摘要:
IntroductionDevelopment of protocols to grow crystals of controllable structure, size, morphology and superstructures of predefined organizational order is an important goal in crystal engineering with tremendous implications in the ceramics industry.1,2Lured by the exquisite control that biological organisms exert over mineral nucleation and growth (both amorphous and crystalline) by a process known as biomineralization,3,4materials scientists are trying to understand biomineralization and, thereby, develop biomimetic approaches for the synthesis of advanced ceramic materials. It is now established that an important requirement for biomineralization is epitaxy between the crystal nucleating face and underlying bioorganic surface and, consequently, biomimetic surfaces such as those presented by Langmuir monolayers,5,6selfassembled monolayers (SAMs) on planar7and nanoscale curved surfaces8as well as functionalized polymer surfaces9have been studied in great detail. Attempts have also been made to control the morphology of crystalsviaaddition of suitable crystallization inhibitors10and carrying out crystal growth in constrained environments such as those afforded by microemulsions.11Very recently, some of us have shown that the growth of SrCO3in thermally evaporated fatty acid bilayer stacks resulted in an unusual flowerlike assembly of strontianite needles.12The liquid–liquid interface is an important area of research in chemistry that impacts understanding of the stability of emulsions, chemical separation processes, interfacial catalysis as well as many processes in biological systems.13Only recently has the liquid–liquid interface been viewed seriously as a medium for the organization of micron sized objects14and growth of nanoparticles of CdS.15To the best of our knowledge, there are no reports in the literature on the use of the liquid–liquid interface in the biomimetic growth of minerals. In this communication, we address this lacuna and investigate the growth of BaSO4(barite) crystals at the interface between an aqueous solution of Ba2+ions and organic solutions of chloroform and hexane containing fatty acid/fatty amine molecules by reaction with sodium sulfate. The processis seemingly similar to the growth of BaSO4crystals at the air–water interface with anionic Langmuir monolayers as the template6with the following important differences. The magnitude of the dielectric discontinuity between water–organic solution and water–air would be different and could lead to important differences in the electrostatics of complexation of the Ba2+ions with the anionic surfactant molecules at the interface. Furthermore, the finite solubility of the two solutions would lead to a region of the interface with a much broader gradation in the dielectric function which would in turn influence the electrostatics of the metal ion complexation with the lipid molecules as well as the organization of the templating lipid molecules in the interfacial region. The solvation of the hydrocarbon chains in the organic phase would also contribute to disruption in the ordering of the surfactant molecules at thewater–organic solution interface with important consequences in the epitaxy associated with crystal nucleation processes.
ISSN:1466-8033
DOI:10.1039/b109533c
出版商:RSC
年代:2001
数据来源: RSC