Self-cleaning silicon nanowire elastomeric composites
The texturing of surfaces has been demonstrated to modify surface energies in order to create self-cleaning surfaces. These superhydrophobic surfaces are typically created using processes that directly modify the surface of interest. Many approaches exist to form textured surfaces ranging from selective etching of nano-scale features to depositing self-assembled monolayers. The surfaces created are usually fixed onto the processed surface and limits the materials choices that can create these self-cleaning structures. We have investigated the use of nanowire embedded composites for surface energy modification, creating super-hydrophobic conditions (contact angles greater than 150°) on elastomeric films. The films can be removed from its process wafer and laminated onto a different substrate, creating a self-cleaning surface by selective layer transfer. A bottom-up approach to fabricating super-hydrophobic surfaces using Si nanowires (SiNWs) embedded in polydimethylsiloxane (PDMS) will be presented. A dense network of SiNWs having ordered (vertically oriented) and disordered structures was first synthesized on Si (111) substrates by chemicalvapor deposition. The as-grown SiNW network, having a nanowire length of ~ 30 microns, was found to be hydrophilic with a water contact angle of ~ 5°. A composite SiNW/PDMS layer (of ~ 20 micron thickness), with the ordered SiNWs protruding out from the PDMS surface, was created by drop-casting the PDMS onto the SiNW surface. A resulting water contact angle of 150° was measured on the composite layer surface, greater than the contact angle of ~80° on bare PDMS. Results for free-standing SiNW/PDMS composite layers and applications towards nanocomposite laminates will be presented. Finally, the effect on the thermal conductivity of the embedded SiNWs on the composite materials will be explored and discussed.
Wong, W. S.; Ng, T. N.; Lujan, R. Self-cleaning silicon nanowire elastomeric composites. 51st Electronic Materials Conference (EMC 2009); 2009 June 24-26; University Park, PA.