Team A–Z

Responsibilities

My research concentrates on the understanding of homogeneous crystallisation processes of calcium silicate hydrates (C-S-H), which is the most important compound in modern cement. The main focus lies here in the pre-nucleation and early post-nucleation regime. Further, the influence of zinc on the nucleation of C-S-H is investigated, since it’s one of the most common impurities in cement. Another topic is the influence of dehydration processes (e. g. due to cosmotropic/chaotropic effects) on pre-nucleation species of C-S-H and the altering on its nucleation pathway. In general, all C-S-H is synthesised with simple silicon and calcium precursors via automated titration set-ups.

The crystallisation process is in-situ monitored with different electrodes and the obtained solid & pre-nucleation species are respectively analysed with the following methods: FT-IR, PXRD, TGA, SEM/EDX & (HR)TEM/EDX/ED, AUC, ToF-MS.

Responsibilities

Physical Chemistry

Towards sustainable cements: Understanding the crystallization of cementitious hydrates in LC3 blends as eco-friendly binder

Limestone calcined clay cements (LC³) are a very special and promising type of new cements. They take advantage of synergistic effects in the interaction of calcined clay and limestone as supplementary cementitious materials. With these cements it is already possible to reduce the clinker content to less than 50% and thus save more than 30% in CO₂ emissions. Additionally, LC³ blends are roughly 15-25% cheaper in production than ordinary Portland Cement (OPC). However, one of the few disadvantages still lies in the rheology of calcined clay-containing materials. Once water has been added, they are not as easy to handle as traditional Portland cement, making them somewhat more difficult to work with on the construction site. 

This is where the research of Yannick Emminger comes in and tries to find a way to firstly investigate and secondly influence the crystallisation of the different hydrates in LC³, making it more applicable for construction. Hereby, the hydrates (C-S-H, C-A-S-H, ettringite, calcium carboaluminates, AFm and AFt phases,...) are synthesised via a precipitation reaction from an aqueous solute phase and subsequently analysed. The aim is to monitor the nucleation and control it through additive assistance. For that, analytical methods like FTIR, SEM, EDX, TEM, SAED, TGA, ITC, XRD, DLS, AUC, 1H-/ 13C-/ 27Al-/ 29Si-NMR, and more, are used.

Responsibilities

Research: The effect of additives on Mg-based cement hydrates

Mg-based cements are a promising cement alternative and have the potential to become CO2-neutral depending on the raw materials and technology used. However, their properties are not yet comparable with ordinary CaO-based cement (Portland cement). They suffer from a high demand for water, and a rapid loss of workability. To ensure the workability of the blends the use of superplasticizers in Mg-based binders is essential.
Phosphorous- and carboxylic-based additives have the potential to reduce the water demand of magnesium silicate cement. Therefore, by synthesizing different Mg-cement hydrates in an automated titration setup, I study the effect of these additives on the main Mg phases (i.e., magnesium silicate hydrate (M-S-H), magnesium hydroxide, magnesium carbonate). By monitoring the pH, conductivity, and transmittance, in combination with ex-situ analysis (FTIR, SEM, TEM, EDX, PXRD, TGA) of the final products, the effect of P- and carboxylic-based additives on Mg-cement hydrates is investigated to identify suitable superplasticizer(s) and the optimal dosages for Mg-based cement to make them applicable for industrial purposes. 

Responsibilities

Writing Crystals with Light

Combining chemical and physical methods in synthesis is opening up a wide variety of new material preparation methods. In my project, I am synthesizing photolabile molecules with different protecting as well as different leaving groups which are split via the impact of light. Therefore, physical techniques such as nanosecond lasers are used. This will ensure a precise targeting of the irradiated area as well as high photon density resulting in a high conversion of the molecule into the individual constituent parts. The fundamental splitting mechanisms are investigated throughout my studies by for example NMR, UV/Vis, or titration studies. Additionally, suitable counter ions or counter molecules of the leaving groups are brought into the system and investigations are made on whether the leaving group and the counterpart are reacting with one another forming a solid material in the end. The nucleation process is analyzed and additionally, the resulting precipitate is characterized by solid-state techniques such as SEM, Raman, IR, and many more to ensure a full characterization. Combining chemical synthesis with physical irradiation techniques is ensuring the best control over the exact precipitate composition in a precise location and with a specified amount.

Responsibilities

Quantitative analysis of nanoparticle interactions and their distributions

The aim of the research is to develop a new methodology to determine size- and shape-dependent distributions of interaction constants, stoichiometry, and cooperativity of the aggregation process, even of polydisperse isotropic and anisotropic nanoparticles using combined sedimentation- and diffusion coefficient distributions from Analytical UltraCentrifugation (AUC).

Regarding anisotropic nanoparticles, face dependent interactions play a fundamental role, and this shall be investigated as well.

Once interactions between similar monodisperse, isotropic nanoparticles have been investigated, more complex systems, made up of polydisperse, isotropic nanoparticles shall be considered.

Despite the large volume of information on nanoparticles, regarding the systems per se, but also their applications in different fields, the determination of the strength of interaction and with it the thermodynamic driving force, as well as the stoichiometry of particle interactions and the cooperativity remains elusive. This is why this investigation is deemed necessary.

AUC is used to compare and implement the result normally obtained with Dynamic Light Scattering (DLS) and Isothermal Titration Calorimetry (ITC): the problem with the DLS, even though it has since been established as a solid analysis to evaluate the size of nanoparticles, is that it overestimates the larger sizes in the sample due to the ratio of scattering intensity to particle radius to the power of 6; on the other hand, ITC only gives average interactions values, and requires a substantial amount of sample.

Considering nanoparticles with broader size and/or shape distribution, a distribution in the interaction constant and stoichiometries is to be expected: AUC permits to physically separate nanoparticles of different size and shape and detects every particle. Thus, AUC is able to determine distributions rather than average values.

Still, the AUC analysis needs to be validated: for this, Field Flow Fractionation (FFF), separating the particles and determining their diffusion coefficient- and particle size distributions, and Transmission Electron Microscopy (TEM), for size and shape analysis, will come in hand to complement the results obtained from AUC.

Planned systems to be investigated are polystyrene and gold spherical nanoparticles, gold nanorods and cubic/cuboids nanoparticles based on oxides of manganese and iron.

Responsibilities

Project title:

Towards Monodispersity in Biomimetic Silica-Carbonate Microstructures

Project description:

In my research, I focus on optimizing the synthesis of biomimetic silica-carbonate microstructures (so-called Silica-Biomorphs) towards a selective, monodisperse production of the individual morphologies.

Silica-Biomorphs are a completely inorganic alternative to form microstructures showing a variety of biomimetic morphologies from atmospheric carbon dioxide and an alkaline solution containing silicate and alkaline earth metal salts. Thus, differently sized and shaped structures that can reach lengths of several hundred micrometres to millimetres can be obtained. They consist of amorphous silicon dioxide and self-assembled alkaline earth metal carbonate nanocrystals.

So far, the exact mechanisms of the formation and the factors influencing the self-assembly of the nanocrystallites and thereby the resulting morphology are still largely unknown. This knowledge, though, is necessary for the selective production of defined structures that allow the investigation of shape-property relationships to lead to new applications.

Therefore, I developed a flow cell setup that allows knowledge and control over system parameters during the reaction. With this, experiments are carried out to screen those system parameters and gain new insights into the dependence of the synthetic parameters on the morphological outcome. This already enabled a new selective synthesis of coral-like structures and could also make deterministic syntheses of other desired morphologies accessible in the future.