# Patent

## Title
Climbing devices based on thermo-reversible dry adhesives

## Abstract

One embodiment of the invention includes an application of multilayer thermo-reversible dry adhesives in climbing devices.

## Background
This application claims the benefit of U.S. Provisional Application No. 60/925,418, filed Apr. 20, 2007.


FIELD OF THE INVENTION
The field to which the disclosure generally relates includes climbing devices utilizing thermo-reversible dry adhesives.
BACKGROUND
Gecko feet pads, with nanohair structures on them, are examples of smart dry adhesives. The working principle of the Gecko adhesion is that the nanohair structure allows the foot pad to make maximum contact with a counter surface regardless of its roughness and chemical composition. This is accomplished by nanohairs that are relatively long and protruding from the foot pad at an angle so that adjacent nanohairs can contact the counter surface regardless of its topography. The maximum contact further allows for accumulation of millions of small van der Waals (in the range of microNewtons) interactions between the Gecko foot pad and the counter surface, leading to an overall adhesion force (pull-off force) of about 10 N/cm2. When the detaching force is employed in a peel-off mode, however, the complete detachment is achieved gradually by overcoming small adhesion forces corresponding to very small areas. Thus, the adhesion is easily reversed. Overall, the attractiveness of the Gecko adhesion lies in the combination of adhesive strength (10 N/cm2), reversibility, and the ability to adapt to a variety of surfaces in terms of both the surface roughness and composition. The above unique features of the Gecko adhesion has stimulated scientific research efforts to produce synthetic smart dry adhesives that work using the same principle as the Gecko feet. Up to now, the two best synthetic Gecko adhesives show maximum pull-off force of 3 and 10 N/cm2, respectively. Both adhesives suffer from severe adhesion loss after only one or two attaching/detaching cycles, as a result of breakdown of the nano structures. Often this occurs when adjacent elongated structures simulating the nano hairs of the Gecko foot pad bond to each other. In addition, synthetic Gecko adhesives are expensive to produce and large-scale manufacturing is practically too difficult.
SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION
One embodiment of the invention includes an application of multilayer thermo-reversible dry adhesives in climbing devices.
Other exemplary embodiments of the invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.



BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1A illustrates a method according to one embodiment.
FIG. 1B illustrates a method according to one embodiment.
FIG. 1C illustrates a method according to one embodiment.
FIG. 1D illustrates a method according to one embodiment.
FIG. 2 illustrates a method according to one embodiment.



DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The following description of the embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
One embodiment of the invention includes a moving or climbing device with a thermo-reversible dry adhesive thereon. In one embodiment, the moving or climbing device may use more than one movable limb, for example arms or legs. In various embodiments, the thermo-reversible dry adhesive may comprise a dry adhesive layer and a shape memory polymer (SMP) layer.
Referring to FIGS. 1A-1D, one embodiment includes a method of moving or climbing of a device 10 with a thermo-reversible dry adhesive thereon. In one embodiment, the device may have a first limb 18, a second limb 20, a third limb 22, and a fourth limb 24. The limbs may be, for example, arms or legs. Each arm or leg includes the thermo-reversible dry adhesive comprising a SMP layer 12 and a dry adhesive layer 14. A means for heating and/or cooling the thermo-reversible dry adhesive may be provided on the climbing device such as, but not limited to, a heating wire, a cooling wire, or a Peltier device. In one embodiment, to attach the leg 18, 20, 22, or 24 to a target counter surface 16, for example but not limited to a wall, the dry adhesive 14 is heated to the glass transition temperature of the SMP by brief electrical current through the heating wire. Then the adhesive is brought into contact with the wall 16. The adhesive is then cooled by natural cooling or using the cooling wire or a Peltier device to form a strong bond with the wall. The strong adhesion between the wall 16 and the climbing device 10 enables the device to climb. In one embodiment, the pull-off force may be approximately 40 N/cm2 relative to glass, but the pull-off force may vary depending upon the object.
To detach the leg 18, 20, 22, or 24 from the wall 16, the dry adhesive 14 is heated again to the glass transition temperature of the SMP. A relatively small pull-off or peel-off force may be applied. In one embodiment, the detachment of the leg from the wall requires only a relatively small force, for example about 0.5 N/cm2. In another embodiment, the detachment requires only a small force of about 0.3 N/cm2. In another embodiment, the detachment of the arm or leg from the wall requires a force of not greater than 2 N/cm2.
Still referring to FIGS. 1A-1D, one embodiment includes a method of climbing for the whole device 10. Each of the legs 18, 20, 22 and 24 are moved up the wall 16 in alternating fashion, for example in a manner similar to the gait of a four-legged animal such as an elephant or a dog. Each of the legs 18, 20, 22, and 24 are detached from the wall 16 and reattached at a new location upward on the wall 16. The process is repeated so that the device 10 climbs the wall.
In another embodiment, the device 10 may have two legs. The first leg is detached from the wall with the second leg attached to the wall. The first leg is moved to a new location and attached to the wall. The second leg is detached from the wall and is moved upward on the wall and attached. The first leg is detached and moved up on the wall and attached. The process is repeated so that the device climbs the wall.
Referring to FIG. 2, in another embodiment the climbing or moving device 10 may be a tank 32 including a rotating traction belt 30. The belt 30 may be constructed to have a relatively long contact surface when engaging the wall 16. The belt 30 includes the thermo-reversible dry adhesive layer including the dry adhesive layer 14 and the SMP layer 12 for contacting the wall 16. As the belt 30 is rotated, the dry adhesive 14 at the front leading edge 34 of the belt is heated to the glass transition temperature of the SMP just prior to contacting the wall, and then the belt is moved so that the heated adhesive contacts the wall and then is cooled to form a strong bond with the wall. The rearward trailing edge 36 of the belt 30 which had been attached to the wall 16 is heated again to detach that section of the belt from the wall. Gears 38 on the device are rotated to move the device up the wall so the section of the belt that previously was at the forward leading edge 34 is now at the rearward trailing edge 36. The process is repeated so that the tank 32 may climb the wall. In one embodiment, the detachment of the traction belt 30 from the wall 16 requires a force of not greater than 2 N/cm2.
In various embodiments, the climbing devices may include, but are not limited to, toys or robots. The climbing devices may carry loads of various weights. The climbing devices may climb a surface of any suitable angle, including vertical and horizontal surfaces. The surface may be, but is not limited to, glass, steel, or concrete.
The adhesive layer may provide a continuous contact surface or the adhesive layer may include a plurality of spaced apart fingers each providing a relatively small contact surface so that the overall contact surface of the adhesive layer is not continuous.
In various embodiments, the dry adhesive layer may be an epoxy elastomeric dry adhesive. In various embodiments, the shape memory polymer layer may be an epoxy shape memory polymer. In various embodiments, the components of the dry adhesive or the components of the shape memory polymer may include a rigid epoxy and a flexible epoxy. The range of possible crosslinking chemistries which may be used to achieve a dry adhesive or shape memory polymer may include alpha, omega-diaminoalkanes, organic multi-carboxylic acid, anhydride, or catalytic (as in imidazole type) crosslinking reactions. There are many different ways to achieve the appropriate relationships between the molecular properties. For example, the dry adhesives or shape memory polymers may include a rigid epoxy, an epoxy extender, and a crosslinking agent; or a rigid epoxy, a flexible crosslinking agent, and a flexible epoxy; or a rigid epoxy, a rigid crosslinking agent, and a flexible epoxy; or a rigid epoxy, a flexible epoxy, and a catalytic curing agent; or a rigid epoxy, a crosslinking agent, and a diluent; or a flexible epoxy, a crosslinking agent, and a diluent; or a rigid epoxy and a flexible crosslinking agent; or a flexible epoxy and a catalytic curing agent; or a flexible epoxy and a crosslinking agent; and wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, the epoxy extender has one epoxide group, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride, and the diluent is a monoamine or a mono-carboxylic acid. In various embodiments, the catalytic curing agent (or catalytic cure) promotes epoxy-to-epoxy or epoxy-to-hydroxyl reactions. The catalytic curing agent may include, but is not limited to, tertiary amines, amine salts, boron trifluoride complexes, or amine borates. In one embodiment, the components of the dry adhesive may be present in an amount sufficient to provide, upon curing of the composition, a dry adhesive having a glass transition temperature (Tg) of −90° C. to 200° C. and having a pull-off strength of 1-200 N/cm2 from a substrate. In another embodiment, the dry adhesive may have a glass transition temperature of −90° C. to 25° C. In one embodiment, the components of the shape memory polymer composition may be present in an amount sufficient to provide, upon curing of the composition, an epoxy shape memory polymer having a change in storage modulus of 2 to 3 orders of magnitude before and after its glass transition.
One embodiment of the invention includes a multilayer thermo-reversible dry adhesive having a first layer made from an aromatic diepoxide (rigid epoxy), an aliphatic diepoxy (flexible epoxy), and a diamine curing agent, and a second layer made from an aliphatic diepoxy and an amine. In one embodiment the multilayer thermo-reversible dry adhesive has a curved structure.
Numerous shape memory polymers may be utilized in various embodiments of the invention. For example, starting with a typical aromatic diepoxy/diamine system with a Tg of about 90° C., the aromatic epoxy component is replaced systematically with an aliphatic diepoxy to yield a series of epoxy shape memory polymers with Tg's ranging from 3° C. to 90° C. As such, a shape memory polymer may be tailored for use with a dry adhesive as desired for a particular application operated within certain temperature ranges.
Some embodiments refer to a multilayer epoxy dry adhesive. It should be understood that more than two layers may be utilized. For example, there may be two or more layers of the shape memory polymer layer, which may be in a side by side relationship or an overlying relationship. Likewise, there may be two or more dry adhesive layers in a side by side relationship or an overlying relationship. As such, a device with custom or tailored properties may be manufactured.
One embodiment of the invention includes a method of making a multilayer thermo-reversible dry adhesive comprising heating 3.6 g of EPON 826 (the diglycidyl ether of bisphenol A epoxy monomer) to about 75° C. and mixing the same with 2.16 g of neopentyl glycol diglycidyl ether (NGDE) and 2.3 g of Jeffamine D-230, which is the curing agent poly(propylene glycol)bis(2-aminopropyl)ether. Jeffamine D-230 is a polyetheramine that is difunctional, primary amine with an average molecular weight of about 230. The primary amine groups are located on secondary carbons at the end of the aliphatic polyether chain. Jeffamine is available from Huntsman.
The mixture was then poured into an aluminum pan and cured in an oven at about 100° C. for 1.5 hours. Then a mixture of 2.6 g of NGDE and 1.15 g of an amine such as Jeffamine D-230 was poured into the aluminum pan on top of the first cured epoxy layer and cured for 1.5 hours at 100° C. In a third step, the oven temperature was raised to 130° C. for post-curing for about one hour. At the end of the post-curing, the cured two-layer epoxy was demolded. A double layer epoxy was obtained with the first layer which had a thickness of about 2 mm and functioned as a shape memory polymer with a glass transition of about 45° C. and a second layer as a dry adhesive having a thickness of about 1 mm. The yielded double layer epoxy structure had a slightly curved structure due to the thermal mismatch between the first and second layers. This curvature can also be created by specifically designed molds to achieve the curved structure.
The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.

## Claims

1. A method of climbing comprising:
providing a device having at least a first movable limb, a second movable limb, a third movable limb, a fourth movable limb, and a thermo-reversible dry adhesive attached to each of the movable limbs, wherein the thermo-reversible dry adhesive comprises a shape memory polymer layer and a dry adhesive layer underlying the shape memory polymer layer;
moving each limb in alternating fashion comprising:
heating the thermo-reversible dry adhesive on the movable limb and pressing the adhesive against a surface to make contact;
cooling down the adhesive so that a strong adhesive bond is formed; and
releasing the movable limb from the surface comprising heating the dry adhesive again and using a force not greater than 2 N/cm2 to detach the limb from the surface.

2. A method as set forth in claim 1 wherein the adhesive bond has a pull-off force greater than 10 N/cm2.

3. A method as set forth in claim 1 comprising using a force not greater than 0.3 N/cm2 to detach the limb from the surface.

4. A method as set forth in claim 1 wherein the heating the thermo-reversible dry adhesive comprises heating to the glass transition temperature of the shape memory polymer layer.

5. A method as set forth in claim 1 wherein the cooling comprises at least one of natural cooling, a cooling wire, or a Peltier device.

6. A method as set forth in claim 1 wherein the device is one of a robot or a toy.

7. A method as set forth in claim 1 wherein the dry adhesive layer comprises:
at least one of a rigid epoxy or a flexible epoxy; and
at least one of a crosslinking agent or a catalytic curing agent;
wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride.

8. A method as set forth in claim 1 wherein the shape memory polymer layer comprises:
at least one of a rigid epoxy or a flexible epoxy; and
at least one of a crosslinking agent or a catalytic curing agent;
wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride.

9. A product comprising a climbing device comprising:
at least two movable limbs; and
a thermo-reversible dry adhesive secured to each of the movable limbs, wherein the thermo-reversible dry adhesive comprises a shape memory polymer layer and a dry adhesive layer underlying the shape memory polymer layer, wherein the dry adhesive layer comprises:
at least one of a rigid epoxy or a flexible epoxy; and
at least one of a crosslinking agent or a catalytic curing agent;
wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride.

10. A product comprising a climbing device comprising:
at least two movable limbs; and
a thermo-reversible dry adhesive secured to each of the movable limbs, wherein the thermo-reversible dry adhesive comprises a shape memory polymer layer and a dry adhesive layer underlying the shape memory polymer layer, wherein the shape memory polymer layer comprises:
at least one of a rigid epoxy or a flexible epoxy; and
at least one of a crosslinking agent or a catalytic curing agent;
wherein the rigid epoxy is an aromatic epoxy having at least two epoxide groups, the flexible epoxy is an aliphatic epoxy having at least two epoxide groups, and the crosslinking agent is one of a multi-amine, an organic multi-carboxylic acid, or an anhydride.

11. A product comprising a climbing device comprising:
at least two movable limbs; and
a thermo-reversible dry adhesive secured to each of the movable limbs, wherein the thermo-reversible dry adhesive comprises a shape memory polymer layer comprising a shape memory polymer and a dry adhesive layer underlying the shape memory polymer layer, and a means for heating the thermo-reversible dry adhesive to the glass transition temperature of the shape memory polymer.

12. A product as set forth in claim 11 wherein said means comprises a heating wire, a cooling wire, or a Peltier device.