Abstract:

The emulsion method with micro-compartmentalization is an effective means to prepare spherical materials. In this paper, calcium carbonate (CaCO₃) microspheres were prepared by using water-in-water emulsion system composed of polyethylene glycol (PEG) and sodium carbonate (Na₂CO₃). Firstly, the formation conditions of the water-in-water emulsion were studied and the phase diagram was drawn. Then, the calcium carbonate (CaCO₃) microspheres with high dispersion and high sphericity were prepared by mixing CaCl₂ solution with PEG/Na₂CO₃ emulsion under stirring in the two-phase emulsion method. The effects of water-in-water emulsion system composition and metathesis reaction conditions on the preparation of CaCO₃ were explored and the optimal preparation conditions of CaCO₃ microspheres were also investigated. The product of CaCO₃ microspheres was characterized using XRD, SEM, laser particle size distributor and static particle image analyzer. The results showed that the CaCO₃ microspheres had the most morphology and highly dispersed when PEG₈₀₀₀ and Na₂CO₃ were 33% and 7% of the mass of in the water-in-water emulsion system, respectively, the volume ratio of CaCl₂ solution to PEG/Na₂CO₃ emulsion was 1∶15, the reaction time was 1min and the aging time was 0.5h. The CaCO₃ microspheres mainly composed of vaterite (up to 95.72%), containing a small amount of calcite. The spheroidization mechanism wasthat Ca²⁺ penetrated into the interior of the tiny spherical droplet and mineralized with CO₃^2- in a fine cavity with micro-compartmentalization, forming crystal nuclei and rapidly generates vaterite. The PEG water environment prevented the dissolution recrystallization of vaterite, inhibited the development trend of vaterite to calcite, and then the crystal nuclei grew in the lower limit of the macromolecule crowding microenvironment of the aqueous two-phase system, finally obtaining spherical structure.

Key words: aqueous two-phase emulsion, vaterite, calcium carbonate microspheres, metathesis reaction, polyethylene glycol

摘要：

具有微隔室化作用的乳液法是制备球形材料的有效手段。本研究利用聚乙二醇（PEG）与碳酸钠（Na₂CO₃）组成的双水相体系制备碳酸钙微球。首先对双水相的形成条件进行了探究，并绘制相图。然后以CaCl₂为钙源、PEG/Na₂CO₃双水相乳液的分散相Na₂CO₃为碳源，制备了高分散性的CaCO₃微球。研究了双水相体系组成、复分解反应条件等因素对CaCO₃成球效果的影响，分析了产物的微观形貌、晶体结构和粒径分布。结果表明，在33% PEG₈₀₀₀-7% Na₂CO₃（质量分数）的双水相乳液中，CaCl₂溶液与PEG/Na₂CO₃乳液体积比为1∶15、反应时间为1min、陈化时间为0.5h的最优条件下，合成了球形度高、粒径为3.4μm的CaCO₃微球，且CaCO₃以球霰石为主（高达95.72%），包含少量方解石；其成球机理为，Ca²⁺渗透至微小球形液滴的内部，在具有微隔室化的细小空腔中与CO₃^2-发生反应，形成晶核并快速生成球霰石，PEG-水环境阻止球霰石发生溶解-重结晶，抑制了球霰石向方解石发展的趋势，然后晶核在双水相体系的大分子拥挤微环境下限域生长，最终得到球形结构。

关键词: 双水相乳液, 球霰石, 碳酸钙微球, 复分解反应, 聚乙二醇