原子力显微镜的云母及煤表面的水化膜测试和界面相互作用

摘要

The hydration film on particle surface plays an important role in bubble-particle adhesion in mineral flotation process. The thicknesses of the hydration films on natural hydrophobic coal and hydrophilic mica surfaces were measured directly by atomic force microscopy (AFM) based on the bending mode of the nominal constant compliance regime in AFM force curve in the present study. Surface and solid-liquid interfacial energies were calculated to explain the forming mechanism of the hydration film and atomic force microscopy data. The results show that there are significant differences in the structure and thickness of hydration films on coal and mica surfaces. Hydration film formed on mica surface with the thickness of 22.5 nm. In contrast, the bend was not detected in the nominal constant compliance regime. The van der Waals and polar interactions between both mica and coal and water molecules are characterized by an attractive effect, while the polar attractive free energy between water and mica (?87.36 mN/m) is significantly larger than that between water and coal (?32.89 mN/m), which leads to a thicker and firmer hydration layer on the mica surface. The interfacial interaction free energy of the coal/water/bubble is greater than that of mica. The polar attractive force is large enough to overcome the repulsive van der Waals force and the low energy barrier of film rupture, achieving coal particle bubble adhesion with a total interfacial free energy of ?56.30 mN/m.%颗粒表面水化膜在浮选颗粒气泡粘附过程中扮演着重要作用.借助原子力显微镜力曲线中名义恒定区的弯曲现象完成对天然亲水性云母和疏水性煤片表面水化膜厚度的测试.同时,对表面能及固液界面自由能进行计算揭示了水化膜的形成机制.结果发现:云母和煤表面的水化膜厚度和结构存在明显的差异,云母表面的水化膜厚度为22.5 nm,而在煤表面并未检测到水化膜的存在.云母及煤与水分子间的范德华和极性作用均为吸引,但云母与水分子间的极性作用能(?87.36 mN/m)远大于煤水间的(?32.89 mN/m),因此,直接导致了更厚而坚固的水化膜.进一步发现煤-水气泡体系的界面作用自由能(?56.30 mN/m)显著大于云母体系的,极性吸引力足以克服排斥性范德华力和颗粒气泡粘附能垒.