Adhesive Properties of Gecko-Inspired Mimetic via Micropatterned Carbon Nanotube Forests

Abstract

The adhesive properties of the gecko foot have inspired designs of advanced micropatterned surfaces with increased contact areas. We have fabricated micropatterned pillars of vertically aligned carbon nanotube forests with a range of pillar diameters, heights, and spacings (or pitch). We used nanoindentation to measure their elastic and orthogonal adhesion properties and derive their scaling behavior. The patterning of nanotube forests into pillar arrays allows a reduction of the effective modulus from 10 to 15 MPa to 0.1–1 MPa which is useful for developing maximum conformal adhesion.

Tribological properties of vertically aligned carbon nanotube arrays

“…The presence of pull-off forces found by other authors can be explained with different testing methods and VACNT arrangements [19,20,22,38]. Testing of adhesion of VACNTs by pressing with a plate led to an anisotropic alignment of the tips of the 200-500 µm long CNTs in parallel to the test surface [20].…”

“…The latter was later predicted by Finite Element Analysis [38]. Chen et al [22] reported significant pull-off forces from micro-patterned 170-230 µm high VACNT pillar-like arrays, and an influence of pillar aspect ratio and spacing on both EEM and adhesion strength. Mechanical testing on 65 µm thick films of VACNT brushes using sharp SPM tips resulted in adhesion forces of 1.6 × 10 -2 nN nm -2 , which was 200 times higher than those of the gecko foot-hairs [19].…”

“…The latter authors explained the changes of the elastic behavior during one test with different regimes of engagement of the nanotubes with the test surface. In the above mentioned micropatterned VACNT pillars, nanoindentation with a spherical sapphire tip (radius 400 µm) yielded EEMs from 0.1 to 10 MPa dependent on both the pillar aspect ratio and spacing [22]. A study, using nanoindentation with a standard Berkovich indenter, reported an EEM of 50 MPa on up to 100 µm thick VACNT arrays [21].…”

“…Elasticity and adhesive properties of VACNT films were measured using a variety of methods, such as scanning probe microscopy (SPM) [19], micro-and nanoindentation [20][21][22], micro force testing using microspheres [23], compression tests [21], and microfabricated resonators [24]. The effective Young´s moduli of VACNT arrays reported in these studies range from 0.1 MPa to 300 MPa.…”

Evaluation of surface properties of epoxy–nanodiamonds composites

“…Adhesion is observed in a loaddisplacement curve as a region of negative load during unloading [62][63]. The principle of this experiment is to put into contact the diamond probe tip and the flat polymer substrate and determine the maximum pull-force necessary to separate both materials.…”