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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.
Using quartz crystal microbalance (QCM) as the main method, the diffusion of water vapor in alkyd varnish and polyurethane varnish coating was studied. The adsorption and desorption kinetics were all fit to Fick when the relative humidity (RH) was more than 30% Second Law of Diffusion, Solubility Complies with Henry’s Law. The average diffusivity, D, is calculated. When the water-absorbed sample is re-exposed to dry air, a portion of the water remains in the coating. FTIR spectroscopy (FTIR) The molecular structure of the coating changes before and after water absorption.The residual water forms a hydrogen bond with the carbonyl group C = O in the coating molecule, and a considerable portion of the water in the coating may be transported by a mutual chain transfer. Hydrogen bonds are much faster than the diffusion rate. When the RH is greater than 30%, the concentration of water in the coating is sufficient to support the reaction. The diffusion is the control step of the absorption process, which is in accordance with Fick’s second diffusion law. When RH Below 30%, the concentration of water in the coating is not sufficient to support the reaction, and the rate of reaction decreases to a rate comparable to the rate of diffusion at which point the absorption process begins to deviate from Fick’s second law of diffusion.