direct programmatic control over material properties.Faraday waves | metafluid | emergent thermodynamics M aterials science seeks not only to understand but also to control the properties of matter. To do so, one must dynamically change the nature of conventional materials at the molecular scale. Recent work circumvents this problem by rejecting the molecule as the fundamental unit and substituting a macroscopic structural element. This approach has successfully created metamaterials with novel optical (1-3), acoustic (4-6), mechanical (7-9), and fluid properties (10, 11) that would otherwise be impossible. However, this approach comes at a cost: by deriving their properties from macroscopic, nonequilibrium, or anisotropic elements, these materials necessarily abandon the physics of thermal systems. In this work, using a combination of active and passive rheology, we show that macroscopic chaotic surface waves on a vertically agitated fluid form a fully thermal metafluid with dynamically tunable material properties. In contrast to a conventional fluid in which viscosity and temperature are inextricably linked, we show that these quantities are independently tunable in our system. We further demonstrate that by satisfying the barest criteria of isotropy and steady-state chaos [as required by kinetic theory (12, 13)], we have created a system that obeys the Einstein relation (14). Thus, despite being macroscopic and nonequilibrium, the system is well described by equilibrium thermal physics.The "molecules" of our metafluid are chaotic Faraday waves (15, 16), generated in a water-filled aluminum dish that is vertically oscillated with rms amplitude A s and at frequency f s (Fig. 1 A and C; see Materials and Methods for technical details). The waves uniformly cover the surface of the water and experience significant pinning only at the boundary, far from where our measurements are conducted. The chaos and wave density is holistically steady state, although the existence of a particular wave is transient. Thus, "collisions" in our syste...

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“…Granular charging is also important in many industries, such as in printing and pharmaceutical formulation [9][10][11][12]. Despite the importance and prevalence of granular charging, its underlying causes remain controversial.…”

Section: Introductionmentioning

confidence: 99%

Field driven charging dynamics of a fluidized granular bed

et al. 2016

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A simplified model has previously described the inductive charging of colliding identical grains in the presence of an external electric field. Here we extend that model by including heterogeneous surface charge distributions, grain rotations and electrostatic interactions between grains. We find from this more realistic model that strong heterogeneities in charging can occur in agitated granular beds, and we predict that shielding due to these heterogeneities can dramatically alter the charging rate in such beds.

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A simple two-dimensional model system to study electrostatic-self-assembly

Cited by 47 publications

References 60 publications

Contact De-electrification of Electrostatically Charged Polymers

Contact De-electrification of Electrostatically Charged Polymers

Fluids by design using chaotic surface waves to create a metafluid that is Newtonian, thermal, and entirely tunable

Field driven charging dynamics of a fluidized granular bed

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