Insights into the precipitation kinetics of CaCO3 particles in the presence of polystyrene sulfonate using in situ small-angle X-ray scattering.

The formation of calcium carbonate (CaCO3) nanoparticles (NPs) in the presence of polystyrene sulfonate (PSS) as an additive was examined by time-resolved small-angle X-ray scattering (SAXS) in a flow system that mimics experimental conditions used at home facilities where the precipitation can be achieved in a beaker. The experiments were carried out at low concentrations to remain in the dilute regime. A model-independent analysis was performed using the Porod invariant which defines the scale factor, leaving only the distribution of radii as the adjustable parameter. The presence of the PSS additive strongly retards the precipitation of CaCO3 NPs. The formation of NPs reaches a state of equilibrium after a few minutes. Here, it is shown that the concentration of precursors at a fixed PSS concentration plays a key role in determining the size of the NPs obtained. A full analysis of the SAXS patterns was carried out using the Hurd-Flower model to account for the weaker intensity decay than the classical Porod behaviour. The temporal evolution of the particle radii was determined. Wide-angle X-ray scattering experiments carried out simultaneously show that the particles formed have the structure of vaterite with growth consistent with the evolution of the Porod invariant.

In-Situ X-ray Tomography Study of Cement Exposed to CO2 Saturated Brine.

For successful CO2 storage in underground reservoirs, the potential problem of CO2 leakage needs to be addressed. A profoundly improved understanding of the behavior of fractured cement under realistic subsurface conditions including elevated temperature, high pressure and the presence of CO2 saturated brine is required. Here, we report in situ X-ray micro computed tomography (µ-CT) studies visualizing the microstructural changes upon exposure of cured Portland cement with an artificially engineered leakage path (cavity) to CO2 saturated brine at high pressure. Carbonation of the bulk cement, self-healing of the leakage path in the cement specimen, and leaching of CaCO3 were thus directly observed. The precipitation of CaCO3, which is of key importance as a possible healing mechanism of fractured cement, was found to be enhanced in confined regions having limited access to CO2. For the first time, the growth kinetics of CaCO3 under more realistic well conditions have thus been estimated quantitatively. Combining the µ-CT observations with scanning electron microscopy resulted in a detailed understanding of the processes involved in the carbonation of cement.

Improving organic tandem solar cells based on water-processed nanoparticles by quantitative 3D nanoimaging.

Organic solar cells have great potential for upscaling due to roll-to-roll processing and a low energy payback time, making them an attractive sustainable energy source for the future. Active layers coated with water-dispersible Landfester particles enable greater control of the layer formation and easier access to the printing industry, which has reduced the use of organic solvents since the 1980s. Through ptychographic X-ray computed tomography (PXCT), we image quantitatively a roll-to-roll coated photovoltaic tandem stack consisting of one bulk heterojunction active layer and one Landfester particle active layer. We extract the layered morphology with structural and density information including the porosity present in the various layers and the silver electrode with high resolution in 3D. The Landfester particle layer is found to have an undesired morphology with negatively correlated top- and bottom interfaces, wide thickness distribution and only partial surface coverage causing electric short circuits through the layer. By top coating a polymer material onto the Landfester nanoparticles we eliminate the structural defects of the layer such as porosity and roughness, and achieve the increased performance larger than 1 V expected for a tandem cell. This study highlights that quantitative imaging of weakly scattering stacked layers of organic materials has become feasible by PXCT, and that this information cannot be obtained by other methods. In the present study, this technique specifically reveals the need to improve the coatability and layer formation of Landfester nanoparticles, thus allowing improved solar cells to be produced.

Crystallization in diblock copolymer thin films at different degrees of supercooling.

The crystalline structures in thin films of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymers were studied in dependence on the degree of supercooling. Atomic force microscopy showed that the crystalline domains (lamellae) consist of grains, which are macroscopic at low and intermediate degrees of supercooling, but of submicrometer size for strong supercooling. Using grazing-incidence wide-angle x-ray scattering, we could determine the grain orientation distribution function which shows that the chain stems are perpendicular to the lamellae at low supercooling, but tilted at intermediate and strong supercooling. These results suggest that, at intermediate and strong supercooling, the crystalline PEO lamellae do not grow homogeneously, but by the formation of small crystallites at the growth front.