Coupled measurement system for investigation of adsorption and complexing behaviour of polymers and nanoparticles in mortar and concrete: FFF-MALS-ICP-MS

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Modern cement-based binder systems are high-performance materials that are characterized by a multi-component composition. During the hardening process many reactions occur simultaneously, for instance solution, nucleation and growth as well as sol-gel reactions. The partially unknown structure of organic admixtures, the complex composition of the entire system and the very small dimensions of the early reaction products make it difficult to study the processes in the early phase of cement hydration. The F.A. Finger Institut für Baustoffkunde (FIB) at the Bauhaus Universität Weimar has been researching these processes on an international level for decades. A coupled measurement system is applied for which is capable of characterizing ions, polymers, complexes, nanoparticles and microparticles of different structure, composition and charge respectively. The system consists of a fractionation module and a detection module. The fractionation module consists of the basic HPLC components pump and autosampler, an asymmetric flux-field flow fractionation channel (AF4 channel) which can be replaced by a GPC/SEC column as well as an AF4 channel with electric field. The separation takes place in an open channel (AF4) with an asymmetrical flow profile depending on the hydrodynamic radii of the particles, whereby particles with small radii elute earlier than larger ones. If an electric field is additionally applied to the hydrodynamic flow profile, the particles are separated according to their electrophoretic mobility. The zeta potential can be calculated by comparing both chromatograms (AF4 and electric-AF4 respectively). The AF4 channel could be replaced by a GPC/SEC column if the molecular mass of pure polymers has to be determined. The detection module consists of a multi-angle laser scattering detector (MALS), a dynamic light scattering detector (DLS), a refractive index detector (RI) and an inductively coupled plasma mass spectrometer (ICP-MS). The MALS is used to determine the gyration radii of the particles, which can be used to calculate the molecular weight of polymers. In combination with static light scattering, the hydrodynamic radius provides important information about the conformation of the polymer and its secondary structure. The special RI detector is a highly concentration-sensitive detector used for quantification of polymers in solution. An inline-coupled ICP-MS possessing low detection limits and high detection speed provides information on the chemical composition of the particles. The transient recording of many mass traces should make it possible to distinguish between the organic and inorganic nature of the particles. The applied coupled measuring system is integrated into the chemical analysis laboratory of the F.A. Finger Institute of building materials and is operated by the Chair of Building Chemistry and Polymer Materials (Prof. Osburg) as well as the Chair of Construction Material Science (Prof. Ludwig).