Cölfen, Helmut

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Helmut
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Morphology-controlled growth of perylene derivative induced by double-hydrophilic block copolymers

2016, Huang, Minghua, Antonietti, Markus, Cölfen, Helmut

Controlled growth of technically relevant perylene derivative 3, 4, 9, 10-perylenetetracarboxylic acid potassium salt (PTCAPS), with tuneable morpologies, has been successfully realized by a recrystallization method using a double-hydrophilic block copolymer poly (ethylene glycol)-block poly (ethyleneimine) (PEG-b-PEI) as the structure directing agent. The {001} faces of PTCAPS are most polar and adsorb the oppositively charged polymer additive PEG-b-PEI well by electrostatic attraction. By simply adjusting the PEG-b-PEI concentration, systematic morphogenesis of PTCAPS from plates to microparticles composed of various plates splaying outwards could be realized. Furthermore, the variation of pH value of the recrystallization solution could induce the change of the interaction strength between PEG-b-PEI additive and PTCAPS and thus modify the morphology of PTCAPS from microparticles composed of various plates to ultralong microbelts.

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Mixed calcium-magnesium pre-nucleation clusters enrich calcium

2012, Verch, Andreas, Antonietti, Markus, Cölfen, Helmut

It is demonstrated that magnesium and carbonate ions can form pre-nucleation clusters in analogy to calcium carbonate. If a mixed calcium and magnesium solution is brought in contact with carbonate ions, mixed pre-nucleation clusters form. The equilibrium constants for their formation are reported revealing that over the entire range of possible cation mixing ratios, calcium gets enriched over magnesium in the pre-nucleation clusters. This can explain high magnesium contents in amorphous calcium carbonate. However, this enrichment alone is not sufficient to explain the magnesium content of less than 41 mol% which is found in magnesium calcite biominerals nucleated from seawater.

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Fabrication of EuF3-Mesocrystals in a Gel Matrix

2010, Lausser, Christine, Kumke, Michael U., Antonietti, Markus, Cölfen, Helmut

Europium(III) fluoride mesocrystals were synthesised in an organic matrix. This matrix is a gel formed by Eu3+ ions and a polycarboxylate/sulfonate copolymer, ACUSOL 588G. In the gel phase, the local amount of europium ions is very high since Eu3+ acts as a crosslinker, and crystallisation occurs upon addition of F . Nucleated seed crystals in the gel phase grow by further ion attachment and form mesocrystals by mutual orientation of the EuF3 particles in the gel. We propose a dipole field as reason for this alignment and that the dipolar character of the particles originates from adsorption of the polyelectrolyte on charged crystal faces.

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Polymer-Controlled Biomimetic Mineralization of Novel Inorganic Materials

2010, Cölfen, Helmut, Antonietti, Markus

Biomineralization processes result in organic-inorganic hybrid materials with complex shape, hierarchical organization, and superior materials properties. Chemistry, which is inspired by these processes, aims to mimic biomineralization principles and to transfer them to the general control of crystallization processes using an environmentally benign route. Recent progress in the field has revealed that polymer controlled crystallization often does not follow the classical textbook view of ion-mediated crystallization but instead is based on nanoparticles as building units. In this chapter, the latest advances in hydrophilic polymer-controlled crystallization are summarized with focus on structures with functionality, i.e., special mechanical or optical properties. Size, shape, phase, dimension, assembly, etc. have significant relevance for the properties of semiconductor nanocrystals, metal nanostructures, or on the magnetism and spectral characteristics of oxides and other inorganic materials. The resulting unique hierarchical materials with structural speciality and complexity and a size range spanning from nanometers to micrometers are expected to be interesting in various fields of applications, such as catalysis, medicine, electronics, ceramics, pigments, and cosmetics.

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Structural evolution of aragonite superstructures obtained in the presence of the siderophore deferoxamine

2015, Willinger, Marc-Georg, Polleux, Julien, Antonietti, Markus, Cölfen, Helmut, Pinna, Nicola, Nassif, Nadine

The effect of amphoteric siderophore deferoxamine on the crystallization behavior of calcium carbonate was investigated under bioinspired conditions. Amphoteric siderophore deferoxamine possesses self-organization ability, surface activity and ion-chelating properties. It induces in the present case the formation of unusual, highly organized aragonite mesocrystals during the precipitation of calcium carbonate from liquid phase. A detailed investigation of the structure and growth of the particles provides an insight into the role of the deferoxamine and its function in the crystallization process.

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How to control the scaling of CaCO(3) : a "fingerprinting technique" to classify additives

2011-10-06, Verch, Andreas, Gebauer, Denis, Antonietti, Markus, Cölfen, Helmut

A titration set-up coupling ion selective electrodes with pH adjustment was used to analyze the effects of additives present during precipitation of calcium carbonate. Besides industrially well-established antiscalants (sodium triphosphate, citrate, polyacrylate and poly(aspartic acid)), also functional polymers being active in morphosynthesis (polystyrene sulfonate and poly(styrene-alt-maleic acid)) were analyzed. Interestingly each additive acts in its specific way, suggesting the notation "fingerprinting" for a complex interplay of up to five "solution modes" of influencing CaCO(3) precipitation and crystallisation. The results provide new insights into the modes of additive controlled crystallisation, and in the long run, the insights may facilitate the design of precipitation systems that yield complex and tailor-made crystals.

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Polymer-Induced Self-Assembly of Small Organic Molecules into Ultralong Microbelts with Electronic Conductivity

2010, Huang, Minghua, Schilde, Uwe, Kumke, Michael, Antonietti, Markus, Cölfen, Helmut

The principle of polymer-controlled crystallization of inorganic materials has been successfully transferred to functional aromatic organic dyes, in this instance 3,4,9,10-perylenetetracarboxylic acid potassium salt (PTCAPS), after its single-crystal structure was determined. The cationic double hydrophilic block copolymer poly(ethylene glycol)-block-branched-poly(ethyleneimine) (PEG-b-PEI) was used as the polymer additive to modify the crystallization of PTCAPS. Ultralong hierarchically structured PTCAPS microbelts with constant width and thickness of each individual belt have been fabricated. The belts are a mesocrystalline assembly of primary nanoparticles with high-energy anionic {001} faces stabilized by polymer complexation. Polarization microscopy, X-ray diffraction, optical absorption spectra, and fluorescence spectra indicate the favorable orientation of the 1D microbelts in the close-stacking direction and reveal a specific 1D superstructure fluorescence. Electrical conductivity measurements performed on a single nanobelt disclose in the doped state a remarkably high electronic conductivity and further demonstrate extended, wirelike π−π interactions along the [020] long axis of the belts. Together with the very large length of the belts and their organic−organic hybrid nanostructure, this makes these organic wires potentially interesting for the field of nano-/micro-optoelectronics.

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Ethanol assisted synthesis of pure and stable amorphous calcium carbonate nanoparticles

2013-10-25, Chen, Shao-Feng, Cölfen, Helmut, Antonietti, Markus, Yu, Shu-Hong

Stable monodispersed amorphous calcium carbonate (ACC) nanoparticles can be synthesized in ethanol media by a facile method, and crystallization of ACC is kinetically controlled, resulting in the formation of three polymorphs in a mixed solvent of ethanol–water at different pH values.

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Mesocrystals of vanadium pentoxide : a comparative evaluation of three different pathways of mesocrystal synthesis from tactosol precursors

2011-01-25, Lausser, Christine, Cölfen, Helmut, Antonietti, Markus

Vanadium pentoxide mesocrystals were synthesized from a mineral liquid crystalline precursor phase, a so-called tactosol. For comparative evaluation of solid formation from that phase, the distance between the vanadium pentoxide particles was lowered by three different modes: (a) by adding a 0.1 M NaCl solution, the electric double layer was compressed and controlled particle aggregation was induced; (b) application of external pressure by ultracentrifugation resulted in particle compression and final crystallization; (c) an acrylic acid/ sulfonic acid copolymer was added to introduce polymer-mediated particle alignment and densification. In all three cases, the preorientation of the particles within the liquid crystal remained, and different mesocrystals were formed. This was demonstrated by comparative analysis of the resulting structures by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and polarization microscopy.

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BaCO3 mesocrystals : new morphologies using peptide–polymer conjugates as crystallization modifiers

2010, Wang, Tongxin, Mitchell, James, Börner, Hans, Cölfen, Helmut, Antonietti, Markus

Nanocrystal superstructures of barium carbonate (BaCO3) which exhibit unusual morphologies are obtained by the carbon dioxide vapor diffusion technique in the presence of poly(ethylene oxide)-block-eicosa aspartate (PEO-b-Asp20). The highly effective bioconjugate acts as a crystal growth modifier over a broad range of concentrations. Instead of commonly observed branched needles, the morphology can be systematically varied along different twinned growth patterns towards well-defined branched dumbbells. Detailed analysis of the crystal substructures with high resolution scanning electron microscopy (HRSEM) and dynamic light scattering (DLS) discloses a potential growth mechanism of the superstructures and reveals the role of the polymeric bioconjugate therein.