Surface characterization, microstructure, and wetting of networks from ,-dihydroxy(polydimethylsiloxane) and 1,1,2,2-tetrahydrotridecafluoro octyltriethoxysilane

Abstract

Surface-modified siloxane networks were prepared using the dibutyltin diacetate catalyzed reaction of α,ω-dihydroxy(polydimethylsiloxane), HO(Me2SiO)nH, with tridecafluoro-1,1,2,2-tetrahydrooctyl triethoxysilane, [CF3(CF2)5(CH2)2Si(OC2H5)3, FTEOS]. Surface characterization of these elastomers was carried out using electron spectroscopy for chemical analysis (ESCA) and atomic force microscopy (AFM). Surface phase separation occurs as a function of increasing ratio of FTEOS to HO(Me2SiO)nH. Dynamic contact angle (DCA) analysis with water as the interrogating fluid showed that water contamination affects DCA data in the compositional range 4x–8x, where “x” is the ratio of ethoxy groups from FTEOS to OH groups in HO(Me2SiO)nH. Diffusion of polydimethylsiloxane oil species from the coatings is blocked in compositions of 10x or greater. Chemical stability is also enhanced for 10x and 12x compositions. (A) Tapping mode AFM images. Image area 30 × 30 × 1 μm. (B) DCA data with arrows showing collapse due to water surface contamination, 4x-0.8 cycle before collapse, 6x-1 cycle, 8x-1.6 cycles, 10x and 12x-stable. Stage speed 100 μm · s−1 and dwell times between sample immersion and withdrawal 10 s.