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Reaction of poly(chlorotrifluoroethylene) (PCTFE) with trimethyl 4-lithioorthobutyrate and hydrolysis produces a surface containing carboxylic acids (PCTFE-CO$\sb2$H). The advancing water contact angle ($\Theta\sb{\rm A}$) varies from ${\sim56}\sp\circ$ at low pH to ${\sim30}\sp\circ$ at high pH. The receding water contact angle ($\Theta\sb{\rm R}$) is 0$\sp\circ$ at all pH values. PCTFE-CO2H could be reduced to the alcohol, creating a less hydrophilic surface $\rm (\Theta\sb{A}/\Theta\sb{R} = 62\sp\circ/22\sp\circ)$ or converted to the n-octyl ester, rendering a hydrophobic surface $\rm (\Theta\sb{A}/\Theta\sb{R} = 99\sp\circ/47\sp\circ).$ PCTFE reacts with acetaldehyde 3-lithiopropyl ethyl acetal at $-$78-$-$15$\sp\circ$C to introduce the acetal into the outer $\sim$30-1000 A of the surface (PCTFE-PEAA). Hydrolysis produces a hydrophilic $\rm (\Theta\sb{A}/\Theta\sb{R} = 67\sp\circ/17\sp\circ),$ alcohol-functionalized surface (PCTFE-OH) which was derivatized to prepare a series of linear hydrocarbon and fluorocarbon ester surfaces. Reactions with multifunctional reagents produced crosslinked surfaces. Gravimetric, XPS, ATR-IR and contact angles results are consistent with the proposed surface structures and high reaction yields. Water contact angles on the hydrocarbon ester surfaces range from 82$\sp\circ/46\sp\circ$ (acetate) to 108$\sp\circ/90\sp\circ$ (stearate), while those on the fluorocarbon esters range from 92$\sp\circ/51\sp\circ$ (trifluoroacetate) to 120$\sp\circ/69\sp\circ$ (perfluorodecanoate). Hexadecane contact angles and XPS results show that the stearate and perfluorodecanoate esters form ordered surfaces. Friction properties of these modified surfaces were also investigated. The effects of varying the ester chain length, crosslinking the surface and varying the modification depth were studied. Contrary to expectations, the perfluorinated surfaces exhibited greater friction than their hydrocarbon analogs. The results show that chemical interactions at the sliding interface have little influence on friction and that it is the deformation behavior of the polymer near the interface that dictates the magnitude of the energy losses. Mixed surfaces were prepared to study the effect of surface composition on wetting. Randomly mixed hydroxyl/hydrocarbon ester surfaces were prepared by kinetic control of the esterification of PCTFE-OH, while compositionally similar, patchy surfaces were prepared by kinetic control of the hydrolysis of PCTFE-Esters. Esterification of the alcohol groups in these two sets of mixed surfaces was utilized to prepare the corresponding hydrocarbon ester/fluorocarbon ester mixed surfaces. As expected, greater contact angle hysteresis was observed on the patchy surfaces. |
