Tuned dielectric, pyroelectric and piezoelectric properties of ferroelectric P(VDF-TrFE) thin films by using mechanical loads J. Appl. Phys. 111, 044102 (2012) Dependence of threshold thickness of crystallization and film morphology on film processing conditions in poly(vinylidene fluoride-trifluoroethylene) copolymer thin films

We describe the preparation and characterization of core-shell latex particles, consisting of a polystyrene core, covered with a perfluoroalkyl acrylate shell. The core-shell particles were prepared by a two-stage emulsion polymerization under kinetically controlled conditions and were characterized by transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction analysis. The surface properties of the latex films produced from the core-shell particles were investigated by the contact angle method. Compared with random copolymers or latex blends of styrene and perfluoroalkyl acrylate, the core-shell particles were the most effective to reduce the surface energy of the latex films. The effect of acetone as a cosolvent on the polymerization process was also considered.

The magnetorheological (MR) performance of suspensions based on core-shell-structured foamed polystyrene (PSF)/FeO particles was investigated by using a vibrating sample magnetometer and a rotational rheometer. Core-shell-structured polystyrene (PS)/FeO was synthesized by using the Pickering-emulsion polymerization method in which FeO nanoparticles were added as a solid surfactant. Foaming the PS core in PS/FeO particles was carried out by using a supercritical carbon dioxide (scCO) fluid. The density was measured by a pycnometer. The densities of PS/FeO and PSF/FeO particles were significantly lowered from that of the pure FeO particle after Pickering-emulsion polymerization and foaming treatment. All tested suspensions displayed similar MR behaviors but different yield strengths. The important parameter that determined the MR performance was not the particle density but rather the surface density of FeO on the PS core surface. The morphology was observed by scanning electron microscopy and transmission electron microscopy. Most FeO particles stayed on the surface of PS/FeO particles, making the surface topology bumpy and rough, which decreased the particle sedimentation velocity. Finally, Turbiscan apparatus was used to examine the sedimentation properties of different particle suspensions. The suspensions of PS/FeO and PSF/FeO showed remarkably improved stability against sedimentation, much better than the bare FeO particle suspension because of the reduced density mismatch between the nanoparticles and the carrier medium as well as the surface topology change.

The surface properties of latex films prepared from heptadecafluorodecyl acrylate and 2,2,2trifluoroethyl methacrylate copolymers were investigated in terms of hydrophobicity and sliding behavior of liquid droplets. The hydrophobicity of fluorinated latex films evaluated from water contact angle was closely related to the chemical composition of the surface. On the other hand, the sliding angle of liquid droplets was not directly proportional to the hydrophobicity or oleophobicity of the latex films in the present study. Although the hydrophobicity of copolymer latex films was significantly enhanced by adding small amount of highly fluorinated heptadecafluorodecyl acrylate, it made water droplets rather difficult to slide down on an inclined surface. The sliding angle of water droplet was quite sensitive to the preparation methods, namely, batch and semicontinuous emulsion polymerizations in contrast to the hydrophobicity. The surface morphology and roughness of the latex films were found to be important to explain the observations.

We report on the preparation of water-and oil-repellent surfaces using surface-attached monolayers of perfluorinated polymer molecules. A covalent attachment of the polymer molecules to the substrate surfaces is achieved by generation of the polymer chains through starting a surface-initiated radical-chain polymerization of a fluorinated monomer. To this, self-assembled monolayers of azo initiators are attached to SiO2 substrates, which are used to kick off the polymerization reaction in situ. The growth of the fluorinated polymer brushes and the characterization of the obtained surfaces by Fourier transform infrared spectroscopy, surface plasmon spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurements is described. It is shown that perfluorinated polymer films can be grown with controlled thicknesses on flat and even on porous silica surfaces, essentially without changing the surface roughness. The combination of the low surface energy coating and the surface porosity allows generation of materials which are both water and oil repellent.