纳米压印技术

Mechanical and Industrial Engineering

University of Massachusetts

Amherst, MA, USA

Nano-Impact

Jonathan P. Rothstein and Mark Tuominen

• A group of researchers at Univ. Del. have impregnated Kevlar vests with a nanoparticle colloidal suspension resulting in a dramatic improvement in projectile impact.

•

The addition of a very small amount of fluid increased performance equivalent to

doubling the number of Kevlar sheets while not changing flexibility of fabric. Why?

Lee, Wetzel and Wagner J. Material Science (2003)

Kevlar Kevlar & Nanoparticle Suspension

• A group of researchers at Univ. Del. have impregnated Kevlar vests with a nanoparticle colloidal suspension resulting in a dramatic improvement in projectile impact.

•The addition of a very small amount of fluid increased performance equivalent to doubling the number of Kevlar sheets while not changing flexibility of fabric. Why?

Kevlar Kevlar & Nanoparticle Suspension

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Shear Rate [s-1] Increasing

Stretch Rate

Why Size Matters

•For large particles the fluid remains Newtonian like air or water below 30wt%•Above 30% interactions between and collisions of particles result shear thickening and elastic effects –particles interact to form large aggregate structures

•For nanoparticles, the effect of nanoparticle addition can be observed at concentrations closer to 1wt% -why?

•Surface area increases with reduced particle size resulting in enhanced interparticle interactions

•At same volume fraction smaller particles are packed closer together –electrostatic interactions are stronger and diffusion is faster so they interact more frequently.

1μm Particles

100nm Particles

10nm Particles

Copying Nature –Biomimetic Superhydrophobic Surfaces •The leaves of the lotus plant are superhydrophobic –water beads up on the surface of the plant and moves freely with almost no resistance making the leaves self-cleaning.

•The surface of the lotus leaf has 10μm sized bumps which are coated by 1nm sized waxy crystals which make the surface extremely hydrophobic -repel water.

•The water does not wet the entire surface of the leaf, but only the tops of the large scale roughness.

•

Synthetic superhydrophobic surfaces have designed to produce stain-resistant clothing

and coatings for buildings and windows to make them self-cleaning. Water Drops on a Lotus Leaf

Using Superhydrophobic Surfaces to Reduce Drag •We are currently using superhydrophobic surfaces

to develop a passive, inexpensive technique that can

generate drag reduction in both laminar and

turbulent flows.

•This technology could have a significant impact on

applications from microfluidics and nanofluidics to

submarines and surface ships.

•How does it work? The water touches only the tops

of the post and a shear-free air-water interfaces is

supported –effectively reducing the surface area.

•Currently capable of reducing drag by over 70% in

both laminar and turbulent flows!

w

d 15μm PDMS

Carbon Nanotubes