https://hal.archives-ouvertes.fr/hal-00144747/document

Modification of surface properties of carbon-based and polymeric materials through fluorination routes: From fundamental research to industrial applications

To investigate the role surface traps play in the charge injection and transfer behavior of alumina-filled epoxy composites, surface traps with different trap levels are introduced by different surface modification methods which include dielectric barrier discharges plasma, direct fluorination, and Cr2O3 coating. The resulting surface physicochemical characteristics of experimental samples were observed using atomic force microscopy, scanning electron microscopy and fourier transform infrared spectroscopy. The surface potential under dc voltage was detected and the trap level distribution was measured. The results suggest that the surface morphology of the experimental samples differs dramatically after treatment with different surface modification methods. Different surface trap distributions directly determine the charge injection and transfer property along the surface. Shallow traps with trap level of 1.03–1.11 eV and 1.06–1.13 eV introduced by plasma and fluorination modifications are conducive for charge transport along the insulating surface, and the surface potential can be modified, producing a smoother potential curve. The Cr2O3 coating can introduce a large number of deep traps with energy levels ranging from 1.09 to 1.15 eV. These can prevent charge injection through the reversed electric field formed by intensive trapped charges in the Cr2O3 coatings.

https://iopscience.iop.org/article/10.1088/0022-3727/49/44/445304/pdf

The control mechanism of surface traps on surface charge behavior in alumina-filled epoxy composites

Epoxy resin sheets were surface fluorinated in a laboratory vessel using a F2/N2 mixture with 12.5% F2 by volume at the different temperatures of 25, 55, 75, and 95 °C for the same time of 30 min, to investigate the effect of fluorination temperature on surface electrical properties. ATR-IR analyses indicate that fluorination led to substantial changes in surface chemical composition and structure, depending on fluorination temperature, and SEM surface and cross section images show an evolution of surface morphology and an increase of thickness of the fluorinated layer with fluorination temperature. Conductivity measurements reveal that the surface fluorinated samples have higher surface conductivities than the unfluorinated sample, and surface conductivity significantly increases with fluorination temperature. Surface potential measurements, performed about 10 s after corona charging, indicate lower initial surface potentials for the surface fluorinated samples than the unfluorinated sample, and a decrease of the initial surface potential with surface conductivity. The initial surface potential was found to decrease dramatically above a critical surface conductivity (3.0×10-14 S), and almost to zero when surface conductivity increased to 10-12 S. Contact angle measurements and surface energy calculations show a much higher surface polarity of the surface fluorinated samples compared to the unfluorinated sample and a dramatic increase of the surface polarity with fluorination temperature. An increase in degree of chain scission is considered to be the main cause for the increases of surface conductivity and surface polarity with fluorination temperature.

Characteristics and electrical properties of epoxy resin surface layers fluorinated at different temperatures

Low Density Polyethylene (LDPE) films were treated by direct fluorination at different conditions, i.e. static and dynamic ones. Modification of the treated films chemical composition was studied by spectroscopic methods (solid state NMR, XPS and infrared spectroscopy). Surface morphology was investigated by SEM and AFM. Also surface energy measurements and electron paramagnetic resonance (EPR) were carried out. Direct fluorination resulted in printability, barrier properties towards O2 and tribological properties enhancement. On the contrary, the barrier properties towards water, initially good, were not improved but maintained.

Surface modification of low-density polyethylene packaging film via direct fluorination

Enhancement of surface properties on Low Density Polyethylene packaging films using various fluorination routes

A change in the surface structure of low-density polyethylene films upon chemical modification by gaseous fluorine has been studied by scanning electron microcopy and X-ray spectral analysis. It has been demonstrated that this treatment leads to formation of the wavy surface; its characteristics depend on the method of polymer synthesis and the initial structure of the test sample. A possible mechanism for structural changes in the surface layer of the polymer during fluorination is considered. It is suggested that the molar volume and the configuration of polymer macromolecules change in the course of replacement of hydrogen atoms with fluorine atoms. Mathematical modeling has been performed for the formation of the fluorinated layer with due regard for chemical transformations of macromolecules and structural heterogeneity of the polymers. The isosurfaces of the polymer with various degrees of fluorination calculated within the framework of the above model indicate that the fluorinated layer being formed is characterized by unequal thickness due to different rates of fluorine diffusion in amorphous and crystalline regions. It has been shown that the degree of fluorination of the polymer is dependent on the duration of treatment. This relationship is in satisfactory agreement with the previous experimental data.

V. P. Stolyarov

Papers

Morphology of the surface layer of polymers modified by gaseous fluorine