浓悬浮液中纳米SiO_2团聚体的渗透率

本文基于悬浮液中渗透性颗粒的短时扩散动力学理论,采用低相干光纤动态光散射方法,测量了相同粒径的纳米SiO_2团聚体在不同体积分数时的扩散系数,利用扩散系数随渗透率的变化关系得到纳米SiO_2团聚体的渗透率.结果表明:恒温条件下,具有一定渗透率的团聚体颗粒扩散得比硬球颗粒快.实验测量得到的团聚体渗透率与采用photoshop CS6对团聚体SEM图像进行处理计算得到的渗透率符合较好.

Permeability of nano SiO2 aggregates in concentrated suspension

The low coherence optical fiber dynamic light scattering method is used to measure the effective diffusion coefficients of nano SiO₂ aggregates suspensions with different volume fractions. The single scattering component can be detected preferentially from the multiply scattered light which is backscattered from the dense suspensions by the low coherence optical fiber dynamic light scattering. Consequently, the measured single-scattering spectrum enables the analysis of the effective diffusion coefficient by the single scattering theory. The numerical calculation results of short-time diffusion dynamics for permeable particles in dense suspension show that the effective diffusion coefficient is a function of particle size and hydrodynamics shielding depth ratio β, and the volum fraction φ. According to the corrected Brinkman theory, the permeability of the nano SiO₂ aggregates is obtained. For the volume fraction φ = 0.01, 0.02, 0.03, 0.04, 0.05 nano SiO₂ aggregate suspensions with the average particle diameter 500 nm, the measured effective diffusion coefficients are 4.14±0.10, 4.06±0.06, 3.97±0.06, 3.90±0.08, 3.80±0.10 (×10^-13 m²/s) respectively. While according to the hard sphere model of impermeable particles, which corresponds to β = ∞ , the calculated effective diffusion coefficients are 3.70, 3.61, 3.52, 3.42, 3.36 (×10^-13 m²/s) respectively. It can be seen that the measured values are much bigger than the theoretical values of impermeable particles: their difference comes from the influence of permeability of porous aggregates on particle diffusion. It is found that the measured values are consistent with that of β = 12, in which the corrsponding permeability of the nano SiO₂ aggregates is k = 4.34× 10^-16 m². The pixel statistic method by Photoshop CS6 is used to deal with the SEM images of SiO₂ aggregates, the calculated permeability of the nano SiO₂ aggregates is k = 4.55× 10^-16 m², compared with the experimental result, the standard error is 4.87%. The results show that under the condition of constant temperature, the particles of permeable aggregates spread faster than the hard sphere particles. For constant temperature, particle size and permeability, the effective coefficient decreases with the increase of the volume fraction. The measured permeability of SiO₂ aggregates in concentrated suspension is consistent with that obtained from the pixel statistics by Photoshop CS6. As a result, the low coherent optical fiber dynamic light scattering can effectively measure the permeability of porous nano particles in concentrated suspension, showing high potential application in the field of chemical engineering and nano materials preparation.