As a solid foam stabilizer, spherical silica particles with diameters ranging from 150 to 190 nm were prepared via an improved Stober methOd and were subsequently modified using three different silane coupling agents ...As a solid foam stabilizer, spherical silica particles with diameters ranging from 150 to 190 nm were prepared via an improved Stober methOd and were subsequently modified using three different silane coupling agents to attain the optimum surface hydrophobicity of the particles. Fourier transform infrared （FTIR） spectra and the measured contact angles were used to characterize the surface properties of the prepared particles. The foam stability was investigated by the foam drainage half-life and the expansion viscoelastic modulus of the liquid film. The results demonstrate that all of the modified silica nanoparticles effectively improve the foam stability. The surface hydrophobicity of the modified particles is found to be a key factor influencing the foam stability. The optimum contact angle of the particles lies in the ap- proximate range from 50° to 55°. The modifier molecular structure used can also influence the stabilizing foam property of the solid particles The foam system stabilized by （CH3）2SiCl2-modified silica particles exhibits the highest stability; its drainage half-life at maximum increases by 27% compared to that of the blank foam system and is substantially greater than those of the foam systems stabilized by KH570- and KH550-modified particles.展开更多
The effect of freezing layer on the crystallization kinetics of poly(ε-caprolactone)(PCL)thin and ultrathin films was investigated by monitor the growth process of it on oriented polyethylene(PE)and CaF_(2)with and w...The effect of freezing layer on the crystallization kinetics of poly(ε-caprolactone)(PCL)thin and ultrathin films was investigated by monitor the growth process of it on oriented polyethylene(PE)and CaF_(2)with and without freezing layer,respectively.It was found that the PCL films with similar thicknesses crystallize much faster on oriented PE than on CaF_(2)substrate.For example,the crystallization rate constant of a 102 nm thick PCL film decreases tremendously by 3 orders of magnitude from 1.1×10^(-1) on PE substrate at 50℃to 7×10^(-4)on CaF_(2)surface at 40℃.Moreover,the crystallization of PCL accelerates on CaF_(2)surface while slows down at PE surface with increasing film thickness.The ultrathin films of PCL with thickness less than 14 nm exhibits the fastest crystallization rate on oriented PE with a rate constant of about 3.5×10^(-1),which is 3 times higher than that of a ca.50 nm thick film.This illustrates the great influence of freezing layer on the crystallization process of PCL.The freezing layer thickness of PCL on PE is estimated to be in the range of 14-17 nm.Taking the radius of gyration(R_(g)~15.6 nm)of the used PCL material into account,the obtained results may imply the existence of a correlation between the R_(g)of PCL and its freezing layer thickness at PE substrate.展开更多
基金financially supported by the National Natural Science Foundation of China(No.21276022)the China National Petroleum Corporation Innovation Foundation(No.2012D-5006-0208)
文摘As a solid foam stabilizer, spherical silica particles with diameters ranging from 150 to 190 nm were prepared via an improved Stober methOd and were subsequently modified using three different silane coupling agents to attain the optimum surface hydrophobicity of the particles. Fourier transform infrared （FTIR） spectra and the measured contact angles were used to characterize the surface properties of the prepared particles. The foam stability was investigated by the foam drainage half-life and the expansion viscoelastic modulus of the liquid film. The results demonstrate that all of the modified silica nanoparticles effectively improve the foam stability. The surface hydrophobicity of the modified particles is found to be a key factor influencing the foam stability. The optimum contact angle of the particles lies in the ap- proximate range from 50° to 55°. The modifier molecular structure used can also influence the stabilizing foam property of the solid particles The foam system stabilized by （CH3）2SiCl2-modified silica particles exhibits the highest stability; its drainage half-life at maximum increases by 27% compared to that of the blank foam system and is substantially greater than those of the foam systems stabilized by KH570- and KH550-modified particles.
基金financially supported by the National Natural Science Foundation of China(Nos.52103017 and 52027804)。
文摘The effect of freezing layer on the crystallization kinetics of poly(ε-caprolactone)(PCL)thin and ultrathin films was investigated by monitor the growth process of it on oriented polyethylene(PE)and CaF_(2)with and without freezing layer,respectively.It was found that the PCL films with similar thicknesses crystallize much faster on oriented PE than on CaF_(2)substrate.For example,the crystallization rate constant of a 102 nm thick PCL film decreases tremendously by 3 orders of magnitude from 1.1×10^(-1) on PE substrate at 50℃to 7×10^(-4)on CaF_(2)surface at 40℃.Moreover,the crystallization of PCL accelerates on CaF_(2)surface while slows down at PE surface with increasing film thickness.The ultrathin films of PCL with thickness less than 14 nm exhibits the fastest crystallization rate on oriented PE with a rate constant of about 3.5×10^(-1),which is 3 times higher than that of a ca.50 nm thick film.This illustrates the great influence of freezing layer on the crystallization process of PCL.The freezing layer thickness of PCL on PE is estimated to be in the range of 14-17 nm.Taking the radius of gyration(R_(g)~15.6 nm)of the used PCL material into account,the obtained results may imply the existence of a correlation between the R_(g)of PCL and its freezing layer thickness at PE substrate.
