Preparation And Property Of Thermo-responsive Silica Nano-spheres

Nano-silica has drawn considerable attention for many years due to the non-toxic, tasteless and less pollution properties. For pure SiO2particles, a large number of hydroxyl groups, Si-OH, are lactated on the surface, and so they exhibit high surface activity. Thermo-sensitive materials refer to the intelligent polymers which could be in response to a temperature stimulus. It is of great significance for thermo-responsive silica nano-spheres that might have potential application in the textile, chemical, biological, and other fields in the future.Firstly, the silica nano-spheres were prepared with hydrolyzing ethyl orthosilicate using ammonia as catalyst and ethanol as solvent. After reaction, the suspension was filtered, and precipitate was processed by washing with ethanol3times and drying in vacuum for8hour. The results show that when the dosage of ethyl orthosilicate was3mL, the optimized conditions for the preparation of nano-SiO2were10mL of ammonia at30℃and4hour. The yield of the as-prepared silica nano-sphere can go up to90%and their average size was about220nm.Secondly, the as-prepared silica nano-spheres were modified with3-methacryloxypropyl trimethoxysilane (KH-570). The mono-factorial experiments are carried out to get the optimum processing conditions. It was found that under the optimized conditions, the dosage of ethyl orthosilicate was3mL, the amount of3-methacryloxypropyl was5mL, the reaction time was8hour, and the reaction temperature was reflux temperature.The oil-affinity degree and water-sorption ratio for the KH-570modified nano-SiO2were55.0%and2.84%, respectively. The unmodified and modified samples were characterized by transmission electron microscopy, water contact angle, respectively. It can be seen that all the samples were uniform and spherical particles, while the hydrophobicity was improved slightly. An improved dispersion property in toluene confirmed the hydrophobic modification.Finally, thermo-responsive silica nano-spheres were prepared with ingrafting N-isopropyl acrylamide on the KH-570modified nano-SiO2. It was found that the optimum reaction condition was73℃and6h,1:1molar ratio of N-isopropyl acrylamide and KH-570,2.5wt%of initiator,2,2-azobisisobutyronitrile. The thermo-responsive samples were characterized by Fourier transform infrared spectroscopy, transmission emission microscope. It shows that N-isopropylacrylamide has been grafted on the surface of KH-570modified nano-SiO2. The result of water contact angle showed that the modified nano-spheres were in response to a temperature stimulus, and the phase transformation temperature was between30℃and33℃.