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Wet Self-Cleaning of Superhydrophobic Microfiber Adhesives Formed from High Density Polyethylene
Lee, Jongho,Fearing, Ronald S. American Chemical Society 2012 Langmuir Vol.28 No.43
<P>Biologically inspired adhesives developed for switchable and controllable adhesion often require repetitive uses in general, dirty, environments. Superhydrophobic microstructures on the lotus leaf lead to exceptional self-cleaning of dirt particles on nonadhesive surfaces with water droplets. This paper describes the self-cleaning properties of a hard-polymer-based adhesive formed with high-aspect-ratio microfibers from high-density polyethylene (HDPE). The microfiber adhesive shows almost complete wet self-cleaning of dirt particles with water droplets, recovering 98% of the adhesion of the pristine microfiber adhesives. The low contact angle hysteresis indicates that the surface of microfiber adhesives is superhydrophobic. Theoretical and experimental studies reveal a design parameter, length, which can control the adhesion without affecting the superhydrophobicity. The results suggest some properties of biologically inspired adhesives can be controlled independently by adjusting design parameters.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2012/langd5.2012.28.issue-43/la303017a/production/images/medium/la-2012-03017a_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la303017a'>ACS Electronic Supporting Info</A></P>
Carbon nanotube active-matrix backplanes for conformal electronics and sensors.
Takahashi, Toshitake,Takei, Kuniharu,Gillies, Andrew G,Fearing, Ronald S,Javey, Ali American Chemical Society 2011 Nano letters Vol.11 No.12
<P>In this paper, we report a promising approach for fabricating large-scale flexible and stretchable electronics using a semiconductor-enriched carbon nanotube solution. Uniform semiconducting nanotube networks with superb electrical properties (mobility of 20 cm2 V(-1) s(-1) and ION/IOFF of 10(4)) are obtained on polyimide substrates. The substrate is made stretchable by laser cutting a honeycomb mesh structure, which combined with nanotube-network transistors enables highly robust conformal electronic devices with minimal device-to-device stochastic variations. The utility of this device concept is demonstrated by fabricating an active-matrix backplane (128 pixels, physical size of 64 cm2) for pressure mapping using a pressure sensitive rubber as the sensor element.</P>
Role of Counter-substrateSurface Energy in MacroscaleFriction of Nanofiber Arrays
Kim, Yongkwan,Limanto, Francesca,Lee, Dae Ho,Fearing, RonaldS.,Maboudian, Roya American ChemicalSociety 2012 Langmuir Vol.28 No.5
<P>The effect of counter-substrate surface energy on macroscalefrictionof nanofiber array is studied. Low-density polyethylene (LDPE) fibrillararray fabricated from silicon nanowire template is tested againstglass substrates modified with various self-assembled monolayers,which exhibit a wide range of surface energy. A large drop in frictionover a narrow range of surface energy is observed and explained interms of drastically reduced number of fibers in actual contact, inaddition to the reduced surface energy. The relationship between surfaceenergy and fiber engagement is discussed with Johnson–Kendall–Roberts(JKR) and elastic beam models.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2012/langd5.2012.28.issue-5/la204078z/production/images/medium/la-2011-04078z_0002.gif'></P>
Nanowire active-matrix circuitry for low-voltage macroscale artificial skin
Takei, Kuniharu,Takahashi, Toshitake,Ho, Johnny C.,Ko, Hyunhyub,Gillies, Andrew G.,Leu, Paul W.,Fearing, Ronald S.,Javey, Ali Nature Publishing Group, a division of Macmillan P 2010 NATURE MATERIALS Vol.9 No.10
Large-scale integration of high-performance electronic components on mechanically flexible substrates may enable new applications in electronics, sensing and energy. Over the past several years, tremendous progress in the printing and transfer of single-crystalline, inorganic micro- and nanostructures on plastic substrates has been achieved through various process schemes. For instance, contact printing of parallel arrays of semiconductor nanowires (NWs) has been explored as a versatile route to enable fabrication of high-performance, bendable transistors and sensors. However, truly macroscale integration of ordered NW circuitry has not yet been demonstrated, with the largest-scale active systems being of the order of 1??cm<SUP>2</SUP> (refs?11,15). This limitation is in part due to assembly- and processing-related obstacles, although larger-scale integration has been demonstrated for randomly oriented NWs (ref.?16). Driven by this challenge, here we demonstrate macroscale (7?7??cm<SUP>2</SUP>) integration of parallel NW arrays as the active-matrix backplane of a flexible pressure-sensor array (18?19?pixels). The integrated sensor array effectively functions as an artificial electronic skin, capable of monitoring applied pressure profiles with high spatial resolution. The active-matrix circuitry operates at a low operating voltage of less than 5??V and exhibits superb mechanical robustness and reliability, without performance degradation on bending to small radii of curvature (2.5??mm) for over 2,000 bending cycles. This work presents the largest integration of ordered NW-array active components, and demonstrates a model platform for future integration of nanomaterials for practical applications.
Zhang, Xiaobo,Pint, Cary L.,Lee, Min Hyung,Schubert, Bryan Edward,Jamshidi, Arash,Takei, Kuniharu,Ko, Hyunhyub,Gillies, Andrew,Bardhan, Rizia,Urban, Jeffrey J.,Wu, Ming,Fearing, Ronald,Javey, Ali American Chemical Society 2011 NANO LETTERS Vol.11 No.8
<P>A simple approach is described to fabricate reversible, thermally- and optically responsive actuators utilizing composites of poly(<I>N</I>-isopropylacrylamide) (pNIPAM) loaded with single-walled carbon nanotubes. With nanotube loading at concentrations of 0.75 mg/mL, we demonstrate up to 5 times enhancement to the thermal response time of the nanotube-pNIPAM hydrogel actuators caused by the enhanced mass transport of water molecules. Additionally, we demonstrate the ability to obtain ultrafast near-infrared optical response in nanotube-pNIPAM hydrogels under laser excitation enabled by the strong absorption properties of nanotubes. The work opens the framework to design complex and programmable self-folding materials, such as cubes and flowers, with advanced built-in features, including tunable response time as determined by the nanotube loading.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-8/nl201503e/production/images/medium/nl-2011-01503e_0002.gif'></P>