物理化学学报 >> 2002, Vol. 18 >> Issue (07): 649-652.doi: 10.3866/PKU.WHXB20020717

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水汽在涂层中的扩散传输行为和存在形式

徐永祥;严川伟;高延敏;曹楚南   

  1. 中国科学院金属研究所,金属腐蚀与防护国家重点实验室,沈阳 110016
  • 收稿日期:2001-11-02 修回日期:2002-01-18 发布日期:2002-07-15
  • 通讯作者: 严川伟 E-mail:cwyan@pub.ln.cninfo.net

Diffusion and Existing Form of Water Vapour in Organic Coatings

Xu Yong-Xiang;Yan Chuan-Wei;Gao Yan-Min;Cao Chu-Nan   

  1. State Key Laboratory for Corrosion and Protection,Institute of Metal Research,The Chinese Academy of Sciences,Shenyang 110015
  • Received:2001-11-02 Revised:2002-01-18 Published:2002-07-15
  • Contact: Yan Chuan-Wei E-mail:cwyan@pub.ln.cninfo.net

摘要: 利用石英晶体微天平(QCM)为主要手段,研究了水汽在醇酸清漆和聚氨酯清漆涂层中的扩散传输行为.当相对湿度(RH)大于30%时,吸附和脱附动力学都符合Fick第二扩散定律,溶解性遵守Henry定律.计算出了平均扩散系数D.当吸水后的样品重新暴露于干燥空气时,总有一部分水残留于涂层中.傅利叶变换红外光谱仪(FTIR)测定表明吸水前和脱水后涂层分子结构发生了变化.残留水与涂层分子中的羰基C=O形成了氢键.水在涂层中有相当部分可能是以相互置换的链传递方式传输.形成氢键的速度比扩散速度快得多,当RH大于30%时,涂层中水的浓度足以支持其反应,扩散为吸水过程的控制步骤,此时表现为符合Fick第二扩散定律;当RH低于30%时,涂层中水的浓度不足以支持其反应,反应速度降到和扩散速度可相比,此时吸水过程开始偏离Fick第二扩散定律.

关键词: 水汽, 涂层, 扩散, 石英晶体微天平(QCM), 傅利叶变换红外光谱(FTIR)

Abstract: Absorption and desorption of water vapour in alkyd and polyurethane varnish were studied by quartz crystal microbalance(QCM).The absorption and desorption kinetics curves were Fickian in nature when the relative humidity was higher than 30%,while the solubility followed Henry′s law.The average diffusion coefficient D increases linearly with relative humidity.A residual amount of water(about 10% of the equilibrium absorption amount under the condition of RH 100%)was found to remain in the coatings after extended exposure to dry air.FTIR analysis showed that the molecular structure of the coatings changed before absorption and after desorption of water vapour.The results showed that the residual water reacted with the coating molecule and H-bond was formed between water molecule and the C=O group.A considerable part of water in the coatings may transport in a chain mode by replacement.The rate of forming H-bond is much faster than that of diffusion.When the relative humidity is higher than 30%,the concentration of the water in the coatings is sufficient to support the reaction; diffusion is the controlling step of the absorption process,so the kinetics is Fickian.When the RH is lower than 30%,the concentration of the water in the coatings is not sufficient to support the reaction; the reaction rate is lowered to the degree that it is comparable to the rate of diffusion,then the kinetics of the whole process begin to deviate from Fick′s law.

Key words: Water vapour, Organic coatings, Diffusion, Quartz crystal microbalance(QCM), Fourier transform infrared spectroscopy(FTIR)