Chemical Design of Self-Propelled Janus Droplets

The study of active colloidal microswimmers with tunable phoretic and self-organizational behaviors is important for understanding out-of-equilibrium systems and the design of functional, adaptive matter. Solubilizing, self-propelling droplets have emerged as a rich chemical platform for exploration of active behaviors, but isotropic droplets rely on spontaneous symmetry breaking to sustain motion. The introduction of permanent asymmetry, e.g. in the form of a biphasic Janus droplet, has not been explored previously as a comprehensive design strategy for active droplets, despite the widespread use of Janus structures in motile solid particles. Here, we uncover the chemomechanical framework underlying the self-propulsion of active, biphasic Janus oil droplets solubilizing in aqueous surfactant. We elucidate how droplet propulsion is influenced by the degree of oil mixing, droplet shape, and oil solubilization rates for a range of oil combinations. A key finding is that for droplets containing both a mobile (solubilizing) and non-mobile oil, the degree of partitioning of the mobile oil across the Janus droplets’ oil-oil interface plays a pivotal role in determining the droplet speed and swimming direction. As a result, we observe propulsion speeds of Janus droplets more than an order-of-magnitude faster than chasing pairs of single emulsion droplets which lack an oil-oil interface. In addition, spatiotemporal control over droplet swimming speed and orientation is demonstrated through the application of local thermal gradients applied via induced via joule heading and laser spot illumination. We also explore the interactions between collections of Janus droplets including the spontaneous formation of multi-droplet spinning clusters that rotate predictably based on symmetry. Our findings provide key insights as to how the chemistry and structure of multiphase fluids can be harnessed to design microswimmers with programmable active and collective behaviors.

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Rheological control on the dynamics of explosive activity in the 2000 summit eruption of Mt. Etna

Solid Earth ◽

10.5194/se-1-61-2010 ◽

2010 ◽

Vol 1 (1) ◽

pp. 61-69 ◽

Cited By ~ 17

Author(s):

D. Giordano ◽

M. Polacci ◽

P. Papale ◽

L. Caricchi

Keyword(s):

Solid Particles ◽

Magma Ascent ◽

Explosive Activity ◽

Summit Eruption ◽

Intermediate Phases ◽

Strombolian Eruption ◽

Mt Etna ◽

Order Of Magnitude ◽

Crystal Content ◽

Fire Fountain

Abstract. In the period from January to June 2000 Mt. Etna exhibited an exceptional explosive activity characterized by a succession of 64 Strombolian and fire-fountaining episodes from the summit South-East Crater. Textural analysis of the eruptive products reveals that the magma associated with the Strombolian phases had a much larger crystal content (>55 vol%) with respect to the magma discharged during the fire-fountain phases (~35 vol%). Rheological modelling shows that the crystal-rich magma falls in a region beyond a critical crystal content where small addition of solid particles causes an exponential increase of the effective magma viscosity. When implemented into the modeling of steady magma ascent dynamics (as assumed for the fire-fountain activity), a large crystal content as the one found for products of Strombolian eruption phases results in a one order of magnitude decrease of mass flow-rate, and in the onset of conditions where small heterogeneities in the solid fraction carried by the magma translate into highly unsteady eruption dynamics. We argue that crystallization on top of the magmatic column during the intermediate phases when magma was not discharged favoured conditions corresponding to Strombolian activity, with fire-fountain activity resuming after removal of the highly crystalline top. The numerical simulations also provide a consistent interpretation of the association between fire-fountain activity and emergence of lava flows from the crater flanks.

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Erosion Rate Testing at High Temperature of Alloys and Coatings for Use in Turbomachinery

Volume 3: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

10.1115/98-gt-025 ◽

1998 ◽

Cited By ~ 2

Author(s):

W. Tabakoff

Keyword(s):

High Temperature ◽

Solid Particles ◽

Surface Erosion ◽

Erosion Testing ◽

Speed Flow ◽

Order Of Magnitude ◽

The University ◽

Work Done ◽

High Temperature Erosion ◽

Reliable Methods

Because of the serious consequences of turbomachinery erosion on their performance and life, it is important to have reliable methods for predicting their erosion when solid particles are ingested with the incoming flow. This is a very challenging problem since turbomachinery erosion is affected by many factors such as blade passage geometry, blade row location, rotational speed flow conditions, blade material and particles’ characteristics. Several studies which are essential to predicting blade surface erosion intensity and pattern, have been conducted at the University of Cincinnati’s Propulsion Laboratory over the past twenty-five years. This paper describes only some of the work done on erosion testing at high temperatures and velocities for different materials and coatings. The testing has been performed with a special high temperature erosion wind tunnel which simulates the aerodynamic conditions on the blades. The coated substrates reveal one order of magnitude less wear compared to some commercial non-CVD coatings on the same alloys. This study demonstrates that some coatings provide an excellent erosion resistance to INCO 718, LNCO 738, MAR-246, X-40 and Tungsten Carbide.

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Rheological control on the dynamics of explosive activity in the 2000 summit eruption of Mt. Etna

Solid Earth Discussions ◽

10.5194/sed-2-19-2010 ◽

2010 ◽

Vol 2 (1) ◽

pp. 19-42 ◽

Cited By ~ 2

Author(s):

D. Giordano ◽

M. Polacci ◽

P. Papale ◽

L. Caricchi

Keyword(s):

Solid Particles ◽

Magma Ascent ◽

Explosive Activity ◽

Summit Eruption ◽

Intermediate Phases ◽

Strombolian Eruption ◽

Mt Etna ◽

Order Of Magnitude ◽

Crystal Content ◽

Fire Fountain

Abstract. In the period from January to June 2000 Mt. Etna exhibited an exceptional explosive activity characterised by a succession of 64 Strombolian and fire-fountaining episodes from the summit South-East crater. Textural analysis of the eruptive products reveals that the magma associated with the Strombolian phases had a much larger crystal content >55 vol% with respect to the magma discharged during the fire-fountain phases (~35 vol%). Rheological modelling shows that the crystal-rich magma falls in a region beyond a critical crystal content where the small addition of solid particles causes an exponential increase of the effective magma viscosity. When implemented into the modelling of steady magma ascent dynamics, the large crystal content of the Strombolian eruption phases results in a one order of magnitude decrease of mass flow-rate, and in the onset of conditions where small heterogeneities in the solid fraction carried by the magma translate into highly unsteady eruption dynamics. Therefore, we argue that crystallization on top of the magmatic column during the intermediate phases when magma was not discharged caused the conditions to shift from fire-fountain to Strombolian activity. The numerical simulations also provide a consistent interpretation of the association between fire-fountain activity and emergence of lava flows from the crater flanks.

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Preparation of Scanning Electron Microscope Specimens from Liquid Dispersions of Solid Particulates

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092190 ◽

1976 ◽

Vol 34 ◽

pp. 446-447

Author(s):

Earl R. Walter

Keyword(s):

Electron Microscopy ◽

Surface Tension ◽

Particle Size ◽

Sewage Treatment ◽

Solid Particles ◽

Thermal Gradients ◽

Transmission Electron ◽

Particle Size Fractionation ◽

Scanning Electron ◽

Effect Of Surface

A variety of techniques have been developed which do not materially alter the state of flocculation of solid particles dispersed in a liquid when that dispersion is prepared for transmission electron microscopy. However, similar techniques have not been developed to minimize the effect of surface tension on the flocculation of particles when dispersions are dried down on a support for scanning electron microscopy. The problem is often compounded by the larger sample size involved and the generally larger particles studied in the SEM. With today's emphasis on air and water polution, sewage treatment, etc., simple, rapid techniques of sample preparation to allow reliable particle size studies are becoming increasingly important.When a liquid dispersion of solid particles is dried down on a substrate for SEM characterization, surface tension and thermal gradients in the evaporating liquid may materially alter the degree of flocculation and introduce severe particle size fractionation in different areas of the specimen.

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Erosion of a Pipe Bend by Solid Particles Entrained in Water

Journal of Engineering for Industry ◽

10.1115/1.3185935 ◽

1984 ◽

Vol 106 (3) ◽

pp. 213-217 ◽

Cited By ~ 21

Author(s):

D. J. Blanchard ◽

P. Griffith ◽

E. Rabinowicz

Keyword(s):

Secondary Flows ◽

Solid Particles ◽

Erosion Process ◽

Pipe Bend ◽

Pipe Elbow ◽

Average Wear ◽

Order Of Magnitude ◽

Set Up ◽

Average Angle ◽

D Value

The erosion process in a 90-deg pipe elbow is studied to determine the magnitude and location of the maximum wear point. A two-dimensional, theoretical model of the erosion process is set up to track the particle trajectories and then calculate the wear at impingement. Erosion tests on electroplated, 1-in. I.D. elbows are made using particle sizes which vary by over an order of magnitude, but the location of maximum wear for an elbow whose R/D value is 1.5 is almost unaffected. The average angle, φ, which locates the point of maximum erosion, is determined to be 85 deg, measured from the beginning of the curve. The average wear coefficient, Ke, is found to be 0.011. Another test using a more gradual bend curvature (R/D = 5.0, and a mitre bend tested as an approximation of an elbow with R/D value of 0.5, give similar results.) There are considerable discrepancies between computed and measured values of the position of maximum wear, because the model does not account for secondary flows. Finally, a simple technique is outlined to predict the erosion depth at the maximum wear point.

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Discrete transitions in turbulent convection

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1954.0196 ◽

1954 ◽

Vol 225 (1161) ◽

pp. 185-195 ◽

Cited By ~ 147

Keyword(s):

Heat Transport ◽

Thermal Gradients ◽

Mean Velocity ◽

Apparent Lack ◽

New Approach ◽

Thermal Turbulence ◽

Order Of Magnitude ◽

Vertical Barriers ◽

Theoretical Paper ◽

Rayleigh Numbers

The convection in a fluid between horizontal conducting surfaces is a very simple example of thermal turbulence, for the mean heat transport is independent of position while the distance between these surfaces is the only geometric parameter. This paper describes measurements of the heat transport and mean velocity in such convection up to Rayleigh numbers of 10 10 . Six discrete transitions in the slope of the heat-transport curve were observed between Rayleigh numbers of 1700 and 1000000. Although the thermal gradients vary by an order of magnitude from a boundary to the mid-regions of the fluid, these transitions appear to agree with those deduced on an assumption of a constant thermal gradient. Various visual observations of the fluctuating velocity field are also reported. Additional vertical barriers in the fluid markedly influence the horizontal flow but have negligible effect on the heat transport. This apparent lack of uniqueness of the flow patterns associated with a given heat transport suggests a new approach to turbulent phenomena discussed in a following theoretical paper.

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Controlling Organization and Forces in Active Matter Through Optically-Defined Boundaries

10.1101/504456 ◽

2018 ◽

Author(s):

Tyler D. Ross ◽

Heun Jin Lee ◽

Zijie Qu ◽

Rachel A. Banks ◽

Rob Phillips ◽

...

Keyword(s):

Fluid Flows ◽

Cellular Structures ◽

Active Matter ◽

Experimental Systems ◽

Order Of Magnitude ◽

Equilibrium Structures ◽

Microtubule Networks ◽

Spatiotemporal Control ◽

Individual Motor ◽

Non Equilibrium

AbstractLiving systems are capable of locomotion, reconfiguration, and replication. To perform these tasks, cells spatiotemporally coordinate the interactions of force-generating, “active” molecules that create and manipulate non-equilibrium structures and force fields that span up to millimeter length scales [1–3]. Experimental active matter systems of biological or synthetic molecules are capable of spontaneously organizing into structures [4, 5] and generating global flows [6–9]. However, these experimental systems lack the spatiotemporal control found in cells, limiting their utility for studying non-equilibrium phenomena and bioinspired engineering. Here, we uncover non-equilibrium phenomena and principles by optically controlling structures and fluid flow in an engineered system of active biomolecules. Our engineered system consists of purified microtubules and light-activatable motor proteins that crosslink and organize microtubules into distinct structures upon illumination. We develop basic operations, defined as sets of light patterns, to create, move, and merge microtubule structures. By composing these basic operations, we are able to create microtubule networks that span several hundred microns in length and contract at speeds up to an order of magnitude faster than the speed of an individual motor. We manipulate these contractile networks to generate and sculpt persistent fluid flows. The principles of boundary-mediated control we uncover may be used to study emergent cellular structures and forces and to develop programmable active matter devices.

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Droplet Shape Control Using Microfluidics and Designer Biosurfactants

10.26434/chemrxiv.12103284 ◽

2020 ◽

Cited By ~ 1

Author(s):

Yuan Gao ◽

Chun-Xia Zhao ◽

Frank Sainsbury

Keyword(s):

Shape Control ◽

Protein Film ◽

Droplet Shape ◽

Precise Control ◽

Mechanical Responses ◽

Emulsion Droplets ◽

Aspect Ratios ◽

Surface Active ◽

Spherical Droplets

Many uses of emulsion droplets require precise control over droplet size and shape. Here we report a ‘shape-memorable’ micro-droplet formulation stabilized by a polyethylene glycol (PEG)-modified protein-surfactant, the droplets are stable against coalescence for months and can maintain non-spherical shapes for hours, depending on the surface coverage of PEGylated protein. Monodisperse droplets with aspect ratios ranging from 1.0 to 3.4 were controllably synthesized with a flow-focusing microfluidic device. Mechanical properties of the interfacial protein network were explored to elucidate the mechanism behind the droplet shape conservation phenomenon. Characterization of the protein film revealed that the presence of a PEG layer at interfaces alters the mechanical responses of the protein film, resulting in interfacial networks with improved strength. Taking advantage of the prolonged stabilization of non-spherical droplets, we demonstrate the possibility of functionalization of the droplet interface with accessible biotin moieties. The stabilization of micro-droplet shape with surface-active proteins that also serve as an anchor for integrating functional moieties, provides a tailorable interface for diverse applications.

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Droplet Shape Control Using Microfluidics and Designer Biosurfactants

10.26434/chemrxiv.12103284.v1 ◽

2020 ◽

Author(s):

Yuan Gao ◽

Chun-Xia Zhao ◽

Frank Sainsbury

Keyword(s):

Shape Control ◽

Protein Film ◽

Droplet Shape ◽

Precise Control ◽

Mechanical Responses ◽

Emulsion Droplets ◽

Aspect Ratios ◽

Surface Active ◽

Spherical Droplets

Many uses of emulsion droplets require precise control over droplet size and shape. Here we report a ‘shape-memorable’ micro-droplet formulation stabilized by a polyethylene glycol (PEG)-modified protein-surfactant, the droplets are stable against coalescence for months and can maintain non-spherical shapes for hours, depending on the surface coverage of PEGylated protein. Monodisperse droplets with aspect ratios ranging from 1.0 to 3.4 were controllably synthesized with a flow-focusing microfluidic device. Mechanical properties of the interfacial protein network were explored to elucidate the mechanism behind the droplet shape conservation phenomenon. Characterization of the protein film revealed that the presence of a PEG layer at interfaces alters the mechanical responses of the protein film, resulting in interfacial networks with improved strength. Taking advantage of the prolonged stabilization of non-spherical droplets, we demonstrate the possibility of functionalization of the droplet interface with accessible biotin moieties. The stabilization of micro-droplet shape with surface-active proteins that also serve as an anchor for integrating functional moieties, provides a tailorable interface for diverse applications.

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