Madeja, Benjamin
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Tuning the growth morphology of gypsum crystals by polymers
True control over the morphology of gypsum crystals formed via homogeneous precipitation from solution has rarely been reported in the literature. In this work, we have tested a large number of dissolved additives (polymers as well as small molecules) with respect to their ability to alter the typical microscopic appearance of precipitated gypsum powders, which is usually characterized by a mixture of single-crystalline needles and twinned plates. Among the many additives studied, a copolymer of vinylpyrrolidone and acrylic acid (PVP-co-PAA) was identified as powerful growth modifier for gypsum already at low concentrations. In both slow titration and rapid mixing experiments, unconventional blocky crystals with tilted stacking edges as well as pseudo-hexagonal plates could be synthesized reproducibly with the help of the copolymer. Systematic characterization revealed the dynamic mode of action of the newly identified growth modifier, which seems to stabilize a highly reactive face of gypsum and promote the formation of macrosteps. The degree of morphological control achieved in this way is unprecedented in the case of calcium sulfate and may devise entirely new concepts for additive design in the areas of plasters and cementitious materials, gypsum wallboard production and/or scale prevention.
Phage Display Screening as a Rational Approach to Design Additives for Selective Crystallization Control in Construction Systems
The design of additives showing strong and selective interactions with certain target surfaces is key to crystallization control in applied reactive multicomponent systems. While suitable chemical motifs can be found through semi-empirical trial-and-error procedures, bioinspired selection techniques offer a more rationally driven approach and explore a much larger space of possible combinations in a single assay. Here we use phage display screening to characterize the surfaces of crystalline gypsum, a mineral of broad relevance for construction applications. Based on next-generation sequencing of phages enriched during the screening process, we identify a triplet of amino acids, DYH, as main driver for adsorption on the mineral substrate. Furthermore, oligopeptides containing this motif prove to exert their influence in a strictly selective manner during the hydration of cements, where the sulfate reaction (initial setting) is strongly retarded while the silicate reaction (final hardening) remains unaffected. In a final step, these desired additive characteristics are successfully translated from the level of peptides to that of scalable synthetic copolymers. The approach described in this work demonstrates how modern biotechnological methods can be leveraged for the systematic development of efficient crystallization additives for materials science.