Paul Day

P. Day, E. V. Eason, N. Esparza, D. Christensen, and M. Cutkosky

Directional dry adhesives are inspired by animals such as geckos and are a particularly useful technology for climbing applications. Previously, they have generally been manufactured using photolithographic processes. This paper presents a micromachining process that involves making cuts in a soft material using a sharp, lubricated tool to create closely spaced negative cavities of a desired shape. The machined material… Show more

P. Day, E. V. Eason, N. Esparza, D. Christensen, and M. Cutkosky

Directional dry adhesives are inspired by animals such as geckos and are a particularly useful technology for climbing applications. Previously, they have generally been manufactured using photolithographic processes. This paper presents a micromachining process that involves making cuts in a soft material using a sharp, lubricated tool to create closely spaced negative cavities of a desired shape. The machined material becomes a mold into which an elastomer is cast to create the directional adhesive. The trajectory of the tool can be varied to avoid plastic flow of the mold material that may adversely affect adjacent cavities. The relationship between tool trajectory and resulting cavity shape is established through modeling and process characterization experiments. This micromachining process is much less expensive than previous photolithographic processes used to create similar features and allows greater flexibility with respect to the microscale feature geometry, mold size, and mold material. The micromachining process produces controllable, directional adhesives, where the normal adhesion increases with shear loading in a preferred direction. This is verified by multi-axis force testing on a flat glass substrate. Upon application of a post-treatment to decrease the roughness of the engaging surfaces of the features after casting, the adhesives significantly outperform comparable directional adhesives made from a photolithographic mold. Show less

Irradiation of polymer-based gecko-like synthetic adhesives (GSAs) using an accelerated beam of He++ ions has been performed. This irradiation simulates large radiation doses that the GSAs may experience if deployed on a robotic platform in some radiological environments. After irradiation, the adhesive samples were tested for adhesion on a three-axis adhesion testing stage and were examined via scanning electron microscope. The GSA samples showed significant changes in surface morphology at… Show more

Irradiation of polymer-based gecko-like synthetic adhesives (GSAs) using an accelerated beam of He++ ions has been performed. This irradiation simulates large radiation doses that the GSAs may experience if deployed on a robotic platform in some radiological environments. After irradiation, the adhesive samples were tested for adhesion on a three-axis adhesion testing stage and were examined via scanning electron microscope. The GSA samples showed significant changes in surface morphology at high radiation doses. Additionally, radiation doses larger than 750 kGy resulted in a significant deterioration of the adhesive performance. Eventually, the adhesive samples lost all ability to generate frictional adhesion. Such results allow us to make quantitative statements about the applicability of GSAs for robotic applications in nuclear environments. Show less

Irradiation of polymer-based directional dry adhesives with gamma photons has been performed. This irradiation is commensurate with the radiation that an adhesive sample would be exposed to if deployed in a nuclear glove box or other high-radiation environment. Before and after irradiation, samples were tested using a three-axis adhesive testing stage and were analyzed via a scanning electron microscope and a water droplet contact angle analyzer. At doses in excess of 270 kGy, the adhesive… Show more

Irradiation of polymer-based directional dry adhesives with gamma photons has been performed. This irradiation is commensurate with the radiation that an adhesive sample would be exposed to if deployed in a nuclear glove box or other high-radiation environment. Before and after irradiation, samples were tested using a three-axis adhesive testing stage and were analyzed via a scanning electron microscope and a water droplet contact angle analyzer. At doses in excess of 270 kGy, the adhesive performance began to deteriorate, continuing to an overall performance reduction of 55% at a dose of [approximately]500 kGy. Significant changes in the surface energy of the bulk polymer are also indicated by changes in water droplet contact angles, contributing to the adhesion performance loss. Such analyses allow for quantitative statements to be made about the expected performance of these adhesives when deployed in high-radiation environments. Show less