High velocity droplet impacts

1. A method of impacting liquid droplets onto a surface comprising providing a series of liquid droplets, directing said liquid droplets at a non-planar target surface to cause a shockwave in the droplets upon impact, the non-planar target surface having a predefined shape and size at the location of impact of the droplet to intensify the shockwave in the droplet, wherein the predefined shape and size of the target surface at the location of impact of the droplet is concave and corresponds to the shape and size of the droplet.

2. A method as claimed in claim 1 , comprising producing a pressurised liquid jet stream comprising a liquid and a nano-particle material, causing the break-up of said jet stream to produce a plurality of droplets containing liquid and nano-particle material, and irradiating the droplets with energy to produce and expand cavities within the droplets.

3. A method as claimed in claim 1 , comprising producing a pressurised liquid jet stream comprising a liquid and a volatile emulsion, and causing the break-up of said jet stream to produce a plurality of droplets containing both said liquid and said volatile emulsion.

4. A method as claimed in claim 1 , wherein the surface is shaped such that when the droplet initially impacts the target, the boundary of the contact patch between the droplet and the surface travels at a supersonic speed for a time period significantly beyond the initial moment of collision.

5. A method as claimed in claim 1 , wherein the target surface comprises a plurality of discrete portions.

6. A method as claimed in claim 1 , wherein the target surface is shaped such that there are a plurality of discrete initial contact points between the droplet and surface.

7. A method as claimed in claim 6 , wherein the target surface comprises a plurality of protrusions to act as the plurality of discrete initial contact points.

8. An apparatus for impacting liquid droplets onto a surface comprising an arrangement for producing a series of liquid droplets, an arrangement for directing said liquid droplets at a non-planar target surface to cause a shockwave in the droplets upon impact, wherein said non-planar target surface has a predefined shape and size at the location of impact of the droplet to intensify the shockwave in the droplet, wherein the predefined shape and size of the target surface at the location of impact of the droplet is concave and corresponds to the shape and size of the droplet.

9. An apparatus as claimed in claim 8 , comprising an arrangement for producing a pressurised liquid jet stream comprising a liquid and a nano-particle material, an arrangement for causing the break-up of said jet stream to produce a plurality of droplets containing liquid and nano-particle material, and an arrangement for irradiating the droplets with energy to produce and expand cavities within the droplets.

10. An apparatus as claimed in claim 8 , comprising an arrangement for producing a pressurised liquid jet stream comprising a liquid and a volatile emulsion, and an arrangement for causing the break-up of said jet stream to produce a plurality of droplets containing both said liquid and said volatile emulsion.

11. An apparatus as claimed in claim 8 , wherein the surface is shaped such that when the droplet initially impacts the target, the boundary of the contact patch between the droplet and the surface travels at a supersonic speed for a time period significantly beyond the initial moment of collision.

12. An apparatus as claimed in claim 8 , wherein the target surface comprises a plurality of discrete portions.

13. An apparatus as claimed in claim 8 , wherein the target surface is shaped such that there are a plurality of discrete initial contact points between the droplet and surface.

14. An apparatus as claimed in claim 13 , wherein the target surface comprises a plurality of protrusions to act as the plurality of discrete initial contact points.