(515c) Effect of the Chemical Structure of the Nanometer-Thick Polymer Coatings On the Simultaneously Oleophobic/Hydrophilic Behavior

Effect of the chemical structure of the nanometer-thick polymer coatings on the simultaneously oleophobic/hydrophilic behavior 

Lei Li and Yongjin Wang

Department of Chemical and Petroleum Engineering, University of Pittsburgh, 3700 O’Hara Street, Pittsburgh, PA 15261

Simultaneously hydrophilic/oleophobic surfaces are highly desirable in many important applications, such as anti-fogging.However, such wetting behavior is not expected for traditional surfaces since previous experimental results showed that, in general, a solid surface is more wettable to oil than to water. Interestingly, a couple of recent studies showed that it is possible to achieve simultaneous oleophobicity/hydrophilicity by applying some nanometer-thick polymer on some solid substrate. However, the underlying mechanism remains unclear to date. In the current study, we investigate the effect of chemical structure of the nanometer-thick polymer on the simultaneous hydrophilic/oleophobic behavior. Three nanometer-thick perfluoropolyethers with different end-groups were dip-coated on the silicon wafer (with native oxides). Both water contact angle (WCA) and hexadecane contact angle (HCA) were measured on these polymer-coated surfaces. The results show that simultaneous oleophobicity/hydrophilicity only occurs to some polymers but not the others. It was also found that the HCA changes significantly with time only for the polymer showing simultaneous oleophobicity/hydrophilicity. These findings further support a mechanism previously proposed by us  [1]. Anti-fogging experiments also indicated that there is a clear correlation between simultaneous oleophobicity/hydrophilicity and the anti-fogging performance.

Acknowledgement: We thank NSF (CMMI 1233161) for the financial support!

[1] Li L.; Wang Y.;GallaschunC.; RischT. and Sun J. “Why can a nanometer-thick polymer coated surface be more wettable to water than to oil?”, JOURNAL OF MATERIALS CHEMISTRY, 2012, 22(33), 16719-16722