Particle Size Measurements of Dark and Concentrated Dispersions by Dynamic Light Scattering

In this paper, we introduce an innovative device for nanoparticle sizes measurement in dark and concentrated media based on dynamic light scattering (DLS). Conventional DLS is a powerful technique to characterisedilute and transparent dispersions of nanoparticles. However, it becomes ineffective in dark media, since the laser beam is absorbed by the sample and can induce an interfering effect. In the case of concentrated samples, the artefact of multiple scattering also biases the measurement. To circumvent these problems, we propose an original optical configuration that combines back-scattered light detection and the capability to control the sample thickness. The benefits of these improvements are discussed through experimental results obtained from measurement on model latex dispersions.

INTRODUCTION
Research on nanoparticles covers a wide range of interests in the fields of physics, chemistry and material science. In particular, the characterisation of particle sizes and aggregates formation is a key issue in some processes of mesoporous materials preparation since they will affect the final network and micropore structures. In this proceeding, we introduce an innovative device for nanoparticle size measurement in dark and concentrated media. The ‘Vasco’ is issued from a mature and patented technology [6] transferred from the Institut Français du Pétrole (IFP) to Cordouan Technologies and was initially developed to study the kinetics of asphaltene aggregation in toluene–heptane mixtures [1]. We first present the principle of conventional dynamic light scattering with dilute state before reviewing the main limitations of this technique. We especially focus on the case of dark and concentrated samples that traditionally present some major difficulties for such an analysis and which are typically the case for many research and industrial applications. Then, we show how the original optical configuration of ‘Vasco’ can overcome these kinds of experimental problems.