AVS 47th International Symposium
    MEMS Wednesday Sessions
       Session MM-WeA

Paper MM-WeA6
Switching of Interfacial Energies in Polymeric Coatings

Wednesday, October 4, 2000, 3:40 pm, Room 309

Session: MEMS Processing
Presenter: B.C. Bunker, Sandia National Laboratories
Authors: B.C. Bunker, Sandia National Laboratories
J.G. Kushmerick, Sandia National Laboratories
W.L. Smith, Sandia National Laboratories
M.S. Kent, Sandia National Laboratories
G.P. Lopez, University of New Mexico
X.-Y. Zhu, University of Minnesota
D.L. Huber, Sandia National Laboratories
T.D. Dunbar, Sandia National Laboratories
Correspondent: Click to Email
Polymeric coatings are under investigation for controlled switching of interfacial energies in microanalytical systems. Switching of water contact angles using films of poly n-isopropylacrylamide (PNIPAM) is of interest for driving liquids in microchannels, while switching of polymer configurations within polyethylene oxide (PEO) films could control properties such as protein adsorption. Films of PNIPAM and PEO have been tethered to gold and silicon substrates. Thermal and electrical stimuli have then been applied to the films to try to induce inverse temperature transitions. Film behavior has been monitored using a combination of contact angle measurements and force-distance profiles obtained using an interfacial force microscope. Results show that below the phase transition, PEO films are hydrated, and are attractive to scanning probe tips. Above the transition, the water is removed and the attractive potential drops by an order of magnitude. Moving above and below the transition temperature in PNIPAM films can induce changes in the water contact angle of from 10° up to 60° depending on how the polymer is tethered to the surface. The number of switching cycles is also dependent on the nature of the polymer-substrate interface. Limited switching is sometimes associated with decomposition or desorption of the active polymer. Such decomposition is illustrated for the specific example of a short-chain PEO film (EG3) attached to gold via a thiol coupling agent.