Crystalline, Porous Microspheres Made from Amino Acids by Using Polymer-Induced Liquid Precursor Phases
✍ Scribed by Sebastian Wohlrab; Helmut Cölfen; Markus Antonietti
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 513 KB
- Volume
- 44
- Category
- Article
- ISSN
- 0044-8249
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✦ Synopsis
Control of the crystallization processes is one of the most important techniques in applied colloid chemistry. With a controlled preparation of crystallites of defined size, the kinetic aspects of solubility (e.g. of pharmaceuticals), crystal superstructures, texture-controlled flow properties, filling degrees, and mechanical properties can be influenced. A high reproducibility of the chosen procedure is necessary to ensure the quality of industrial products.
As nucleation and growth are very sensitive processes, crystallization is usually controlled by addition of nucleation agents, stabilizers, or other ternary components. The use of special cosolvents, [1] low molecular additives, surfactants, and functional polymers is regularly reported (for recent reviews, see refs. [2-4]). Recent progress in the field of morphosynthesis indicates that there are non-classical pathways of crystallization via colloidal intermediates and subsequent mesoscale transformation. [3,[5][6][7] In this process, crystalline structures are constructed by assembly and/or transformation from larger units (instead of by the addition of single molecules). Both Addadi et al. [8] and Cölfen and Mann [3] reviewed independently the role of amorphous nanoparticles in bio-and biomimetic mineralization. The experimental verification and role of similar intermediates in the sizedirected formation of CaCO 3 particles is a question of industrial relevance. [9,10] Taden et al. analyzed a model system based on dye nanodroplets and found extraordinarily ordered dye crystals formed by mesoscale transformation. [7] Such colloidal intermediates are a manifestation of the Ostwald rule of stages, which describes structural growth in the practically relevant kinetic control limit. [11] High-concentration liquid intermediates seem to be especially promising for rapid crystallization leading to objects with a controlled outer shape. Gower et al. were the first to describe the fine droplets of a polymer-induced liquid precursor phase (PILP) for a CaCO 3 /polypeptide system, [12,13] the subsequent crystallization of which leads to bent, corrugated, and curved crystal superstructures. A special feature of [