Study On Preparation Of Calcium Carbonate With Controlled Morphologies And Performance Of Stable Pickering Emulsions

Pickering emulsions is a system that micro/nano solid particles replace surfactants to adsord on the liquid-liquid interface to stabilize the emulsion.The Pickering emulsions prepared by calcium carbonate has the advantages of non-toxicity,environmental protection,good stability and dispersion,it is widely used in the synthesis of new materials,food,cosmetics,sustained release of drugs.Therefore,this article mainly prepared calcium carbonate with different morphologies which were used as stabilizers to prepare Pickering emulsions,and the emulsions had a long stable time and good dispersion performance.First,calcium carbonate particles with various morphologies were prepared by adding surfactants,controlling temperature and reaction time with sodium carbonate and calcium chloride as the starting materials.The morphology and size of calcium carbonate were measured by scanning electron microscope,the crystal structure of calcium carbonate was measured by X-ray diffractometer,the functional group of calcium carbonate was measured by Fourier transform infrared spectrometer,and the surface charge of calcium carbonate was measured by Zeta potentiometer.The results showed that the cubic,rod-like and spherical calcium carbonate was of calcite,aragonite and vaterite,respectively.The flower-like calcium carbonate was composed of calcite and vaterite.Except for the cubic calcium carbonate which was negatively charged,other morphologies calcium carbonate were positively charged.Secondly,calcium carbonate with different morphologies was used as a stabilizer in the preparation of Pickering emulsions,and the type of Pickering emulsions was inferred by the method of dilution.The influence of stable emulsion was investigated by oil-water ratio,concentration and particle size,the size and stability of the droplets of Pickering emulsions were observed through an optical microscope.The results indicated that the Pickering emulsions stabilized by calcium carbonate particles was of O/W type.Cubic and spherical calcium carbonate adsorbed at the interface by a single particle layer,and rod-like and flower-like calcium carbonate adsorbed in a multi-particle layer at the interface.As the oil-water ratio and particle size increased,the droplets of Pickering emulsions became larger and the stability decreased.As the concentration increased,the droplets gradually became smaller and stable.Pickering emulsions were prepared by mixing calcium carbonate particles with opposite charges as a stabilizer,the droplets of the Pickering emulsions preferentially adsorbed the positively charged particles.When using calcium carbonate with different particle sizes as a stabilizer to prepare Pickering emulsion,the droplets of Pickering emulsions preferentially adsorbed the smaller particle size.Finally,O/W type Pickering emulsions were prepared by using differently charged calcium carbonate particles and positively charged cetyltrimethylammonium bromide(CTAB)as stabilizers.The surface tension of CTAB solution with or without particles was measured by a surface tension meter,the surface wettability of particles was measured by contact angle meter and particle precipitation method,and a Zeta potential meter was used to detect the charge of particles in CTAB solutions of different concentrations.Finally,the charge and stability of Pickering emulsions were measured by zeta potential measurement and observed by optical microscope.The results show that when the concentration of CTAB was less than the critical micelle concentration,CTAB did not change the surface wettability of rod-like calcium carbonate particles,and the hydrophobicity of the surface of cubic calcium carbonate particles increased with the increase of CTAB concentration.The addition of particles reduced the surface tension of the CTAB solution.The Zeta potential of rod-like particles dispersed in CTAB solutions of different concentrations remained basically unchanged,while the Zeta potential of cubic calcium carbonate particles increased with the increase of CTAB concentration.In the Pickering emulsion prepared by rod-like calcium carbonate particles and CTAB,the oil-water interface preferentially adsorbed CTAB and then continued to adsorb the particles,which reduced the interfacial tension and enhanced the electrostatic repulsion between the droplets to make the emulsion stable.Pickering emulsions were prepared from particles with cubic calcium carbonate particles and CTAB,CTAB was preferentially adsorbed on the surface of the particles,which changed the surface charge of the particles,and then the oil-water interface adsorbed the activated particles to stabilize the emulsion.