Colloidal aggregation and critical Casimir forces

TL;DR

This paper critically examines experimental observations of colloidal aggregation in a liquid mixture, questioning the validity of the existing model based solely on electrostatic and critical Casimir forces, and highlighting inconsistencies in the data interpretation.

Contribution

It challenges the previous interpretation of colloidal aggregation data, showing that the proposed model does not account for all experimental observations and suggesting the need for alternative explanations.

Findings

Reported aggregation occurs outside the model's parameter ranges

Significant experimental data cannot be explained by the electrostatic and Casimir force model

The existing model is insufficient to fully describe colloidal aggregation phenomena

Abstract

A recent Letter [Phys. Rev. Lett. 103, 156101 (2009)] reports the experimental observation of aggregation of colloidal particles dispersed in a liquid mixture of heavy water and 3-methylpyridine. The experimental data are interpreted in terms of a model which accounts solely for the competing effects of the interparticle electrostatic repulsion and of the attractive critical Casimir force. Here we show, however, that the reported aggregation actually occurs within ranges of values of the correlation length and of the Debye screening length ruled out by the proposed model and that a significant part of the experimental data presented in the Letter cannot be consistently interpreted in terms of such a model.