Diakova B, Filiatre C, Platikanov D, Foissy A, Kaisheva M
Department of Physical Chemistry, University of Sofia, Bulgaria.
Adv Colloid Interface Sci. 2002 Feb 25;96(1-3):193-211. doi: 10.1016/s0001-8686(01)00081-1.
The stability and rupture of thin wetting films from aqueous NaCl or Na2SO4 solutions of different concentrations on silicon carbide were investigated. The flat surface of SiC was obtained by plasma-enhanced chemical vapor deposition (PE-CVD) on top of a silicon wafer. The microinterferometric method was used for measuring the film thickness with time. The light reflectance was calculated as a function of film thickness for the four-layer system: air/aqueous solution/SiC/Si wafer. The microinterferometric experiments showed that films from aqueous NaCl and Na2SO4 solutions with concentrations up to 0.01 M were stable independent of the pre-treatment of the substrate. The pre-treatment of the SiC surface was crucial for the wetting film stability at electrolyte concentrations greater than 0.01 M. The films were unstable and ruptured if SiC was washed with 5% hydrofluoric acid and concentrated sulfuric acid, while they were stable if washing was in sulfuric acid only, without immersing SiC in HF. The average equilibrium film thickness was determined as a function of electrolyte concentration. Measurements of the electrokinetic potential zeta were performed by electrophores of SiC powder in 0.001 M NaCl. It was shown that silicon carbide surface was negatively charged. The theory of heterocoagulation was used for the interpretation of the results. Besides the DLVO forces, the structural disjoining pressure (both positive and negative) has been included in the analysis.
研究了不同浓度的NaCl水溶液或Na₂SO₄水溶液在碳化硅上形成的薄润湿膜的稳定性和破裂情况。碳化硅的平面是通过在硅片顶部进行等离子体增强化学气相沉积（PE-CVD）获得的。采用微干涉测量法测量薄膜厚度随时间的变化。对于空气/水溶液/碳化硅/硅片的四层系统，计算了光反射率随薄膜厚度的变化关系。微干涉测量实验表明，浓度高达0.01 M的NaCl水溶液和Na₂SO₄水溶液形成的薄膜是稳定的，与基底的预处理无关。在电解质浓度大于0.01 M时，碳化硅表面的预处理对润湿膜的稳定性至关重要。如果用5%的氢氟酸和浓硫酸清洗碳化硅，薄膜不稳定且会破裂，而仅用硫酸清洗（不将碳化硅浸入氢氟酸中）时，薄膜是稳定的。测定了平均平衡膜厚度随电解质浓度的变化关系。通过在0.001 M NaCl中对碳化硅粉末进行电泳测量了电动电位ζ。结果表明碳化硅表面带负电。采用异质凝聚理论对结果进行解释。除了DLVO力外，分析中还考虑了结构分离压力（包括正压力和负压力）。
