# Novel Microscopic Approach to Particle Size Evaluation in Colloidal Systems
In this ambit, the most effective methods for nanoparticle characterization involve microscopy-based methods [4]. Recent developments in nanoscience have been inspired by the observation that materials and their properties can be improved by tuning and adjusting particle size to match the desired outcome. However, the possibility of unpredictable and undesirable systemic effects which can be brought about by enhanced reactivity and modified properties has recently been a source of concern. Therefore, the proper characterization of the physicochemical properties of the nanomaterials in question is very important [5; 6; 7]. The colloidal model system used in this study is bitumen, which is a multidisciplinary micellar colloidal system (in particular, a sol) with a complex internal structure of the colloidal particles (solid asphaltene micelles) uniformly dispersed and suspended in an oily maltene phase. The asphaltene phase structure, which depends on the nature of the dispersion of the asphaltene micelles, has a significant effect on bitumen's rheological properties. Maltenes are believed to constitute a continuous dispersing phase in which the asphaltenes are dispersed. During the aging of bitumen, its aromatic components and resins become oxidized and are reduced to saturates leading to the hardening of the bitumen binder [8; 9]. This oxidation results in an increase in the size of the asphaltene micelles, thereby changing the bitumen's structure and reducing the fluidity of the system [10]. It has been observed that the asphaltene aggregates which form during bitumen aging form a dispersed'sol' structure in the continuous maltene phase instead of an expected network 'gel' structure [11]. The aging phenomenon brings about a degradation in the quality of the road pavement (bituminous conglomerate) and so the bituminous layers need to be removed and replaced using a new bituminous conglomerate. It is important to state that in view of a circular economy, a practice promoting resource conservation and recycling can be implemented. Using this approach, degraded bituminous layers, after removal, can be milled and processed to extract valuable asphalt binder (bitumen) and inorganic store aggregates. This is known as reclaimed asphalt pavement (RAP). In recent years, researchers have investigated the use of RAP in the production of recycled asphalt. The use of RAP for the production of new road pavements is at the center of research in the asphalt industry. The use of chemical additives is aimed at increasing the percentage of RAP in the production of bituminous conglomerates while maintaining the performance and life span of the road. The most common problem faced by both those who carry out quality control on bituminous conglomerates and those who research new additives to improve the performance of road pavements with RAP is to distinguish a potential rejuvenating effect from a fluxing effect. In fact, a flux-improving additive does not interact with the oxidized parts of the bitumen, leaving them unchanged while merely reducing the viscosity of the asphalt concrete. For this reason, the resulting road pavement will be very fragile and, therefore, its lifespan will be very short. On the contrary, a rejuvenating additive, thanks to its chemical interaction with the parts of the oxidized bitumen, will restore elasticity to the bitumen binder, thus restoring its physicochemical properties to the initial pre-oxidation state. In this study, only the solid part of bitumen, the asphaltenes, was considered due to the fact that studies in the literature [10; 12; 13] have shown that during the oxidation process, they tend to increase in size, thus stiffening the system. It is evident how fundamental it is to have techniques that can efficiently analyze the size distribution of these solid dispersed particles within bitumen. The present study is aimed at finding and validating new and cost-effective methods for size distribution analysis in this kind of material.