W.J. Ooij

Bio: W.J. Ooij is an academic researcher from University of Cincinnati. The author has contributed to research in topics: Plasma polymerization & Specific surface area. The author has an hindex of 1, co-authored 1 publications receiving 10 citations.

Plasma polymerization of acetylene onto silica: an approach to control the distribution of silica in single elastomers and immiscible blends

Abstract: Surface modification of silica by acetylene plasma polymerization is applied in order to improve the dispersion in and compatibility with single rubbers and their blends. Silica, used as a reinforcing filler for elastomers, is coated with a polyacetylene (PA) film under vacuum conditions. Water penetration measurements show a change in surface energy due to the PA-film deposition. The weight loss measured by thermo-gravimetric analysis (TGA) is higher for the PA-coated silica compared to the untreated filler, confirming the deposition of the PA film on the silica surface. Time of flight-secondary ion mass spectrometry (ToF-SIMS) shows the well-defined PA cluster peaks in the high mass region. Scanning electron microscopy (SEM) measurements show silica aggregates, coalesced by the coating with smooth and uniform surfaces, but without significant change in specific surface area. Elemental analysis by energy dispersive X-ray spectroscopy (EDX) measurements also confirms the deposition of the polymeric film on the silica surface, as the carbon content is increased. The performance of single polymers and their incompatible blends based on S-SBR and EPDM, filled with untreated, PA- and silane-treated silica, is investigated by measurements of the bound rubber content, weight loss related to bound rubber, cure kinetics, reinforcement parameter, Payne effect, and mechanical properties. The PA- and silane-modified silica-filled pure S-SBR and EPDM samples show a lower filler–filler networking compared to the unmodified silica-filled elastomers. Decrease in the reinforcement parameter (F) for the plasma-polymerized silica-filled samples also proves a better dispersion compared to silane-modified and untreated silica-filled samples. On the other hand, the PA-silica-filled samples show a higher bound rubber content due to stronger filler–polymer interactions. Finally, the PA-silica-filled pure EPDM and S-SBR/EPDM blends show high tensile strength and elongation at break values, considered to be the result of best dispersion and compatibilization with EPDM.

Slowing Down versus Acceleration in the Dynamics of Confined Polymer Films

Abstract: We have performed molecular dynamics (MD) simulations on coarse-grained polymer films which are confined between two attractive crystalline Lennard-Jones substrates with three different substrate–substrate separations Two different polymer–substrate interactions strengths have been studied Detailed analysis of the structural properties of each film showed a layering of the monomers close to the polymer–substrate interface and a preferential orientation of the bonds parallel to the substrate surface; both depend on substrate attraction strength and temperature, but not on film thickness The rotational and translational segmental dynamics were analyzed for each film thickness in different film layers, for a wide range of temperatures and for both substrate attraction strengths For all simulated films, the segmental dynamics was found to be faster than that in the bulk For relatively thick films and energetically neutral polymer–substrate interaction, a dramatic slowing down of the polymer mobility was

Synergistic effect of plasma‐modified halloysite nanotubes and carbon black in natural rubber—butadiene rubber blend

Abstract: Halloysite nanotubes (HNTs) were investigated concerning their suitability for rubber reinforcement. As they have geometrical similarity with carbon nanotubes, they were expected to impart a significant reinforcement effect on the rubber compounds but the dispersion of the nanofillers is difficult. In this work, HNTs were surface-modified by plasma polymerization to change their surface polarity and chemistry and used in a natural rubber/butadiene rubber blend in the presence of carbon black. The aim of the treatment was to improve the rubber–filler interaction and the dispersion of the fillers. A thiophene modification of HNTs improved stress–strain properties more than a pyrrole treatment. The surface modification resulted in a higher bound rubber content and lower Payne effect indicating better filler–polymer interaction. Scanning electron microscopy measurements showed an increased compatibility of elastomers and fillers. As visualized by transmission electron microscopy, the thiophene-modified HNTs formed a special type of clusters with carbon black particles, which was ultimately reflected in the final mechanical properties of the nanocomposites. The addition of HNTs increased loss angle

Surface Modification of Fumed Silica by Plasma Polymerization of Acetylene for PP/POE Blends Dielectric Nanocomposites

Abstract: Novel nanocomposites for dielectric applications-based polypropylene/poly(ethylene-co-octene) (PP/POE) blends filled with nano silica are developed in the framework of the European ‘GRIDABLE’ project. A tailor-made low-pressure-plasma reactor was applied in this study for an organic surface modification of silica. Acetylene gas was used as the monomer for plasma polymerization in order to deposit a hydrocarbon layer onto the silica surface. The aim of this modification is to increase the compatibility between silica and the PP/POE blends matrix in order to improve the dispersion of the filler in the polymer matrix and to suppress the space charge accumulation by altering the charge trapping properties of these silica/PP/POE blends composites. The conditions for the deposition of the acetylene plasma-polymer onto the silica surface were optimized by analyzing the modification in terms of weight loss by thermogravimetry (TGA). X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray fluorescence spectroscopy (EDX) measurements confirmed the presence of hydrocarbon compounds on the silica surface after plasma modification. The acetylene plasma modified silica with the highest deposition level was selected to be incorporated into the PP/POE blends matrix. X-ray diffraction (XRD) showed that there is no new crystal phase formation in the PP/POE blends nanocomposites after addition of the acetylene plasma modified silica. Differential scanning calorimetry results (DSC) show two melting peaks and two crystallization peaks of the PP/POE blends nanocomposites corresponding to the PP and POE domains. The improved dispersion of the silica after acetylene plasma modification in the PP/POE blends matrix was shown by means of SEM–EDX mapping. Thermally stimulated depolarization current (TSDC) measurements confirm that addition of the acetylene plasma modified silica affects the charge trapping density and decreases the amount of injected charges into PP/POE blends nanocomposites. This work shows that acetylene plasma modification of the silica surface is a promising route to tune charge trapping properties of PP/POE blend-based nanocomposites.

Nonmonotonic fracture behavior of polymer nanocomposites

Abstract: Polymer composite materials are widely used for their exceptional mechanical properties, notably their ability to resist large deformations. Here, we examine the failure stress and strain of rubbers reinforced by varying amounts of nano-sized silica particles. We find that small amounts of silica increase the fracture stress and strain, but too much filler makes the material become brittle and consequently fracture happens at small deformations. We thus find that as a function of the amount of filler there is an optimum in the breaking resistance at intermediate filler concentrations. We use a modified Griffith theory to establish a direct relation between the material properties and the fracture behavior that agrees with the experiment.