Diffusiophoresis of latex driven by anionic nanoparticles and their counterions

Hypothesis: Diffusiophoresis of colloidal latex particles has been reported for molecular anions and cations of comparable size. In the present study, this phenomenon is observed for two types of charged colloids acting as multivalent electrolyte: (i) anionic charge-stabilised silica nanoparticles or (ii) minimally-charged sterically-stabilised diblock copolymer nanoparticles. Experiments: Using a Hele-Shaw cell, a thin layer of relatively large latex particles is established within a sharp concentration gradient of nanoparticles by sequential filling with water, latex particles and nanoparticles. Asymmetric diffusion is observed, which provides strong evidence for diffusiophoresis. Quantification involves turbidity measurements from backlit images. Findings: The latex particles diffuse across a concentration gradient of charged nanoparticles and the latex concentration front scales approximately with time1/2. Moreover, the latex particle flux is inversely proportional to the concentration of background salt, confirming electrostatically-driven motion. These observations are consistent with theory recently developed to account for diffusiophoretic motion driven by multivalent ions.

Automated summary

This study observes the diffusion behavior of two types of charged colloidal particles (silica particles and diblock copolymer particles) under concentration gradient conditions, and finds that the concentration of the particles scales approximately with the square root of time. These observations are consistent with a recently developed theory that explains diffusiophoretic motion driven by multivalent ions.