Low-friction and low-adhesion materials and coatings
Disclosed are materials that possess both low adhesion and the ability to absorb water. The material passively absorbs water from the atmosphere and then expels this water upon impact with debris, to create a self-cleaning layer. The lubrication reduces friction and surface adhesion of the debris (such as an insect), which may then slide off the surface. The invention provides a material comprising a continuous matrix including a polymer having a low surface energy (less than 50 mJ/m 2 ) and a plurality of inclusions, dispersed within the matrix, each comprising a hygroscopic material. The continuous matrix and the inclusions form a lubricating surface layer in the presence of humidity. The material optionally contains porous nanostructures that inject water back onto the surface after an impact, absorbing water under pressure and then releasing water when the pressure is removed. The material may be a coating or a surface, for example.
1. A low-friction, low-adhesion material comprising:
a substantially continuous matrix including a low-surface-energy fluoropolymer having a surface energy between about 5 mJ/m 2 to about 50 mJ/m 2 ; and
a plurality of inclusions, dispersed within said matrix, each comprising a hygroscopic material,
wherein said low-surface-energy fluoropolymer and said hygroscopic material are covalently connected in a block copolymer, and
wherein said continuous matrix and said inclusions form a lubricating surface layer in the presence of 30% to 90% relative humidity,
wherein said material is characterized by a coefficient of friction, measured at 50% relative humidity, less than 0.9,
and wherein said material is characterized by a water absorption capacity of at least 5 wt % water based on total weight of said material.
2. The material of claim 1 , wherein said material is characterized by a water absorption capacity of at least 10 wt % water based on total weight of said material.
3. The material of claim 1 , wherein said surface energy of said fluoropolymer is between about 10 mJ/m 2 to about 40 mJ/m 2 .
4. The material of claim 1 , wherein said fluoropolymer is selected from the group consisting of perfluoroethers, fluoroacrylates, fluorosilicones, and combinations thereof.
5. The material of claim 1 , wherein said hygroscopic material is selected from the group consisting of poly(acrylic acid), poly(ethylene glycol), poly(2-hydroxyethyl methacrylate), poly(vinyl imidazole), poly(2-methyl-2-oxazoline), poly(2-ethyl-2-oxazoline), poly(vinylpyrolidone), cellulose, modified cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, hydrogels, PEG diacryalate, monoacrylate, and combinations thereof.
6. The material of claim 1 , said material further comprising a nanoporous material within at least some of said inclusions, wherein said nanopores have an average pore diameter less than 100 nanometers, and wherein said nanoporous material optionally comprises a hydrophobic component and/or optionally is surface-modified to increase hydrophobicity.
7. The material of claim 6 , wherein said nanoporous material is selected from the group consisting of silica, alumina, silicates, aluminosilicates, carbonates, carbon, and combinations thereof.
8. The material of claim 1 , wherein said material is hydrophobic.
9. The material of claim 1 , wherein said material is characterized by a coefficient of friction, measured at 85% relative humidity, less than 0.7.
10. The material of claim 1 , wherein said material is characterized by a delay in the formation of ice on a surface of said material.
11. The material of claim 1 , wherein said material is lipophobic.
12. The material of claim 1 , wherein said material is a coating.
13. The material of claim 1 , wherein said material is present at a surface of an object or region.