Number Density Distribution of Small Particles around a Large Particle: Structural Analysis of a Colloidal Suspension

Ken-ichi Amano, Mitsuhiro Iwaki, Kota Hashimoto, Kazuhiro Fukami, Naoya Nishi, Ohgi Takahashi, and Tetsuo Sakka
Some colloidal suspensions contain two types of particles—small and large particles—to improve the lubricating ability, light absorptivity, etc. Structural and chemical analyses of such colloidal suspensions are often performed to understand their properties. In a structural analysis study, the observation of the number density distribution of small particles around a large particle (gLS) is difficult because these particles are randomly moving within the colloidal suspension by Brownian motion. We obtained gLS using the data from a line optical tweezer (LOT) which can measure the potential of mean force between two large colloidal particles (ΦLL). We propose a theory that transforms ΦLL into gLS. The transform theory is explained in detail and tested. We demonstrate for the first time that LOT can be used for the structural analysis of a colloidal suspension. LOT combined with the transform theory will facilitate structural analyses of the colloidal suspensions, which is important for both understanding colloidal properties and developing colloidal products.

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