Low Free Energy Surfaces Using Blends of Fluorinated Acrylic Copolymer and Hydrocarbon Acrylic Copolymer Latexes

Blends of small particle size fluorinated acrylic copolymer latexes with a large particle size styrene/acrylic copolymer latex were examined with regard to formation of low free energy surfaces, amount of incorporated fluorinated copolymer, particle size, and particle size asymmetry. The styrene/acrylic latex was prepared by emulsion polymerization of n-butyl acrylate and styrene. Several varieties of fluorinated latexes were prepared. One was prepared by copolymerization of n-butyl acrylate and the fluorinated monomer, FMA, H2CC(CH3)CO2(CH2)2(CF2)nF (n̄ ≈ 7.7). Two types of copolymer core/fluorinated copolymer shell latex systems were prepared. One was comprised of a highly cross-linked core of poly(divinylbenzene) and a shell of poly(n-butyl acrylate-co-FMA). The other had a lightly cross-linked core of poly(n-butyl acrylate-co-divinylbenzene) and a shell of poly(n-butyl acrylate-co-FMA). Films cast from blends of styrene/acrylic and fluorinated copolymer latexes were examined by contact angle goniometry, X-ray photoelectron spectroscopy (XPS), time-of-flight static secondary ion mass spectroscopy (ToF-SIMS), and tapping mode atomic force microscopy (TMAFM). In some cases, low free energy surfaces were created at small mole fractions (∼10-4−10-2) of fluorinated monomer copolymerized with acrylic monomers in the mixture. AFM images were used to differentiate fluorinated, phase-segregated regions in the mixtures. Because of the disparity in particle size (asymmetry) between the styrene/acrylic and fluorine-containing latexes, the phenomena of percolation and excluded volume can be used to establish a substantial excess of fluorinated, low free energy material at the surface of an asymmetric blend of the two.