In Situ Synchrotron X‐Ray Techniques for Real‐Time Probing of Colloidal Nanoparticle Synthesis

Solution‐phase synthesis of colloidal nanoparticles with precisely tailored properties is one of the fastest growing research topic and represents the most critical foundation to implant nanotechnology in a variety of areas to boost performance of traditional systems. Comprehensive understanding of the nucleation and growth mechanisms involved in the formation of colloidal nanoparticles is very important to realize rational design and synthesis of well‐tailored nanoparticles and requires appropriate in situ techniques to probe the kinetics of the synthetic reactions. Synchrotron hard X‐rays represent a class of promising probes for solution‐phase reactions due to their strong penetration in ambient environment and solutions. This review completely summarizes the in situ synchrotron X‐ray techniques emerged in the recent years for real‐time probing nanophase evolution of colloidal nanoparticles. Typical examples of colloidal nanoparticle syntheses are discussed in detail to shed the light on the advantages and disadvantages of individual techniques.     

Nanoparticles: Implication of Ligand Choice on Surface Properties,Crystal Structure,and Magnetic Properties of Iron Nanoparticles (Part. Part. Syst. Charact. 3/2013)

The behavior of iron nanoparticles is heavily influenced by their highly reactive surfaces. A better understanding of organic ligand/particle interactions must be achieved in order to synthesize iron nanoparticles with magnetic saturations (σ _sat) equivalent to bulk iron. Even when synthesized using careful, air‐free chemistry techniques and ligands more weakly interacting than those often reported in the literature, the magnetic saturation of iron nanoparticles generally only approaches, but not equals, the magnetic saturation of bulk iron. Here, iron nanoparticles are synthesized using Schlenk line chemistry methods and two different weakly interacting ligands: 2,4‐pentanedione and hexaethylene glycol monododecylether. These particles have saturation magnetizations slightly lower than bulk iron, which is believed to be caused by interactions between the passivating ligands and the surface of the nanoparticles. Using X‐ray absorption fine structure studies, it is shown that oxidized species of iron exist at the nanoparticles’ surface and can be attributed to iron/ligand interaction. The percentage of oxidized species scales with the surface to volume ratio of the nanoparticles, and therefore appears limited to the nanoparticle surface. X‐ray absorption fine structure analysis also shows that the nanoparticles have an expanded crystalline lattice, which can further impact their magnetic properties.     

Colloidal Nanoparticles: Formation of Large 2D Arrays of Shape‐Controlled Colloidal Nanoparticles at Variable Interparticle Distances (Part. Part. Syst. Charact. 1/2013)

A method for the production of homogeneous layers of nanoparticles of arbitrary shape is presented. The method relies on a ligand exchange with a functionalized polymer and a subsequent self‐assembly of a thin film on the substrates. The interparticle distances in the layer can be adjusted by the length of the polymer. In the case of spherical particles, the approach yields quasi‐hexagonal structures; in the case of anisotropic particles, the minimum distance between adjacent particles is controlled. Regular arrangements of the nanoparticles covering areas of several square centimeters are achieved.     

In situ observation of water distribution and behaviour in a polymer electrolyte fuel cell by synchrotron X‐ray imaging

In situ visualization of the distribution and behaviour of water in a polymer electrolyte fuel cell during power generation has been demonstrated using a synchrotron X‐ray imaging technique. Images were recorded using a CCD detector combined with a scintillator (Gd₂O₂S:Tb) and relay lens system, which were placed at 2.0 m or 2.5 m from the fuel cell. The images were measured continuously before and during power generation, and data on cell performance was recorded. The change of water distribution during power generation was obtained from X‐ray images normalized with the initial state of the fuel cell. Compared with other techniques for visualizing the water in fuel cells, this technique enables the water distribution and behaviour in the fuel cell to be visualized during power generation with high spatial resolution. In particular, the effects of the specifications of the gas diffusion layer on the cathode side of the fuel cell on the distribution of water were efficiently identified. This is a very powerful technique for investigating the mechanism of water flow within the fuel cell and the relationship between water behaviour and cell performance.     

Janus Particles: Metallic Janus and Patchy Particles (Part. Part. Syst. Charact. 1/2013)

The concepts of Janus and patchy particles are relatively new in nanoscience. Much effort has been made during recent years to devise and fabricate asymmetric particles with multiple compositions and functionalities due to their interesting properties and potential applications in a variety of fields such as catalysis, optical imaging, or drug delivery. Here, recent advances in the field of Janus particles are highlighted, focusing on nanoparticles comprising (at least) one metallic component, which is responsible for the most interesting properties of the particles. First, the main synthetic approaches are summarized, i.e., phase separation, masking, and self‐assembly techniques, and then the special properties, applications, and future prospects of metallic Janus particles are described.     

Multicore Capsules: Thermo‐Stimulable Wax@Water@SiO2 Multicore‐Shell Capsules (Part. Part. Syst. Charact. 2/2013)

Complex wax@water@SiO₂ multicore capsules are synthesized by combining sol‐gel process and formulation of wax‐in‐water‐in‐oil double emulsions. The inner direct wax‐in‐water emulsion is stabilized with modified silica nanoparticles using limited coalescence occurring in Pickering emulsions. In a second step, this obtained liquid dispersion is emulsified in poly‐dimethylsiloxane (PDMS) using a non ionic surfactant to stabilize the second water/oil interface. Finally, a sol‐gel process is employed to mineralize the as‐generated double emulsions giving rise to wax@water@SiO₂ multicore capsules. Due to the wax volume expansion through melting, the as‐synthesized multicore capsules offer thermally stimulated release that is enhanced when surfactant is added in the surrounding continuous oil phase. In addition, the melted wax release can be tuned from a one‐step process to a more sequential dropping mode by varying the mineral precursor tetraethoxy‐orthosilane (TEOS) concentration in the oily phase during mineralization.