(112e) Vapor Deposition of Functionally Graded Polymer Nanocoatings
We report an innovative method of synthesizing graded polymer nanocoatings using a single-step vapor deposition process. By adjusting the flow ratio of the precursor vapors at different deposition stages, the composition of the polymer nanocoatings can be continuously altered at different deposition thickness, resulting in significantly different chemical functionalities across the entire thickness of the nanocoatings. We demonstrated synthesis of graded pH-responsive hydrogel nanocoatings directly on vertically aligned carbon nanotubes. The nanocoatings have an ultrathin (< 50 nm) crosslinked bottom layer above which the structure gradually changes to a pH-responsive hydrogel. The bottom layer has strong adhesion to the nanotube sidewalls, while the hydrogel layer changes the surface property of aligned nanotubes from hydrophobic (CA ~ 112°) to superhydrophilic (CA ~ 0°). The hydrogel nanocoatings show thickness expansion of more than 30% by responding to a pH change of 1. We also demonstrated one-step synthesis of graded nanocoatings that bears functionalities at the bottom for strong substrate adhesion and cationic polymer brushes at the top for antibacterial function. The polymer nanocoatings kill bacteria quickly (~100% bacteria reduction) by disrupting the cell membrane and does not leach from the surface after repeated washing. Characterizations results of the graded polymer nanocoatings, including SEM, FTIR, AFM, and fluorescence microscopy, will be presented.