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According to the types of dental ceramic, various surface treatment techniques have been tried for adhesive cementation, but each treatment has its shortcomings. A simple and universal surface treatment for intraoral and chair-side adhesion promotion is needed for resin cements. This study investigated whether hexamethyldisiloxane (HMDSO) and benzene, when deposited using a low-power non-thermal atmospheric pressure dielectric barrier discharge jet, were effective precursor monomers in dental ceramic adhesion. Their effect on adhesion was evaluated with shear bond strength test (SBS), contact angle measurement, X-ray photoelectron spectroscopy, and Fourier transform infra-red spectrophotometer in an attenuated total reflectance mode. The bonded interfaces and fractured surfaces were evaluated using a scanning electron microscope. Plasma polymerization of HMDSO resulted in formation of a siloxane network (Si2 peak), but its surface hydrophobicity hindered adhesive wetting. Additional deposition of benzene onto the HMDSO-coated ceramic surface increased the C1 peak, which partly corresponded to the C=C double bonds, and the hydrophilic peaks (C-O, C=O and O-C=O bonds). Benzene deposition itself improved the adhesion between the ceramic and the overlying adhesive through the chemical interaction of C=C double bonds and the increased hydrophilic groups. Additional deposition of HMDSO before benzene mediated the chemical adhesion of benzene to the ceramic surface and led to an additional increase of bond strength. Plasma polymerization of benzene and HMDSO/benzene increased the bond strength of composite resin to dental ceramic by improving wettability and adaptation with hydrophilic ether, carbonyl and ester groups, and chemical bonding with active species, such as C=C double bonds and silanol groups. Open image in new window

A pencil-type floating electrode dielectric barrier discharge (FE-DBD) jet was designed to improve adhesion of composite resin to dental ceramic by plasma deposition. Among various monomers used for plasma deposition, 1,3-butadiene (BD) merged as a promising monomer. Shear bond strength (SBS) and fracture modes were evaluated with specimens prepared at various flow rates of BD. The SBS values of the experimental groups were significantly higher than that of the negative control group and approached that of the positive control group when flow rate was higher than or equal to 2 sccm. Surface characterizations of plasma polymer-deposited ceramic surfaces were performed with FTIR-ATR and XPS. The deposited polymer on the ceramic surface contained methyl and methylene groups, ether and ester groups, and carbon–carbon double bonds. Formation of plasma deposited layer from BD was verified with TEM and EDS from specimens prepared using a focused ion beam technique. Adhesion between ceramic and composite resin was enhanced with BD plasma deposition using the FE-DBD jet. The adhesion effect was stemmed from chemical reactions between C=C double bonds remaining in the plasma deposited polymer and those in the adhesive monomers as well as increased wettability due to the ester and ether groups involved in deposited polymer.

Contact angles of various monomers are measured by goniometer to calculate surface energies in order to select the monomer with highest surface energy. The highest surface energy is obtained with hexamethyl-disiloxane and is used in plasma coating the wood flour to improve its bonding and dispersion with the polypropylene (PP). The mechanical test results and SEM inspections indicate the good dispersion and the good compatibility between the wood flour and the PP. Also, this method is considered as a nontoxic process as compared to other chemical bonding method.

The direct hydroxylation of benzene using molecular oxygen by atmospheric pulse DC corona discharge was investigated. The conversion of benzene increased with the increase of oxygen content and input voltage but the selectivity of phenol decreased due to the formation of polymerized products. The reactivity was also influenced by the kind and content of background inert gas. By using argon as background gas, we could get 2.2% of phenol yield at 60°C and 1 atm with energy consumption of 50 W. The strategy of reductive oxidation, which added hydrogen to the reactant, was not favorable to the phenol formation in this reaction system. The polymerized product showed the oligomeric character and the analysis of its chemical structure with FT–IR was presented.

NOx conversion to N2 was investigated by a plasma/catalyst system in rich oxygen similar to a lean-burn engine exhaust. Catalytic activity was enhanced by the assistance of plasma, and the plasma/catalyst system showed higher NOx conversion over a wider temperature window than did catalyst alone. The plasma/catalyst (Ag/Al2O3) system showed a remarkable improvement in NOx conversion in the lower temperature range under 400 °C. The NOx conversion of plasma/catalyst (Ag/Al2O3) was 40%–50%, and its selectivity to N2 was over 96% under the conditions that the hydrocarbon (C1 base) to NOx ratio was about 3 and 10% O2 existed over the temperature range of 300–500 °C. Ag/Al2O3 showed a better performance than Al2O3 when assisted by plasma. Helium was used as a balance gas to measure N2 formation by gas chromatography, and NOx conversion was measured by a chemiluminescence NOx analyzer in N2 balance as well as He balance. The result in N2 balance gas was compared with the result in helium balance gas at the 300 °C where the largest enhancement by plasma was observed. The NOx conversion in N2 balance gas was similar to that in helium balance gas, which verified that the plasma effect obtained in helium balance gas is consistent with that of N2 balance gas, which is the largest component of the real exhaust gas.