Effect Of CaCO₃ Nanocrystals On Foaming Properties Of Non-aqueous Solvents

Non-aqueous foams are widely used in oil and gas field development,food processing,porous functional materials and medicine,etc.However,its low interfacial tension and low dielectric constant lead to poor foaming performance,which restricts the development of related engineering operations.CaCO₃ nanocrystals have attracted wide attention in the field of foam due to their rich morphology,structure and anisotropy.At present,the foaming properties of CaCO₃ nanocrystals have only been studied in aqueous solvents,while the relevant research work has not been carried out in non-aqueous foams.Therefore,in this paper,CaCO₃ nanocrystals with different morphologies were prepared and hydrophobic modified by lauric acid and two modifiers,1H,1H,2H,2H-perfluoro-decyl triethoxy silane,and the foaming properties of the nanocrystals in different polar solvents were explored.The following research works were carried out:（1）Preparation of CaCO₃ nanocrystals.CaCO₃ nanocrystals with different morphologies were prepared by double decomposition using anhydrous Na₂CO₃ and anhydrous Ca Cl₂ as raw materials.The effects of reaction temperature,reaction time,the type and dosage of crystal shape control agent on the morphology were studied.TEM,FT-IR,TGA and XRD were used to characterize the samples.The results show that four kinds of crystal particles with different morphologies of flake,spherical,spindle-shaped and cubic can be prepared by adding different crystal shape control agents.For spherical CaCO₃ nanocrystals,the factors affecting the particle size of the spherical CaCO₃ nanocrystals were studied by single factor experiment.The results show that when the reaction temperature is controlled at 15℃,20℃and 25℃,the crystal particle sizes are 5.09 nm,45.6 nm and 121.4 nm,respectively.（2）Hydrophobic modification of CaCO₃ nanocrystals.The wettability of hydrophilic CaCO₃ nanocrystals was controlled by wet modification.Lauric acid modification:the modification time was 60 min,the modification temperature was 75℃,the modifier dosage was 0.5%～5%,and the contact Angle range of the crystal particles was 24.8°～121°.1H,1H,2H,2H-perfluoro-decyltriethoxy silane modification:control modification time 180 min,modification temperature 60℃,adjust the modifier dosage 0.5%～20%,the contact Angle of the crystal particles prepared in 35.8°～134.2°.（3）The foaming performance of different polarity solvents.The foaming properties of CaCO₃ nanocrystals with different morphologies and wettability for different polarity solvents were studied by Waring-Blender method.The results show that the foam formed by flake-like CaCO₃ nanocrystals with crystal particle content of 5%and contact Angle of 73.9°has a gas content of 50.98%and a stability of 88 h.Non-aqueous foam:lauric acid modified CaCO₃ nanocrystals can form non-aqueous foam in strong polar organic solvents.CaCO₃nanocrystals modified by 1H,1H,2H,2H-perfluoro-decyltriethoxy silane form non-aqueous foams in weak polar and non-polar organic solvents.It was found that the foaming performance of the flake crystal particles was the best,and the gas content of the non-aqueous foam formed was between 10%and 56.9%.The contact angles of crystal particles that can form foams in strong polar organic solvents range from 53.5°to 73.9°,and those that can form foams in weak polar and non-polar organic solvents range from 47.5°to 66°.