Search

[Display omitted] Understanding deagglomeration, agglomerate formation and structure for very small nanoparticles (NPs), due to their more facile agglomeration, is critical for processing or tailoring agglomerates for nanostructured materials. We propose that by controlling and fine-tuning the interplay of agglomeration (colloidal interaction) and deagglomeration (hydrodynamic forces), the design of agglomerate size, microstructure and morphology is possible even for very small NPs. Here, we investigate very small SnO 2 NPs (10 nm) generated in the gas phase as model system. Small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) are used to study dispersions in aqueous media across the entire pH range (2–12) at various NaCl concentrations treated with ultrasound. Parallel to size and size distribution, agglomerate morphology and microstructure are analyzed by means of the mass fractal dimension, d m and modeled with ab initio shape simulations. The critical coagulation concentration (CCC) is determined for the alkaline region where the SnO 2 NPs are highly charged. Quantitative analysis of SAXS and DLS data reveals that size and size distribution of the agglomerates depend similarly on the electrostatic interaction influenced by pH and salinity as observed by the zeta potential. In contrast d m is mainly influenced by the salt concentration. Ab initio shape simulations support these experimental findings. [ABSTRACT FROM AUTHOR]

An important goal for the development of novel nanomaterials based on magnetic nanoparticles dispersed in liquid crystals is the improvement of the sensitivity to magnetic fields. Despite the continuous research of the magnetically-controlled properties of such hybrid composite materials, known as ferronematics, a persistent challenge lies in achieving consistent homogeneity and colloidal stability of the nanoparticles in liquid crystal media. Therefore, the design of the magnetic nanoparticles needs to be compatible with the liquid crystal matrix. Coating nanoparticles with (pro)mesogenic ligands has been shown to be a versatile way of stabilizing magnetic nanoparticles in liquid crystal matrices. Here, we report about the effect of dendrimer-functionalized cobalt ferrite nanoparticles (CoFe 2 O 4 @dend) on structure and magnetic sensitivity in the thermotropic liquid crystal 4-pentyl-4 ′ -cyanobiphenyl (5CB) confirmed by small angle X-ray scattering (SAXS), magnetization and capacitance measurements. Our measurements reveal that for dendronized magnetic nanoparticles, the sensitivity to magnetic fields is improved. However, they exhibit a tendency to form clusters in the liquid crystal medium. These clusters induce a tilting of the overall ordering of the nematic director field due to magneto-nematic coupling. • Dendrimer-functionalized cobalt ferrite nanoparticles have been synthesized. • Nano-suspensions of CoFe 2 O 4 nanoparticles in 5CB liquid crystal have been prepared. • Magnetization, SAXS, and capacitance measurements were conducted. • Presence of magnetic nanoparticles' clusters in a liquid crystal matrix was observed. • Molecular tilt in the vicinity of these clusters is reported. [ABSTRACT FROM AUTHOR]

Abstract: Ligand‐layer structure and stability of gold nanoparticles (AuNP) coated with α‐methoxypoly(ethylene glycol)‐ω‐(11‐mercaptoundecanoate) (PEGMUA) layers and mixed layers of PEGMUA and 11‐mercaptoundecanoic acid (MUA) at high AuNP concentrations are studied in situ by small‐angle X‐ray scattering (SAXS). The thickness of the ligand layer is modified by the molecular weight of the PEG‐ligands (2 and 5 kDa), and the PEG‐grafting density is decreased by coadsorption of MUA. The response of the conjugates to a pressure of up to 4 kbar is probed. The results indicate strongly hydrated PEG layers at high grafting densities. The stability of the mixed ligand‐layer conjugates is lower. This is most probably due to enhanced interparticle PEG–PEG interactions at lower grafting densities. The presented study demonstrates that a detailed structural characterization of polymer ligand layers in situ and in response to external stimuli is possible with SAXS. [ABSTRACT FROM AUTHOR]