On the absence of structure factors in concentrated colloidal suspensions and nanocomposites

• Published in: The European physical journal. E, Soft matter and biological physics Soft matter and biological physics, 2023-06, Vol.46 (6), p.46-46, Article 46
• Main Authors: Genix, Anne-Caroline, Oberdisse, Julian
• Format: Article
• Language: English
• Subjects: 50 years of Small Angle Neutron Scattering at the ILL in Grenoble; Biological and Medical Physics; Biophysics; Colloids; Complex Fluids and Microfluidics; Complex Systems; Condensed Matter; Condensed matter physics; Correlation; Form factors; Nanocomposites; Nanoparticles; Nanotechnology; Physics; Physics and Astronomy; Polydispersity; Polymer Sciences; Regular Article - Soft Matter; Scattering; Soft and Granular Matter; Soft Condensed Matter; Structure factor; Surfaces and Interfaces; Thin Films
• ISSN: 1292-8941; 1292-895X
• DOI: 10.1140/epje/s10189-023-00306-6

Small-angle scattering is a commonly used tool to analyze the dispersion of nanoparticles in all kinds of matrices. Besides some obvious cases, the associated structure factor is often complex and cannot be reduced to a simple interparticle interaction, like excluded volume only. In recent experiments, we have encountered a surprising absence of structure factors ( S ( q ) = 1) in scattering from rather concentrated polymer nanocomposites (Genix et al. in ACS Appl Mater Interfaces 11(19):17863–17872, 2019). In this case, quite pure form factor scattering is observed. This somewhat “ideal” structure is further investigated here making use of reverse Monte Carlo simulations in order to shed light on the corresponding nanoparticle structure in space. By fixing the target “experimental” apparent structure factor to one over a given q -range in these simulations, we show that it is possible to find dispersions with this property. The influence of nanoparticle volume fraction and polydispersity has been investigated, and it was found that for high concentrations only a high polydispersity allows reaching a state of S  = 1. The underlying structure in real space is discussed in terms of the pair-correlation function, which evidences the importance of attractive interactions between polydisperse nanoparticles. The calculation of partial structure factors shows that there is no specific ordering of large or small particles, but that the presence of attractive interactions together with polydispersity allows reaching an almost “structureless” state. Graphical abstract