SURFACE MICROSTRUCTURES

Abstract

A method of manufacturing and a surface microstructure that includes a surface; and a plurality of protrusions on the surface, where each of the protrusions has a width that changes along its length, where the protrusions are all oriented in substantially the same direction; and where the protrusions each have a length between 10 and 1000 μm and a maximum width between 5 and 100 μm.

Claims

1-25. (canceled)

26. A surface microstructure, the surface microstructure comprising: a surface; and a plurality of protrusions on the surface, wherein each of the protrusions has a width that changes along its length, wherein the protrusions are all oriented in substantially the same direction; and wherein the protrusions each have a length between 10 and 1000 μm and a maximum width between 5 and 100 μm.

27. The surface microstructure according to claim 26, wherein the surface microstructure has improved self-cleaning properties compared to the same surface without the protrusions.

28. The surface microstructure according to claim 26, wherein each protrusion is connected to the surface along its entire length.

29. The surface microstructure according to claim 26, wherein the protrusion decreases in width along its length to a point at one end of the protrusion, wherein each protrusion is triangular.

30. The surface microstructure according to claim 26, wherein the maximum width of each protrusion is between 9 to 45 μm, and/or the length of each protrusion is between 45 μm to 225 μm.

31. The surface microstructure according to claim 26, wherein the protrusions are all be substantially identical.

32. The surface microstructure according to claim 26, wherein the surface microstructure is hydrophobic.

33. The surface microstructure according to claim 26, wherein over 50% of the surface is covered by the protrusions.

34. The surface microstructure according to claim 26, wherein the surface microstructure is coated with a reflector so as to provide a structural colour to the surface microstructure.

35. The surface microstructure according to claim 26, wherein the surface is a fiber, and wherein the protrusions have been formed by cutting grooves into the surface of the fibre.

36. An article comprising the surface microstructure of claim 26.

37. The article according to claim 36, wherein the surface microstructure is a first surface microstructure provided on a first region of the article and wherein the article comprises a second region with a second surface microstructure, wherein the first and second microstructures have different properties.

38. A method of manufacturing a surface microstructure, the method comprising: providing a surface; and providing a plurality of protrusions on the surface, wherein each of the protrusions has a width that changes along its length, wherein the protrusions are all oriented in substantially the same direction; and wherein the protrusions each have a length between 10 and 1000 μm and a maximum width between 5 and 100 μm.

39. The method according to claim 38, wherein the protrusions are formed by at least one of stamping, moulding, 3D-printing, or a self-assembly technique.

40. The method according to claim 39, wherein the self-assembly technique is self-assembly of the protrusions in a drying liquid, wherein the liquid is manipulated to self-form the protrusions by including structures into the liquid, and wherein each structure causes one protrusion.

41. The surface microstructure according to claim 26, wherein each protrusion has a length to maximum width ratio between 1:0.08 and 1:0.33.

42. The surface microstructure according to claim 26, wherein a height of each protrusion is between 15 and 75 μm.

43. The surface microstructure according to claim 26, wherein a distance between each protrusion at its base is substantially the same as a width of the protrusions and/or a distance between each protrusion at its tip end is between 1 and 200 μm.

44. The surface microstructure according to claim 26, wherein the protrusions are in rows, and wherein each row is separated by a gap between 1 and 100 μm.

45. The surface microstructure according to claim 26, wherein a material of the protrusions is different to that of the surface.

Description

[0097] Certain preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0098] FIG. 1 shows a plan view of a surface microstructure;

[0099] FIG. 2 shows a side view of the surface microstructure;

[0100] FIG. 3 shows a perspective view of the surface microstructure;

[0101] FIG. 4 shows a plan view of a self-assembling surface microstructure;

[0102] FIG. 5 shows a side view of the self-assembling surface microstructure;

[0103] and

[0104] FIG. 6 shows a side view of a surface microstructure formed in a fibre.

[0105] FIGS. 1, 2 and 3 show a surface microstructure 1 with a plurality of protrusions 2, i.e. raised elements, on a surface 4.

[0106] The protrusions 2 each decrease in width along their length and in this particular embodiment are each triangular.

[0107] The protrusions 2 are all oriented in substantially the same direction, i.e. their longitudinal axes are all substantially parallel.

[0108] The protrusions 2 each have a length (I) between 10 and 1000 μm and a maximum width (w) between 5 and 100 μm.

[0109] In this embodiment the protrusions 2 are ordered and in a number of parallel rows.

[0110] The distance between each protrusion 2 in a row may be between 1 and 200 μm. For example the distance between each protrusion 2 at its widest end (bs), i.e. its base end, may be between 1 and 100 μm.

[0111] The distance between each protrusion 2 at its narrowest end (ts), i.e. its tip end, may be between 1 and 200 μm.

[0112] The rows may be separated by a gap (rs) that is between 1 to 100 μm, i.e. the distance between the end of the protrusions 2 in one row and the start of the protrusions in the next row may be between 1 and 100 μm.

[0113] These protrusions 2 have the effect of improving the self-cleaning (e.g. mud and/or water shedding) properties of the surface compared to a surface without such protrusions but that is otherwise identical.

[0114] These protrusions 2 may be formed by any known method such as stamping, moulding, photolithography and/or 3D printing.

[0115] FIGS. 4 and 5 show a surface microstructure 1′ where the protrusions 2′ are formed from a self-assembly method.

[0116] This may be achieved through self-assembly in a drying viscous liquid such as paint, varnish or lacquer. Drops, i.e. protrusions 2′, may form as the liquid dries. This may be caused by the liquid slowly running down the surface as it dries due to gravity. As the liquid dries, the surface may be oriented so that it has a component that is at least parallel to the direction of gravity such that all of the protrusions 2′ extend in substantially the same direction.

[0117] As the liquid runs down the surface 4′ the tip of the drops (i.e. protrusions 2′) may become increasingly smaller until the drops halt. The wake of each drop takes the form of a raised, elongated isosceles triangle.

[0118] The liquid is manipulated to self-form the protrusions 2′ by including structures 6 into the liquid (e.g. microspheres), where each structure causes one drop/protrusion. The structures may be sized to cause the protrusions 2′ to each have a length between 10 and 1000 μm and a maximum width between 5 and 100 μm.

[0119] FIG. 6 shows a surface microstructure 1″ in which the protrusions 2″ are formed by cutting grooves 8 into the surface of a fibre 4″.

[0120] The surface of the microstructure 1″ in this case is a fiber 4″.

Experimental Results

[0121] Substrates made of silicon 0.7 mm thick, <100> orientated, doping unknown were tested with regard to their mud shedding properties. The microstructures had been formed using photolithography.

[0122] A first group, the (A) group, was coated with an evaporated chemical FDTS to make them hydrophobic.

[0123] A second group, the (B) group, had no coating so had a surface SiO.sub.2 layer which is naturally hydrophilic.

[0124] In each group (A and B) five different samples were tested (i.e. 10 samples in total). This was a smooth, i.e. microstructure-less unstructured, reference sample referred to as samples A0 and B0, and four microstructures sampled having a surface microstructure as shown in FIGS. 1, 2 and 3, wherein the first (samples A1 and B1) had triangular protrusions in ordered rows on a flat substrate each protrusion having a length (l) of 45 μm, a maximum width (w) of 9 μm, a height (h) of 15 μm, a base separation (bs) of 9 μm, a tip separation (ts) of 18 μm and a row separation (rs) of 3 μm. The second microstructured surface (A2 and B2) had an identical microstructure except all of the dimensions are twice the size, i.e. 2×. The third microstructured surface (A3 and B3) had an identical microstructure except all of the dimensions are 3×. The fourth microstructured surface (A5 and B5) had an identical microstructure except all of the dimensions are 5×.

[0125] Each substrate was tested with sand, dry soil (i.e. dry mud) and wet soil (i.e. wet mud). For the sand and dry soil, if any particles stuck to the surface, the surface was banged a few times to see if the particles dislodged and for the wet soil, if it stuck to the surface, a water wash (using a syringe) was used to see if it washed off easily.

[0126] Sand and Dry Mud Testing:

[0127] 1) For all the hydrophobic (A samples), no mud/sand particles stuck to any of the surfaces including the reference surface.

[0128] 2) This was not the case for the hydrophilic (B samples):

[0129] B0 (reference surface): mud and sand particles stuck to this surface.

[0130] B1 (1×): this structure performed better than B0; less particles stuck and when banged a few times, many of the particles dislodged.

[0131] B2 (2×): This performed better than B1 and B0 with regards dry mud, with no particles sticking to the surface. However, it performed worse than B1 and B0 on sand with more particles sticking to its surface.

[0132] B3 (3×): this performed better with mud than B1 and B0.

[0133] With regards sand, B3 performed better than all the other surfaces (but one stubborn sand particle stuck to surface).

[0134] B5 (5×): Some sand particles stuck to this surface but were easily dislodged upon tapping. No mud particles stuck to this surface and was found to be the best performer all round for the hydrophilic samples.

[0135] Wet Mud Testing:

[0136] 1) For the hydrophobic (A samples), wet mud stuck only to the micro-structure-less reference sample (A0) but was easily washed off its surface. For all the other A surfaces, no wet mud stuck and so no wash was required.

[0137] 2) For the hydrophilic (B samples), all performed poorly with wet mud easily sticking to all the surfaces but mud washing off each easily using water from a syringe lightly squirted onto each surface

[0138] These results are summarised in the below tables.

TABLE-US-00001 Hydrophobic structures (A) Sand Dry soil Wet soil Unstructured ✓ ✓ X (A0) No particles No particles Wet mud stuck but was stuck stuck easily washed off 1x ✓ ✓ ✓ (A1) No particles No particles no wet mud stuck stuck stuck 2x ✓ ✓ ✓ (A2) No particles No particles no wet mud stuck stuck stuck 3x ✓ ✓ ✓ (A3) No particles No particles no wet mud stuck stuck stuck 5x ✓ ✓ ✓ (A5) No particles No particles no wet mud stuck stuck stuck

TABLE-US-00002 Hydrophillic structures (B) Dry soil Wet soil Sand (i.e. dry mud) (i.e. wet soil) Unstructured X X X (B0) particles stuck Particles stuck wet mud stuck but was washed off easily using water from a syringe lightly squirted onto each surface 1x ✓ ✓ X (B1) Fewer particles Fewer particles wet mud stuck stuck than stuck than but was washed B0 and many B0 and many off easily using dislodged when dislodged when water from a the structure was the structure was syringe lightly banged a few times banged a few times squirted onto each surface 2x X ✓ X (B2) performed worse performed better wet mud stuck than B1 and B0 on than B1 and B0 but was washed sand with more with no particles off easily using particles sticking sticking to the water from a to its surface surface syringe lightly squirted onto each surface 3x ✓ ✓ X (B3) performed better (performed better wet mud stuck than all the other than B1 and B0 but was washed surfaces (but one with no particles off easily using stubborn sand sticking to the water from a particle stuck surface syringe lightly to surface) squirted onto each surface 5x ✓ ✓ X (B5) Some sand particles No mud particles wet mud stuck stuck to this stuck to this but was washed surface but wer surface off easily using easily dislodged water from a upon tapping syringe lightly squirted onto each surface

[0139] The samples were also tested with regard to their effect on water. When water droplets were dropped onto the hydrophobic samples (A samples), the droplet beads sat on the surfaces. However for the A0 sample (unstructured reference samples) the water spread a little and even though water ran off the surface easily, traces of a water trail could be seen. This was not the case for the other structured A samples on which the water drop spread less than the A0 sample and did not leave a water trail.

[0140] For the hydrophilic B samples, the water run-off was tested and with regards to the microstructured samples it was found that water ran-off much easier either when running down parallel to the direction of the protrusions but not across the structures (i.e. perpendicular to the longitudinal axis of the protrusions) whereby the water stuck and often did not move across the surface.