Colloidal aggregation in microgravity by critical Casimir forces

TL;DR

This study investigates how critical Casimir forces influence colloidal aggregation in microgravity versus ground conditions, revealing that gravity significantly affects aggregate structure and growth kinetics, with microgravity promoting diffusion-limited, more open aggregates.

Contribution

It provides the first detailed comparison of colloidal aggregation driven by critical Casimir forces in microgravity and Earth conditions, highlighting gravity's role in aggregation dynamics.

Findings

Microgravity leads to diffusion-limited aggregation behavior.

Ground experiments are dominated by sedimentation effects.

Aggregates become more open with increasing attractive strength.

Abstract

By using the critical Casimir force, we study the attractive strength dependent aggregation of colloids with and without gravity by means of Near Field scattering. Significant differences were seen between microgravity and ground experiments, both in the structure of the formed fractal aggregates as well as the kinetics of growth. Ground measurements are severely affected by sedimentation resulting in reaction limited behavior. In microgravity, a purely diffusive behavior is seen reflected both in the measured fractal dimensions for the aggregates as well as the power law behavior in the rate of growth. Formed aggregates become more open as the attractive strength increases.