Institute of Particle Science and Engineering, University of Leeds, Leeds, LS2 9JT, United Kingdom.
J Colloid Interface Sci. 2010 Dec 1;352(1):99-106. doi: 10.1016/j.jcis.2010.08.044. Epub 2010 Aug 19.
Dried deposits of spherical Ludox silica and disk-like laponite clay nanoparticles have been examined by dark-field optical microscopy and atomic force microscopy (AFM) to investigate the effects of nanoparticle shape on the deposit structure. Dark-field optical images indicated that a higher concentration of Ludox nanoparticles was required, compared to laponite, for an optically visible deposit to be formed. Compared with the relatively simple ring-like features observed at the edges of Ludox deposits, the laponite deposits were more complex, with dendritic features appearing below 10ppm that disappeared at higher laponite concentrations. AFM images revealed that whilst the Ludox rim deposit structure gradually increased in height and width with increasing nanoparticle concentration, the laponite rim deposits increased steadily in height up to 1ppm, above which the rim height suddenly decreased and the deposit structure became smoother. The widths of the rim deposits were observed to increase in a similar manner for both nanoparticle types. Nanoparticle shape is suggested as the main reason for differences in the structural features of the rim for each nanoparticle type. The disk-like laponite forms tall thin rim profiles at low concentrations, before creating a more uniform rim profile at higher concentrations. We suggest that a critical laponite rim height is reached before partial collapse of the nanoparticle stack at the rim takes place as the particle concentration is further increased. This produces much thinner and smoother films of laponite at high particle concentrations than is found for similar concentrations of Ludox. Our work suggests that both the shape and the concentration of the nanoparticles themselves are crucial in determining the structure of the final dried nanoparticle deposit.
已通过暗场光学显微镜和原子力显微镜（AFM）检查了球形 Ludox 硅溶胶和盘状皂土纳米颗粒的干燥沉积物，以研究纳米颗粒形状对沉积物结构的影响。暗场光学图像表明，与皂土相比，形成可见的光沉积需要更高浓度的 Ludox 纳米颗粒。与在 Ludox 沉积物边缘观察到的相对简单的环形特征相比，皂土沉积物更为复杂，在低于 10ppm 时出现枝状特征，而在较高的皂土浓度下消失。AFM 图像显示，虽然 Ludox 边缘沉积物结构随着纳米颗粒浓度的增加逐渐增加高度和宽度，但皂土边缘沉积物的高度稳定增加到 1ppm，高于该浓度，边缘高度突然降低，沉积物结构变得更加光滑。边缘沉积物的宽度也以类似的方式观察到对于两种纳米颗粒类型都增加。纳米颗粒形状被认为是每种纳米颗粒类型边缘结构特征差异的主要原因。盘状皂土在低浓度下形成高而细的边缘轮廓，然后在高浓度下形成更均匀的边缘轮廓。我们建议，当粒子浓度进一步增加时，在边缘处的纳米粒子堆积部分坍塌之前，达到临界的皂土边缘高度，从而在高粒子浓度下产生比 Ludox 类似浓度更薄且更光滑的皂土薄膜。我们的工作表明，纳米颗粒的形状和浓度本身都是决定最终干燥纳米颗粒沉积物结构的关键因素。
