Dispersion forces acting between silica particles across water: influence of nanoscale roughness.
Dispersion forces acting between silica particles across water: influence of nanoscale roughness.
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DOI：
10.1039/c6nh00070c
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发表时间：
2016-06
影响因子：
9.7
通讯作者：
Valentina Valmacco;M. Elżbieciak-Wodka;C. Besnard;P. Maroni;G. Trefalt;M. Borkovec
中科院分区：
文献类型：
--
作者：
Valentina Valmacco;M. Elżbieciak-Wodka;C. Besnard;P. Maroni;G. Trefalt;M. Borkovec
使用原子力显微镜（AFM）测量一价盐的浓缩水溶液中的二氧化硅颗粒对之间的力分布。在这样的条件下，双层力可以忽略不计，并且在较大的距离处，分布由货车德瓦耳斯分散力支配。颗粒的热处理强烈影响分散力的强度。在1200 °C下加热的颗粒之间的分散力具有强烈的吸引力，其特征在于Hamaker常数为2.4 × 10-21 J。然而，对于未经处理的颗粒，分散力要弱得多，Hamaker常数为7 × 10-23 J。Hamaker常数可以通过在1000和1200 °C之间调节加热温度来连续调节。Hamaker常数的这种实质性变化是由纳米级表面粗糙度的适度差异引起的。粗糙度的均方根（RMS）与Hamaker常数成反比，由此在1200 °C下处理的颗粒具有0.63nm的RMS值，而未处理的颗粒具有2.5nm的RMS值。可以排除可能影响Hamaker常数的其他效应，例如结晶度、孔隙率和颗粒形状的变化。
Force profiles between pairs of silica particles in concentrated aqueous solutions of a monovalent salt are measured using atomic force microscopy (AFM). Under such conditions, the double layer forces are negligible, and the profiles are dominated by van der Waals dispersion forces at larger distances. Heat treatment of the particles strongly influences the strength of dispersion forces. The dispersion force between the particles heated at 1200 °C was strongly attractive, and was characterized by a Hamaker constant of 2.4 × 10-21 J. This value is in good agreement with the current best theoretical estimate of the Hamaker constant for silica across water. For untreated particles, however, the dispersion force is much weaker and the Hamaker constant is 7 × 10-23 J. The Hamaker constant can be continuously tuned by adjusting the heating temperature between 1000 and 1200 °C. Such substantial variations of the Hamaker constant are caused by moderate differences in surface roughness on the nanoscale. The root mean square (RMS) of the roughness correlates inversely with the Hamaker constant, whereby the particles treated at 1200 °C have an RMS value of 0.63 nm, while the untreated particles have an RMS value of 2.5 nm. Other effects that could influence the Hamaker constant, such as changes in the degree of crystallinity, porosity, and shape of the particles, could be excluded.