Investigation On The Morphology Of Crystal Growth In Low Restricted System

As a historical subject, the ability to tailor the micro-and nanoscale architecture of crystalline substances is a critical step toward application. When inorganic crystals are formed under equilibrium conditions, their crystal habit is determined by the relative order of surface energies. However, the morphological evolution with crystal modifiers usually resulted in a limited variation of the intrinsic shape of crystal; the impressive structures/architectures have rarely been reported. There has been active research in the area exploring novel synthetic chemical methods for the synthesis of heterogeneous and hierarchical architectures with controllable sizes and shapes. Alternatively, during real crystal growth process, the diffusion effect usually plays an important role in the formation of complex heterogeneous and hierarchical architectures. Recent advances have demonstrated that it is possible to control the growth processes of complex heterogeneous and hierarchical architectures with interfacial growth at air/liquid, liquid/liquid or solid/liquid interfaces. Here, we report a unified approach to the synthesis of water-soluble salts crystal with stunning structure at the metastable liquid-liquid interface between the organic solvent and aqueous droplets. The metastable liquid-liquid interface of the two compatible liquids offered a platform for the controlled formation of water-soluble salts.(1) Hopper-Like Single Crystals of Sodium Chloride Grown at Interface of Metastable Water DropletsSodium chloride (NaCl), the most classical topic in crystallization chemistry, has always been dedicated as the representative of regular cubic crystals. To change the growth habit of water-soluble salts for the production of impressive structures/architectures has not yet been achieved. Herein, we report the hopper-like single crystals of NaCl and KCl and their self-assembly at interface of metastable water microdroplets. When the undersaturated NaCl aqueous solution was introduced into the mixture of acetone and cyclohexane, the metastable water microdroplets were temporally formed under vigorously stirring. With the diffusion of acetone into the water phase, NaCl nucleated at the metastable interface of water/acetone-cyclohexane. Meanwhile, nonpolar cyclohexane adsorbed at the nuclei’s (001) plane faced to the organic phase, preventing the growth at this<001> direction. However, the growths of other{001} planes and the{111} planes maintained the original growth rates. Interestingly, the changed growth habit and the water droplet template resulted in the hopper-like single crystals and their uniform arrangement in the form of hollow microspheres, respectively. The reported results open a new avenue to control the crystallization of water-soluble species and shed significant insights to understand the growth mechanism of nanocrystals in the natural and artificial systems.(2) Pyramidic-Hopper-Like Single Crystals of Sodium Chloride Grown at Interface of Metastable Water DropletsIt has been found for over a century that the nucleation, growth, and morphology of crystals can significantly altered by the presence of low concentrations of additives. Additives can reduce crystal growth rate and alter morphology by binding to crystal faces and interfering with propagation steps. Interestingly, sodium chloride crystals form octahedrons in the presence of urea or formamide. Therefore, we have examined the interaction of urea with sodium chloride at the meteastable interface of water droplets. We synthesized microparticles of NaCl octahedron single crystal with hopper polyhedral shapes. SEM shows that the formation products are mainly composed of many hollow microspheres, most of which are in the size range10-40μm. The micro structure is in fact built by uniform octahedral NaCl single crystals and the size is about2μm. The products consist of tens of octahedrons single crystals.(3) Hopper-Like Single Crystals of Water-soluble salts Grown at Interface of Metastable Water DropletsHerein, we chose water-soluble salts with different crystal system, the cubic system of KBr and NH4Cl, the orthorhombic system of (NH4)2SO4and the hexagonal system of Na2SO3, as examples to demonstrate the effectiveness of this method in yielding sidewalls and hopper-like crystallites and their self-assembly into hollow microspheres.