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Carbon-Nanotube-Based Adhesives

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					Carbon-Nanotube-Based (Gecko-
      Inspired) Adhesives
         Bryan Schubert
         March 3, 2008
                                Gecko Adhesion
                                                         • Notable features
                                                            – Strength: 10 N/cm2 from
                                                              van der Waals forces
                                                            – Reusable: 30 days
                                                              between molts
                                                            – Directional
                                                            – Adheres to most
                                                              surfaces; smooth or
                                                              rugged
                                                            – Self-cleaning


1. K. Autumn et al., J. Exper. Biol. 209, 3569 (2006).
                                Gecko Adhesion
  • Basic principle of operation – Contact splitting
     – Density of contacts scales by contact radius as N ~ R-2
     – Force per contact scales as F ~ R-1 (JKR: F = 3πRW)
     – Force per unit area scales as FN ~ R-1




                                                         50 μm   5 μm

                           1 μm


           R


1. K. Autumn et al., J. Exper. Biol. 209, 3569 (2006).
               Carbon Nanotube Adhesives -
                       Fabrication
  • Vertically-aligned multi-walled carbon nanotubes (VA-
    MWNTs)
        – Chemical vapor deposition (CVD) on silicon substrate using thin film
          iron as catalyst layer and aluminum film as adhesion layer2,3.



                                     Oxygen                       Diameter: 20-30 nm
                                   plasma etch
                                                                  Length: 5-100 μm
                                                                  Density: 1010-1011 cm-2
                  5 μm                                     1 μm

        Top view

2. L. Delzeit et al., J. Phys. Chem. B 106, 5629 (2002).
3. L. Delzeit et al., J. Phys. Chem. B 106, 5629 (2002).
               Carbon Nanotube Adhesives -
                       Fabrication
  • Vertically-aligned single-walled carbon nanotubes (VA-
    SWNTs)
        – Plasma-enhanced CVD on SiO2/Si wafer with iron layer as catalyst and
          pre-coated aluminum adhesion layer. Fast heating4 was used to
          minimize catalytic particle aggregation, creating single-walled carbon
          nanotubes.


                                                          Nanotube diameter: 2-3 nm
                                                          Bundle diameter: 20-30 nm
                                                          Length: 5-100 μm
                                                          Bundle density: 1011 cm-2




4. Y. Q. Xu et al., J. Am. Chem. Soc. 128, 6560 (2006).
                               Carbon Nanotube Adhesives -
                                      Performance
                            • VA-MWNTs
Adhesion Strength (N/cm2)




                                                              Attachment Cycle   glass 4 mm2   Si 5 mm2
                                                                                 glass 6 mm2   parylene 7 mm2
               5. Y. Zhao et al., J. Vac. Sci. Technol. B 24, 331 (2006).        Au 4 mm2      GaAs 7.8 mm2
               Carbon Nanotube Adhesives -
                      Performance
  • VA-SWNTs
                                                                4 mm x 4 mm
        – Normal Adhesion: 12-29                        N/cm2
        – Shear Adhesion: 4-16 N/cm2
        – Performance decreases with use




              Before use                            After use

6. L. Qu and L. Dai, Adv. Mater. 19, 3844 (2007).
               Carbon Nanotube Adhesives -
                      Performance
  • VA-SWNTs
        – Mostly semi-conducting nanotubes                            4 mm x 4 mm




                                                             4.70 N




                                                    0.01 N




6. L. Qu and L. Dai, Adv. Mater. 19, 3844 (2007).
                                       Comparison
  Material              Gecko             VA-MWNTs                   VA-SWNTs

  Maximum               10 N/cm2          12 N/cm2                   29 N/cm2
  Adhesion

  Surfaces              Any               Smooth (glass)             Smooth (glass)

  Reusable              Yes               Yes but degrades           Yes but degrades

  Self-cleaning         Yes               Maybe (uses Lotus effect)7 Maybe (using Lotus effect)

  Directional           Yes               Probably not               Probably not

  Electrically          No                Yes                        Yes
  Conductive

  Thermally             No                Yes                        Yes
  Conductive
7. S. Sethi et al., Nano Lett., 10.1021/nl0727765 (2008).

				
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