Whitesides Research

Techniques

Self-Assembly of Concentric Circles with MagLev

Magnetic levitation (MagLev) of diamagnetic objects (“components”) in a paramagnetic fluid, positioned in a magnetic field gradient, orders the positions of those components in three dimensions (3D).  This type of self-assembly proceeds by suspending the components, with shapes and distributions of densities designed to control their position and orientation, in an aqueous solution of MnCl2 or GdCl3, and placing this suspension between two permanent NdFeB magnets oriented with like poles facing.  The balance of magnetic and gravitational forces acting on the components—here mm-scale mirrors, lenses, filters, diffraction gratings, droplets, and soft polymeric sheets—determines their final position and orientation in 3D.  MagLev positions and aligns components without mechanical support, and eliminates solid friction and stiction.  Draining of the paramagnetic medium from a system in the magnetic field gradient stacks or positions the components into ordered structures.

Last updated on January 25, 2012

Real time video of the extinction of a methane/air non-premixed flame by an AC inhomogeneous electric field.

This video (real time) shows the effect of an oscillating electric field on a methane flame burning in air (the flame is ~15 cm tall in this case).
The field is applied via a wire electrode (shown on the left of the flame, pointed at the base of the flame), which is insulated by a glass shell, raised to a large oscillating potential.
The counterelectrode is outside the field of view and consists of a 50x50cm vertically oriented grounded plate.
The field conditions here have been chosen to show effective suppression in ~100 ms. 

Last updated on December 1, 2011

Extinction of a methane/air non-premixed flame by an AC inhomogeneous electric field

This video (three loops, the first two loops are in real time, the third loops is half speed) shows the effect of an oscillating electric field on a methane flame burning in air (the flame is ~50 cm tall in this case).
The field is applied via a wire electrode (shown on the left of the flame, pointed at the base of the flame), which is insulated by a glass shell, raised to a large oscillating potential.
The counterelectrode is on the right side of the box containing the flame and consists of a 50x50cm vertically oriented grounded plate.
The field conditions here have been chosen to show effective suppression in ~300 ms. 

Last updated on December 1, 2011

Slow motion video of the extinction of a methane/air non-premixed flame by an AC inhomogeneous electric field.

This video (slow motion) shows the effect of an oscillating electric field on a methane flame burning in air (the flame is ~15 cm tall in this case).
The field is applied via a wire electrode (shown on the left of the flame, pointed at the base of the flame), which is insulated by a glass shell, raised to a large oscillating potential.
The counterelectrode is outside the field of view and consists of a 50x50cm vertically oriented grounded plate.
The field conditions here have been chosen to show effective suppression in ~50 ms. 

Last updated on December 1, 2011

Effect of field strength on the interaction of a methane/air non-premixed flame with an AC inhomogeneous electric field.

This video (real time) shows the effect of an oscillating electric field of varying intensity and constant frequency on a methane flame burning in air (the flame is ~15 cm tall in this case).
The field is applied via a wire electrode (shown on the left of the flame, pointed at the base of the flame), which is insulated by a glass shell, raised to a large oscillating potential.
The counterelectrode is outside the field of view and consists of a 50x50cm vertically oriented grounded plate.
The field conditions here have been chosen to show the field-dependent transition between attractive interaction and repulsive interaction.

Last updated on December 1, 2011

Effect of frequency on the interaction of a methane/air non-premixed flame with an AC inhomogeneous electric field.

This video (real time) shows the effect of an oscillating electric field of constant intensity and increasing frequency on a methane flame burning in air (the flame is ~15 cm tall in this case).
The field is applied via a wire electrode (shown on the left of the flame, pointed at the base of the flame), which is insulated by a glass shell, raised to a large oscillating potential.
The counterelectrode is outside the field of view and consists of a 50x50cm vertically oriented grounded plate.
The field conditions here have been chosen to show the increase of repulsion with frequency.

Last updated on December 1, 2011

Repulsion of a methane/air non-premixed flame by a AC inhomogeneous electric field.

This video shows the effect of an oscillating electric field on a methane flame burning in air (the flame is ~15 cm tall in this case).
The field is applied via a wire electrode (shown on the left of the flame, pointed at the base of the flame), which is insulated by a glass shell, raised to a large oscillating potential.
The counterelectrode is outside the field of view and consists of a 50x50cm vertically oriented grounded plate.
The field conditions here have been chosen to show a level of repulsion just below the suppression threshold.

Last updated on December 1, 2011

Multigait Soft Robot

Video of a multigait soft robot undulating under a glass obstacle.

See our PNAS paper -\"Multi-Gait Soft Robot\", Shepherd, R.F., Ilievski.F., Choi.W., Morin.S.A., Stokes.A.A., Mazzeo.A.D., Chen.X., Wang.M., and Whitesides.G.M., PNAS, 2011

Last updated on December 1, 2011

Soft Robot Fabrication

Dr. Robert Shepherd demonstrates soft robot fabrication technique.

Last updated on December 1, 2011

Droplet microfluidics for nucleation studies - Part II

Ice nucleation in a microfluidic chip, part 2

Metastable fluids, such as supercooled water, can be difficult to produce and maintain in a metastable state using large-scale containers. We produced supercooled water as cold as is possible: approximately -37 degrees Celsius in our system (further cooling is impossible due to the homogenous nucleation of ice).We used droplet microfluidics to produce special containers for supercooled water: water is contained in small droplets ~100 microns in diameter that are surrounded by a liquid container – a moving stream of liquid fluorocarbon.

This movie shows how drops of water freeze after the homogenous nucleation of ice. Such freezing is a two-stage process: (1) crystals of ice grow rapidly until the drop becomes a mixture of ice and water at a temperature of 0 degrees Celsius, then (2) the ice-water mixture freezes completely, at a slower pace, being cooled by the carrier fluid which has a temperature around -40 degrees Celsius.

Last updated on November 17, 2011

Droplet microfluidics for nucleation studies - Part I

Ice nucleation in a microfluidic chip, part 1

Metastable fluids, such as supercooled water, can be difficult to produce and maintain in a metastable state using large-scale containers. We produced supercooled water as cold as is possible: approximately -37 degrees Celsius in our system (further cooling is impossible due to the homogenous nucleation of ice). We used droplet microfluidics to produce special containers for supercooled water: water is contained in small droplets ~100 microns in diameter that are surrounded by a liquid container – a moving stream of liquid fluorocarbon.

This movie shows how we produce drops of supercooled water on a microfluidic chip, continuously cooling water from room temperature until it freezes due to homogeneous nucleation at temperatures close to -40 degrees Celsius

Last updated on November 17, 2011

Templated Self Assembly Using Magnetic Levitation

Last updated on August 18, 2011

Soft Robotic Gripper

Last updated on August 16, 2011

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