Cationic ring opening polymerization of octamethylcyclotetrasiloxane （Da） initiated by acid treated bentonite was investigated. The experimental conditions were chosen on the basis of preliminary experiments.Higher ...Cationic ring opening polymerization of octamethylcyclotetrasiloxane （Da） initiated by acid treated bentonite was investigated. The experimental conditions were chosen on the basis of preliminary experiments.Higher temperature was found beneficial for the reaction process while stirring intensity beyond a certain level showed no obvious effect on the reaction rate. Polymers were characterized by Fourier transform infrared, proton nuclear magnetic resonance （IH-NMR） and gel perneation chromotography. The width of molecular mass distribution was found ranging between 1.2 and 1.4, which is extraordinarlly narrow compared with that of cationic polymerizations reported elsewhere （〉 1.9）. The results were believed due to the absence of free proton and counter ion which simplifies the polymerization process and the huge steric hindrance provided by bentonite particles which keeps the propagation of polysiloxane onto the surface of bentonite particles in a much more regular way. A feasible mechanism is proposed and seems to be supported well by experiments. Additionally, from the results of α, ω-dihydrogen terminated polysiloxanes prepared, the possibility of applying this potential environmentally friendly heterogeneous catalyst in industrial polymerization of cyclosiloxanes is anticipated.展开更多
Polydimethylsiloxane （PDMS）, tetraethoxysilane （TEOS）, ethyl alcohol （EtOH） and deionized water were main raw materials to prepare silicone-modified hybrid thin films using sol-gel method. The effect of the cont...Polydimethylsiloxane （PDMS）, tetraethoxysilane （TEOS）, ethyl alcohol （EtOH） and deionized water were main raw materials to prepare silicone-modified hybrid thin films using sol-gel method. The effect of the contents of H2O and PDMS on thin films was studied. When the volume ratio of H20 to TEOS is 0.5, the optimum quality of thin films is obtained. And the gelation time is affected slightly by H20 content. Uniform thin films are obtained when the volume ratio of PDMS to TEOS is 0.2. Yet, the sol would be inactive in 6 d. Various properties of thin films were studied, including hardness, adhesive quality, hydrophobic property, corrosion protection property, and abrasion resistance. Test results show that the pencil hardness is generally 3-6 H, and adhesive quality achieves the highest standard of 0. When the sintering temperature is below 400℃, the contact angle is about 95° and hydrophobic films are obtained. The abrasion resistance of thin films is better than that of aluminum alloy when the sintering temperature is higher than 300℃. And the excellent corrosion protective effect is obtained by single-layer coating when the sintering temperature is higher than 400℃.展开更多
The kinetics of bulk polymerization of octamethylcyclotetrasiloxane under acid circumstance is studied. A kinetic model is put forward and kinetic parameters are obtained through optimization.
An optimal concentration of the etching solution for deep etching of silicon, including 3% tetramethyl ammonium hydroxide and 0.3% (NH4)2S2O8, was achieved in this paper. For this etching solution, the etching rates o...An optimal concentration of the etching solution for deep etching of silicon, including 3% tetramethyl ammonium hydroxide and 0.3% (NH4)2S2O8, was achieved in this paper. For this etching solution, the etching rates of silicon and silicon dioxide were about 1.1μm·min-1 and 0.5nm·min-1, respectively. The etching ratio between (100) and (111) planes was about 34:1, and the etched surface was very smooth.展开更多
基金Supported by the National Natural Science Foundation of China （No.20576117）
文摘Cationic ring opening polymerization of octamethylcyclotetrasiloxane （Da） initiated by acid treated bentonite was investigated. The experimental conditions were chosen on the basis of preliminary experiments.Higher temperature was found beneficial for the reaction process while stirring intensity beyond a certain level showed no obvious effect on the reaction rate. Polymers were characterized by Fourier transform infrared, proton nuclear magnetic resonance （IH-NMR） and gel perneation chromotography. The width of molecular mass distribution was found ranging between 1.2 and 1.4, which is extraordinarlly narrow compared with that of cationic polymerizations reported elsewhere （〉 1.9）. The results were believed due to the absence of free proton and counter ion which simplifies the polymerization process and the huge steric hindrance provided by bentonite particles which keeps the propagation of polysiloxane onto the surface of bentonite particles in a much more regular way. A feasible mechanism is proposed and seems to be supported well by experiments. Additionally, from the results of α, ω-dihydrogen terminated polysiloxanes prepared, the possibility of applying this potential environmentally friendly heterogeneous catalyst in industrial polymerization of cyclosiloxanes is anticipated.
基金supported partly by the School of Mechanical,Electronic and Control Engineering,Beijing Jiaotong university,China
文摘Polydimethylsiloxane （PDMS）, tetraethoxysilane （TEOS）, ethyl alcohol （EtOH） and deionized water were main raw materials to prepare silicone-modified hybrid thin films using sol-gel method. The effect of the contents of H2O and PDMS on thin films was studied. When the volume ratio of H20 to TEOS is 0.5, the optimum quality of thin films is obtained. And the gelation time is affected slightly by H20 content. Uniform thin films are obtained when the volume ratio of PDMS to TEOS is 0.2. Yet, the sol would be inactive in 6 d. Various properties of thin films were studied, including hardness, adhesive quality, hydrophobic property, corrosion protection property, and abrasion resistance. Test results show that the pencil hardness is generally 3-6 H, and adhesive quality achieves the highest standard of 0. When the sintering temperature is below 400℃, the contact angle is about 95° and hydrophobic films are obtained. The abrasion resistance of thin films is better than that of aluminum alloy when the sintering temperature is higher than 300℃. And the excellent corrosion protective effect is obtained by single-layer coating when the sintering temperature is higher than 400℃.
文摘The kinetics of bulk polymerization of octamethylcyclotetrasiloxane under acid circumstance is studied. A kinetic model is put forward and kinetic parameters are obtained through optimization.
文摘An optimal concentration of the etching solution for deep etching of silicon, including 3% tetramethyl ammonium hydroxide and 0.3% (NH4)2S2O8, was achieved in this paper. For this etching solution, the etching rates of silicon and silicon dioxide were about 1.1μm·min-1 and 0.5nm·min-1, respectively. The etching ratio between (100) and (111) planes was about 34:1, and the etched surface was very smooth.
