Duong Lillian by GX28pI3P


									                                       Observation of Contact Angle Hysteresis of Water on Self Assembled
                                                 Monolayer by using Contact Angle Goniometry
                                                        Lillian Duong and Steven Baldelli
                                       University of Houston, Department of Chemistry, Houston, TX 77204

                      Abstract                                                                                                                     Tilting plate goniometry
 Self-assembled monolayers (SAMs) have been
       studied in a variety of ways such as in                                        Goal:                                        • Tilt plane of the stage that the drop of water is on
   electrochemistry, corrosion protection, and                To discover the contact angle hysteresis of the SAMs
   wetting. The construction of a contact angle                                                                                         •Stop when reach point of incipient motion
                                                                 that are formed using contact angle goniometry
       goniometer was for the studies of the
                                                                                                                             •Point of incipient motion – when the drop of water is about to
 interaction between liquids and solid surfaces.
  Using a 2-lens system, a CCD camera, and the
sessile drop method, observations were made of                                                                                   • Contact angle after tilt: advancing and receding angle
   water's contact angle on SAM. The contact
 angle of water on the SAM was measured to be
    99° while the contact angle on a good film
would be ≈ 118°. The hysteresis is then found to         Formation of SAMs
be 6° by using the tilting plate goniometry. The                                                                                                        Results:
 resulting contact angle hysteresis suggests that        •Thiol: Octadecanethiol(ODT)
  the SAM are relatively even and smooth, but                                                                                  Contact Angle on a Flat Stage
  still have certain defects that occur based on         •Substrate: Gold                                                     Trials      CA (left)    CA (right)       Average CA
                                                         •Solution: 1mM ethanolic solution of octadecanethiol                 Trial 1     99.1̊        99.1̊            99.1̊
                                                                                                                              Trial 2     99.2̊        99.0̊            99.1̊
                                                         •Adsorption time in solution: ~8-18 hours at room temperature
                                                                                                                              Trial 3     99.7 ̊       99.8 ̊           99.8 ̊
Self Assembled Monolayer Formed of Thiols on Gold
                                                         • After adsorption time: Take sample out of solution, rinse with
                                                         ethanol ,and dry with nitrogen gas                                                                     Average
               • Well-ordered and stable                                                                                                                        CA: ~ 99°
  •Alkane chains are tilted and in close proximity to
                       each other
 •Gold is the standard substrate because it does not                                                                         Contact Angle After Using Tilting Plate
             oxidize at room temperature                                                                                     Goniometry
                                                                   Structure of ODT:
                                                                                                                             Trials     CA               CA                 CA
                                                                   CH3 (CH2)17 SH           HS                                          (advancing)      (receding)         hysteresis
                                                                                                                             Trial 1    102 ̊            97 ̊               5̊
                                                                                                                             Trial 2    100 ̊            93 ̊               7̊
                                                                                                                             Trial 3    100 ̊            95 ̊               5̊
                                                                                                                                                            Average CA
            Contact Angle and Hysteresis

Hysteresis occur because of:
•Roughness on surface
•Chemically and structurally nonhomogeneous                                                                                  Potential Reasons for Contact Angle Hysteresis on SAMs
                                                                                                                                                •Preparation of SAMs
                                                                                                                                   •Contamination Chemically nonhomogeneous

          ∆θ = θa -θr                 θr                Light Source
                                                                          Filter                                High
                                                                                        Stage        Lens       resolution                      Acknowledgement:
                                                                                                                CCD camera
                                                                                                                                Graduate students in Dr. Baldelli’s lab and Dr. Baldelli

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