PhD abstract

In Europe, regulatory requirements for labelling obligation for food, cosmetics or biocides impose to the additives users to know if the substances should be considered as a nanomaterial (NM) or not. A reliable metrology is therefore necessary for the nano-objects identification and characterization. This metrological characterization remains a challenge due to the numerous parameters to be considered in order to fully describe these nano-objects (size, size distribution, agglomeration/aggregation state, shape, specific surface area, chemical composition, surface chemistry and surface charge), which are listed in the ISO/TC 229 (PDTR 13014) standard. The thesis general context is the NMs characterization and more specifically dimensional characterization at the nanometric scale. The study focus on the Titanium dioxide (TiO2) (nano) particles which are ranked among the 5 most produced nanoparticulate substances (based on tonnage) in the world and used in many applications. The objective is to evaluate and compare measurands of several dimensional characterization techniques for nanoparticles and thus determine their constituent particle size. In this way, ensemble and integral techniques such as SAXS (small angle X-ray scattering), DLS (dynamic light scattering) and BET (Brunauer-Emmett-Teller) have been compared to the direct measurement technique, SEM (scanning electron microscopy). Emphasis is placed on the influence evaluation of several factors, namely, the size, the shape as well as the particles crystallinity and the complex matrix (set of elements in coexistence with the particles of interest), on the realized measurements. The selection of a large materials variety (reference, synthetic, raw material or finished products) enables the NMs characterization difficulties identification according to their sources. After a literature review to place the thesis in its context, a first part is devoted to the elaboration of a sample preparation protocol for SEM in order to improve the image processing step to comply with the regulations and to determine isolated particles size and/or constituents particles from agglomerates. Following the size of particles/agglomerates by DLS, the sonication step impact on the dispersion and dissociation of agglomerated (nano)-objects present in suspension was highlighted. In a second part, a multi-technique approach is implemented to compare two measurands from different instruments (an equivalent diameter to a projected surface area for SEM and a specific surface area for SAXS and BET), in order to access the dimensions of the studied (nano)-objects. The influence of different parameters such as the size distribution (or polydispersity), the purity of the samples (and thus the NMs extraction step from their matrix), the interaction between the particles and the particles anisotropy, are discussed. Interaction between particles and shape anisotropy are the most influential factors on specific surface area measurements, or SAXS/BET equivalent diameters. The achieved results illustrate the (nano)-objects characterization difficulties but they confirm the complementarity of the techniques used in this study (SEM, SAXS and BET).

Key words

Nanoparticle, Complex medium, Characterization method, Metrology