I. Composite polymer coatings prepared in supercritical carbon dioxide. II. Chemical modification of atomic force microscope probes. III. Liquid mobility on surfaces with patterned chemistry and topography
The initial part of this dissertation describes the preparation of the first reported poly(p-xylylene) polymer/polymer composites. Poly(p-xylylene) (PPXN) and its derivatives, known collectively as parylenes, are solvent resistant and blends or composites cannot be easily made by conventional methods. Supercritical carbon dioxide was used as both a plasticizer and solvent to infuse and polymerize a variety of vinyl monomers inside the parylene films. Infrared spectroscopy, wide angle X-ray diffraction, and thermal gravimetric analysis were used to characterize the composites. Multilayer coatings of PPXN and other polymer films were prepared and selectively modified with metal nanoparticles.
The second part details the modification of atomic force microscope (AFM) probes using a variety of monochlorosilanes to improve the chemical sensitivity of AFM. X-ray photoelectron spectroscopy revealed that the silane reaction was successful. Adhesion force measurements between the modified probes and similarly modified silicon wafers were performed, but showed only a slight variance between the different tip chemistries. Surfaces with patterned chemistry were prepared and examined with the modified probes using tapping mode AFM. The contrast in the phase images was dependent on the tip chemistry.
The ability to confine and direct the motion of liquid droplets on a surface using only gravity and differences in surface chemistry is discussed in the first chapter of Part III. A hydrophobic alkylsilane surface with low contact angle hysteresis was patterned with lines of a more hydrophobic fluoroalkyl silane. Liquid droplets moved easily on the low hysteresis matrix, but pinned at the more hydrophobic lines. A variety of patterns were used to demonstrate that a decrease in the hysteresis reduces the force needed to induce drop motion and also lowers the barriers that are needed to confine the droplets.
Condensation on a variety of ultrahydrophobic surfaces was examined in the second chapter of Part III. Optical microscopy showed that water condensed between the hydrophobic surface features before being expelled to the top. The condensed liquid pinned the contact line of a macroscopic droplet and dynamic contact angle measurements revealed an increase in hysteresis which corresponded to a decrease in liquid mobility.
0486: Analytical chemistry