High pressure soft lithography for micro-topographical patterning of molded polymers and composites

Patent metadata

Field	Value
Publication number	US-10899045-B2
Application number	US-201414206457-A
Country	US
Kind code	B2
Filing date	Mar 12, 2014
Priority date	Mar 12, 2013
Publication date	Jan 26, 2021
Grant date	Jan 26, 2021

Abstract

A soft lithography template or stamp is made by casting a polydimethysiloxane (PDMS) or other suitable elastomeric precursor onto a master pattern. The master pattern may be formed utilizing known micro-fabrication techniques. The PDMS template includes an inverse copy of the micro-structures on the master pattern, and can be placed into a mold used to prepare a carbon-fiber reinforced polymer composite part or other polymer molding systems where a matrix material passes through a fluid state during the cure process. The liquid resin material flows into the structures on the surface of the PDMS template and hardens during the curing cycle. After the part is released from the mold, the PDMS template can be peeled from the surface of the part to reveal the free standing micro structures which are a replica of the master pattern.

First claim

The invention claimed is:

1. A method of forming an outer surface of an aerodynamic or hydrodynamic structure including an object surface of a composite object, the method comprising;
forming a flexible template having a template surface comprising a plurality of surface features that are inverses of micro-structures to be formed on a surface of a composite material, wherein the flexible template comprises a plurality of casted pieces, and wherein dimensions of respective micro-structures are in a range up to about 100 microns;
positioning the plurality of casted pieces of the flexible template in a mold tool having curved surfaces such that the plurality of pieces engage concave and convex portions of the curved surfaces of the mold tool and are directly adjacent to one another, the plurality of casted pieces are un-affixed to the mold tool, and the template surface faces away from the curved surfaces;
flexing the plurality of casted pieces of the flexible template to conform to the curved surfaces of the mold tool;
covering at least a portion of the template surface with one or more layers of the composite material after flexing the flexible template such that the flexible template separates the composite material from the curved surfaces, wherein the composite material comprises a matrix material having a flowable state and fiber reinforcement;
positioning an impermeable envelope over the one or more layers of the composite material and the flexible template and subjecting the layers to a vacuum pressure;
heating the one or more layers of the composite material to a flow temperature and applying pressure to the one or more layers of the composite material to cause at least some of the matrix material to flow into the surface features of the template surface;
solidifying the matrix material to form the composite object having the object surface with defined micro-structures comprising protrusions that are inverses of the surface features of the template surface;
removing the composite object and the flexible template from the mold tool together; and
peeling the flexible template from the composite object to expose the object surface after removing the composite object and the flexible template from the mold tool together.

2. The method of claim 1 , wherein:
at least some of the surface features of the template surface comprise cavities or openings.

3. The method of claim 2 , wherein:
the protrusions are sized and positioned relative to one another in a manner that tends to reduce a contact area of fluids that are brought into contact with the object surface.

4. The method of claim 3 , wherein:
the protrusions on the object surface form a superhydrophobic surface whereby fluids are suspended over air trapped between the protrusions when a fluid comes into contact with the object surface.

5. The method of claim 2 , wherein:
the protrusions are generally columnar in shape.

6. The method of claim 2 , wherein:
the protrusions have an aspect ratio of about 1.0 to about 10.0.

7. The method of claim 6 , wherein:
the protrusions are spaced apart from each other about 1.0 microns to about 100 microns.

8. The method of claim 6 , wherein:
the protrusions have a variable cross sectional area.

9. The method of claim 2 , wherein:
the protrusions are spaced apart in rows to form a grid.

10. The method of claim 1 , including:
forming a planar master pattern defining micro-structures on a surface of the master pattern;
forming the template by casting an elastomeric material onto the master pattern.

11. The method of claim 10 , wherein:
pressure is applied to the composite material in a curing device or a pressure and/or temperature vessel.

12. The method of claim 1 , wherein:
the object surface comprises an aerodynamic surface that is, in use, exposed to airflow, and wherein the micro-structures of the object surface are configured to reduce aerodynamic or hydrodynamic drag and/or reduce adhesion of foreign matter.

13. The method of claim 1 , wherein:
at least some of the micro-structures of the object surface are configured to improve bond strength of an adhesive joint and define an average surface roughness in a range of about 100 nanometers to about 100 microns; and including:
providing a second component;
adhesively bonding the composite object to the second component by bringing at least a portion of the object surface and the second component into contact with an adhesive material;
wherein at least some of the micro-structures of the composite object surface are ridges and channels having tapered surfaces to provide a composite object dovetail structure, and where the second component has correspondingly shaped dovetail surfaces configured to interlock with the composite object dovetail structure, and wherein the corresponding dovetail surfaces on the composite object and the second component are brought into contact.

14. A method of forming an outer surface of an aerodynamic or hydrodynamic structure including an object surface having a plurality of micro-structures, the method comprising:
forming a flexible template having a plurality of microscopic cavities or openings, the flexible template comprising a plurality of casted pieces;
deforming the flexible template by positioning the flexible template in contact with a non-planar surface such that the plurality of casted pieces engage portions of curved surfaces of a mold tool and are directly adjacent to one another, the plurality of casted pieces are un-affixed to the non-planar surface, and the cavities or openings face away from the non-planar surface;
subjecting a material and the flexible template to a vacuum and heating the material to a flow temperature to cause it to flow into at least a portion of the cavities or openings while the flexible template is in contact with the non-planar surface, wherein the flexible template separates the material from the non-planer surface;
removing the material and the flexible template from the non-planar surface together;
disengaging the material from the template to form the object surface having the plurality of micro-structures including protrusions formed by the cavities or openings after removing the material and the flexible template from the non-planar surface together, wherein dimensions of respective micro-structures are in a range up to about 100 microns; and
wherein at least some of the micro-structures of the object surface are elongated ridges and elongated channels having tapered surfaces to provide a composite object dovetail structure and are configured to provide a mechanical bond of an adhesive joint.

15. The method of claim 14 , including:
applying pressure to the material to cause the material to flow into at least a portion of the cavities or openings.

16. The method of claim 15 , wherein:
the material is in a flowable state at a time that it flows into at least a portion of the cavities or openings; and including:
causing the material to cure prior to disengaging the material from the template.

17. The method of claim 16 , wherein;
the material comprises a polymer material forming a matrix of a fiber reinforced composite material; and wherein:
the material is cured utilizing heat.

18. The method of claim 14 , including:
forming a planar master surface having a plurality of protrusions; and wherein:
the flexible template is formed from an elastomeric material that is brought into contact with the planar master surface in a flowable form and cured.

19. The method of c

Assignees

• Nasa

Inventors

• Palmieri Frank L
• Cruz Vincent B
• Wohl Jr Christopher J

Classifications

• B29C33/38

  characterised by the material or the manufacturing process (B29C33/44 takes precedence) · CPC title

• B29C33/302

  Assembling a large number of mould elements to constitute one cavity · CPC title

• B29C33/405

  Elastomers, e.g. rubber (B29C33/50 takes precedence) · CPC title

• B29C33/3857 Primary

  by making impressions of one or more parts of models, e.g. shaped articles and including possible subsequent assembly of the parts · CPC title

• B29K2883/00

  Use of polymers having silicon, with or without sulfur, nitrogen, oxygen, or carbon only, in the main chain, as mould material · CPC title