Novel Microscopic Approach to Particle Size Evaluation in Colloidal Systems

Abstract

Colloidal systems are peculiar mixtures formed by the uniform dispersion of sub-micro sized particles of one substance through another substance. In this framework, a particular colloidal system, known as sol, is a colloid in which the dispersed particles are solid, and the dispersing medium is fluid. Sols have extensive applications in industries ranging from material science to food to pharmaceuticals and cosmetics. The size and size distribution of colloidal particles within these systems play a pivotal role in determining their stability, rheological properties, and overall functionality (which in turn directly influence material quality, performance, and shelf life). As a result, this study is aimed at devising a new method to analyze the dimensions of the colloidal particles (dispersed phase) of a colloidal system (sol), like bitumen, by (i) a cheap and common technique, optical microscopy, and (ii) the more complex confocal laser scanning microscopy. To do so, a validation by comparison with a standard technique—in this case, atomic force microscopy is presented. Both optical and confocal microscopies turned out to be suitable, valid, and effective for particle size determination. Both techniques effectively revealed, upon bitumen aging, a shift of the size distribution to slightly larger sizes. Large particles, whose abundance did not increase significantly, appeared to be more inert than small ones. A huge advantage of optical microscopy is its popularity and cost-effectiveness as it is commonly featured in laboratories independently of the research topic. On the other hand, confocal microscopy can observe more particles, thus providing better statistics. It also appears to be more efficient for particles smaller than 1 µm2. These microscopy techniques were used to evaluate the dimensions of the asphaltenes present in a complex colloidal system; bitumen; the model colloidal system for this study, which was examined before and after an aging process which is expected to change the size distribution.

Keywords

• atomic force microscopy
• optical microscopy
• confocal laser scanning microscopy
• size distribution analysis and bitumen