Modification of surface energy via direct laser ablative surface patterning

Abstract

Surface energy of a substrate is changed without the need for any template, mask, or additional coating medium applied to the substrate. At least one beam of energy directly ablates a substrate surface to form a predefined topographical pattern at the surface. Each beam of energy has a width of approximately 25 micrometers and an energy of approximately 1-500 microJoules. Features in the topographical pattern have a width of approximately 1-500 micrometers and a height of approximately 1.4-100 micrometers.

Claims

1. A method of changing the surface energy of a substrate to promote abhesion, the method comprising: directly ablating a completely uncovered surface of the substrate using at least one laser beam of energy to form a predefined topographical pattern at the surface, the at least one laser beam having a width of 25 micrometers and an energy of 1-200 microJoules; wherein directly ablating the completely uncovered surface of the substrate includes moving the at least one laser beam along a 0/90 crosshatch pattern such that the predefined topographical pattern includes an array of square pillars having a width of 10-250 micrometers and a height of 1.4-50 micrometers; wherein the directly ablating step renders the substrate hydrophobic without applying any template, mask, or additional coating medium to the substrate; and wherein the substrate is selected from the group consisting of metals, metal alloys, ceramics, polymers, fiber-reinforced composites thereof, and combinations thereof.

2. The method of claim 1, wherein the predefined topographical pattern has at least one property selected from the group consisting of anti-icing, de-icing, anti-insect adhesion, low friction, light modifying, and self-cleaning properties.

3. The method of claim 1, wherein: the predefined topographical pattern is characterized by a water contact angle at or above 90 and a sliding angle of less than 15, the sliding angle being an angle at which the substrate is tilted to induce rolling of an incident water droplet.

4. The method of claim 1, wherein: the step of directly ablating a completely uncovered surface of the substrate using at least one laser beam of energy to form a predefined topographical pattern at the surface comprises a multi-step process further including moving the at least one laser beam along second pattern comprising an orthogonal rotation of linear arrays.

5. A method of changing the surface energy of a substrate to promote abhesion, the method comprising: directly ablating a completely uncovered surface of a substrate using at least one laser beam of energy to form a predefined topographical pattern at the surface, the at least one laser beam of energy having a width of 25 micrometers and an energy of 3-175 microJoules; wherein directly ablating the uncovered surface of the substrate includes moving the at least one laser beam along a 0/90 crosshatch pattern such that the predefined topographical pattern includes an array of square pillars having a width of 15-100 micrometers and a height of 10-30 micrometers; and wherein the directly ablating step comprises controlling laser-ablation parameters selected from the group consisting of beam size, laser power, laser frequency, scan speed, number of pattern iterations, and combinations thereof, with the laser-ablation parameters controlled so that the laser ablation forms the predefined topographical pattern and thereby renders the substrate hydrophobic without applying any template, mask, or additional coating medium to the substrate.

6. The method of claim 5, having the pattern, wherein the predefined topographical pattern has at least one property selected from the group consisting of anti-icing, de-icing, anti-insect adhesion, low friction, light modifying, and self-cleaning properties.

7. The method of claim 6, wherein the substrate comprises one or more components selected from the group consisting of metals, metal alloys, ceramics, polymers, fiber-reinforced composites thereof, and any combinations thereof.

8. The method of claim 5, wherein: the substrate is composed of a metal alloy; and the metal alloy is at least one of Ti-6Al-4V and Al 6061.

9. The method of claim 5, wherein: the substrate is composed of a polymer; and the polymer is selected from a group consisting of polyimide, copoly(imidesiloxane), copoly(imide butadiene), copoly(imidebutadiene acrylonitrile), polycarbonate, poly(arylene ether), fluoropolymer, epoxy resins, and polyphenylene.

10. The method of claim 5, wherein the substrate is composed of a fiber-reinforced composite of T800H/3900-2.

11. The method of claim 5, wherein: the predefined topographical pattern is characterized by a water contact angle at or above 90 and a sliding angle of less than 15, the sliding angle being an angle at which the substrate is tilted to induce rolling of an incident water droplet.

12. A method of changing the surface energy of a substrate, the method comprising: directly ablating an uncovered surface of a substrate using at least one laser beam to form a predefined topographical pattern, including: etching a first series of parallel lines at a predefined line spacing; moving the at least one laser beam along the first series of parallel lines such that the predefined topographical pattern includes a linear array; wherein the uncovered surface of the substrate is rendered hydrophobic without any template, mask, or additional coating medium applied to the substrate; and wherein the predefined topographical pattern is characterized by a water contact angle at or above 90 and a sliding angle of less than 15, the sliding angle being an angle at which the substrate is tilted to induce rolling of an incident water droplet.

13. The method of claim 12, further comprising: etching another set of parallel lines with a 90 orientation to the first series of parallel lines with the predefined line spacing to create a 0/90 crosshatch pattern; and moving the at least one laser beam along the 0/90 crosshatch pattern such that the predefined topographical pattern includes an array of square pillars having a width of 1-100 micrometers and a height of 1.4-100 micrometers.

14. The method of claim 12, further comprising: etching another set of parallel lines with a 45 orientation to the first series of parallel lines with the predefined line spacing to create a 0/45 crosshatch pattern; and moving the at least one laser beam along the 0/45 crosshatch pattern to create the predefined topographical pattern.

15. The method of claim 12, wherein the at least one laser beam has a width of 25 micrometers and an energy of 3-175 microJoules.

16. The method of claim 12, wherein: the substrate is composed of a polymer; and the polymer is selected from a group consisting of polyimide, copoly(imide siloxane), copoly(imide butadiene), copoly(imidebutadiene acrylonitrile), polycarbonate, poly(arylene ether), fluoropolymer, epoxy resins, and polyphenylene.

17. The method of claim 12, wherein the predefined line spacing is 25 micrometers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a laser ablation set-up in accordance with the present invention;

(2) FIG. 2 is a perspective view of a substrate material illustrating a 0/90 laser-ablated crosshatch pattern in accordance with an embodiment of the present invention;

(3) FIG. 3 is a schematic view of a substrate and adhesive in accordance with the present invention;

(4) FIG. 4 is a schematic view of a substrate material illustrating a 0/45 laser-ablated crosshatch pattern in accordance with an embodiment of the present invention; and

(5) FIG. 5 depicts characterization results for surface treatment of various copoly(imide siloxane)s as described in Example 10.

DETAILED DESCRIPTION OF THE INVENTION

(6) The present invention pertains to a laser ablative method to controllably alter the surface energy of a material via direct topographical modification using specific geometric patterns. The word direct as used herein is used to describe modification of a substrate without the need or use of any template, mask, or additional coating medium being applied to the surface of the substrate. More specifically, the present invention precisely controls laser ablation parameters including but not limited to beam size, laser power, laser frequency, scan speed, and number of pattern iterations. This enables the generation of topographical features that influence the surface energy of the material, which in turn control adhesive and abhesive properties. Since laser ablation is a material dependent process, laser ablation parameters requisite for introduction of the desired material property (surface energy) will vary depending on the substrate utilized. This laser ablative method is useful in a variety of applications including but not limited to replacing of Pasa-Jell or other chemical treatments for titanium bonding, replacing of peel-ply treatments for carbon-fiber reinforced composite bonding, generating coatings or surfaces for anti-icing, de-icing, and anti-insect adhesion on aerospace vehicles, generating low friction coatings or surfaces, generating light-absorbing coatings or surfaces, and generating self-cleaning coatings or surfaces.

(7) This laser ablative method can be performed on metals, metal alloys, ceramics, polymers, and fiber reinforced metal, polymer, or ceramic composites or combinations thereof. Preferred materials include titanium and aluminum substrates, carbon fiber reinforced composite materials, and polymeric materials. The method is applicable to any polymeric material. Preferred materials include but are not limited to commodity or engineering plastics including but not limited to polycarbonate, polyacrylate, polyacrylonitrile, polyester, polyamide, polystyrene (including high impact strength polystyrene), polyurethane, polyurea, polyurethaneurea, epoxy resins, poly(acrylonitrile butadiene styrene), polyimide, polyarylate, poly(arylene ether), polyethylene, polypropylene, polyphenylene, polyphenylene sulfide, poly(vinyl ester), polyether ether ketone, polyvinyl chloride, poly(vinyl alcohol), bismaleimide polymer, polyanhydride, liquid crystalline polymer, cellulose polymer, fluorinated polymers, or any combination thereof. The method is also applicable to copolymers of the aforementioned polymeric materials and preferred copolymers are copoly(imide siloxane)s, copoly(imide butadiene)s, copoly(imide butadiene acrylonitrile)s. Many of these polymers are available from multiple, well-known commercial suppliers.

(8) The materials can be in a variety of forms such as foams, films, coatings, fibers, adhesives, molded or machined parts consisting of a single or multiple material compositions. The method can be used to modify surfaces during the original manufacture or to modify surfaces in the field as part of a remanufacturing or repair process.

(9) A simplified view of the approach used in the present invention is illustrated in FIG. 1. In this method, a substrate 10 to be laser-ablation-patterned is positioned in reference to the irradiation source such as a laser 12 that transmits a beam of energy 14 towards substrate 10. For the purposes of demonstrating the invention described herein, a frequency tripled (=355 nm, 7 W) Nd:YAG laser was utilized in a pulsed mode. However, any source of laser irradiation of sufficient energy to supersede the ablation threshold of the substrate material can be envisioned including but not limited to a CO.sub.2 laser source, an excimer laser source, a high power diode laser source, a Ti:Sapphire laser source, and different frequencies of a Nd:YAG laser source or a combination thereof. Although the Nd:YAG laser was operated in a pulsed mode, continuous wave laser irradiation can also be used to controllably alter the surface energy of an exposed material through topographical modification. For the purposes of pattern transcription, a galvanometrically driven beam scanner (not shown) was utilized to precisely and programmatically control the position and speed of the laser beam. Other embodiments for pattern transcription include but are not limited to programmatically-controlled movement of the substrate, manually-controlled movement of the laser, and manually-controlled movement of the substrate or any combination thereof.

(10) In general, a predefined pattern is transcribed on the substrate while controlling the beam size, laser power, laser frequency, scan speed, and number of pattern iterations. Preferred ablation patterns include 0/90 crosshatch patterns, 0/45 crosshatch patterns, linear array patterns, and orthogonal rotating linear arrays. Other patterns that can be envisioned include but are not limited to circular arrays, fractal geometries, triangular arrays, concentric patterns, diamond arrays, curved linear arrays, curved crosshatch patterns, and crosshatch patterns with other relative angles. FIG. 2 is an example of a 0/90 crosshatch pattern in which substrate 10 has its surface ablated to yield rectangular pillars 16 of width W and height H. Pillars 16 are separated by gaps 18 formed during laser ablation. Similarly, FIG. 4 schematically shows an example of a 0/45 crosshatch pattern transcribed on a substrate material.

(11) A variety of substrate materials were laser ablated in accordance with the method of the present invention. These examples are presented later herein. In some examples, laser ablation patterning resulted in the formation of adhesion promoting surfaces (i.e., surfaces with increased surface energy). Laser ablation patterning for adhesion promotion requires that the laser parameters be adjusted to transcribe topographical features within geometric constraints. The maximal spacing between ablation lines should be no greater than about 300 m. Similarly, an ablation depth of about 10 m or greater must be achieved. These surfaces will exhibit a water contact angle lower than the un-ablated surface and typically less than about 50 corresponding to surface energy values greater than about 49 milliJoules per meter squared (mJ/m.sup.2) as calculated by water contact angle measurement.

(12) In other examples, the use of laser ablation patterning resulted in low surface energy materials with abhesive properties. Laser ablation patterning for the lowering of surface energy and abhesion promotion also requires that the laser parameters be adjusted to transcribe topographical features within geometric constraints. The topographical features on surfaces engineered for abhesive applications should possess a minimal ablation depth of about 1.4 m. Ablation depth maxima will depend on the spacing of topographical features, the dimensions of the features, and the rigidity of the ablated material. For highly rigid materials possessing a flexural modulus of at least about 1.5 GPa, there will be no ablation depth maximum. For materials with low rigidity possessing a modulus equal to or less than about 1.5 GPa, an ablation depth maximum would be the maximum depth that would enable maintenance of the orientation of the topographical features (i.e., the features would not persist in an orientation different than the one in which they were generated). The spacing and dimensions of the topographical features will be dependent on the ablation depth. In some embodiments it is preferred that the surface topographical features not be spaced much further apart than the magnitude of the feature dimension multiplied by the ablation depth. Typical properties exhibited by abhesion promoting laser ablation patterned surfaces include increased water contact angle values relative to the un-ablated surface and typically greater than about 90 resulting in surface energy values less than about 18.2 mJ/m.sup.2. Similarly, for the purposes of generating superhydrophobic surfaces, the resultant geometry should generate a highly discontinuous three-phase contact line. These surfaces may exhibit contact angle hysteresis values (the difference in advancing and receding contact angles) less than about 30 and sliding angles (the angle at which the substrate is tilted to induce rolling of the incident water droplet) less than about 15.

(13) In some embodiments it may be desirable to have more than one laser treatment step. For example, an Nd:YAG laser may be used to produce a patterned surface. A secondary laser treatment, with the same or different laser, may be used to further treat the surface to create the desired surface patterns and properties. In other embodiments, it may be desirable to use multiple lasers to produce a surface pattern with hierarchical dimensional features (i.e., smaller features on top of larger features) as a means to generate desired surface properties.

(14) Articles incorporating materials with surfaces modified by the laser ablation methods described herein include articles such as, but not limited to, titanium and aluminum bonding specimens enabling the replacement of Pasa-Jell or other chemical treatments, carbon-fiber reinforced composite bonding specimens enabling the replacement of peel-ply treatments, and articles requiring anti-icing, de-icing, and anti-insect adhesion, low friction surfaces, light absorbing and/or scattering surfaces, and self-cleaning surfaces. These articles could also be a component of a larger assembly including but not limited to terrestrial and aerospace vehicles, solar panel assemblies, black body detectors, microelectronic components and the fabrication process thereof, dust-resistant articles, and moisture uptake resistant materials.

(15) In summary, the present invention discloses a method to controllably modify the surface energy of a material by generating topographical patterns via direct laser ablation. Depending on the laser parameters utilized, hydrophilic materials can be transformed into hydrophobic and superhydrophobic surfaces, or can be modified to exhibit increased hydrophilicity. Contrarily, hydrophobic materials can be modified to exhibit surface properties ranging from hydrophilic to superhydrophobic. The laser ablation patterning method is rapid, scalable, environmentally benign, precise, and can be performed directly on a wide variety of materials. The resultant articles of manufacture have surfaces that can be utilized for adhesive bonding, self-cleaning, particle adhesion mitigation, low friction surfaces, anti-icing, de-icing, and anti-insect adhesion applications, and light scattering devices such as black body instruments among other embodiments.

(16) Prior to describing specific examples fabricated using the method of the present invention, the general parameter constraints associated with some embodiments of the present invention will be presented. In one embodiment of the present invention, ablation is performed using one (or more) beams of energy having a beam width of approximately 25 micrometers and an energy of approximately 1-500 microJoules. The resulting features can have a width of approximately 1-500 micrometers and a height of approximately 1.4-100 micrometers. In another embodiment of the present invention, ablation is performed using one (or more) beams of energy having a beam width of approximately 25 micrometers and an energy of approximately 1-200 microJoules. The resulting features can have a width of approximately 10-250 micrometers and a height of approximately 1.4-50 micrometers. In still another embodiment of the present invention, ablation is performed using one (or more) beams of energy having a beam width of approximately 25 micrometers and an energy of approximately 3-175 microJoules. The resulting features can have a width of approximately 15-100 micrometers and a height of approximately 10-30 micrometers.

EXAMPLES

(17) Having generally described the invention, a more complete understanding thereof may be obtained by reference to the following examples that are provided for purposes of illustration only and do not limit the invention.

Example 1. Generation of Hydrophilic Titanium Ti-6Al-4V Surfaces

(18) The surface of titanium alloy (Ti-6Al-4V) lap shear specimens was modified by either grit-blasting, laser ablation patterning, or grit-blasting followed by laser ablation patterning. For laser ablation patterning an Nd:YAG laser (=355 nm) with a beam size of 25 m, operating at 6.3 W and 30 kHz (resulting in a pulse energy of 210 J) with a scan speed of 25.4 cm/s was used to transcribe a 0/90 crosshatch pattern using a single transcription step. The pattern was transcribed in the surface by first etching parallel lines in one direction. Next, parallel lines were drawn over the same sample space with a perpendicular orientation to the first series of lines at the same line spacing. The line spacing between features for each surface ablation treatment is indicated in Table 1. This ablation pattern created a square pillar array with a pillar width of 220 m and an average feature height of 20 m. The surface energy was determined using water contact angle values (Table 1). The treated titanium surfaces were subsequently coated with a primer or coupling agent consisting of imide oligomers with phenylethynyl pendant functionalities end-capped with trimethoxysilane groups following a procedure described by Park et al. in Polyimide-Silica Hybrids Using Novel Phenylethynyl Imide Silanes as Coupling Agents for Surface-Treated Alloy, International Journal of Adhesion and Adhesives, 20, 457-465 (2000). These samples were then bonded as described in Park et al. and the apparent shear strength was determined according to ASTM D1002-05 (Table 1).

(19) As seen in Table 1, laser ablation patterning resulted in a dramatic decrease in water contact angle, a dramatic increase in surface energy, and comparable, if not superior, apparent shear strength values relative to samples that were only grit-blasted. Thus, it is clear that the present invention affords a rapid, scalable, highly precise, reproducible method for surface energy modification for titanium.

(20) TABLE-US-00001 TABLE 1 Characterization results for surface treatment of titanium Ti6Al4V lap shear specimens as described in Example 1. Water Apparent Line Contact Surface Shear Surface Spacing Angle Energy Strength Treatment (m) () (mJ/m.sup.2) (MPa) Pristine N/A 74 29.6 N/A Surface Grit- N/A 91 17.6 29.3 0.9 Blasted Laser 102 2 72.7 30.2 0.9 Ablation Patterned Laser 254 2 72.7 18.4 0.6 Ablation Patterned Laser 406 2 72.7 15.5 1.5 Ablation Patterned Grit- 254 2 72.7 29.6 0.6 Blasted and Laser Ablation Patterned

Example 2. Generation of a Hydrophilic Aluminum 6061 Surface

(21) An aluminum coupon (Al 6061) was exposed to the same laser ablation conditions as described in Example 1 except the laser scan rate was 12.7 cm/s, and the line spacing for the crosshatch pattern was 25 m. This ablation pattern created a square pillar array with pillar width of 22 m on the treated surface with an average feature height of 18 m. The surface energy was determined using water contact angle values. A pristine Al 6061 surface exhibited a water contact angle value of 98 corresponding to a surface energy of 13.5 mJ/m.sup.2. The laser ablation patterned surface exhibited a water contact angle of 2.0 corresponding to a surface energy of 72.7 mJ/m.sup.2.

Example 3. Generation of a Hydrophobic Aluminum 6061 Surface

(22) An aluminum coupon (Al 6061) was modified by laser ablation patterning with an Nd:YAG laser (=355 nm) with a beam size of 25 m, operating at 6.3 W and 80 kHz (resulting in a pulse energy of 78.8 J) with a scan speed of 25.4 cm/s. A 0/90 crosshatch pattern with a line spacing of 25 m was transcribed four times. This ablation pattern created a square pillar array with pillar widths of 22 m and an average feature height of 15 m. The surface energy was determined using water contact angle values. A pristine Al 6061 surface exhibited a water contact angle of 102 corresponding to a surface energy of 11.4 mJ/m.sup.2. The laser ablation patterned surface exhibited a water contact angle of 108 corresponding to a surface energy of 8.7 mJ/m.sup.2.

Example 4. Generation of Hydrophilic Carbon Fiber Reinforced Composite Surfaces

(23) Carbon fiber reinforced composite specimens (16 plies of unidirectional Torayca P2302-19 prepreg, a T800H/3900-2 carbon fiber-toughened epoxy system) were modified by grit-blasting, wet-peel ply (material), dry peel ply (material), and laser ablation patterning. Two different laser ablation patterns were utilized. Pattern A was a 0/90 crosshatch while Pattern B was created to replicate that of a peel ply treated surface and consisted of an orthogonal rotation of linear arrays with line widths of 25 m and linear arrays consisting of 15 lines with a line spacing of 200 m. Each linear array, 0.3 cm in length and width, was oriented at 90 to the surrounding linear arrays. For laser ablation patterning, an Nd:YAG laser (=355 nm) with a beam size of 25 m, a line spacing of 25 m, and a scan speed of 25.4 cm/s was used. These patterns were transcribed into the surface using a single transcription step. Laser power and frequency were varied as indicated in Table 2. The surface energy was determined using water contact angle values (Table 2).

(24) The treated composite surfaces were subsequently bonded with AF-555M adhesive (available commercially from the 3M Company) according to the manufacturer's specifications and the apparent shear strength was determined using a slight modification of ASTM D3165-00 regarding how the bonded test specimens were gripped (Table 2).

(25) As seen in Table 2, laser ablation patterning dramatically reduced the water contact angle and increased the surface energy. Also, the apparent shear strength of the laser ablation patterned specimens is comparable, if not superior, to values obtained with other surface preparation techniques. This approach affords a rapid, scalable, highly precise, reproducible method for surface treatment of carbon fiber reinforced composites and eliminates contamination sources for bonded areas compared to peel-ply surface treatments.

(26) TABLE-US-00002 TABLE 2 Characterization results for surface treatment of carbon fiber reinforced composite specimens as described in Example 4. Laser Power (W)/ Water Apparent Frequency Contact Surface Shear Surface (kHz)/Pulse Angle Energy Strength Treatment Energy (J) () (mJ/m.sup.2) (MPa) Pristine N/A 79 25.8 23.9 1.2 Grit- N/A 86 20.8 25.1 1.0 Blasting Wet Peel N/A 76 28.1 25.5 0.7 Ply Dry Peel N/A 83 22.9 26.7 1.7 Ply Pattern A 5.6/40/140 2 72.7 27.4 1.3 Pattern A 5.6/60/93.3 14 70.6 27.6 0.9 Pattern A 6.3/30.sup.a/210 2 72.7 26.4 0.6 Pattern B 5.6/40/140 26 65.6 26.7 0.7 .sup.aThe crosshatch pattern line spacing was 50 m.

Example 5. Generation of a Hydrophobic Carbon Fiber Reinforced Composite Surface

(27) Carbon fiber reinforced composite specimens (16 plies of unidirectional Torayca P2302-19 prepreg, a T800H/3900-2 carbon fiber-toughened epoxy system) were modified via laser ablation patterning using Patterns A and B from Example 4 with the same laser ablation parameters except the laser power was 4.9 W operating at 60 kHz (resulting in a pulse energy of 81.7 J).

(28) The surface energy was determined using water contact angle values. Pristine carbon fiber reinforced composite surfaces exhibited a water contact angle of 79 corresponding to a surface energy of 25.8 mJ/m.sup.2. The laser ablation patterned surfaces exhibited water contact angles of 100 and 101 corresponding to surface energies of 12.4 mJ/m.sup.2 and 11.9 mJ/m.sup.2 for Patterns A and B, respectively.

Example 6. Generation of a Hydrophilic Polymer Surface

(29) The surface of a polyphenylene material (Primospire PR250, Solvay Advanced Polymers) was modified by laser ablation patterning similar to Example 3 except the laser was operated at 5.6 W and 80 kHz (resulting in a pulse energy of 70 J). This ablation pattern created a square pillar array with pillar widths of 15 m on the treated surface and an average feature height of 10 m.

(30) The surface energy was determined using water contact angle values. Pristine Primospire PR250 exhibited a water contact angle of 87 corresponding to a surface energy of 20.1 mJ/m.sup.2. The laser ablation patterned surface exhibited a water contact angle of 46 corresponding to a surface energy of 52.2 mJ/m.sup.2.

Example 7. Generation of a Hydrophobic Polymer Surfaces

(31) Kapton HN polyimide film specimens (available commercially from DuPont de Nemours Co.) were modified by laser ablation patterning in a manner similar to Example 3 except the laser was operated at power settings and transcription steps as indicated in Table 3. This ablation pattern created a square pillar array with pillar widths of 25 m and average feature heights as indicated in Table 3. The surface energy was determined using water contact angle values and is indicated in Table 3.

(32) TABLE-US-00003 TABLE 3 Characterization results for surface treatment of Kapton HN specimens as described in Example 7. Water Laser Power Number of Contact Surface Surface (W)/Pulse Pattern Angle Energy Feature Energy (J) Transcriptions () (mJ/m.sup.2) Height (m) Pristine Surface 81 24.3 N/A 4.9/61.3 1 83 22.9 1.4 4.9/61.3 2 82 23.6 2.2 4.9/61.3 4 92 16.9 4.1 5.1/63.8 1 83 22.9 3.5 5.1/63.8 2 91 17.6 4.4 5.1/63.8 4 98 13.5 12.5 5.3/66.3 1 85 21.5 5.9 5.3/66.3 2 89 18.8 6.5 5.3/66.3 4 108 8.7 8.5

Example 8. Generation of Hydrophobic Polymer Surfaces from Commercial Source Materials

(33) Film specimens from several commercial sources including: APEC 2097 (Bayer Materials Science, LLC), Teflon (DuPont de Nemours Co.), and a crystalline PEEK film (Ajedium Films Croup, LLC.) were modified by laser ablation patterning in a manner similar to Example 3 except the laser was operated at power settings as indicated in Table 4. The surface energy was determined using water contact angle values and is indicated in Table 4.

(34) TABLE-US-00004 TABLE 4 Characterization results for surface treatment of commercial materials as described in example 8. Water Laser Power Contact Surface (W)/Pulse Angle Energy Material Energy (J) () (mJ/m.sup.2) APEC 2097 Pristine 93 16.3 Surface APEC 2097 5.3/66.3 95 15.2 APEC 2097 5.6/70 102 11.4 Teflon Pristine 109 8.3 Surface Teflon 5.3/66.3 109 8.3 Teflon 5.6/70 120 4.5 Teflon 6.3/78.8 121 4.3 PEEK Pristine 85 21.5 Surface PEEK 5.3/66.3 96 14.6 PEEK 5.6/70 88 19.5

Example 9. Generation of a Hydrophobic Copoly(Imide Siloxane) Surface

(35) Copoly(imide siloxane) specimens were generated from the condensation reaction of an aromatic dianhydride (2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 6FDA) with a mixture of an aromatic diamine (4,4-oxydianiline, 4,4-ODA) and an amine-terminated polydimethyl siloxane (DMS-A21, Gelest, 10 wt. %). Reactions were carried out under nitrogen using a 1:1 ratio of dianhydride and diamine (20 wt. % solids) in a 4:1 mixture of N-methylpyrrolidinone (NMP) and tetrahydrofuran (THF). The diamine was dissolved in NMP, to which a THF solution of DMS-A21 was added, followed by the dianhydride and additional NMP. The reaction mixture was mechanically stirred overnight. Films were cast on a Teflon coated surface or polished stainless steel using a doctor's blade and placed in a forced air drying chamber until tack-free. Films were then thermally imidized under nitrogen using a cure cycle with stages at 150, 175, 200, and 250 C.

(36) Film specimens were modified by laser ablation patterning in a manner similar to Example 3 except the laser was operated at power and frequency settings as indicated in Table 5. This ablation pattern created a square pillar array with pillar widths and average feature heights indicated in Table 5. The surface energy was determined using water contact angle values and is indicated in Table 5.

(37) TABLE-US-00005 TABLE 5 Characterization results for surface treatment of copoly(imide siloxane), 6FDA:4,4-ODA: DMS-A21 (5 wt. %) as described in Example 9. Surface Laser Power Number of Water Surface Feature (W)/Pulse Pattern Contact Energy Height Energy (J) Transcriptions Angle () (mJ/m.sup.2) ( m) Pristine Surface 112 7.1 N/A 4.9/61.3 1 132 2.0 1.5 4.9/61.3 2 134 1.7 1.8 4.9/61.3 4 139 1.1 1.9 5.1/63.8 1 139 1.1 3.6 5.1/63.8 2 143 0.7 6.0 5.1/63.8 4 149 0.4 9.1 5.3/66.3 1 142 0.8 7.2 5.3/66.3 2 151 0.3 10.5

Example 10. Generation of a Superhydrophobic Copoly(Imide Siloxane) Surface

(38) Copoly(imide siloxane) specimens were generated from the same condensation reaction described in Example 9 except the aromatic dianhydride used was either 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 6FDA, or 4,4-oxydiphthalic anhydride, ODPA and the aromatic diamine was: 3,4-oxydianiline, 3,4-ODA; 4,4-oxydianiline, 4,4-ODA; 1,3-bis(3-aminophenoxy) benzene, 1,3-APB; or 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane, 4-BDAF. Specific monomer combinations are indicated in Table 6. The DMS-A21 weight percent was also varied as indicated in Table 6. Film specimens were modified by laser ablation patterning in a manner similar to Example 3 except the laser was operated at 5.25 W (resulting in a pulse energy of 65.6 J).

(39) The surface energy was determined using water contact angle values and is indicated in Table 6. Advancing and receding contact angle measurements and sliding angle measurements were made by tilting axis water contact angle measurements.

(40) TABLE-US-00006 TABLE 6 Characterization results for surface treatment of various copoly(imide siloxane)s as described in Example 10. Laser Ablation Patterned Surface Pristine Surface Surface DMS-A21 Surface Feature Surface Material Content .sub.adv Energy Sliding Height .sub.adv Energy Sliding Composition (wt. %) (.sub.reg), (mJ/m.sup.2) Angle (m) (.sub.reg), (mJ/m.sup.2) Angle 6FDA: 4,4-ODA 5 112 7.1 43 11.3 167 0.01 10 (88) (140) 6FDA: 4,4-ODA 10 102 11.4 31 16.5 163 0.03 10 (80) (154) 6FDA: 4,4-ODA 20 113 6.8 >60 13.0 171 0.002 2 (95) (164) 6FDA: 3,4-ODA 10 115 6.1 27 18.3 170 0.004 2 (90) (159)

Example 11. Generation of a Superhydrophobic Copoly(Imide Butadiene) Surface

(41) Copoly(imide butadiene) specimens were generated from the condensation reaction of an aromatic dianhydride (2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 6FDA) with a mixture of an aromatic diamine (1,3-bis(3-aminophenoxy) benzene, 1,3-APB) and an amine-terminated polybutadiene (generated by the reaction of hydroxyl-terminated polybutadiene with p-nitrobenzoyl chloride and the subsequent reduction of the nitro functionalities using tin chloride dihydrate). Reactions were carried out under nitrogen using a 1:1 ratio of dianhydride and diamine (20 wt. % solids) in a 4:1 mixture of N-methylpyrrolidinone (NMP) and toluene. The diamine was dissolved in NMP, to which a toluene solution of amine-terminated polybutadiene was added, followed by the dianhydride and additional NMP. The reaction mixture was mechanically stirred overnight. Films were cast on glass plates using a doctor's blade and placed in a forced air drying chamber until tack-free. Films were then thermally imidized under nitrogen using a cure cycle with stages at 150, 175, 200, and 250 C. Film specimens were modified by laser ablation patterning in a manner similar to Example 10.

(42) The surface energy was determined using water contact angle values. Pristine copoly(imide butadiene) exhibited a water contact angle of 83 corresponding to a surface energy of 22.9 mJ/m.sup.2. The laser ablation patterned surface exhibited a water contact angle of 175 corresponding to a surface energy of 0.0003 mJ/m.sup.2. The surface also exhibited a contact angle hysteresis of 9.5 and a sliding angle of 3.

Example 12. Generation of a Superhydrophobic Copoly(Imide Butadiene Acrylonitrile) Surface

(43) Copoly(imide butadiene acrylonitrile) specimens were generated from the condensation reaction of an aromatic dianhydride (2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 6FDA) with a mixture of an aromatic diamine (3,4-oxydianiline, 3,4-ODA) and an amine-terminated copoly(butadiene acrylonitrile) (Polysciences Inc., Product No. 09753). Reactions were carried out under nitrogen using a 1:1 ratio of dianhydride and diamine (20 wt. % solids) in a 4:1 mixture of N-methylpyrrolidinone (NMP) and toluene. The diamine was dissolved in NMP, to which a toluene solution of amine-terminated copoly(butadiene acrylonitrile) was added, followed by the dianhydride and additional NMP. The reaction mixture was mechanically stirred overnight. Films were cast on glass plates using a doctor's blade and placed in a forced air drying chamber until tack-free. Films were then thermally imidized under nitrogen using a cure cycle with stages at 150, 175, 200, and 250 C. Film specimens were modified by laser ablation patterning in a manner similar to Example 10.

(44) The surface energy was determined using water contact angle values. Pristine copoly(imide butadiene acrylonitrile) exhibited a water contact angle of 86 corresponding to a surface energy of 20.8 mJ/m.sup.2. The laser ablation patterned surface exhibited a water contact angle of 173 corresponding to a surface energy of 0.001 mJ/m.sup.2. The surface also exhibited a contact angle hysteresis of 20.8 and a sliding angle of 7.

(45) The examples provided herein serve to demonstrate the nature of this invention, which is a method to controllably modify the surface energy of a variety of materials by the generation of topographical patterns of specific dimensional sizes and geometric shapes via direct laser ablation. The examples demonstrate that depending on the laser parameters utilized, hydrophilic materials can be rendered more hydrophilic, hydrophobic or superhydrophobic, and hydrophobic materials can be modified to exhibit hydrophilic, more hydrophobic or superhydrophobic surface properties. The laser ablation patterning method is rapid, scalable, environmentally benign, precise, and can be performed on a wide variety of materials. The resultant surfaces can be utilized for adhesive bonding, self-cleaning, particle adhesion mitigation, low friction surfaces, and anti-icing surfaces to name a few.

(46) Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.