Department of Chemical Engineering, National Taiwan University , Taipei, Taiwan 10617.
Langmuir. 2016 Dec 27;32(51):13620-13626. doi: 10.1021/acs.langmuir.6b03602. Epub 2016 Dec 15.
In this work, the long-term stability of titanium oxide nanowire suspensions was accessed by an accelerated sedimentation with centrifugal forces. Titanium oxide (TiO) nanoparticle (NP) and nanowire (NW) dispersions were prepared, and their sizes were carefully characterized. To replace the time-consuming visual observation, sedimentation velocities of the TiO NP and NW suspensions were measured using an analytical centrifuge. For an aqueous TiO NP suspension, the measured sedimentation velocities were linearly dependent on the relative centrifugal forces (RCF), as predicted by the classical Stokes law. A similar linear relationship was also found in the case of TiO NW aqueous suspensions. However, NWs preferred to settle parallel to the centrifugal direction under high RCF because of the lower flow resistance along the long axis. Thus, the extrapolated sedimentation velocity under regular gravity can be overestimated. Finally, a stable TiO NW suspension was formulated with a shear thinning fluid and showed great stability for weeks using visual observation. A theoretical analysis was deduced with rheological shear-thinning parameters to describe the nonlinear power-law dependence between the measured sedimentation velocities and RCF. The good agreement between the theoretical predictions and measurements suggested that the sedimentation velocity can be properly extrapolated to regular gravity. In summary, this accelerated assessment on a theoretical basis can yield quantitative information about long-term stability within a short time (a few hours) and can be further extended to other suspension systems.
在这项工作中，通过离心力加速沉降来评估氧化钛纳米线悬浮液的长期稳定性。制备了氧化钛（TiO）纳米颗粒（NP）和纳米线（NW）分散体，并对其尺寸进行了仔细表征。为了替代耗时的目视观察，使用分析离心机测量了 TiO NP 和 NW 悬浮液的沉降速度。对于水性 TiO NP 悬浮液，测量的沉降速度与相对离心力（RCF）呈线性关系，如经典 Stokes 定律所预测。在 TiO NW 水性悬浮液的情况下也发现了类似的线性关系。然而，由于沿长轴的流动阻力较低，在高 RCF 下 NW 更倾向于沿离心方向平行沉降。因此，在常规重力下推断的沉降速度可能会被高估。最后，用剪切稀化流体配制了稳定的 TiO NW 悬浮液，通过目视观察，该悬浮液在数周内保持了很好的稳定性。通过流变剪切稀化参数推导出了一个理论分析，以描述测量的沉降速度和 RCF 之间的非线性幂律关系。理论预测和测量之间的良好一致性表明，可以适当地将沉降速度外推到常规重力。总之，这种基于理论的加速评估可以在短时间（数小时）内提供关于长期稳定性的定量信息，并可进一步扩展到其他悬浮液系统。
