Physical Properties and Responsive Behavior of Semi-fluorinated Polymer Interfaces*

The macromolecular platform for this research is a polyoxetane, which has a {\-}C{\-}C-C-O- main chain, specifically P[({\-}CH$_{2}$CMe(\textbf{A)}CH$_{2}$O{\-})(CH$_{2}$CMe(\textbf{B)}CH$_{2}$O-)]. If side chain \textbf{A} = \textbf{B}, the polyoxetane is semicrystalline; If \textbf{A} $\ne $ \textbf{B}, the copolyoxetane is an amorphous low $T_{g}$ telechelic used as a soft block. Dynamic interfacial behavior is described for (\textbf{\textit{1}}) \textbf{A} = \textbf{B} = CF$_{3}$CH$_{2}$OCH$_{2}$-, P(B-3FOx), and (\textbf{\textit{2}}) a soft block where \textbf{A} = 3FOx and \textbf{B} = C12, a CH$_{3}$(CH$_{2})_{11}$N$^{+}$(CH$_{3})_{2}$-(CH$_{2})_{4}$O- side chain used for introducing surface quaternary charge as a \textit{polymer surface modifier} (PSM). For P(B-3FOx) (21kDa), differences in cooling rates from the melt have substantial effects on crystal phase, percent crystallinity, surface topography, and wetting behavior. DSC and WAXD reveal that slow cooling from the melt ($\le $ 5 \r{ }C /min) gives $\alpha $-P(B-3FOx) while quenching from the melt results in $\beta $-P(B-3FOx), which forms an ordered mesophase. TM-AFM and SEM for $\alpha $-P(B-3FOx) shows cold crystallization (25 \r{ }C) brings about sharp asperities and lath-shaped crystals. A 30\r{ } increase in water contact angle is associated with the change from a relatively smooth surface (Wenzel) to an asperity-rich surface yielding a discontinuous three-phase contact line (composite of Wenzel and Cassie-Baxter). Prior research established P[\textbf{AB}]-copolyoxetane polyurethanes having soft blocks \textbf{\textit{2}} with\textbf{ A} = 3FOx and \textbf{B} = dodecylammonium-butoxy (C12) are effective \textit{contact} antimicrobial PSMs, but accessible quaternary charge density was unknown. Streaming potential (SP) measurements in microfluidic capillaries have been employed for estimating surface accessible charge. Inner capillary walls were coated with a base polyurethane modified by 1 wt{\%} \textbf{\textit{2}}\textbf{-PU}, that is, [HMDI{\-}BD(30){\-}P[(3FOx)(C12){\-}87:13-(5100)]. The neat PSM has a constant SP, but SPs for 1 wt{\%} PSM coatings decreased with time. TM-AFM showed that the dynamic behavior of modified surfaces was correlated with PSM phase separation. The results are important in providing a facile method for screening candidate coatings prior to time consuming antimicrobial testing.