Young Investigators Seminar
◥Title: Poly(vinyl alcohol) Based Hydrogen-Bonded Multilayers: From pH-Controlled Multi-stage Dissolution to Zwitter-Wettable Films
◥Speaker: Dr. Hyomin Lee (School of Engineering and Applied Sciences, Harvard University)
◥Date: 8 July, 2014 (Tue) 14:00-15:00
◥Place: Seminar room 1 (#1101) @ W1-3 Bldg.
Poly(vinyl alcohol)(PVA) is a hydrophilic synthetic polymer that has been broadly used due to its biocompatibility, ease of chemical functionalization and cross-linking. However, because of its hydrophilic nature, PVA is subjected to rapid dissolution in water and this limits its broad applicability as a thin film. Stabilizing this water-soluble PVA with conventional solvent-casting methods often lacks the ability to control the nanometer scale structure of the resulting films. Thus, it is highly desirable to develop a method which allows precise tuning of physicochemical properties of PVA based films. The first part of this talk will focus on developing a systematic framework in which PVA can be incorporated into Layer-by-Layer (LbL) assembled multilayer thin films. The optimal assembly conditions as well as their broad range of pH-stability were explored through investigation on the degree of PVA hydrolysis, molecular weight and the type of weak polyacids in order to design pH-programmable systems and multi-functional freestanding films. In the second part of this talk, I will present its application to optically transparent antifogging coatings by proposing a new physical concept “zwitter-wettability”, defined as the simultaneous capability to resist wetting by water in the condensed liquid state (hydrophobicity), while remaining highly hydrophilic to water vapor that diffuses rapidly into the film. These mechanistic concepts and the quantitative morphological characterizations enabled us to design PVA based zwitter-wettable films with significantly enhanced antifog and even frost-resistant behavior.