van der Waals-Zeeman Institute, University of Amsterdam, Valckenierstraat 65, 1018XE Amsterdam, The Netherlands.
Phys Rev Lett. 2009 Oct 9;103(15):156101. doi: 10.1103/PhysRevLett.103.156101. Epub 2009 Oct 8.
We present a refractive-index-matched colloidal system that allows direct observation of critical Casimir induced aggregation with a confocal microscope. We show that in this system, in which van der Waals forces are negligible, a simple competition between repulsive screened Coulomb and attractive critical Casimir forces can account quantitatively for the reversible aggregation. Above the temperature T(a), the critical Casimir force drives aggregation of the particles into fractal clusters, while below T(a), the electrostatic repulsion between the particles breaks up the clusters, and the particles resuspend by thermal diffusion. The aggregation is observed in a remarkably wide temperature range of as much as 15 degrees. We derive a simple expression for the particle pair potential that accounts quantitatively for the temperature-dependent aggregation and aggregate breakup.
我们提出了一种折射率匹配的胶体系统，该系统可使用共焦显微镜直接观察临界 Casimir 诱导的聚集。我们表明，在这个范德瓦尔斯力可以忽略不计的系统中，简单的排斥屏蔽库仑力和吸引力临界 Casimir 力之间的竞争可以定量解释可逆聚集。在温度 T(a)以上，临界 Casimir 力促使颗粒聚集形成分形团簇，而在 T(a)以下，颗粒之间的静电排斥力会使团簇解体，颗粒通过热扩散重新悬浮。在高达 15 度的宽温度范围内观察到了聚集。我们导出了一个简单的粒子对势表达式，该表达式可以定量地解释温度依赖性聚集和聚集体解体。
