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Semi-solid metal alloys, as used in thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The complex rheological properties are strongly influenced by the local solid fraction, particle shape, particle size and state of agglomeration. There is a high demand for models and software tools allowing the simulation of semi-solid casting processes. The material under investigation is a tin-lead alloy (Sn-15%Pb) which exhibits a similar microstructure to aluminium alloys. The experiments were performed with a concentric cylinder rheometer of the Searle type. Initially, the liquid alloy is cooled down to the semi-solid range under constant shearing and then kept under isothermal conditions for further experimentation. Based on the experimental data, a single-phase model has been derived where the semi-solid alloy is regarded as a homogeneous material with thixotropic properties and the microstructure is characterised by a structural parameter. The model consists of two parts: the equation of state, including a finite yield stress, and a rate equation for the structural parameter. The model equations are employed in numerical software and used for the simulation of characteristic filling cases and the comparison with the conventional filling.
The current study presents a new class of functional derivatives (1–3) consisting of a dicationic viologen (4,4’-bipyridinium unit) (V21) capped by nucleobases thymine (NB1), adenine (NB2), thymine/adenine (NB1, NB2), and ion-paired with amphiphilic anion 3,4,5-tris(dodecyloxy)benzene sulfonate (DOBS-). The target of our work focuses on the design and synthesis of molecular building blocks in which three different functionalities are combined: chromophore (V21 unit), molecular recognition (NB unit), and thermotropic liquid crystal (DOBS unit). The resulted materials exhibit liquid crystalline properties at ambient temperature with significant particularities-induced by nucleobases in the mesogen structure. Structure–properties relationship study focuses on providing knowledge about (1) how the thermotropic, redox properties, thermochromism, or ionic conductive properties are influenced by the presence of purinic or pyrimidinic nucleobases, and (2) how effective is their ability to selfassembly by hydrogen bonding in nonpolar solvents. The presence of nucleobases has been proved to have a substantial impact on electron transfer rate during the reduction of viologen moieties by intermolecular aggregation. Ionic conductivity and thermochromic properties of derivatives 1–3 were investigated and compared to a non-containing nucleobase analog methyl viologen with 3,4,5 tris(dodecyloxy)benzene sulfonate anion (MV) as reference.