Synthetic Dry Adhesives

Abstract

A method of forming synthetic dry adhesives is provided that includes using a wedge-shaped tool to form mold cavities in a mold, filling the mold cavities with an elastomeric adhesive, removing the elastomeric adhesive from the mold, where a tapered lamellar ridge extends from a surface of the elastomeric adhesive, treating a tip of the extending ridge with a film of uncured elastomeric material, and curing the film of uncured material while the extending ridge is pressed against a substrate surface having a smoothness or texture. The synthetic dry adhesive comprises a close-packed array of tapered lamellar ridges, where the centerline of a ridge is angled relative to a direction normal to the synthetic dry adhesive and the cross section includes an internal taper. The tapered ridge bends when it contacts a surface, whereupon the radius of curvature of the ridge increases monotonically with increasing shear load.

1 . A method of forming synthetic dry adhesives, comprising:
 a. using a wedge-shaped tool to form mold cavities in a mold, wherein said mold cavities comprise a depth t and a spacing h;   b. filling said mold cavities with an elastomeric adhesive;   c. removing said elastomeric adhesive from said mold, wherein a tapered lamellar ridge extends from a surface of said elastomeric adhesive;   d. treating a tip of said extending tapered lamellar ridge with a film of uncured elastomeric material; and   e. curing said film of uncured material while said extending tapered lamellar ridge is pressed against a substrate surface.   
     
     
         2 . The method according to  claim 1 , wherein said mold comprises a homogeneous wax composition having a Young's modulus to yield stress ratio E/Y greater than 100. 
     
     
         3 . The method according to  claim 1 , wherein said wedge-shaped tool comprises at least a primary bevel. 
     
     
         4 . The method according to  claim 1 , wherein said wedge-shaped tool comprises a primary bevel, a secondary bevel and a tertiary bevel. 
     
     
         5 . The method according to  claim 1 , wherein said wedge-shaped tool comprises a lubricated surface. 
     
     
         6 . The method according to  claim 1 , wherein said wedge-shaped tool is moved along a 2-dimensional or 3-dimensional trajectory into said mold until a tip of said wedge-shaped tool reaches said depth t below a top surface of said mold. 
     
     
         7 . The method according to  claim 1 , wherein a trajectory of said tool is controlled to move displaced mold material in a desired direction, wherein said mold cavities are desirably spaced and a shape of said cavities is controlled. 
     
     
         8 . The method according to  claim 1 , wherein a centerline of said wedge-shaped tool is set at an angle λ with respect to a top surface of said mold, wherein a trajectory of said tool is at an intermediate angle θ with respect to a top surface of said mold, wherein said angle θ is in a range of 0<θ<λ. 
     
     
         9 . The method according to  claim 1 , wherein said elastomeric adhesive comprises an elastomer selected from the group consisting of silicones, polyurethanes, and polypropylene. 
     
     
         10 . The method according to  claim 1 , wherein treating a tip of said extending tapered lamellar ridge with a film of uncured elastomeric material comprises said uncured elastomeric material disposed on one or both sides of said lamellar ridge. 
     
     
         11 . The method according to  claim 1 , wherein said substrate surface comprises a smooth or textured surface, wherein said surface is disposed to transfer a desired smoothness or desired texture to a film of said uncured elastomeric material as said uncured elastomeric material cures. 
     
     
         12 . The method according to  claim 1 , wherein a siping step is used when said adhesive is de-molded, wherein said siping step comprises a cut perpendicular to said extending tapered lamellar ridge at a desired frequency to improve adhesion on textured surfaces having micro-scale roughness, wherein independent adhesive sections of said extending tapered lamellar ridge conform to said textured surface. 
     
     
         13 . A synthetic dry adhesive, comprising:
 a. a close-packed array of elastomeric adhesive wedge-shaped lamellar ridges, wherein a cross section of said close-packed array comprises a base of a leading edge of one said lamellar ridge contacting a base of a trailing edge of an adjacent said lamellar ridge, wherein said lamellar ridge comprises an internal taper spanning from a base of said lamellar ridge to a pointed tip of said lamellar ridge, wherein a centerline of said lamellar ridge is angled relative to a direction normal to said synthetic dry adhesive; and   b. a secondary elastomeric adhesive layer disposed on one or both sides of said wedge-shaped lamellar ridge, wherein said secondary layer comprises a textured or flat surface.   
     
     
         14 . The synthetic dry adhesive of  claim 13 , wherein said wedge-shaped lamellar ridge bends into a curve when it contacts a surface, whereupon the radius of curvature of said wedge-shaped lamellar ridge increases monotonically with increasing shear load. 
     
     
         15 . The synthetic dry adhesive of  claim 13 , wherein the tip-to-tip spacing between adjacent said lamellar ridges is as low as 6 μm. 
     
     
         16 . The synthetic dry adhesive of  claim 13 , wherein said angle of said centerline of said lamellar ridge is up to 50 degrees relative to said normal direction. 
     
     
         17 . The synthetic dry adhesive of  claim 13 , wherein both sides of said lamellar ridge is angled relative to said normal direction. 
     
     
         18 . The method according to  claim 13 , wherein said elastomeric adhesive comprises an elastomer selected from the group consisting of silicones, polyurethanes, and polypropylene. 
     
     
         19 . The synthetic dry adhesive of  claim 13 , wherein said tip of said wedge-shaped lamellar ridge comprises a film of cured elastomeric material having a desired smoothness or texture on one or both sides of said wedge-shaped lamellar ridge. 
     
     
         20 . The synthetic dry adhesive of  claim 14 , wherein said lamellar ridge comprises siping, wherein said siping is disposed across said wedge-shape lamellar ridge.